I have stock 16" nissan maxima se rims with kuhmos that i hear are quite heavy. If I bump up to a 17 with light tires and a light rim. How much will this hurt performance opposed to some big time heavy rim. And what about moving up to 18's in SSR competions, and light toyos. Will there be a serious, big time, slow as a snail on a turtles back, effect? soon it will be time for the tires and rims and im alreayd sweating it. i want 18's but dont want to kill my speed and acceleration. what thoughts do you guys have? is it possible to spend the extra cash on light tires and racing rims, without seeing a horrible loss? or no matter if its a super light combo ..YOUR GOING TO Lose no matter what? any info and experience or findings will be great. on my budget, i only have one shot of getting this right.

 

You need to calculate the intertial resistance of your wheel/tire combo, and you can do that roughly via the following formula.

I = mr^2

I = moment of inertia
m = mass of wheel/tire combo
r = radius (use rim radius) squared

Assume that the center of mass of the wheel/tire combination is the radius of the wheel. Add up the wheel weight and tire weight and calculate it out... The 4th Gen 16" rims and tires average about 42lb so we'll use that as an example.

I = mr^2
I = (42 lb)x(16/2)^2
I = 2688 lb-in^2

So to go up to a 17" wheel/tire combination and not lose any performance as far as inertial drag goes, you can rearrange the equation a bit to get a rough idea of what your wheel/tire comination would need to be...

I = mr^2

You already know "I" and you know the radius, so rearrange and solve for "m" the mass.

m = I/r^2
m = (2688)/(17/2)^2
m = 37 lb

So you need to keep your 17" wheel/tire combo to around 37 lb for it not to not have negative impact on performance. If you want to go up to 18" rims, that would come out to around 33 lb.

 

stevtec...
very nice explanation. I was just wondering this same thing today b/c I want 18" volk racing's to replace my heavey AE wheels. Performance to me is more important though and this helps a lot. thanks.

 

This does not account for where the weight is located as weight on the outside of a circle is more important than the center as comparison goes, but this is good just for comparison sake.

 

great explanation except for the relativity when comparing...how much different 3396lb is vs.2688lb...is that a big difference?

i think my wheel tire combo weighs 47lb approx. i have 17 in rims. so 3396 is what i figured my number to be.
does that affect my performance drastically?

if i get RX7 or 300zx rims my combo will weigh about 39lb and that comes to 2496lb....how much of a difference from what i have now will i notice?

 

just posted similar thread in the supercharged/turbocharged forum. My friend and I ran 40-90 with similar setups, his 99 vs my 01. his 16lb kosei wheels and my stock AE wheels (47lb w/ tire). I lost. read about it. Post is titled "just owned and shocked....etc"