leetski

Just a thought. If I were to replace my custom wheels which weight ~70lbs (with tires) with a lighter set (~50lbs, same diameter) would there be a significant increase in performance, in terms of acceleration? What about handling? I am guessing yes, but is it possible to quantify these gains mathematically?

Also, how heavy is the stock rear '03 CL55 wheel+tire?

Thanks guys.

Vadim @ FD

Yes, there will be less losses going through the wheels and you will see more power at the wheels on acceleration type (i.e. Dynojet) dyno.

I have dynoed a lot of cars when switching wheels. Figure about 15-20 RWHP.

DFW01E55

That's a really good question. There must be an equation.
(Not that I could do it, but Excel can help!)

leetski

Here is what I know, horsepower is a measure of energy per second, it can be computed at any time (rev/rpm) if you know the time history of the torque and the velocity of the wheel. hp = torque x velocity.
More importantly, if we know the time history of the torque at the wheel, then we can compute the acceleration as follows from Newtons laws, Net_Torque = Inerita_of_Wheel?*Angular_Acceleration.
Then, what we really care about is translational acceleration which is just: Trans_acceleration=Radius*Angular_acceleration.
Below is a graph that I generated using some dyno numbers I dug up online for a stock '03 CL55. It compares Trans_acceleration of a 70lbs wheel+tire to a 50lbs wheel+tire.



I know for a fact that these numbers mean nothing as far as Acceleration comptuation is concerned. The reason being is that I don't know if the torque numbers are given for just one wheel or the entire rear setup (2 wheels / axles). In my calculations I only used inertia of one wheel, which I doubt is correct but gives you a back of the napkin type calculation.
Then certainly, in real life conditions, the net torque is not just what the dyno graph reads, we also have to account for friction between tire and contact surface if nothing else..?

Maybe a better way to calculate acceleration would be to use torque readings along with horsepower readings. Dividing hp by torque would give us velocity and then we could differentiate to obtain acceleration? Would be more realistic and we wouldnt have to worry about detailed modeling since we have empirical data.

DFW01E55

Wow!
So how 'bout them Celtics?

IngenereAMG

Aside from the obvious fact that you are making the car 80 pounds lighter, you are taking the weight fro a very important area...... unsprung weight.

Your car will accelerate better, but you will really notice how much more crisply the car turns in.