Hello,

I am curious if changing my stock iron rims for lighter allow rims will make any performance improvements. Will going from 15 to 17 size with lower profile tires make any difference?

Rgds

 

You will actually loose acceleration time cause 17'' of course have a bigger diameter to go around

 

This all depends...

Bigger rims tend to move the rotational mass further out, so the wheels won't spin up as fast. Also, bigger rims tend to weigh more, which also increases unsprung weight, which in turn, gives the suspension a harder time controlling wheel movement.

I upgraded from what's generally accepted as one of the lightest stock wheels around (the 14" stock alloys on my Miata) to really light 16" rims for my Miata. Granted this isn't the same car, but I think generalizations can be made here.

I went from a stock tire size of 185/60R14 to 215/40R16 tires. The overall diameter of the combinations are exactly the same, so no additional speedo error is introduced, and there's no additional leverage against the car. The offset is pretty close to, except that these wheels move the wheels out about .5" increase track slightly (and since the rims are wider, this is needed to clear the suspension!) However, I did notice that the brakes don't seem to stop as well. Why? Even though the wheels weigh roughly the same, the mass in spread to the edge of the wheel instead of being more centralized. The redistribution of mass give that mass more leverage against the brakes, therefore, requiring more braking effort.

For a time, I also had some really heavy 15" wheels/tires on the car. I noticed the car would bottom more. Why? Well, everytime I hit a big bump now, the road would force the wheel up into the wheel well. However, because of the increase in unsprung weight, the stock suspension was no longer capable of slowing it down and damping the travel.

The lighter the wheel, the better. Plus sizing helps, but only up to a point. It helps by shortening the sidewall. By shortening the sidewall, the sidewall needs to be stiffer to handle the same load. The stiffer sidewalls deflect less under load and cornering, and therefore, feel sharper in handling and give you a harsher ride (less absorbtion of road irregularities). The bigger factor is how good the tires are. If you're looking for pure performance, spend the money on tires (if on a SE, 225/40WR16 but your speedo will be optomistic by several mph). Putting too wide a tire on too narrow of a rim also hurts performance, by actually lessening the size of the footprint.) If you want look, go for the biggest rim possible. Most people try to strike a balance somewhere in between.

Hope that helps. Good luck!

-V