Something interesting I saw when playing with the numbers.
The first set of wheels were 245/40-18. The 2nd set was 215/45-17. I plugged these numbers in at
Miata Tire Calculator. It comes up with a -4.3% difference. I then multiplied this number times two and got -8.6% difference (Can't remember why I did this. I'm horrible with math).
I then multiplied -8.6% time the whp (283whp X .086) and came up with 24.338whp. I was thinking that this horsepower difference should be the difference between the old wheels and the new ones only based on wheel size.
When you add 24.338whp to 283whp (24.338 + 283whp) the new number is
307.338whp. Our new number.
I am taking this same approach on the 10th Gen civic I have now.
Stock wheels are 215/50-17. My new wheels are 225/50-15. That is a -6.3% difference. -6.3% X 2 = -12.6%.
My stock hp is 174hp. 174hp X 12.6% (174 X .126) is equal to 21.924hp. So I add 21.924hp to 174hp (174 + 21.924hp) is equal too
195.924hp. I'm expecting my wheels to bring me right up to par with the new Si in terms of horsepower. Old wheel weight is about 50lbs. New wheel weight tis 36.6lbs. A weight reduction of 13.4lbs per wheel. This not counting the rotors I'm getting which I expect to be a little lighter as well.
This is my bullshi* math but I just like to do this to justify my purchase. Carry on! :wigglesmiley: