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-   -   how much power is lost? (http://www.ramforumz.com/showthread.php?t=140482)

AlmostSleezy 04-25-2013 04:18 PM

how much power is lost?
 
Was curious to see how much power / speed / time etc was lost between tire sizes.
Like stock 31s, 33s and 35s. I currently have 35s and was curious how much quicker id be with even 33s.

Am I over thinking this or is difference between those sizes hardly noticeable.. thanks!

S.C. Express 04-25-2013 11:11 PM

Depends on the weight, rolling resistance and traction characteristics. Dropping 2" of tire diameter will make a very nice improvement. Putting an exact number on it is kinda hard without actually doing it. I have done it on one of my older Nissan trucks, it made a huge difference dropping 2-3"

CdnoilRAM 04-25-2013 11:39 PM

You would really have to look at several factors and S.C. named the main ones. The one with the biggest factor is the wheel's inertia, namely it's rotational mass and how far away it is from the center of inertia. Since you're running 35s, I bet they're m/t's which have a very heavy tread, so your tire's mass is located a long way from the wheel hub, which requires more torque to get it moving.

The relationship between everything is T=I*a, so if your Torque stays the same (power from axles) and you shrink your distance (smaller tire), you end up with a higher moment of inertia value. Take a look at your wheel weight of the 35s and then look at 33s, or even 31s. A good thing to remember when looking at wheels/rubber for track use, you want to use the smallest wheel possible and the diameter that will give you the most effective launch without over revving the engine at the track.

I ran stock diameter 30" tires with a decent street compound on a set of 22" wheels, and just switching to a set of 17" wheels and keeping the diameter the same made a difference in ETs because I reduced the center of mass

AlmostSleezy 04-26-2013 11:33 AM

Awesome, thanks for the advice! Very helpful :)

RAM EM 04-26-2013 02:55 PM

Quote:

Originally Posted by CdnoilRAM (Post 1080991)
You would really have to look at several factors and S.C. named the main ones. The one with the biggest factor is the wheel's inertia, namely it's rotational mass and how far away it is from the center of inertia. Since you're running 35s, I bet they're m/t's which have a very heavy tread, so your tire's mass is located a long way from the wheel hub, which requires more torque to get it moving.

The relationship between everything is T=I*a, so if your Torque stays the same (power from axles) and you shrink your distance (smaller tire), you end up with a higher moment of inertia value. Take a look at your wheel weight of the 35s and then look at 33s, or even 31s. A good thing to remember when looking at wheels/rubber for track use, you want to use the smallest wheel possible and the diameter that will give you the most effective launch without over revving the engine at the track.

I ran stock diameter 30" tires with a decent street compound on a set of 22" wheels, and just switching to a set of 17" wheels and keeping the diameter the same made a difference in ETs because I reduced the center of mass

How much difference?

CdnoilRAM 04-26-2013 09:51 PM

The 22s were 53lbs each and the 17s were 47lbs. ETs dropped .3-.4 on nitrous.

S.C. Express 04-27-2013 10:51 PM

This is the major reason I tend to go high end forged wheels, super strong and uber light. My last ride had 18x7.5" factory alloy wheels weighing 27lbs each. They had 225/45/18's for rubber. I went with a quality forged wheel. 18x8.5 with 5mm more offset. They weighed 18.5 lbs. each. I mounted 245/40/18's w rated performance tires that weighed 2 pounds more than the factory tires. They where about 1/2" smaller in diameter than stock.. Very minor
My end result was roughly 10-11 pounds less rotational mass, that included forged al. lug nuts too. The results where amazing, better acceleration, better braking and the car really shined at highway speed pickup. It made more difference than the average bolt on mods.


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