BoP Lab / Classes / STU

STU vs SRF3 vs F5 vs SM pace at every track

Lap times across years say as much about the weather as the class. % of STU is each class's best lap as a share of STU's on the same day, so the conditions drop out: 100% is level, less is quicker, and a move in it is the class getting faster or slower against the field.

Class · click a class to switch, + to compare alongside (up to 4: remove one to add another)

ASB-SpecEPvsF5 ×FAFCFE2FFFPFVFXGT1GT2GTXHPPP2vsSM ×SMXvsSRF3 ×STLSTU×T1T2T3T4Show 50 inactive classes

Series Runoffs Super Tour Both

Reference class · the yardstick the % column and chart are measured against

Tracks · untick to narrow Auto Club Speedway Barber Motorsports Park Blackhawk Farms Raceway Buttonwillow Raceway Park Circuit of St. Louis (formerly Gateway Motorsports Circuit of the Americas Daytona International Speedway Grattan Raceway Hallett Motor Racing Circuit Homestead-Miami Speedway Indianapolis Motor Speedway Laguna Seca Michelin Raceway Road Atlanta Mid-Ohio Sports Car Course New Jersey Motorsports Park NOLA Motorsports Park Pacific Raceways Pittsburgh International Race Complex Portland International Raceway Pueblo Motorsports Park Road America Sebring International Raceway Sonoma Raceway Summit Point Raceway Thunderhill Raceway Park Virginia International Raceway Watkins Glen International Willow Springs Raceway World Wide Technology Raceway

Quickest here: STU 1:19.234 Franklin Church, Runoffs 2018 qualifying · SRF3 1:34.363 John Black, Runoffs 2016 qualifying · F5 1:28.528 Calvin Stewart, Runoffs 2016 qualifying · SM 1:40.514 Justin Hille, Runoffs 2016 qualifying

% of STULap times

STUSRF3F5SMsolid race · dashed qualifying · slower is lower

STUSRF3F5SMsolid race · dashed qualifying · each class's best lap as a share of STU's at the same event (the reference class, changeable above); 100% is level, less is quicker, so up the chart is quicker

	Event	STU			SRF3					F5					SM
	Event	Qual best	Race best	Trap	Qual best	Race best	Trap	vs STU	% of STU	Qual best	Race best	Trap	vs STU	% of STU	Qual best	Race best	Trap	vs STU	% of STU
	Road America Runoffs 20262026-09-28	2:24.912Richard Astacio · fastest of 17 · top 5 within 2.6s+1.829s (+1.28%)	2:26.416Richard Astacio · fastest of 16 · top 5 within 1.5s+1.919s (+1.33%)	145.1Hugh Stewart+0.8 mph (+0.5%)	2:27.443Tyler Stephens · fastest of 44 · top 5 within 0.3s-0.783s (-0.53%)	2:29.257Peyton Long · fastest of 42 · top 5 within 0.3s-0.582s (-0.39%)	134.1Bobby Sak+0.4 mph (+0.3%)	+2.841squal +2.531s	101.9%qual 101.7%						2:42.173Brett Kowalski · fastest of 34 · top 5 within 0.3s-0.938s (-0.58%)	2:42.725Francisco Barroso · fastest of 35 · top 5 within 0.2s-1.705s (-1.04%)	119.6Wyatt Couch+0.3 mph (+0.3%)	+16.309squal +17.261s	111.1%qual 111.9%
19 rule changes (STU: 15, SRF3: 2, SM: 2)4 cars added · 3 weight · 2 engine · 2 induction · 2 tyres & wheels · 5 wording · 1 other · GT3U wheel and tyre options clarified: 15x7 with 225 section at +275 lbs; 15x9 with 245 section at +275 lbs plus 1.5%; 16–18x9 with 245 section at +275 lbs plus 3.0%. · SM/SMX Mazda rear toe link part number revised from 0000-04-5361426 to 0000-04-5361. · STU cars at or under 2,825 lbs minimum weight limited to 8-inch wheels; over 2,825 lbs limited to 9-inch wheels. · STU GT3U minimum weight increases from GT3 race weight plus 225 to plus 275 pounds; 2.0L unrestricted engines add 75 lbs. · STU adds BMW M50B20TU engine, 1991 cc, minimum weight per chart, must meet all STU engine regulations. · STL, STU weight calculation procedure clarified: positive percentages added first, negative subtracted second, then fixed weights applied. · STU Honda K20C1 Turbo I4 turbo restrictor increases from 35mm to 36mm TIR. · STU GT86 Cup car must meet 2022 Toyota GR Cup rules, tires maximum 245 section width. · SM/SMX part number 0000-10-6900 replaced with 0000-06-5016-KT in GCR 9.1.7.C.1.j.1.c. · STU Mazda Renesis Street Port added to Table B with 2450 lbs minimum weight and 70mm throttle body options. · STU eliminates 33 and 34 mm inlet restrictor options, removing minimum weights of 2380 and 2525 lbs. · SRF3 spark plugs limited to NGK LTR7IX-11 P/N G301041 only; washers and sealing rings prohibited. · STU Mazda MZR engines may now use Fab 9 Elite NC MX5 Performance Intake manifold as alternative option. · STU Mazda MZR (LF, L3, L5) Turbo added; Goodwin intake removed, Jack Spania Racing 70 mm intake and Fab9 Tuning bottom-mount turbo kit approved. · STU 36mm restrictor revised to 2830 cc, 37mm to 2980 cc. · STU removes 275 tire option and 2% weight adder for cars over 3150 lbs; maximum section width now 245. · STU Honda K20 and K24 engines lose 2% weight penalty; minimum weight now per chart only. · STU Honda K24 engine swap weight increases by 2 percent, effective November 1, 2025. · SRF3 adds HD Oil Cooler P/N G1148500 option alongside standard P/N G480503, no fan permitted.showhide 2026-09-01 STU Wheel and tire requirements for GT3U #40679wordingwordingGT3U wheel and tyre options clarified: 15x7 with 225 section at +275 lbs; 15x9 with 245 section at +275 lbs plus 1.5%; 16–18x9 with 245 section at +275 lbs plus 3.0%. 2026-07-01 SM Rear Toe Link #40271wordingwordingSM/SMX Mazda rear toe link part number revised from 0000-04-5361426 to 0000-04-5361. 2026-07-01 STU 9” Wheels #40433tyres & wheelsslower · tyres & wheelsSTU cars at or under 2,825 lbs minimum weight limited to 8-inch wheels; over 2,825 lbs limited to 9-inch wheels. 2026-07-01 STU Weight adjustment to former GT3U cars #40474weightslower · weightSTU GT3U minimum weight increases from GT3 race weight plus 225 to plus 275 pounds; 2.0L unrestricted engines add 75 lbs. 2026-06-01 STU Request to allow BMW M50B20TU engine in STU #40202cars addedaddedSTU adds BMW M50B20TU engine, 1991 cc, minimum weight per chart, must meet all STU engine regulations. 2026-06-01 STU Calculating Weight #40224wordingwordingSTL, STU weight calculation procedure clarified: positive percentages added first, negative subtracted second, then fixed weights applied. 2026-05-01 STU Turbo Restrictor Size Increase Request #40008inductionfaster · inductionSTU Honda K20C1 Turbo I4 turbo restrictor increases from 35mm to 36mm TIR. 2026-05-01 STU GT86 Cups Car in STU #40028wordingwordingSTU GT86 Cup car must meet 2022 Toyota GR Cup rules, tires maximum 245 section width. 2026-04-01 SM Part Number Change Request #39914otherunclearSM/SMX part number 0000-10-6900 replaced with 0000-06-5016-KT in GCR 9.1.7.C.1.j.1.c. 2026-04-01 STU Mazda Rx-8 Renesis - Streetported Variant & Added Weight #39785cars addedaddedSTU Mazda Renesis Street Port added to Table B with 2450 lbs minimum weight and 70mm throttle body options. 2026-04-01 STU Eliminate 33 and 34 mm TIRs #39872inductionremoved · inductionSTU eliminates 33 and 34 mm inlet restrictor options, removing minimum weights of 2380 and 2525 lbs. 2026-03-01 SRF3 SRF3 Spark Plugs #39899engineengineSRF3 spark plugs limited to NGK LTR7IX-11 P/N G301041 only; washers and sealing rings prohibited. 2026-03-01 STU Fab 9 Racing Intake Manifold in STU #39767cars addedaddedSTU Mazda MZR engines may now use Fab 9 Elite NC MX5 Performance Intake manifold as alternative option. 2026-01-01 STU Request for Permission on Aftermarket Turbo Kit and Intake #39529cars addedaddedSTU Mazda MZR (LF, L3, L5) Turbo added; Goodwin intake removed, Jack Spania Racing 70 mm intake and Fab9 Tuning bottom-mount turbo kit approved. 2025-12-01 STU Turbo Inlet Restrictor Table #38961wordingwordingSTU 36mm restrictor revised to 2830 cc, 37mm to 2980 cc. 2025-12-01 STU 275 Tire Rule #38983tyres & wheelsslower · tyres & wheelsSTU removes 275 tire option and 2% weight adder for cars over 3150 lbs; maximum section width now 245. 2025-12-01 STU STU Honda Engine weight penalty #39375weightfaster · weightSTU Honda K20 and K24 engines lose 2% weight penalty; minimum weight now per chart only. 2025-11-01 STU Non-Homologated Engine Swaps - Specifically K24A2 w/ Honda CRZ #38746weightslower · weightSTU Honda K24 engine swap weight increases by 2 percent, effective November 1, 2025. 2025-10-01 SRF3 Add HD Oil Cooler #38979engineadded · engineSRF3 adds HD Oil Cooler P/N G1148500 option alongside standard P/N G480503, no fan permitted.
	Road America Runoffs 20252025-09-29	2:23.083Peter Cunningham · fastest of 16 · top 5 within 2.6s-3.144s (-2.15%)	2:24.497Chip Herr · fastest of 15 · top 5 within 3.8s-1.327s (-0.91%)	144.3Chip Herr-1.0 mph (-0.7%)	2:28.226Bobby Sak · fastest of 43 · top 5 within 0.6s+0.453s (+0.31%)	2:29.839Morgan Burkhard · fastest of 42 · top 5 within 0.3s+1.710s (+1.15%)	133.7Bobby Sak-1.5 mph (-1.1%)	+5.342squal +5.143s	103.7%qual 103.6%						2:43.111Bobby Gossett · fastest of 32 · top 5 within 0.3s+2.005s (+1.24%)	2:44.430Kyle Greenhill · fastest of 28 · top 5 within 0.3s+2.944s (+1.82%)	119.3Francisco Barroso-0.6 mph (-0.5%)	+19.933squal +20.028s	113.8%qual 114.0%
25 rule changes (STU: 18, SRF3: 3, SM: 4)6 weight · 4 cars added · 3 tyres & wheels · 2 engine · 1 induction · 6 wording · 3 other · SRF3 adds oil cooler options P/N G480503 and P/N G1148500; brake rule restructured to list Hawk Blue pads, Wilwood rotor, caliper kit, master cylinder options. · STU Lotus Elise SC and Exige SC weight reduced from 2450 to 2250 lbs. · STU-TCR gains GT3 TCR spec lines; 275 tyre option now costs 150 lb adder, up from 100 lb. · Lotus Evora GT4 minimum weight drops to 2700 lbs; Elise Cup R to 2250 lbs; Elise SC and Exige SC to 2450–2550 lbs. · STU 2.8–3.2L N/A engines now permit 245 max tyre width; over 3150 lbs cars may run 275 with 2% weight penalty. · STU Mazda MZR intake manifold now allows Goodwin 61-2510 or Gato Performance 31972. · STU Honda JDM H23a added, 2259 cc, minimum weight per chart, must meet ST engine regulations. · SMX drivers must submit data acquisition files on time or face suspension and $250 fine. · SMX penalty language clarified: level 1 and 3 infractions may carry $1,000 fines, level 2 and 4 may carry $500 fines. · SM tire marking rules clarified: one Hoosier SM 7.5 P205/50/ZR17 set per Super Tour weekend, impound after first dry session, damaged tires may be replaced with used tires only. · STU wheels capped at 18 inches diameter; under 2,850 lbs max 8 inches wide, over 2,850 lbs max 9 inches wide. · STU-GT3U minimum weight reduced from plus 250 to plus 225 pounds; wheel and tyre options clarified with weight adjustments. · SRF drivers with disabilities may modify seat and controls for safety and comfort with SCCA approval, noted in logbook, for that driver only. · SRF SADEV-SRF3 6-speed sequential transmission: effective date clarified to 1 April 2025 onward. · STU BMW N54/N55 3.0 classified at chart plus 3% minimum weight; N54 twin turbo not allowed. · STU Mini Cooper S SC pulley diameter reduced to 2.185 inches. · STU Honda K20C1 Turbo I4 exempted from 3% direct injection weight adder. · STU GT3U minimum weight increases 150 pounds to 250 pounds. · STU Audi 1.8T Wagon removed; Porsche 944 1800cc weight to Chart, turbo inlet restrictor deleted. · STU-GT3 reclassified as STU-GT3U, effective 1 January 2026. · STU GT3 TCR may run 275-wide DOT tires with 100 lb weight penalty; A compound prohibited at 275. · SMX OE instrument cluster must stay unmodified and connected; aftermarket dash allowed if wiring only re-routed; alternate gauges now permitted; foot pedal comfort mods allowed without relocation. · STL STU Mazda Miata alternate front hubs Mazda Motorsports Development Part #0000-04-5HUB-S1 approved. · STU BMW N54/N55 turbo inlet restrictors now required per GCR definition; twin turbo conversion to single turbo clarified. · STU Mini Cooper S SC: 1900 stock pulley spec to 2.565 diameter; 2100 now permits 2.285 diameter pulley.showhide 2025-09-01 SRF3 SRF Rule Updates #38853otheraddedSRF3 adds oil cooler options P/N G480503 and P/N G1148500; brake rule restructured to list Hawk Blue pads, Wilwood rotor, caliper kit, master cylinder options. 2025-09-01 STU Lotus Weight Reduction E&O #38919weightfaster · weightSTU Lotus Elise SC and Exige SC weight reduced from 2450 to 2250 lbs. 2025-08-01 STU STU-TCR Adjustments #38723weightslower · weightSTU-TCR gains GT3 TCR spec lines; 275 tyre option now costs 150 lb adder, up from 100 lb. 2025-08-01 STU Lotus Weight Reduction #38772weight -50 lbsfaster · weightLotus Evora GT4 minimum weight drops to 2700 lbs; Elise Cup R to 2250 lbs; Elise SC and Exige SC to 2450–2550 lbs. 2025-07-01 STU 2.8-3.2L N/A Engine Allowances #38007tyres & wheelsfaster · tyres & wheelsSTU 2.8–3.2L N/A engines now permit 245 max tyre width; over 3150 lbs cars may run 275 with 2% weight penalty. 2025-07-01 STU 2006-2015 Mazda Miata Intake Manifold #38422engineadded · engineSTU Mazda MZR intake manifold now allows Goodwin 61-2510 or Gato Performance 31972. 2025-07-01 STU Requesting Approval of the JDM Honda h23a #38489cars addedaddedSTU Honda JDM H23a added, 2259 cc, minimum weight per chart, must meet ST engine regulations. 2025-06-01 SM SMX Data Submission - Penalties #38248otheraddedSMX drivers must submit data acquisition files on time or face suspension and $250 fine. 2025-06-01 SM Committee) SMX Penaly Clarification updated language #38337wordingwordingSMX penalty language clarified: level 1 and 3 infractions may carry $1,000 fines, level 2 and 4 may carry $500 fines. 2025-05-01 SM Clarify Tire Marking Regs #38005wordingwordingSM tire marking rules clarified: one Hoosier SM 7.5 P205/50/ZR17 set per Super Tour weekend, impound after first dry session, damaged tires may be replaced with used tires only. 2025-05-01 STU Wheel Size Inconsistency #38018tyres & wheelstyres & wheelsSTU wheels capped at 18 inches diameter; under 2,850 lbs max 8 inches wide, over 2,850 lbs max 9 inches wide. 2025-05-01 STU Table C: STU-GT3U Clarification #38268weightfaster · weightSTU-GT3U minimum weight reduced from plus 250 to plus 225 pounds; wheel and tyre options clarified with weight adjustments. 2025-04-01 SRF3 Driver Safety & Comfort #37966otheraddedSRF drivers with disabilities may modify seat and controls for safety and comfort with SCCA approval, noted in logbook, for that driver only. 2025-04-01 SRF3 Update SADEV transmission specs #37992wordingwordingSRF SADEV-SRF3 6-speed sequential transmission: effective date clarified to 1 April 2025 onward. 2025-03-01 STU BMW N54/N55 Engine Allowance Follow Up #37447cars addedaddedSTU BMW N54/N55 3.0 classified at chart plus 3% minimum weight; N54 twin turbo not allowed. 2025-03-01 STU STU Mini Cooper pulley size clarification re: letter #36980 #37717inductionfaster · inductionSTU Mini Cooper S SC pulley diameter reduced to 2.185 inches. 2025-03-01 STU Question About a Weight Modifier #37782weightfaster · weightSTU Honda K20C1 Turbo I4 exempted from 3% direct injection weight adder. 2025-03-01 STU Increase Minimum Weight #37919weight +100 lbsslower · weightSTU GT3U minimum weight increases 150 pounds to 250 pounds. 2025-01-01 STU Audi 1.8t Wagon STU Table B #36685cars addedremoved · cars addedSTU Audi 1.8T Wagon removed; Porsche 944 1800cc weight to Chart, turbo inlet restrictor deleted. 2025-01-01 STU Merger GT3 to STU #37486wordingunclearSTU-GT3 reclassified as STU-GT3U, effective 1 January 2026. 2025-01-01 STU GT3 TCR Tire allowance #37494tyres & wheelsadded · tyres & wheelsSTU GT3 TCR may run 275-wide DOT tires with 100 lb weight penalty; A compound prohibited at 275. 2024-12-01 SM E&O SMX Regs 9.1.7.1.D.5.u-.w #37070wordingwordingSMX OE instrument cluster must stay unmodified and connected; aftermarket dash allowed if wiring only re-routed; alternate gauges now permitted; foot pedal comfort mods allowed without relocation. 2024-12-01 STU Request to Remove Miata Hubs from General category #37138cars addedaddedSTL STU Mazda Miata alternate front hubs Mazda Motorsports Development Part #0000-04-5HUB-S1 approved. 2024-12-01 STU BMW N54/N55 Engine Allowance #37146wordingwordingSTU BMW N54/N55 turbo inlet restrictors now required per GCR definition; twin turbo conversion to single turbo clarified. 2024-11-01 STU R53 15% Pulley Request #36980enginefaster · engineSTU Mini Cooper S SC: 1900 stock pulley spec to 2.565 diameter; 2100 now permits 2.285 diameter pulley.
	Road America Runoffs 20242024-10-01	2:26.227Thomas Noble · fastest of 18 · top 5 within 2.3s-1.656s (-1.12%)	2:25.824Thomas Noble · fastest of 17 · top 5 within 2.4s-2.586s (-1.74%)	145.3Thomas Noble+1.1 mph (+0.8%)	2:27.773Denny Stripling · fastest of 57 · top 5 within 0.3s-2.013s (-1.34%)	2:28.129S Sandy Satullo III · fastest of 52 · top 5 within 0.7s-2.909s (-1.93%)	135.2Denny Stripling+3.4 mph (+2.6%)	+2.305squal +1.546s	101.6%qual 101.1%						2:41.106Ethan Goulart · fastest of 49 · top 5 within 0.5s-1.103s (-0.68%)	2:41.486Brett Kowalski · fastest of 43 · top 5 within 0.3s-2.262s (-1.38%)	119.9Alex Bertagnoli-1.4 mph (-1.2%)	+15.662squal +14.879s	110.7%qual 110.2%
18 rule changes (STU: 4, SRF3: 10, SM: 4)2 aero · 2 suspension & brakes · 1 engine · 1 induction · 1 tyres & wheels · 1 weight · 5 wording · 5 other · SRF3 air filter rule removes K&N RC-9160 option, specifies Weems P/N WM301020 only. · SRF Wilwood vented rotor minimum thickness increases to 13.25mm, 0.522 inches. · SRF3 Hoosier decal placement changed from four logos on nose and tail to three logos on sides and center front. · SMX Spec MX-5 camera requirement: non-functioning recorder now will instead of may warrant penalty or disqualification. · SM and SMX must run latest AIM Data Logger Spec MX-5 ECU Protocol, effective 2024-09-01. · SMX Mazda MX-5 OE versus OEM definitions clarified in GCR section 9.1.7.1; wording change only. · SM and SMX now allow an alternate shifter bushing at the bottom of the shift lever. · SRF Hoosier contingency decal requirement reduced from four decals in specific locations to three decals with simplified placement. · SRF wet tyres: front P185/60R13 H20 or W2 and rear P205/60R13 H20 or W2 removed; front P185/65R13 W2 and rear P205/60R13 W2 now required. Hoosier decal placement specified. · STU RWD turbo cars no longer required to reduce inlet restrictor by 1 mm from table minimum. · SRF3 alternator pulley minimum weight drops from 12 to 11 oz, adds P/N G902131 six-row option. · STU Mini Cooper S SC gains alternate LEAP OMICRON hood scoop part LEP-OMICRON3 as permitted option. · STU BMW S54 B32 OEM dry sump oiling system now permitted. · STL and STU now permit electric power steering pumps, OEM electric-assisted steering, or column-mounted electric steering assist systems. · SRF rain/brake light must be Super Bright LEDs Inc. P/N PT-STRB-R24; secondary filament must connect to rain light switch. · SRF brake light must be Super Bright LEDs Inc. P/N PT-STRB-R24, with SCCA Enterprises P/N 180427A pigtail and strobing rain light kit. · SRF adds mandatory front brake ducts 12–36 inches, throttle pedal heel-toe extension, braided stainless flex lines, camber limit 5.0 degrees, radiator opening height 3½ ± ½ inches, rear shift cable clamp P/N WM302007A. · SRF radiator options expanded: Enterprises P/N 480465 with baffle 480464, 480466, or Automotive 1R698 and CU698 allowed if cross-reference equivalent.showhide 2024-10-01 SRF3 Update SRF3 Air Filter Rule #36681wordingremovedSRF3 air filter rule removes K&N RC-9160 option, specifies Weems P/N WM301020 only. 2024-10-01 SRF3 Update SRF Brake Rotor Thickness #36687suspension & brakessuspension & brakesSRF Wilwood vented rotor minimum thickness increases to 13.25mm, 0.522 inches. 2024-10-01 SRF3 Hoosier Tire Decal Placement #36739wordingwordingSRF3 Hoosier decal placement changed from four logos on nose and tail to three logos on sides and center front. 2024-09-01 SM SMX Camera Rule Correction #36496wordingwordingSMX Spec MX-5 camera requirement: non-functioning recorder now will instead of may warrant penalty or disqualification. 2024-09-01 SM Committee) AIM ECU Protocol #36556engineadded · engineSM and SMX must run latest AIM Data Logger Spec MX-5 ECU Protocol, effective 2024-09-01. 2024-09-01 SM Committee) OE versus OEM Definitons #36608wordingwordingSMX Mazda MX-5 OE versus OEM definitions clarified in GCR section 9.1.7.1; wording change only. 2024-09-01 SM Committee) Shifter Bushing #36611otheraddedSM and SMX now allow an alternate shifter bushing at the bottom of the shift lever. 2024-09-01 SRF3 Update to Letter 36619 with new Hoosier Contingency Decal Info #36624wordingwordingSRF Hoosier contingency decal requirement reduced from four decals in specific locations to three decals with simplified placement. 2024-08-01 SRF3 Update Rain Tire Rule and Hoosier Decal Placement #36436tyres & wheelstyres & wheelsSRF wet tyres: front P185/60R13 H20 or W2 and rear P205/60R13 H20 or W2 removed; front P185/65R13 W2 and rear P205/60R13 W2 now required. Hoosier decal placement specified. 2024-08-01 STU RWD Turbo Disadvantage #36255inductionfaster · inductionSTU RWD turbo cars no longer required to reduce inlet restrictor by 1 mm from table minimum. 2024-06-01 SRF3 SRF3 Alternator Pulley Update In #36095weightfaster · weightSRF3 alternator pulley minimum weight drops from 12 to 11 oz, adds P/N G902131 six-row option. 2024-03-01 STU Letter #35397 addendum #35453aeroadded · aeroSTU Mini Cooper S SC gains alternate LEAP OMICRON hood scoop part LEP-OMICRON3 as permitted option. 2024-03-01 STU S54 Drysump #35464otheraddedSTU BMW S54 B32 OEM dry sump oiling system now permitted. 2024-02-01 STU ST Electric-Assisted Steering Systems #35066aeroadded · aeroSTL and STU now permit electric power steering pumps, OEM electric-assisted steering, or column-mounted electric steering assist systems. 2024-01-01 SRF3 Update SRF Rain / Brake Rule #34706otherotherSRF rain/brake light must be Super Bright LEDs Inc. P/N PT-STRB-R24; secondary filament must connect to rain light switch. 2024-01-01 SRF3 Update SRF Brake Light Rule v1 #34853otherotherSRF brake light must be Super Bright LEDs Inc. P/N PT-STRB-R24, with SCCA Enterprises P/N 180427A pigtail and strobing rain light kit. 2024-01-01 SRF3 SRF / SRF3 Rule Updates #35268suspension & brakessuspension & brakesSRF adds mandatory front brake ducts 12–36 inches, throttle pedal heel-toe extension, braided stainless flex lines, camber limit 5.0 degrees, radiator opening height 3½ ± ½ inches, rear shift cable clamp P/N WM302007A. 2023-10-01 SRF3 SRF Radiator Rule Update #34805otheraddedSRF radiator options expanded: Enterprises P/N 480465 with baffle 480464, 480466, or Automotive 1R698 and CU698 allowed if cross-reference equivalent.
	Virginia International Raceway Runoffs 20232023-09-23	2:00.389Johan Schwartz · fastest of 13 · top 5 within 2.3s-0.226s (-0.19%)	2:02.302Mark Liller · fastest of 14 · top 5 within 1.6s-30.055s (-19.73%)	144.0Mark Liller+0.1 mph (+0.1%)	2:03.842Morgan Burkhard · fastest of 40 · top 5 within 0.2s+0.126s (+0.10%)	2:04.911David Ogburn · fastest of 39 · top 5 within 0.3s-17.155s (-12.08%)	134.5Bobby Sak+0.1 mph (+0.0%)	+2.609squal +3.453s	102.1%qual 102.9%						2:14.986Danny Steyn · fastest of 52 · top 5 within 0.1s+0.322s (+0.24%)	2:16.229Julian DaCosta · fastest of 46 · top 5 within 0.3s-2.878s (-2.07%)	120.3Jim Drago+1.1 mph (+0.9%)	+13.927squal +14.597s	111.4%qual 112.1%
8 rule changes (STU: 3, SRF3: 4, SM: 1)2 engine · 2 tyres & wheels · 2 weight · 1 cars added · 1 wording · STU adds 2022 Toyota GR Cup and GR86 Cup, both 2387cc, 2700 lbs, 18-inch wheels, 245/620R18 slicks. · SRF wet front tyre changes to Hoosier P/N 46100 P185/60R13 H20 or W2 with 2.5" ground clearance. · SRF front W2 rain tyre Hoosier part number changes from 46100 to 46101 P185/65R13. · STU Mazda BP5A now classified at 1839 cc displacement, 2510 lbs minimum weight, alternate intake manifold permitted. · SRF removes 1985 Renault Alliance solid front rotor option; restrictor sizes decrease 1mm for newer Kawasaki and multi-brand engines; minimum weights increase to 1100 lbs. · SRF3 alternate dash panel P/N 180100 or 180101 moved from optional to required bodywork section. · STU minimum weights adjusted: 2450 cc to 2595 lbs, 2600 cc to 2710 lbs. · SM Mazda MX-5 Miata 01-05 minimum weight rises to 2450 lbs, or 2465 with alternate bore.showhide 2023-07-01 STU 2022 Toyota GR Cup for STU #34449cars addedaddedSTU adds 2022 Toyota GR Cup and GR86 Cup, both 2387cc, 2700 lbs, 18-inch wheels, 245/620R18 slicks. 2023-06-01 SRF3 Hoosier SRF Wet Front Tire Rule Update #34189tyres & wheelstyres & wheelsSRF wet front tyre changes to Hoosier P/N 46100 P185/60R13 H20 or W2 with 2.5" ground clearance. 2023-05-01 SRF3 Update SRF Front W2 Rain Tire Part Number #34118tyres & wheelstyres & wheelsSRF front W2 rain tyre Hoosier part number changes from 46100 to 46101 P185/65R13. 2023-04-01 STU Alternate OEM Miata Intake Manifold #33827engineadded · engineSTU Mazda BP5A now classified at 1839 cc displacement, 2510 lbs minimum weight, alternate intake manifold permitted. 2023-03-01 SRF3 Update SRF Brake Rule #33469enginefaster · engineSRF removes 1985 Renault Alliance solid front rotor option; restrictor sizes decrease 1mm for newer Kawasaki and multi-brand engines; minimum weights increase to 1100 lbs. 2023-03-01 SRF3 Update SRF Bodywork Fitment Rule #33765wordingwordingSRF3 alternate dash panel P/N 180100 or 180101 moved from optional to required bodywork section. 2023-03-01 STU E&O STU NA Weight Chart. #33737weightfaster · weightSTU minimum weights adjusted: 2450 cc to 2595 lbs, 2600 cc to 2710 lbs. 2023-01-01 SM BOP for NB1 and NB2 #32309weightslower · weightSM Mazda MX-5 Miata 01-05 minimum weight rises to 2450 lbs, or 2465 with alternate bore.
	Virginia International Raceway Runoffs 20222022-09-24	2:00.615Johan Schwartz · fastest of 21 · top 5 within 2.6s+0.667s (+0.56%)	2:32.357Mark Liller · fastest of 19 · top 5 within 4.3s+31.874s (+26.46%)	143.9Johan Schwartz+0.1 mph (+0.1%)	2:03.716Franklin Futrelle · fastest of 44 · top 5 within 0.6s-0.908s (-0.73%)	2:22.066Franklin Futrelle · fastest of 40 · top 5 within 1.2s+17.311s (+13.88%)	134.5David Ogburn+2.1 mph (+1.6%)	-10.291squal +3.101s	93.2%qual 102.6%	1:57.689James Weida · fastest of 11 · top 5 within 3.9s+0.328s (+0.28%)	2:21.862Sven de Vries · fastest of 10 · top 5 within 14.3s+24.290s (+20.66%)	142.9Calvin Stewart+0.1 mph (+0.1%)	-10.495squal -2.926s	93.1%qual 97.6%	2:14.664Danny Steyn · fastest of 60 · top 5 within 0.2s+0.112s (+0.08%)	2:19.107Travis Wiley · fastest of 58 · top 5 within 0.9s+2.648s (+1.94%)	119.2Jonathan Neudorf-0.6 mph (-0.5%)	-13.250squal +14.049s	91.3%qual 111.6%
31 rule changes (STU: 21, SRF3: 3, F5: 6, SM: 1)6 weight · 5 engine · 2 aero · 2 cars added · 2 tyres & wheels · 10 wording · 4 other · F500 Rotax 493 and 593 intake boots: removed Moto Tassinari V3124-873B-2 from 493/593 non-HO allowance, added Moto Tassinari V3120-794A-2 option for non-HO. · F500 Rotax engines now permit Ingi Tech Sparker ignition DCP-CDI-P2 as alternate ECU. · STU Mazda 13B Turbo added as Chart Limited displacement, streetport only, alternative turbos only. · STU OEM louver vents no longer count against vent allowance or 200 square inch limit. · STU non-4-valve engines gain 9% base engine weight reduction allowance; 2400cc minimum weight drops 1 lb to 2595. · F500 clarifies stepped diameter exhaust headers prohibited except at cylinder head flange area. · STU normally-aspirated engines 2976cc–3200cc with single throttle body lose 10% base engine weight reduction allowance. · ST removes redundant language about engine balance shaft removal and alternate pulley installation. · F500 Rotax 593 intake boot options clarified; oil injection pump removal now permitted. · SRF tire rule wording clarified: tires must be run as delivered. · SRF brake rotor minimum thickness reduced from 13.25 mm to 12.20 mm; seals and air filter specs clarified. · STU cars that qualified for 9 inch wheels in 2021 may continue running them through 2022 only. · STU splitter definition clarified: must attach to lowest point of front, have no vertical deviations. · SM Majors must run authorized Penske shock and mount; Regional competitors not required until further evaluation. · STU BMW E36 M3 (95-99) S52B32 minimum weight cut to 3110 lbs from 3200, displacement to 3152 cc. · STU BMW S50B32 Euro maximum displacement 3201 cc, minimum weight 3300 lbs, permits 0.040 overbore and 0.5 compression increase. · ST engine swap origin rule narrowed: North America changed to United States only for case-by-case approval. · STU Honda CRX 84-91 and Civic Del Sol 93-97 both ineligible for front-wheel-drive weight reductions. · STU wheel width rule clarified: under 2950 lbs uses max 8.0 inches, 2950 lbs and over uses max 9.0 inches. · STU single-throttle body cars get lower minimum weights: 2450cc to 2596 lbs, 2500cc to 2635 lbs, 2550cc to 2675 lbs. · F500 Majors and Runoffs cars must install AIM part #X47KPFSOLO2R0 data box mount for Solo or Solo 2. · STU single throttle body weight reduction removed; minimum weights revised down to 2990 lbs at 3000cc from 3300 lbs. · STU Audi A4 1.8T minimum weight fixed to 3050 lbs, K04 turbo removed, VF30 with 35mm restrictor required; Porsche 944 1800 weight fixed to 3050 lbs, VW/Audi 1.8L engine removed, 35mm inlet restrictor required. · STL and STU Improved Touring vehicles must now conform to section 9.1.4 Tires & Wheels. · STU engines may delete balance shafts and plug openings; alternate pulleys or gears allowed only for timing belt or chain operation. · STU hood vents now allow louvers within 200 square inches. · F5 cars must install AIM part #X47KPFSOLO2R0 data box mount for Majors and Runoffs. · STU adds Honda K23 with 2354 cc displacement and chart minimum weight, K24 block allowed with K23 internals and head. · STU Honda K23 relaxes internal engine requirement, now needs only K23 crankshaft. · STL/STU intake manifold and cylinder head porting clarified as free; intake and exhaust porting wording removed. · SRF wet tyres front P185/65R13 W2 option added; air box clarified as-delivered; SRF3 restrictor plate G301048 mandatory Jan 1 2022; P2 motorcycle engines up to 1005cc with 35mm restrictor, 2009+ stock 1075 lbs, 2008 stock 1025 lbs, modifie…showhide 2022-09-01 F5 Intake Boots Correction #33028wordingwordingF500 Rotax 493 and 593 intake boots: removed Moto Tassinari V3124-873B-2 from 493/593 non-HO allowance, added Moto Tassinari V3120-794A-2 option for non-HO. 2022-08-01 F5 Ensure availability of ECU for Rotax engines #32695engineadded · engineF500 Rotax engines now permit Ingi Tech Sparker ignition DCP-CDI-P2 as alternate ECU. 2022-08-01 STU Request Mazda 13 B turbo #32668cars addedaddedSTU Mazda 13B Turbo added as Chart Limited displacement, streetport only, alternative turbos only. 2022-08-01 STU Hood Vents and Intercooler Scoops #32733aeroadded · aeroSTU OEM louver vents no longer count against vent allowance or 200 square inch limit. 2022-08-01 STU Non 4 valve weight reduction removed #32808weightfaster · weightSTU non-4-valve engines gain 9% base engine weight reduction allowance; 2400cc minimum weight drops 1 lb to 2595. 2022-07-01 F5 Clarify stepped exhaust header references #32743wordingwordingF500 clarifies stepped diameter exhaust headers prohibited except at cylinder head flange area. 2022-07-01 STU Error in new minimum weight table when combined with other text #32711engineslower · engineSTU normally-aspirated engines 2976cc–3200cc with single throttle body lose 10% base engine weight reduction allowance. 2022-07-01 STU Redundant Language in May GCR #32713wordingwordingST removes redundant language about engine balance shaft removal and alternate pulley installation. 2022-06-01 F5 593 carb boot availability and oil pump clarification #32527wordingwordingF500 Rotax 593 intake boot options clarified; oil injection pump removal now permitted. 2022-06-01 SRF3 SRF Tire Rule Update #32614wordingwordingSRF tire rule wording clarified: tires must be run as delivered. 2022-06-01 SRF3 Brake, seal, and air filter clarifications #32670otherfasterSRF brake rotor minimum thickness reduced from 13.25 mm to 12.20 mm; seals and air filter specs clarified. 2022-05-01 STU Opposed to the Proposed STU Weight Chart #32381tyres & wheelsadded · tyres & wheelsSTU cars that qualified for 9 inch wheels in 2021 may continue running them through 2022 only. 2022-05-01 STU Clarification request for GCR 9.1.4.D.3.a Splitter Definition #32414wordingwordingSTU splitter definition clarified: must attach to lowest point of front, have no vertical deviations. 2022-04-01 SM Update GCR Section 9.1.7.3.A.1. #32217wordingwordingSM Majors must run authorized Penske shock and mount; Regional competitors not required until further evaluation. 2022-04-01 STU Request Adjustment to Min Weight for STU BMW E36 M3 (95-99) #31535weight -90 lbsfaster · weightSTU BMW E36 M3 (95-99) S52B32 minimum weight cut to 3110 lbs from 3200, displacement to 3152 cc. 2022-04-01 STU BMW E36 M3 Canadian (North American) S50B32 engine #31866engineadded · engineSTU BMW S50B32 Euro maximum displacement 3201 cc, minimum weight 3300 lbs, permits 0.040 overbore and 0.5 compression increase. 2022-04-01 STU Engine Swap Origin Country #32209wordingwordingST engine swap origin rule narrowed: North America changed to United States only for case-by-case approval. 2022-04-01 STU CRX/Civic Del Sol #32214weightslower · weightSTU Honda CRX 84-91 and Civic Del Sol 93-97 both ineligible for front-wheel-drive weight reductions. 2022-04-01 STU Error correction #32383wordingwordingSTU wheel width rule clarified: under 2950 lbs uses max 8.0 inches, 2950 lbs and over uses max 9.0 inches. 2022-04-01 STU Single TB Weight Modifiers Add to Chart #32393weightfaster · weightSTU single-throttle body cars get lower minimum weights: 2450cc to 2596 lbs, 2500cc to 2635 lbs, 2550cc to 2675 lbs. 2022-03-01 F5 E&O class name #32194otheraddedF500 Majors and Runoffs cars must install AIM part #X47KPFSOLO2R0 data box mount for Solo or Solo 2. 2022-03-01 STU Single TB Weight Modifiers #31449weightfaster · weightSTU single throttle body weight reduction removed; minimum weights revised down to 2990 lbs at 3000cc from 3300 lbs. 2022-03-01 STU Request to Remove A4 1.8t from STU Spec Line Tables #31465weightslower · weightSTU Audi A4 1.8T minimum weight fixed to 3050 lbs, K04 turbo removed, VF30 with 35mm restrictor required; Porsche 944 1800 weight fixed to 3050 lbs, VW/Audi 1.8L engine removed, 35mm inlet restrictor required. 2022-03-01 STU Improved Touring Tires #32063tyres & wheelstyres & wheelsSTL and STU Improved Touring vehicles must now conform to section 9.1.4 Tires & Wheels. 2022-02-01 STU Request Allowance for Balance Shaft Delete in STU #31434enginefaster · engineSTU engines may delete balance shafts and plug openings; alternate pulleys or gears allowed only for timing belt or chain operation. 2022-02-01 STU Request Louvers in hood vents #31916aeroadded · aeroSTU hood vents now allow louvers within 200 square inches. 2022-01-01 F5 Data Box Mounting Plate #31638otheraddedF5 cars must install AIM part #X47KPFSOLO2R0 data box mount for Majors and Runoffs. 2022-01-01 STU Request to Add Honda K23 Spec Line #30682cars addedaddedSTU adds Honda K23 with 2354 cc displacement and chart minimum weight, K24 block allowed with K23 internals and head. 2022-01-01 STU RE: Aug FT letter 30682 #31060enginefaster · engineSTU Honda K23 relaxes internal engine requirement, now needs only K23 crankshaft. 2022-01-01 STU Throttling Device Clarification #31323wordingwordingSTL/STU intake manifold and cylinder head porting clarified as free; intake and exhaust porting wording removed. 2021-12-01 SRF3 Three Updates to SRF Rules #31523otherotherSRF wet tyres front P185/65R13 W2 option added; air box clarified as-delivered; SRF3 restrictor plate G301048 mandatory Jan 1 2022; P2 motorcycle engines up to 1005cc with 35mm restrictor, 2009+ stock 1075 lbs, 2008 stock 1025 lbs, modifie…
	Indianapolis Motor Speedway Runoffs 20212021-09-25	1:47.078Joe Moser · fastest of 30 · top 5 within 2.0s-1.843s (-1.69%)	1:47.441Joe Moser · fastest of 28 · top 5 within 1.8s-1.946s (-1.78%)	146.9Kip VanSteenburg	1:49.520Franklin Futrelle · fastest of 84 · top 5 within 0.5s-0.304s (-0.28%)	1:50.095John Black · fastest of 82 · top 5 within 0.2s+0.313s (+0.29%)	132.1Matthew Horst	+2.654squal +2.442s	102.5%qual 102.3%	1:42.619Ryan Mayfield · fastest of 22 · top 5 within 1.6s-0.517s (-0.50%)	1:43.140Sven de Vries · fastest of 20 · top 5 within 1.7s+0.280s (+0.27%)	144.4James Weida	-4.301squal -4.459s	96.0%qual 95.8%	1:57.695Brian Henderson · fastest of 90 · top 5 within 0.5s-0.611s (-0.52%)	1:58.837Brian Henderson · fastest of 88 · top 5 within 0.3s-0.263s (-0.22%)	119.8Kyle Greenhill	+11.396squal +10.617s	110.6%qual 109.9%
22 rule changes (STU: 12, SRF3: 6, F5: 3, SM: 1)4 cars added · 2 engine · 1 aero · 1 suspension & brakes · 1 tyres & wheels · 1 weight · 10 wording · 2 other · F5 clarifies mechanical shifting only; throttle-cut and flat-shifter devices permitted if driver retains full control. · F5 single-seat open-wheel cars: rigid suspension becomes limited suspension in class definition. · SRF wet tyres add Hoosier W2 option alongside existing H20 from October 4, 2021. · SRF adds SADEV-SRF3 6-speed sequential transmission option with ratios 3.0–0.92:1 and 3.20 final drive. · SRF seal requirements clarified: seals now must be on driveline components in designated locations; unsealed components removed and inspected by CSR or Enterprises rather than engine shipped for testing. · STU fender flare wording clarified: flare of exterior contour may not change wheel opening size, location or shape from side view. · STU Mazda 12A Bridgeport weight reduced from 2550 lbs to 2350 lbs. · F500 Rotax 593 HO engine now permitted; 875 lbs minimum weight, MA0242SP1020A or MA0242SP1063A restrictor, specific intake boots and piston required. · SRF3 alternator pulley specified as P/N G902130 or G902130A, minimum 12oz. · STU fender flare rules clarified: maximum 2 inches total, must cover tire contact patch from above, cannot alter body configuration or wheel opening geometry. · SM adds procedure for CRB-approved obsolete parts and BOP testing in sanctioned events with point forfeiture. · STU Honda S2000 now allows F20/F22 K24 crankshaft with chart weight for achieved displacement. · ST oil coolers and filters now explicitly listed as addable or substitutable parts in vents and breathers section. · SRF and SRF3 mandatory identification revised: removed Ford Performance and Blue Oval decals, added Hoosier logo placement. · ST 90-05 Mazda Miata allowed alternate front wheel hub Mazda Motorsports Development Part #0000-04-5HUB-S1. · ST cars may now relocate ABS actuation hardware and wiring anywhere in the engine compartment. · STU Porsche PDK automatic transmission limited to 8 forward speeds; sequential DCT systems require 3.5% minimum weight increase. · STU Mazda 13B Street Port 2400 removes choke location rule, allows auto-type 2bbl with any dual-Y manifold. · STU driveshaft and half-shafts now explicitly permitted in steel or aluminum, removing OEM material requirement. · STU Mazda 13B Spec and Bridge Port removed; Street Port added at 2400 lbs minimum weight. · SRF rear springs limited to P/N 280390 only, previous part numbers no longer allowed; ground clearance wording clarified. · ST aero devices and reference areas must include end plates, exclude fasteners under 1/2" protrusion.showhide 2021-08-01 F5 Clarify allowable assisted shifting systems #30871wordingwordingF5 clarifies mechanical shifting only; throttle-cut and flat-shifter devices permitted if driver retains full control. 2021-08-01 F5 Request to correct terminology #30976wordingwordingF5 single-seat open-wheel cars: rigid suspension becomes limited suspension in class definition. 2021-08-01 SRF3 SRF Wet Tires #30849tyres & wheelsadded · tyres & wheelsSRF wet tyres add Hoosier W2 option alongside existing H20 from October 4, 2021. 2021-08-01 SRF3 SADEV-SRF3 Transmission #30926cars addedaddedSRF adds SADEV-SRF3 6-speed sequential transmission option with ratios 3.0–0.92:1 and 3.20 final drive. 2021-08-01 SRF3 SRF Update Maintenance, Repairs and Seals #30961wordingwordingSRF seal requirements clarified: seals now must be on driveline components in designated locations; unsealed components removed and inspected by CSR or Enterprises rather than engine shipped for testing. 2021-07-01 STU STU Fender flares #30696wordingwordingSTU fender flare wording clarified: flare of exterior contour may not change wheel opening size, location or shape from side view. 2021-07-01 STU Request weight reduction for 12A bridgeport motor in Miata #30751weight -200 lbsfaster · weightSTU Mazda 12A Bridgeport weight reduced from 2550 lbs to 2350 lbs. 2021-06-01 F5 Request to Allow Rotax 593 HO Engine #30712cars addedaddedF500 Rotax 593 HO engine now permitted; 875 lbs minimum weight, MA0242SP1020A or MA0242SP1063A restrictor, specific intake boots and piston required. 2021-06-01 SRF3 SRF3 Alternator Pulley #30684engineadded · engineSRF3 alternator pulley specified as P/N G902130 or G902130A, minimum 12oz. 2021-05-01 STU Request for Fender Flare Clarification #30375wordingwordingSTU fender flare rules clarified: maximum 2 inches total, must cover tire contact patch from above, cannot alter body configuration or wheel opening geometry. 2021-04-01 SM Updates - Obsolete Parts & BOP Parts #30438wordingaddedSM adds procedure for CRB-approved obsolete parts and BOP testing in sanctioned events with point forfeiture. 2021-04-01 STU Provision for Interchangeable Engine Components Already Allowed #30342engineadded · engineSTU Honda S2000 now allows F20/F22 K24 crankshaft with chart weight for achieved displacement. 2021-04-01 STU ST Oil Coolers E&O Correction to 9.1.4.2.H #30388wordingwordingST oil coolers and filters now explicitly listed as addable or substitutable parts in vents and breathers section. 2021-03-01 SRF3 Mandatory identification: #30223wordingwordingSRF and SRF3 mandatory identification revised: removed Ford Performance and Blue Oval decals, added Hoosier logo placement. 2021-03-01 STU Super Touring Alternate Miata Hubs #30345cars addedaddedST 90-05 Mazda Miata allowed alternate front wheel hub Mazda Motorsports Development Part #0000-04-5HUB-S1. 2021-02-01 STU Brake Component Relocation #29990suspension & brakessuspension & brakesST cars may now relocate ABS actuation hardware and wiring anywhere in the engine compartment. 2021-02-01 STU Porsche PDK #30081wordingwordingSTU Porsche PDK automatic transmission limited to 8 forward speeds; sequential DCT systems require 3.5% minimum weight increase. 2021-02-01 STU Reference Letter #29333 Proposed STU 13B Spec Line Changes #30086wordingwordingSTU Mazda 13B Street Port 2400 removes choke location rule, allows auto-type 2bbl with any dual-Y manifold. 2021-02-01 STU Drive Shaft Request #30087otherotherSTU driveshaft and half-shafts now explicitly permitted in steel or aluminum, removing OEM material requirement. 2021-01-01 STU 13B Rules Adjustment #29333cars addedremoved · cars addedSTU Mazda 13B Spec and Bridge Port removed; Street Port added at 2400 lbs minimum weight. 2020-12-01 SRF3 SRF Shocks, Springs and Ride Height. #29688otherotherSRF rear springs limited to P/N 280390 only, previous part numbers no longer allowed; ground clearance wording clarified. 2020-12-01 STU Request clarification on wing measurement #29640aeroaeroST aero devices and reference areas must include end plates, exclude fasteners under 1/2" protrusion.
	Road America Runoffs 20202020-10-02	2:27.883David Fiorelli · fastest of 14 · top 5 within 4.1s	2:28.410Anthony Geraci · fastest of 14 · top 5 within 3.1s	144.2David Fiorelli	2:29.786TJ Acker · fastest of 59 · top 5 within 0.5s	2:31.038Justin Hille · fastest of 55 · top 5 within 0.2s	131.9Charles Russell Turner	+2.628squal +1.903s	101.8%qual 101.3%	2:20.954Calvin Stewart · fastest of 16 · top 5 within 1.8s	2:21.391James Weida · fastest of 14 · top 5 within 1.5s	143.2Aaron Ellis	-7.019squal -6.929s	95.3%qual 95.3%	2:42.209Kyle Greenhill · fastest of 77 · top 5 within 0.5s	2:43.748Preston Pardus · fastest of 75 · top 5 within 1.0s	121.3Kyle Greenhill	+15.338squal +14.326s	110.3%qual 109.7%
32 rule changes (STU: 17, SRF3: 7, F5: 6, SM: 2)6 engine · 3 weight · 2 cars added · 2 suspension & brakes · 1 induction · 1 tyres & wheels · 15 wording · 2 other · F500 Suzuki GSXR600 engine years extended from 2003-2013 to 2003-2019. · SM allows aftermarket radiators in original location with stock OEM cooling fan, and permits 1990-1997 cars to install upper radiator seal NA75-50-OK7A. · STU fender flare rule reworded: now per-corner up to 2" total, 1% weight penalty applies to entire modification. · SM rear brake caliper may use single bracket under upper retaining bolt head to prevent pin failure. · STL and STU clarify weight adjustment calculation order: engine adjustments first, then chassis percentage additions, subtractions, and fixed pounds. · STL STU rear wing Gurney flap terminology clarified from wicker to Gurney flap in mounting and chord rules. · F5 request to adjust external jetting device cockpit control denied; no rule change made. · F5 driver adjustable carburettor mixture: refer to separate Fastrack letter #28359 for ruling. · F5 cockpit adjustment request response published in Fastrack letter 28359. · STU request for alternate intake manifold denied; no change to rules. · GT3 and STU add Borg-Warner EFR6258 turbocharger to approved turbo lists. · STU large displacement turbo engines limited by GCR turbo list; no BoP change granted. · STU sequential shifters referred to Board of Directors for approval; no rule change effective. · SRF3 shocks no longer require the same brand in all positions; only SCCA P/N 280407 bump stops allowed, one per shock, all must be sealed by Enterprises. · STU Mazda 13B Bridge Port and Street Port added with 2550 lbs and 2250 lbs minimum weight respectively. · SRF3 bump stop must be SCCA P/N 280407, no modifications, optional, maximum one per shock. · SRF Penske shock P/N 280396 bump stop P/N 280407 becomes mandatory, maximum one per shock, effective 05/01/2020. · STU Honda S2000 gains HKS Supercharger kits 12001-AH006 and 12001-AH010 as allowed options. · STU Lotus Elise Cup R and SC Exige SC gain 100 lbs minimum weight to 2300, 2500. · STU Volkswagen GTI/GLI MK5 and Jetta Mk4 may now install turbo inlet restrictor in OEM housing, per TIR spec. · STU Honda K20C1 Turbo I4 restrictor reduces from 36mm to 35mm. · STU GM Ecotech LNF now permitted without turbo, with LE5 head and intake manifold, meeting STL specs. · STU Porsche 944 now permits VW/Audi 1.8L and 2.0L turbo engines as alternates to original. · STU vehicles over 2951 lbs base weight may use 9 inch wide wheels, changed from 2950 lbs. · STU turbocharged engines now use base weight instead of minimum weight; DFI cars add 3% to base weight. · F500 Honda CBR600RR, Suzuki GSXR600, Yamaha R6 restrictor reduced to 28mm from 29mm. · SRF rain and brake rule supersedes GCR 9.3.32.B.2 effective 1/1/2024 through 12/31/2024. · SRF adds tire warmer prohibition and specifies Hoosier dry and wet tire part numbers. · SRF front nose weight minimum reduced from 35 to 32 lbs. · SRF2 becomes Regional Only; SRF3 nomenclature changed from GEN3 to Ford 1.6L conversion; SRF and SRF3 no longer compete together for points. · STU allows OEM electronic throttle bodies, manual conversion, cam changes, and manual-to-electronic conversion with same inner diameter.showhide 2020-10-01 F5 Request to Update Suzuki Engine Years for F500 #29453engineadded · engineF500 Suzuki GSXR600 engine years extended from 2003-2013 to 2003-2019. 2020-10-01 SM Radiator E&O Clarifications #29294wordingwordingSM allows aftermarket radiators in original location with stock OEM cooling fan, and permits 1990-1997 cars to install upper radiator seal NA75-50-OK7A. 2020-09-01 STU Request for Advanced Aero Rule Wording Clarification. #29124wordingwordingSTU fender flare rule reworded: now per-corner up to 2" total, 1% weight penalty applies to entire modification. 2020-08-01 SM Modifications to prevent failures of Rear Brake Caliper Pin #28953suspension & brakessuspension & brakesSM rear brake caliper may use single bracket under upper retaining bolt head to prevent pin failure. 2020-08-01 STU Minimum Weight Determination #27695wordingwordingSTL and STU clarify weight adjustment calculation order: engine adjustments first, then chassis percentage additions, subtractions, and fixed pounds. 2020-08-01 STU ST Gurney flap Wicker clarification #29012wordingwordingSTL STU rear wing Gurney flap terminology clarified from wicker to Gurney flap in mounting and chord rules. 2020-07-01 F5 Request for Cockpit Adjustment of External Jetting Devices #28359wordingunclearF5 request to adjust external jetting device cockpit control denied; no rule change made. 2020-07-01 F5 Two Stroke Motors (reply to #28359 WDYT) #28816engine 2020-07-01 F5 Re letter requesting driver adjustable carb mixture #28840wordingunclearF5 driver adjustable carburettor mixture: refer to separate Fastrack letter #28359 for ruling. 2020-07-01 F5 #28359 WDYT Request for Cockpit Adjustment #28875wordingunclearF5 cockpit adjustment request response published in Fastrack letter 28359. 2020-07-01 STU Request for Alternate Intake Manifold #26514wordingunclearSTU request for alternate intake manifold denied; no change to rules. 2020-07-01 STU Request for Addition to GT3 Approved Turbo List #27576cars addedaddedGT3 and STU add Borg-Warner EFR6258 turbocharger to approved turbo lists. 2020-07-01 STU Request BoP for my Car #29004wordingunclearSTU large displacement turbo engines limited by GCR turbo list; no BoP change granted. 2020-07-01 STU Sequential Shifters in STU #29031wordingunclearSTU sequential shifters referred to Board of Directors for approval; no rule change effective. 2020-06-01 SRF3 SRF Shocks #28791wordingwordingSRF3 shocks no longer require the same brand in all positions; only SCCA P/N 280407 bump stops allowed, one per shock, all must be sealed by Enterprises. 2020-06-01 STU Rotary Help #27833cars addedaddedSTU Mazda 13B Bridge Port and Street Port added with 2550 lbs and 2250 lbs minimum weight respectively. 2020-05-01 SRF3 Update Bump Stop Rule #28712suspension & brakessuspension & brakesSRF3 bump stop must be SCCA P/N 280407, no modifications, optional, maximum one per shock. 2020-05-01 SRF3 SRF Bump Stop Correction #27019wordingwordingSRF Penske shock P/N 280396 bump stop P/N 280407 becomes mandatory, maximum one per shock, effective 05/01/2020. 2020-04-01 STU Request to approve Honda S2000 HKS supercharger #27281otheraddedSTU Honda S2000 gains HKS Supercharger kits 12001-AH006 and 12001-AH010 as allowed options. 2020-04-01 STU Request BoP on the Lotus #27637weight +100 lbsslower · weightSTU Lotus Elise Cup R and SC Exige SC gain 100 lbs minimum weight to 2300, 2500. 2020-04-01 STU Turbo Inlet Restrictor On MK5 Volkswagen #27704otherslowerSTU Volkswagen GTI/GLI MK5 and Jetta Mk4 may now install turbo inlet restrictor in OEM housing, per TIR spec. 2020-04-01 STU Honda K20C1 removal #27732engineslower · engineSTU Honda K20C1 Turbo I4 restrictor reduces from 36mm to 35mm. 2020-04-01 STU Change GM LNF 2.0 Allowance to LSJ Engine for Viable STL 2.0 #27884engineadded · engineSTU GM Ecotech LNF now permitted without turbo, with LE5 head and intake manifold, meeting STL specs. 2020-04-01 STU Alternate Engine for Porsche 944 #28259engineadded · engineSTU Porsche 944 now permits VW/Audi 1.8L and 2.0L turbo engines as alternates to original. 2020-03-01 STU Please Modify the STU Wheel Size Rule for Clarity #27694weightfaster · weightSTU vehicles over 2951 lbs base weight may use 9 inch wide wheels, changed from 2950 lbs. 2020-03-01 STU Turbo Engine Cars Base Weight #28032wordingwordingSTU turbocharged engines now use base weight instead of minimum weight; DFI cars add 3% to base weight. 2020-01-01 F5 Change 600cc restrictor size #27883inductionslower · inductionF500 Honda CBR600RR, Suzuki GSXR600, Yamaha R6 restrictor reduced to 28mm from 29mm. 202-01-01 SRF3 SRF Rain / Brake Rule - BoD approved as follows #34958wordingwordingSRF rain and brake rule supersedes GCR 9.3.32.B.2 effective 1/1/2024 through 12/31/2024. 2019-12-01 SRF3 SRF Tire Warmer Rule #27622tyres & wheelstyres & wheelsSRF adds tire warmer prohibition and specifies Hoosier dry and wet tire part numbers. 2019-12-01 SRF3 SRF / SRF3 Nose Weight Reduction #27706weightfaster · weightSRF front nose weight minimum reduced from 35 to 32 lbs. 2019-12-01 SRF3 SRF / SRF3 Majors & Regional Class Updates #27723wordingwordingSRF2 becomes Regional Only; SRF3 nomenclature changed from GEN3 to Ford 1.6L conversion; SRF and SRF3 no longer compete together for points. 2019-12-01 STU Request for an electronic throttle body #27342engineadded · engineSTU allows OEM electronic throttle bodies, manual conversion, cam changes, and manual-to-electronic conversion with same inner diameter.
	Virginia International Raceway Runoffs 20192019-10-05	1:59.948Kevin Boehm · fastest of 25 · top 5 within 3.5s	2:00.483Kevin Boehm · fastest of 25 · top 5 within 2.5s	143.8Kevin Boehm	2:04.624Brian Schofield · fastest of 54 · top 5 within 0.6s	2:04.755Bobby Sak · fastest of 53 · top 5 within 0.3s	132.4Bobby Sak	+4.272squal +4.676s	103.5%qual 103.9%	1:57.361Wiley Mcmahan · fastest of 15 · top 5 within 3.8s	1:57.572Wiley Mcmahan · fastest of 15 · top 5 within 4.0s	142.8Eric McRee	-2.911squal -2.587s	97.6%qual 97.8%	2:14.552Todd Buras · fastest of 60 · top 5 within 0.2s	2:16.459Elivan Goulart · fastest of 56 · top 5 within 0.4s	119.8Jim Drago	+15.976squal +14.604s	113.3%qual 112.2%
30 rule changes (STU: 22, SRF3: 3, F5: 1, SM: 4)5 aero · 5 cars added · 4 engine · 3 induction · 1 weight · 8 wording · 4 other · F500 Honda CBR600RR, Suzuki GSXR600, and Yamaha R6 minimum weights increase to 900 lbs. · STU wing assembly wording corrected: no part may be higher than roof height. · SRF drivers may now use Dash Windscreen Kit P/N 1180103 or P/N 180102. · STU Nissan SR20DET removes -2mm penalty from Table B. · STU allows alternate intake manifolds on case-by-case basis; stock throttle device and manifold otherwise required. · SRF3 multi-piece nose assembly approved for use; no other nose modifications allowed. · STU aftermarket side skirts now allowed if they meet 3-inch ride height, lack ducts except jacks or exhaust, don't exceed fascia width, stay below door bottom, and don't reinforce chassis. · STU wheel flare wording clarified: each fender may be flared to 2" with 1% weight penalty, maintaining OEM profile. · SRF3 brakes now accept Hawk Blue 9012 pads P/N 801993 only; Wilwood vented rotor P/N 800065 minimum 13.25mm as delivered; caliper bushings P/N 1196185 A or B permitted. Shock absorbers: Penske P/N 280396 only, sealed, with SCCA bump rubber… · STL and STU ride height measurement clarified: lowest rocker panel point without driver, excluding pinch weld. · STU Mazda 13B Bridge Port now permits ELITE ROTARY SHOP FD V2.0 intake manifold; stock throttle body requirement removed. · STU Mazda MZR gains alternate Goodwin intake manifold option with stock or Acura throttle body. · STU alternate suspension components rule moved from section E to section D. · STU Honda/Acura B20 now permits B16 or B18 VTEC cylinder head and matching intake manifold. · STU flared fenders up to 2" with 1% weight penalty moved from base to Advanced Aero. · STU Honda Civic Si TCA 2017- requires 37mm TIR throttle as of June 1, 2019. · STU BMW S54B32 OEM classified separately from E46, displacement 3246 cc, minimum weight 3300 lbs, OEM engine mandatory. · SM fuel pump and filter now permitted as Mazda or OEM equivalent part. · Honda Civic Si 2017- added to STU with 1500cc displacement, 2800 lbs minimum weight, OEM engine and bodywork, specific HPD parts allowed. · STU BMW E46 S54 OEM 3246cc added at 3300 lbs minimum; no Super Touring allowances, OEM intake and cams, 1mm overbore, compression +0.5 permitted. · STU Mazda 13B and 13B Bridge Port may use 13B RE or REW housings and intake with turbo removed. · STU Honda K24 may use intake part numbers 17100-RRB-A00 or 17100-PRB-A10. · STU Mazda 12A Bridge Port added, minimum weight 2550 lbs, Nikki or Auto-type carburettor with specified modifications. · STU World Challenge car weight rule deleted; no replacement specified. · STU AWD/RWD cars no longer must reduce restrictor 1 mm from table. · STU rear wing maximum 12" cord, 72 sq in end plates each, roof height max, body width limit. · SM allows factory Mazda ECU and injector harnesses (P/N 0000-10-020E-99, 0000-10-080D-99) on 1999–2000 model year cars, unmodified. · SM electrical rules reorganized and clarified; alternator now externally regulated only by OEM ECU or master kill switch; harness repair by splicing permitted. · SM tire tread protrusion language removed from GCR 9.1.7.C.5. · STU adds Honda K20C1 Turbo I4, 1996 cc, 3025 lbs minimum weight, 36mm TIR required.showhide 2019-08-31 F5 Request for Weight Increase for Motorcycle Powered Cars #27214weight +25 lbsslower · weightF500 Honda CBR600RR, Suzuki GSXR600, and Yamaha R6 minimum weights increase to 900 lbs. 2019-08-31 STU Request to correct E&O advanced aerodynamics #27290wordingwordingSTU wing assembly wording corrected: no part may be higher than roof height. 2019-07-01 SRF3 SRF Dash Windscreen Kit #27028aeroadded · aeroSRF drivers may now use Dash Windscreen Kit P/N 1180103 or P/N 180102. 2019-07-01 STU Remove -2mm penalty from SR20DET Nissan #26982enginefaster · engineSTU Nissan SR20DET removes -2mm penalty from Table B. 2019-07-01 STU Request clarification for manifold and throttle in STU #27004wordingwordingSTU allows alternate intake manifolds on case-by-case basis; stock throttle device and manifold otherwise required. 2019-05-31 SRF3 New SRF Sectional Nose Rule Addition #26914aeroadded · aeroSRF3 multi-piece nose assembly approved for use; no other nose modifications allowed. 2019-05-31 STU Request to clarify afterrmarket side skirts exhaust exit #26814aeroadded · aeroSTU aftermarket side skirts now allowed if they meet 3-inch ride height, lack ducts except jacks or exhaust, don't exceed fascia width, stay below door bottom, and don't reinforce chassis. 2019-05-31 STU Wheel Flare wording #26872wordingwordingSTU wheel flare wording clarified: each fender may be flared to 2" with 1% weight penalty, maintaining OEM profile. 2019-05-01 SRF3 SRF Brakes and Shock Rule Changes #26629otherotherSRF3 brakes now accept Hawk Blue 9012 pads P/N 801993 only; Wilwood vented rotor P/N 800065 minimum 13.25mm as delivered; caliper bushings P/N 1196185 A or B permitted. Shock absorbers: Penske P/N 280396 only, sealed, with SCCA bump rubber… 2019-05-01 STU Request Ride Height Clarification #26597wordingwordingSTL and STU ride height measurement clarified: lowest rocker panel point without driver, excluding pinch weld. 2019-04-01 STU Request to Use Japanese Mazda 13b Intake Manifold #25790engineadded · engineSTU Mazda 13B Bridge Port now permits ELITE ROTARY SHOP FD V2.0 intake manifold; stock throttle body requirement removed. 2019-04-01 STU Request Alternate Intake for Mazda MZR In a Rear Wheel Drive App. #26352inductionadded · inductionSTU Mazda MZR gains alternate Goodwin intake manifold option with stock or Acura throttle body. 2019-04-01 STU E&O Suspension #26424wordingwordingSTU alternate suspension components rule moved from section E to section D. 2019-04-01 STU Revisit B20 VTEC #26530engineadded · engineSTU Honda/Acura B20 now permits B16 or B18 VTEC cylinder head and matching intake manifold. 2019-04-01 STU Move Flared Fenders to STU Advanced Aero #26564aeroaeroSTU flared fenders up to 2" with 1% weight penalty moved from base to Advanced Aero. 2019-04-01 STU TCA Civic SI E&O #26606inductionslower · inductionSTU Honda Civic Si TCA 2017- requires 37mm TIR throttle as of June 1, 2019. 2019-04-01 STU S54 Spec line #26620cars addedcars addedSTU BMW S54B32 OEM classified separately from E46, displacement 3246 cc, minimum weight 3300 lbs, OEM engine mandatory. 2019-03-01 SM Request to allow aftermarket fuel filters. #26370otheraddedSM fuel pump and filter now permitted as Mazda or OEM equivalent part. 2019-03-01 STU Request to Class Assignment for 2017 Civic #24287cars addedaddedHonda Civic Si 2017- added to STU with 1500cc displacement, 2800 lbs minimum weight, OEM engine and bodywork, specific HPD parts allowed. 2019-03-01 STU Request to run E46 3246cc in STU #25126cars addedaddedSTU BMW E46 S54 OEM 3246cc added at 3300 lbs minimum; no Super Touring allowances, OEM intake and cams, 1mm overbore, compression +0.5 permitted. 2019-03-01 STU Engine Classification for Rotary #25564engineadded · engineSTU Mazda 13B and 13B Bridge Port may use 13B RE or REW housings and intake with turbo removed. 2019-03-01 STU K24/K20 Head Swap Clarification/Amendment #25899otheraddedSTU Honda K24 may use intake part numbers 17100-RRB-A00 or 17100-PRB-A10. 2019-03-01 STU Request to Classify 12a Bridge Ported Rotary Engine #25985cars addedaddedSTU Mazda 12A Bridge Port added, minimum weight 2550 lbs, Nikki or Auto-type carburettor with specified modifications. 2019-03-01 STU World Challenge Car Eligibility #26387wordingunclearSTU World Challenge car weight rule deleted; no replacement specified. 2019-03-01 STU Request a phone call for discussion regarding weight #26398inductionfaster · inductionSTU AWD/RWD cars no longer must reduce restrictor 1 mm from table. 2019-03-01 STU Advanced Aero E&O #26413aeroadded · aeroSTU rear wing maximum 12" cord, 72 sq in end plates each, roof height max, body width limit. 2019-02-01 SM Request 99-00 replacement Wire harnesses #25602otheraddedSM allows factory Mazda ECU and injector harnesses (P/N 0000-10-020E-99, 0000-10-080D-99) on 1999–2000 model year cars, unmodified. 2019-02-01 SM Organize and Clarify 9.1.7.C.1.o. #25913wordingwordingSM electrical rules reorganized and clarified; alternator now externally regulated only by OEM ECU or master kill switch; harness repair by splicing permitted. 2019-02-01 SM Strike Tire Tread Language #26123wordingremovedSM tire tread protrusion language removed from GCR 9.1.7.C.5. 2019-01-01 STU Request to Equalize Direct Injected Turbo Cars #24890cars addedaddedSTU adds Honda K20C1 Turbo I4, 1996 cc, 3025 lbs minimum weight, 36mm TIR required.
	Sonoma Raceway Runoffs 20182018-10-10	1:19.234Franklin Church · fastest of 10 · top 5 within 21.5s	1:46.514Kevin Boehm · fastest of 9 · top 5 within 7.4s	103.0Franklin Church	1:46.117Robeson Clay Russell · fastest of 36 · top 5 within 0.5s	1:47.053TJ Acker · fastest of 35 · top 5 within 0.2s	110.2Steve Fogg	+0.539squal +26.883s	100.5%qual 133.9%	1:41.807Jeff Jorgenson · fastest of 5 · top 5 within 6.6s	1:42.491David Lapham · fastest of 5 · top 5 within 9.5s	113.3David Lapham	-4.023squal +22.573s	96.2%qual 128.5%	1:54.355Ken Sutherland · fastest of 48 · top 5 within 0.7s	1:55.278Michael Carter · fastest of 48 · top 5 within 0.3s	102.2Danny Steyn	+8.764squal +35.121s	108.2%qual 144.3%
No rule changes on record between these events
	Indianapolis Motor Speedway Runoffs 20172017-09-25	1:48.921Rob Huffmaster · fastest of 34 · top 5 within 2.0s	1:49.387Rob Huffmaster · fastest of 31 · top 5 within 2.4s		1:49.824John Black · fastest of 101 · top 5 within 0.5s	1:49.782Tray Ayres · fastest of 94 · top 5 within 0.4s		+0.395squal +0.903s	100.4%qual 100.8%	1:43.136Wiley Clinton McMahan · fastest of 38 · top 5 within 1.4s	1:42.860Wiley Clinton McMahan · fastest of 37 · top 5 within 1.6s		-6.527squal -5.785s	94.0%qual 94.7%	1:58.306Chris Haldeman · fastest of 86 · top 5 within 0.5s	1:59.100Michael Gagliardo · fastest of 83 · top 5 within 0.6s		+9.713squal +9.385s	108.9%qual 108.6%
No rule changes on record between these events
	Mid-Ohio Sports Car Course Runoffs 20162016-09-19	1:32.738Joe Moser · fastest of 16 · top 5 within 2.5s	1:34.597Cameron Maugeri · fastest of 16 · top 5 within 0.8s		1:34.363John Black · fastest of 41 · top 5 within 0.5s	1:34.947Cliff White · fastest of 39 · top 5 within 0.3s		+0.350squal +1.625s	100.4%qual 101.8%	1:28.528Calvin Stewart · fastest of 14 · top 5 within 3.9s	1:29.853Steven Thompson · fastest of 12 · top 5 within 4.5s		-4.744squal -4.210s	95.0%qual 95.5%	1:40.514Justin Hille · fastest of 45 · top 5 within 0.3s	1:40.764Michael Carter · fastest of 44 · top 5 within 0.3s		+6.167squal +7.776s	106.5%qual 108.4%
No rule changes on record between these events
	Daytona International Speedway Runoffs 20152015-09-21	2:05.494Eric Heinrich · fastest of 18 · top 5 within 4.6s	2:06.756Eric Heinrich · fastest of 17 · top 5 within 3.5s		2:08.557Kerry Jacobsen · fastest of 29 · top 5 within 1.1s	2:10.215Chad Galloway · fastest of 29 · top 5 within 0.3s		+3.459squal +3.063s	102.7%qual 102.4%	2:01.824W. Clint McMahan · fastest of 16 · top 5 within 3.0s	2:03.298Matthew Strand · fastest of 15 · top 5 within 4.9s		-3.458squal -3.670s	97.3%qual 97.1%	2:18.661Andrew Carbonell · fastest of 62 · top 5 within 0.6s	2:24.067Todd Lamb · fastest of 59 · top 5 within 0.8s		+17.311squal +13.167s	113.7%qual 110.5%

By track

Track	Events	Typical % of STU	Best	Latest
Road America	4	100.0%	100.0%Runoffs 2020	100.0%Runoffs 2026
Virginia International Raceway	3	100.0%	100.0%Runoffs 2019	100.0%Runoffs 2023
Indianapolis Motor Speedway	2	100.0%	100.0%Runoffs 2017	100.0%Runoffs 2021
Daytona International Speedway	1	100.0%	100.0%Runoffs 2015	100.0%Runoffs 2015
Mid-Ohio Sports Car Course	1	100.0%	100.0%Runoffs 2016	100.0%Runoffs 2016
Sonoma Raceway	1	100.0%	100.0%Runoffs 2018	100.0%Runoffs 2018

About this data

Every event the class ran, at any track, oldest to newest on the chart and newest first in the table. Each point is the class's best lap as a share of STU's best on the same day: the weather, the track and its configuration cancel out, so one figure compares across tracks and years where lap times cannot. It still moves when the yardstick's own balance changes or its field thins, and an event the yardstick did not run has no point. A best from fewer than three cars is greyed. The rule changes that took effect between two events are folded between their rows.