Just wondering what wheels you guys usually run on in autocross. I know that a smaller overall diameter can increase torque - but everybody seems to upgrade to bigger wheels. Maybe that's just for the look.

I'm considering some 15" wheels, and some think it's crazy to go from stock 16" to a smaller 15". Doing this, though, I would maintain the same overall tire diameter, creating a bigger sidewall. Would that make handling squishier? Hope not. This option makes tires cheaper though

What tires are you guys running, too?



Oh, and on top of that, how’s the season going for everybody? I hope all is well.

 

There are just more performance tires in 15s than 16s, plus overall 16s weigh more than 15s - so you get rid of rotational mass, which helps accelerate the car quicker, and help he suspension and brakes work better.

For every 1lb wheel weight you drop it works out to about 9lbs static body weight. So 15x7" Kosei TS which weigh 10.5lbs compared to 17x7" 18lb wheels equal difference of 7.5lbs*9=67.5lbs you just got rid of off your car (static body weight).

 

My 1991 Civic Si I purchased the guy threw in the 15x7" Enkei RPF1s which weight 9.5lbs. I put my 205/50x15" Falken Azenis (RT215) on for now. I'm waiting for my RT615s to put on those wheels and put the RT215s on my 15x7" Kosei K1s which weigh 14lbs for rain events.

 

Ahh. Very nice! I was just wondering about that today! Somebody had explained that less rotational mass decreases moment of inertia. I thought, well that's wonderful but your car weighs so much more it shouldn't make a noticeable difference. This comparison helps - thanks good sir!

 

Yeah it's like the difference of a merry-go-round with all the people closer to the center. The merry-go-round can start-up faster than with all the people on the outside of the merry-go-round.

Takes more energy and time to get up to speed with people on the outside.

 

Makes sense to me, and I like it!



Man I want these! 13.2 pounds and about $120 bucks each. Now's time to fantasize about tires...

 

Get the Kosei K1 TS they are 10.5lbs 15x7" and about $150

 

15" wheels also give you more power to the ground over 16" wheel (less distance to travel through a shorter radius)...smaller wheels also give you better acceleration also through less total mass and the mass is more centered and less at the outer rim/axis'

 

Well even though I'll have 15" wheels, the overall tire diameter will be the same. This helps maintain spedo readings and gear ratios. I'm not sure they'll even sell you tires+wheels with a smaller diameter at most tire stores (I've heard of discount tire refusing to do this)

The question arises, then, that with this increased sidewall height - will the tire absorb more force and decrease the rigidity of handling? I know I could counteract this with increased pressures if needed.

 

You can keep the overall diameter the same by decreasing the sidewall height. With 15s you get 195/55x15" (23.3") with 16s you get 205/45x16" (23.3").

You can get 205/50x15" which is 23" in diameter and doesn't throw off the speedo and odometer too much. Feels more peppy and get a wider contact patch.

205/40x17" is 23.5" which is why most cars feel sluggish and get a little worse mpg (also because it's a heavier wheel and tire), but your gearing gets changed to a high gear in effect.