Track Guys: Are You Running 15/16 Wheels

[Sherman]

Hey guys I'm thinking of ditching my 16/17 wheel set up and going with a 15/16 wheel set up. Is there any performance gains to be had? I'd love to hear from guys with first hand experience. Tire choices using 16/17 wheels suck. I hate the Yokes and R888s. I would love to run on RA1s. Oh and I'd have to also ditch my AP brakes and get a smaller brake to fit in the 15s. I drive my car on the track so I'm interested to know what you track guys think. My car is an 08 S240.

[carphoria]

I'm not a track guy, just on occasion... I run the 15/16 set up, seems fine. Just make sure the e-brake cable doesn't run.

[Sherman]

Anyone else want to chime in? Please give me some details about how it changed the driving dynamic on the track. How does the car feel compared to the 16/17 wheels.

[LarryB]

I’ve got a set of 15/16” wheels. For the first 5-6 years it was more of my street setup (using Toyo RA-1, 205/225/50). Also track them once in a while. Compared to the LSS with stock sized Yoko 048 or even Toyo R888 what I notice most is the taller softer side-walls.

For more of a direct comparison you’d need to be able to run the same type wheels in the different sizes along with the same type of tires (off hand the R888 come to mind). Than the lighter weight of the 15/16 combo and tire sizing can come into play. If you went with a 225/50/16 in the rear, you’d change the gearing a bit. All leading to a subtle improvement to acceleration. Personally the biggest difference is the tire selection that becomes available. Currently am using Hankook Ventus Z214 C71 (205/50 and 245/45) and like them.

[Kermit]

I have a set of 15/16 with R888 for track on my Elise, but stock wheels and tires for street. Since they are used differently, I can't give you direct comparison on the Elise. But the physics is against a heavier tire/rim combo with the mass farther from the hub. The larger and heavier rim/tire has a higher moment-of-inertia (flywheel effect) and is harder to change direction, slower to accelerate, etc. None of that is good.

With the slightly undersized tires, the speedometer error increases from "normal" +7% to about 10% over.

On my BMW E30 M3 race car, I once used +2 (17") and the difference was very noticeable. Slower to turn in and accelerate. I got rid of that combo right away.

On another race car, I fitted slightly oversize tires (Mich Pilot Sport Cups) on standard rims. and compared to the standard sized tires (Hoosiers) they were again heavier, slower to accelerate and turn-in. And again required speedo recalibration.

It's just physics.

[Elige]

FWIW I bet you get more replies in the Track and Technique forum: Track and Technique - LotusTalk - The Lotus Cars Community