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Hi! I'm new to the forum and just recently picked up a new 2015 Cayman 2.7 manual, with X73 Sport Suspension and Sports Exhaust (unfortunately no Sport Chrono or PTV). I've been autocrossing with the local Philly/SJ/NEPA SCCA chapters for a few years now and plan to run the Cayman in A Street next year. I know it's probably not the car to have in A Street, but I'm hopeful all of the base Caymans will eventually be moved to B Street (I've already submitted a letter, and will keep trying). My plans are to purchase a set of 19x8.5/19x10 wheels and RE71R's in 255/35R19 and 285/35R19. I'm currently looking at Forgestar, because there seems to be so few options within the SCCA +/-7mm offset rule. I also just ordered an adjustable GT3 front bar, as I heard it's a must have without PTV and will help keep the rear end planted. My main concern is around the tire size. I like the slightly smaller diameter of the 19's to help with gearing, but I'm not sure how wide to go up front. I don't want to throw off the balance of the car or run into PSM issues. I’ve also read that the 987 Caymans have a catalytic converter located within the rear muffler, so changing out the exhaust system is not SCCA Street class legal. Is this the same with the 981's? Another thought I had was to run 19x8.5 up front with 265/35R19 and 20x10 in the rear and put on 295/30R20 (when they are available next summer). Does anyone know if the SCCA Street class wheel +/- 1" rule is allowed for just one end of the car? Any thoughts or suggestions would be greatly appreciated. Cheers.
Hi! I'm new to the forum and just recently picked up a new 2015 Cayman 2.7 manual, with X73 Sport Suspension and Sports Exhaust (unfortunately no Sport Chrono or PTV). I've been autocrossing with the local Philly/SJ/NEPA SCCA chapters for a few years now and plan to run the Cayman in A Street next year. I know it's probably not the car to have in A Street, but I'm hopeful all of the base Caymans will eventually be moved to B Street (I've already submitted a letter, and will keep trying). My plans are to purchase a set of 19x8.5/19x10 wheels and RE71R's in 255/35R19 and 285/35R19. I'm currently looking at Forgestar, because there seems to be so few options within the SCCA +/-7mm offset rule. I also just ordered an adjustable GT3 front bar, as I heard it's a must have without PTV and will help keep the rear end planted. My main concern is around the tire size. I like the slightly smaller diameter of the 19's to help with gearing, but I'm not sure how wide to go up front. I don't want to throw off the balance of the car or run into PSM issues. I’ve also read that the 987 Caymans have a catalytic converter located within the rear muffler, so changing out the exhaust system is not SCCA Street class legal. Is this the same with the 981's? Another thought I had was to run 19x8.5 up front with 265/35R19 and 20x10 in the rear and put on 295/30R20 (when they are available next summer). Does anyone know if the SCCA Street class wheel +/- 1" rule is allowed for just one end of the car? Any thoughts or suggestions would be greatly appreciated. Cheers.
I got nuthin' to say on your build, but that is one damn nice looking Cayman. Just beautiful.
The 987.2 and I think the 981's do not have the cats in the muffler. You can legally do a "catback" exhaust swap on those cars. Or even remove it altogether if you can still meet sound reqs.
I don't believe the +/- rule applies to the F/R independently.
I don't believe the +/- rule applies to the F/R independently.
I don't think there's an issue at all with running 3 diameters total on the car if you really wanted to. IIRC Corvette people had to run a weird wheel diameter stagger to get the best tire size combo last year.
13.4 WHEELS
Any type wheel may be used provided it complies with the following:
A. It is the same width as standard and as installed it does not have an offset more than ±7.00 mm (±0.275”) from a standard wheel for the car. The resultant change in track dimensions is allowed.
B. Wheel (rim) diameter may be increased or decreased 1” from the standard part.
Wheel spacers are permitted
And I'll also second that the 981 is just stupid pretty.
IIRC Corvette people had to run a weird wheel diameter stagger to get the best tire size combo last year.
Could be. I didn't notice that specifically, though I did see several that ran 285 Bridgestone F with /315 BFG R because of the limited sizes of the RE-71R.
I don't think there's an issue at all with running 3 diameters total on the car if you really wanted to. IIRC Corvette people had to run a weird wheel diameter stagger to get the best tire size combo last year.
And I'll also second that the 981 is just stupid pretty.
Thanks. That's what I was thinking, but I just received some feedback on another forum, where an SCCA BOD member said that the rule applies to all four wheels only. I guess that idea is off the table for now.
Thanks. That's what I was thinking, but I just received some feedback on another forum, where an SCCA BOD member said that the rule applies to all four wheels only. I guess that idea is off the table for now.
Thanks!
There are two rules here. One is the base wheel size: you can change to another optional size, but only if you completely match that option at all 4 wheels. You can't choose 2 wheels from one option package and 2 from another.
For the +/-1" diameter rule, one of the SEB members said on other board that +/-1 it applies independently to each wheel and you could, in theory, run a different size wheel legally at each corner on a corvette.
I just received some feedback on another forum, where an SCCA BOD member said that the rule applies to all four wheels only. I guess that idea is off the table for now.
That's indisputably wrong. You can increase or decrease the diameter of any of your wheels independently of the others.
As Burglar alluded to, almost all of the BS and AS C5 Corvettes at Nationals this year (myself included) ran 18" front wheels instead of the stock 17" diameter because the widest 17" RE-71R or Rival S available was a 255, and that's just not a whole lot of tire on a Corvette.
Here's the complete Street wheel rule, from the 2016 draft rules:
13.4 WHEELS
Any type wheel may be used provided it complies with the following:
A. It is the same width as standard and as installed it does not have an offset more than ±7.00 mm (±0.275”) from a standard wheel for the car. The resultant change in track dimensions is allowed.
B. Wheel (rim) diameter may be increased or decreased 1” from the standard part.
Wheel spacers are permitted provided the resultant combination complies with the offset requirements of this Section. On vehicles supplied with an OE wheel spacer, the wheel spacer shall be considered as a part of the wheel. Wheel studs, lug nuts, valve stems (including pressure-relief types), and/or bolt length may be changed. Tire pressure monitoring sensors may be removed.
Centerlock/Spline Drive/Knock-off type hubs may be converted to lug type hubs provided the resultant combination complies with the offset requirements of this Section.
Note that there's no mention of it applying to four wheels.
There are two rules here. One is the base wheel size: you can change to another optional size, but only if you completely match that option at all 4 wheels. You can't choose 2 wheels from one option package and 2 from another.
For the +/-1" diameter rule, one of the SEB members said on other board that +/-1 it applies independently to each wheel and you could, in theory, run a different size wheel legally at each corner on a corvette.
I'm with you on this interpretation. I was thinking I would need to use the SportTechno Specs as the "standard" wheels. Specs are:
Front: 8.5 J x 20 ET 57 (+/- 7mm)
Rear: 10 J x 20 ET 50 (+/- 7mm)
Then go with a 8.5 x 19 ET57 (+/- 7mm) up front as the - 1" option.
That's indisputably wrong. You can increase or decrease the diameter of any of your wheels independently of the others.
As Burglar alluded to, almost all of the BS and AS C5 Corvettes at Nationals this year (myself included) ran 18" front wheels instead of the stock 17" diameter because the widest 17" RE-71R or Rival S available was a 255, and that's just not a whole lot of tire on a Corvette.
Thanks for the info! It's good to know that people competing at Nationals were actually running this type of stagger. I'm now confident that this could be a feasible option for the Cayman.
Thanks. That's what I was thinking, but I just received some feedback on another forum, where an SCCA BOD member said that the rule applies to all four wheels only. I guess that idea is off the table for now.
01-04-2016, 11:56 PM
A Street 981 Cayman 2.7 build
