Wheel Sizes

[soareyes]

I asked this on the Birkin-owners forum, and I wanted to get other owner's opinions:

 

 

 

I'm considering the purchase of a set of 13" wheels for the track. From previous discussion it seems 13x7 fronts and 13x8 rears are the generally recommended sizes for Birkins. If I went with 13x7 all around, what would I be giving up in potential performance and handling? I'm just wondering if the ability to rotate the wheels/tires would make it worthwhile for the 4 to 6 track days I plan to do a year (not racing, just track days). Thanks for any opinions!

 

 

 

Also thanks to those involved in researching the tires spreadsheet as it is very useful.

[Boxologist]

Stan, how much power are u putting down? on my 7, with a stock zx-1 zetec, i have 5 of the same size tyres. thats at 150 crank hp. i understand why more powerful setups go to staggered sizes, as traction for the drive wheels can quickly overwhelm the traction needs of the steering wheels.

[soareyes]

Stan, how much power are u putting down? on my 7, with a stock zx-1 zetec, i have 5 of the same size tyres. thats at 150 crank hp. i understand why more powerful setups go to staggered sizes, as traction for the drive wheels can quickly overwhelm the traction needs of the steering wheels.

 

 

 

It's a nearly stock Zetec (larger throttle body, Pectel ECU, light flywheel), and I'm told about 165 hp. The wheels the car came with are 15x7 all around with 195/50/15 tires. I've since put new tires on these wheels, retaining the 195's up front but 215/50/15's on the rear. Honestly, the only reason I went larger in the rears is because I think they look better filling out the wheel wells! On the street I don't think I could tell any performance difference in the slightly wider tire.

[Boxologist]

i would have to say then stay with the same size all around. u'll probably get better advice on the next CCC blat.

[slngsht]

i would have to say then stay with the same size all around. u'll probably get better advice on the next CCC blat.

 

 

 

I got the same advice from my autox instructor. He said keep the same size all the way around, then use suspension to dial in the handling characteristics.

[roll a 7]

I doubt if you would notice any difference with 1" wider rear rims. For convenience the same dimension at every corner seems best, whatever you choose. You will probably get more than six track days out of the V 710s. Magnus said he got around 2000 miles on his between street and track. Ask him about low flying/aquaplaning @ 30 mph.

[slngsht]

I doubt if you would notice any difference with 1" wider rear rims. For convenience the same dimension at every corner seems best, whatever you choose. You will probably get more than six track days out of the V 710s. Magnus said he got around 2000 miles on his between street and track. Ask him about low flying/aquaplaning @ 30 mph.

 

 

 

I totally aquaplaned my vette coming back from an autox on shaved 305's in the back and 275's in the front... The highway turned, and the car went straight. Went over 1.5 lanes. Fortunately no cars next to me, and tracks from another car was there to keep me from stamping "CORVETTE" on the concrete.

[locostv8]

i would have to say then stay with the same size all around. u'll probably get better advice on the next CCC blat.

 

 

 

I got the same advice from my autox instructor. He said keep the same size all the way around, then use suspension to dial in the handling characteristics.

 

Mine would look funny with 315 35 17s on the front.

[scudracer]

Any idea why the Caterham R500 used 13" wheels? Is it because the overall weight of the wheel/tyre combination is best compared to 14" or 15"?

[Al N.]

Scud-I'm sure that had something to do with it...pretty sure that the smaller diameter wheel/tires have less inertia, so they can get up to speed more quickly given the same input force. I also remember reading something in Grassroots Motorsports about a test between 13, 14, and 15 in rims that bore this theory out. Also, those Magnesium 2 piece wheels on the R500 are pretty damn cool.