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2020 ST/TT Car Classification Rules Revisions Proposed


Greg G.

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Brian Sasser

Hey everyone. New guy here from NC.

I'm hoping to start participating in TT soon and prepping my 2016 mustang GT so it's ready when I make the jump up from HPDE.

I just stumbled across this thread and would like to bring up the tire size limitation in TT4. If reading the rulebook correctly, maximum allowed tire size is 282mm section width for cars over 3000lbs, while cars <3000lbs are restricted to 266mm. It seems to me that cars weighing significantly more than 3000lbs are at a pretty big disadvantage here. Weight reduction gets expensive quickly as you all know.

Why not allow heavyweights (~3500lbs+) in TT4 to run a larger tire (~295mm)?

Selfish, I know 😜

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Agree with David, or increase tolerance (5% currently) to 45% and limit height to 4”.

If I'm understanding this correctly: This effectively kicks Hoosier's R7's or Hancook's our of the competition. Given that Hoosier is a strong supporter of NASA and has a great contingency pr

Agree with David and Marco.     

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32 minutes ago, Brian Sasser said:

Hey everyone. New guy here from NC.

I'm hoping to start participating in TT soon and prepping my 2016 mustang GT so it's ready when I make the jump up from HPDE.

I just stumbled across this thread and would like to bring up the tire size limitation in TT4. If reading the rulebook correctly, maximum allowed tire size is 282mm section width for cars over 3000lbs, while cars <3000lbs are restricted to 266mm. It seems to me that cars weighing significantly more than 3000lbs are at a pretty big disadvantage here. Weight reduction gets expensive quickly as you all know.

Why not allow heavyweights (~3500lbs+) in TT4 to run a larger tire (~295mm)?

Selfish, I know 😜

Welcome! Your mustang will fit nicely in TT3. I think it probably makes a bit too much power for TT4 unless you weight over 4300 pounds?

The rule is there to keep costs down on tires in TT4.

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Brian Sasser
On 2/6/2020 at 7:49 PM, Roman V. said:

Welcome! Your mustang will fit nicely in TT3. I think it probably makes a bit too much power for TT4 unless you weight over 4300 pounds?

Thank you. FWIW, people have stated that the actual Max Avg HP as calculated by NASA regulations is only about 380. Curb weight is claimed at over 3800lbs and I weigh about 230lbs. With the available modifiers for weight, street tires, manual transmission and a lack of aero (TMF=1.90), the numbers seem to place me in TT4. I'm going in for a Dyno test soon to confirm all this but considering that I'm new to the sport, TT4 would be ideal for it's lower spending requirements. Competitiveness is secondary to wheel time at this stage for me but I do want to get a feel for the game.

I might add, should the expected Dyno results mesh closely with real life results, I can probably whittle away some extra weight with a target somewhere close to, but not under 3901lbs. (Someone please correct me if I'm wrong)

On 2/6/2020 at 7:49 PM, Roman V. said:

The rule is there to keep costs down on tires in TT4.

I understand that completely however, I can not safely run P-metric tires at my weight. (Again, someone please correct me if I'm wrong)

Simply for arguments sake, Toyo RRs are available in an appropriate 295 size tire at a lower cost than the 275 P-METRIC tire which has a load rating of approximately 1200lbs.

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dwesterwick

I ran a 245/40R18 Hoosier R7 on a 3800-lb (comp weight) 2011 Mustang back when I ran in TTB, and I never had a tire failure or thought they were unsafe. You'll be running a little more weight and the 275/35R18 Hoosier R7 and Toyo RR have slightly lower load capacities, but it's pretty close. Just make sure you keep tire pressure high enough and try not to slide around too much.

That being said, the grip was (not surprisingly) noticeably worse with the 245mm R7 I ran in TTB than the 315mm R7 I ran in TT3 - especially under braking. I think the compromises needed to squeeze a 2011+ Mustang into TT4 aren't worth it, and TT3 is a much better fit for your car. If seat time is more important to you than being competitive, I'm not sure why you would want to run in TT4 with a tire you think might be unsafe. You can find used tires in a variety of sizes and types that would work fine in TT3, and that would help keep your consumable expenses down while you're still learning.

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Brian Sasser
16 hours ago, dwesterwick said:

That being said, the grip was (not surprisingly) noticeably worse with the 245mm R7 I ran in TTB than the 315mm R7 I ran in TT3 - especially under braking. I think the compromises needed to squeeze a 2011+ Mustang into TT4 aren't worth it, and TT3 is a much better fit for your car. If seat time is more important to you than being competitive, I'm not sure why you would want to run in TT4 with a tire you think might be unsafe. You can find used tires in a variety of sizes and types that would work fine in TT3, and that would help keep your consumable expenses down while you're still learning.

I've experimented with tires a little bit over the last year and have mostly been running 305 MPSSs. It seems like I can move to 275 width competition DOTs without compromising too much grip (relative to current setup).

There are some tire choices out there with appropriate load rating and decent performance (R888R; Rival; etc.) which should receive the same modifiers the RRs do if I'm not mistaken. Finding the optimal setup that fits the 282mm template is gonna be a challenge without the good graces of a local tire shop.

I still have to earn my TT license but I'm trying to be as prepared as possible and get myself acquainted with whatever equipment I'll be running when the time comes.

All that being said, you are probably right and my whole game plan will probably change by the time I'm actually racing. For now I'll continue to get my seat time up in HPDE and compare my lap times to the guys running TT3&4. Thanks for the input!

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On 1/15/2020 at 9:20 AM, endless.pain said:

What ever happen to this? Seems there is enough interest to change this rule but have not seen it being addressed.

Having to add .7 to the sheet because my BRZ has an 'A-Arm' in the rear while utilizing Macpherson at the fronts is a bit extreme.

Edgar

What is the official ruling on this. I am planning to run an e82 bmw which uses a multi link rear suspension and strut front. It is not technically an a-arm so I am trying to figure out if I need to take the hit or not.

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9 hours ago, Phloozy said:

What is the official ruling on this. I am planning to run an e82 bmw which uses a multi link rear suspension and strut front. It is not technically an a-arm so I am trying to figure out if I need to take the hit or not.

If it doesn't have an "A-arm" suspension, there is no A-arm or Wishbone suspension Modification Factor.

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