Some regions have a very robust and competitive street tire class. In our region 4 of the top 10 ranked drivers are in this class. If you're not max prepped, you don't trophy. Milwaukee has their National Street Tire Challenge and SCCA National Tours may be adding a street tire stock index class for 2012.

It's no longer for people who are underprepped or "lazy."

To that end, would like to discuss ways of making up time on those freaking GS Genesis.

I think that AP2>>AP1 for street tire autocross due to lack of appropriate 16" tire choices.

I normally run 235 front and 255 rear Star Specs or Toyo R1Rs. Normally I single drive so I haven't purchased RS3s as they like heat.

I have seen people in Milwaukee fit a 245 Star Spec up front. Supposedly there's someone in Chicago that runs a 255 front street tire on the 7 inch rim. Now I'm hearing a rumor that a 275 street tire may fit in the rear.

With our classes being separated by thousandths, even small advantages are key.

I'd think a 255 front / 275 rear street tire would be great. With a tire like Toyo, it'd heat up fast enough.

Anyone with experience running something larger than 235f / 255r on standard wheels in "stock legal" rules?

 

I'm pretty sure the guy in Chicago running a 255 front is me. I'm not sure if you would consider me max prepped but my car is at the same level my AP1 was at in 2002 when I coned out of 10th at Nationals. I'm running a Gendron style sway bar, it's a (near exact) copy I fabricated myself. 1.25" Hollow set to the stiffest setting. -2 camber front zero toe, -2.2 camber rear with 1/8 toe in (hmm... maybe it's 1/4... I forgot). 255 square Star Specs. I normally run stock pads but I've tried my track pads (Hawk Blues F&R) and I really liked the bite, but not the dust. Mugen Exhaust. Stock shocks. It's hard to fault the stock shocks, and since I don't know enough about tuning them I figure the less I can mess up the better. I just get in and drive.

With the 255 fronts there is some dead feel and lag in the steering inputs, but they sure do make the car stop, and I can't fault the grip. I've driven a bone stock AP2 instructing and I just can't get over how undertired these cars come from the factory. But then it keeps people from killing themselves, more or less.

I'm a lot rusty from not having as much time to dedicate to racing as I used to. If I don't cone every run I can finish in the top 5. I've been able to run raw times faster than the STR competition (on occasion). I've even had the pleasure of beating BStock open. There is however a very well driven purple M3 that comes from Michigan that I just can't seem to beat. I would blame the CS index but I can't match him raw so I know it's me. And to be quite honest, I'm terrified to run in Milwaukee so I won't be making that trip any time soon.

I wouldn't object to trying a 235 front to see what I would give up in grip in exchange for response. I agree with you on the 255/275 combo, but I have a solid 1.25 center for my bar but haven't felt the need to try since I'm pretty happy with the balance of my current setup. Perhaps the solid bar would add weight and understeer, just as the same might happen with a 275 rear tire.

 

The purple M3 is Adam. He's a good driver, but still a little off the Milwaukee Genesis pace. The 235s up front are the minimum front tire I would run with a 255 rear. I have an extra pair of 255s lying around that I might try mounting up front. It'd be interesting to see how much additional contact patch you'd actually get with that combo (vs just crowning).

 

Hey, can you stack your fronts together and rears together and take a picture (sometime, whenever you swap wheels). I can do the same with our 235s compared to 255s.

 

Why are you thinking of running a staggered setup when both BS and STR run square?

 

Disagree. Even though the tire sizes in B-stock are non-staggered, the contact patch IS staggered due to rim size and pinch.

The relative effective stagger of a 235 / 255 street tire is not very far off a 275 on asymmetric wheels.

A 245 / 255 stagger might be closer.

I have no experience on how the 255 would sit on the front 7". Also would wonder if it would rub without fender rolling (illegal in stock). I'm thinking they fit, but the gain in real width might be less than advertised on the sidewall.

 

I also wonder if an unshaved oversized tire could wind up acting like a camber tire after broken in and eventually dismounted and flipped.

 

I'm not sure how we can be disagreeing when I was just asking a question.

I run 245s all around on stock rims on the street, 275 R-compounds on stock rims for B Stock, and have 245 R-compounds on the stock AP1 rims left over from when I ran an AP1 in B Stock -- I'll measure all three combinations later today to validate your thinking.

 

But why would you want to do that? Camber Tire has it backwards, since it effectively adds positive camber (i.e. reduces contact patch when the car rolls).

 

I have to admit, I know nothing about "Camber tire" and was talking about a tire that would be cambered with an extra lateral "wing" of overhanging tread block.

The initial driving on a street tire squeezed on a rim has a vague feeling and potentially less grip as evidenced by crowning in the pinched area. As the "bulge" wears flat, it grips up. I wouldn't want to run a fresh "crowned" street tire in an important competition. But having more surface area that comes into play in cornering sounds attractive.