Posted By snaponbob on 10 Apr 2013 08:55 AM
Although I do look lighter wheels for race rubber, I often wonder how much objective testing has been done. I mean, if one has a 3000 pound car, how much real benefit MIGHT be achieved by installing (for instance) 3 pound lighter wheels, 6 pound lighter wheels, etc. That said, doing so on a much lighter car certainly would "bend" that curve some.
You have to do it car by car because there are a lot of factors. Weight savings at the wheels will benefit lower-hp cars more than higher-hp; car weight is a much smaller of a factor.
I did some engineering calcs on this a few weeks ago looking at different wheel/tire combinations, and determined that on my car (3000lbs, 250hp, 25" tire diameter), that 2lbs/wheel (8lbs total) penalty I'd get for running wider tires on my 18" wheels worked out to effectively about 1hp loss in acceleration and I reckoned about 5 hundredths of a second difference over a 60 second autocross course; much bigger difference on the track where you spend more time in accelleration. It's a much smaller (maybe a quarter of that) difference during braking because the brake pads are absorbing the rotational inertia, leaving just the plain ole ordinary weight; since most cars brake much faster than they accelerate, the straight time difference is proportionately smaller, too. For cornering, lighter wheels would be removing well balanced weight from low on the car and yield an even smaller (extremely difficult to calculate, even for estimation purposes) difference.