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      09-05-2017, 11:09 PM   #1
CLH
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B-street setup

The car gets here in ~2 weeks and I'm already knee-deep in research for what wheel/tire combo I'm going to pick up for B-street auto-x next year. I've scoured through the threads but don't see any general setup threads.

The big question is 18" or 19"?

If I stay with 19" I *think* I can run 265/35 up front and 305/30 rear. Anyone tried that yet with stock width/offset wheels?

Going down to 18" means 265/35 front and 275/35 rear (RE-71R) or 265/35 front and 285/35 rear ('kook RS-4), and a slight gearing reduction.

Any other general thoughts or setup hints?

I'm going back to street tires and a "stock" class after several years or campaigning an ASP Solstice GXP (with giant Hoosiers), so this will be a bit of a change for me.
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      09-06-2017, 09:14 AM   #2
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I'm burning up the stock Conti tires in BS this year and plan to stick with 19. Keith said I can use Bridgestone Potenza RE-71R in

Front - 255/35/19
Rear - 275/35/19

But hoping the choices expand in 2019.
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      09-12-2017, 11:27 AM   #3
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If you stay 19" I've seen 275 RE71R mounted up front with evidence of rubbing the wheel liner. 305 RE71R fit the rear. This would keep your gearing near stock which is pretty much perfect for the manual but still very short for the DCT.

If you drop to 18" wheels you can run the 285/30R18 RE71R up front with no rubbing. The rear you can run the same or even fit the 315 Rival S. They stick out the fenders and throw rocks everywhere but do not rub. Besides cheaper tires, either of these setups have the advantage of lowering the car's high CG (relative to the rest of the class), increasing the thrust a bit, but gearing will suffer. The DCT will top out at a pathetic 57mph with the 285 on the rear and the Manual will only be in the mid low 60s.

Another option is to stagger...18" front wheels with crisp short sidewall 285s and 19" rears with 305s.
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      09-13-2017, 08:17 AM   #4
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Sprockett - thanks for this info, it's very helpful!

I was actually considering going down the path of staggered, but with the 275/35-18 up front and the 305/30-19 in the rear. Seems like the 18" 275 up front makes for a better compromise with the wheel width, and should avoid the rubbing problems that a 19" 275 would have.

Any thought on swaybars? Does the M2 benefit from the typical RWD tactic of going bigger up front?
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      09-13-2017, 09:13 AM   #5
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I am assuming so...I have a Dinan set on the way as we speak from Turner Motorsports to test at an event this weekend. The car's biggest (only?) advantage in the class is power and in totally stock form getting that power to the ground was a challenge. Hoping that a bigger bar and toe changes in the rear alignment will help. I wish toe was set by a threaded link...it was a good and easy tuning tool in a previous Corvette.

CLH - Is your car manual or DCT?
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      09-13-2017, 10:28 AM   #6
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It's not here yet (still on the boat heading this way), but it's a 6MT

I like that 2nd gets into the mid-60's - my Solstice GXP on 315 Hoosiers tops out in the mid-50's, so I end up using 3rd quite often. Not ideal. It has a tune on it and has trouble putting power down as well.

I've been researching the most cost-effective way to get a set of staggered 18"/19" wheels. Not very many options unless I go with a mismatched set. I have Forgestars on my GXP, so I may just go that route again and have a custom set made.

Would love to hear any other observations or tips you could share!

Cheers
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      09-17-2017, 07:19 PM   #7
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Ran the car today after installing the Dinan 4 way adjustable front sway bar. Started on the 2 stiffest setting and the car is transformed completely in the slaloms. It went from being very nervous and impossible to feed throttle on exit until nearly straight to now being able to turn very aggressively throughout and be hard on the gas past the last two or even three cones.

This was on a medium to low grip asphalt lot.

The course today was all decreasing turns so unsure how that balance has suffered. I should have gone softer for the afternoon but the car was working well enough for the course that I just left it...

Also had done an alignment...had planned to dial in more rear camber due to observed wear but with any more than -1.7 or -1.8 toe begins to be limited by the short links so chose to keep -1.7 and crank the toe in 1/4". The front is now slightly toe out as well but nearly zero.
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      09-17-2017, 08:00 PM   #8
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Good setup info Sprockett!

I was assuming that a bigger front bar would be a good choice. Every RWD car I've driven in stock class benefitted from it. Even my Miatas needed a big front bar.

I saw your comments over on the Autox/RR forum too. What wheels/tires are you running at present? 275/285 on 18s?

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      09-17-2017, 08:51 PM   #9
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I've tried 285/285 Bridgestone, 285 Bridgestone/315 bfg, and today was 275/315 BFG. I'm not sure what I really like better. This is my first time ever on bfgs on any car.

I suspect the 19" 305 Bridgestone might actually be best choice.
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      09-20-2017, 02:19 PM   #10
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Quote:
Originally Posted by Sprockett View Post
I've tried 285/285 Bridgestone, 285 Bridgestone/315 bfg, and today was 275/315 BFG. I'm not sure what I really like better. This is my first time ever on bfgs on any car.

I suspect the 19" 305 Bridgestone might actually be best choice.

Did 285 front fit? Will running 285 square work?
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      09-29-2017, 08:57 AM   #11
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Quote:
Originally Posted by M2Driven View Post
Did 285 front fit? Will running 285 square work?
My understanding is that the short 285/30/18 Bridgestone fits in front because the smaller diameter allows it to clear the spring perch and the wheel well liner. The taller 275/35/19 and 285/35/19 will not fit without rubbing with the spring perch or the wheel well liner.

Running 285/30/18 square should work, but will shorten the already short second gear for cars with the dct transmission.
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      10-29-2017, 09:14 PM   #12
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Quote:
Originally Posted by Sprockett View Post
I've tried 285/285 Bridgestone, 285 Bridgestone/315 bfg, and today was 275/315 BFG. I'm not sure what I really like better. This is my first time ever on bfgs on any car.

I suspect the 19" 305 Bridgestone might actually be best choice.
Are you using the same offsets?
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      10-29-2017, 09:50 PM   #13
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Quote:
Originally Posted by CLH View Post
The big question is 18" or 19"?

If I stay with 19" I *think* I can run 265/35 up front and 305/30 rear. Anyone tried that yet with stock width/offset wheels?
Iíve been running RE71s all year with pretty good results. Looking to add wider rubber for 2018 as the car needs it. Iím also considering the adjustable front sway bar.

Iím interested to learn what, if any choice you made on wheel tire combos to stay in B-Street.
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      10-30-2017, 02:38 AM   #14
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Is it possible to put adjustable camber plates in the B Street class?
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      10-31-2017, 05:08 PM   #15
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Quote:
Originally Posted by Hasan Shaikh View Post
Is it possible to put adjustable camber plates in the B Street class?
Some local BMWCCA clubs may allow it but SCCA does not. You can only go up or down one inch on wheel diameter and change one sway bar. You can put any width tire on the rims so long as you donít change the offset by more than 7mm.
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      10-31-2017, 05:12 PM   #16
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Quote:
Originally Posted by Sprockett View Post
Also had done an alignment...had planned to dial in more rear camber due to observed wear but with any more than -1.7 or -1.8 toe begins to be limited by the short links so chose to keep -1.7 and crank the toe in 1/4". The front is now slightly toe out as well but nearly zero.
What are your conclusions on alignment with the sway bar in place? Can you share your alignment sheet?
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      10-31-2017, 05:54 PM   #17
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Don't forget to consider using different diameter wheels, front and rear, if needed to obtain the tire widths and diameters you desire.

For example, in 18", the rear widths will be limited to 275/35 or 285/30 with RE-71Rs and 275/35 and 315/30 with Rival S.

One setup possibility if you want to run RE-71R is 275/35-18 front and 305/30-19 rears. Whether or not the rears will fit on the M2, I have no idea.
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      10-31-2017, 06:22 PM   #18
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Will it fit?

Quote:
Originally Posted by CSBM5 View Post
Whether or not the rears will fit on the M2, I have no idea.
Fair point about using different diameters front and rear. Though the fitting question really needs an answer before buying.... hoping to hear from someone who has done this successfully on their M2.

Http://wheel-size.com has useful data ... but nothing like actually putting a wheel on a car and testing.
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      11-03-2017, 06:35 AM   #19
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Quote:
Originally Posted by omasou View Post
I'm burning up the stock Conti tires in BS this year and plan to stick with 19. Keith said I can use Bridgestone Potenza RE-71R in

Front - 255/35/19
Rear - 275/35/19

But hoping the choices expand in 2019.
with smaller diameter rear tyres - is speedo accuracy an issue ?
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      11-03-2017, 08:09 PM   #20
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Quote:
Originally Posted by Bee Pee View Post
Quote:
Originally Posted by omasou View Post
I'm burning up the stock Conti tires in BS this year and plan to stick with 19. Keith said I can use Bridgestone Potenza RE-71R in

Front - 255/35/19
Rear - 275/35/19

But hoping the choices expand in 2019.
with smaller diameter rear tyres - is speedo accuracy an issue ?
I didn't do the math assumed Keith gave me the correct sizes?
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      11-04-2017, 06:55 AM   #21
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Quote:
Originally Posted by omasou View Post
I didn't do the math assumed Keith gave me the correct sizes?
Those are 1 increment is size larger than stock not smaller. It will slightly increase actual speed for the same indicated value. If you haven't coded your car to indicate true speed, it will be showing (speed - 3.1 mph) anyway, so if anything it will indicate a tad closer to true speed.

On my E90 M3 I run the same sizes (stock sizes are same as M2: 245/35-19, 265/35-19), and even with the car coded for true speed, my GPS verified speed is spot on accurate.
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      11-05-2017, 02:33 AM   #22
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Quote:
Originally Posted by CSBM5 View Post
Those are 1 increment is size larger than stock not smaller. It will slightly increase actual speed for the same indicated value. If you haven't coded your car to indicate true speed, it will be showing (speed - 3.1 mph) anyway, so if anything it will indicate a tad closer to true speed.

On my E90 M3 I run the same sizes (stock sizes are same as M2: 245/35-19, 265/35-19), and even with the car coded for true speed, my GPS verified speed is spot on accurate.
How do you code m2 to show true speed ?

It reads like 275/35/19 is a size that actually makes M2 speedo read more accurately - is this really the case ?
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