Effect of Smaller Tires???

[Vipera Russelli]

Has anyone dynoed a car with larger and then smaller rear wheels so as to determine to what extent power to the ground is affected? If not, any mathematicians out there, hehe? I assume the torque would go up and horsepower down with a switch to smaller rear wheels, but by how much? I'm asking just in case Michelin or someone else doesn't come out with a 19-inch track tire soon for us SRT owners, thus causing me to switch to 18-inchers all around. My preference, I think, is to stick with stock tires sizes (18 front and 19 back) so that the driving characteristics of the car don't change between track and street driving. Or maybe I wouldn't even notice a difference? Any thoughts whatsoever on the matter would be greatly appreciated.

 

[Big Medicine]

It's harder to spin a big ferris wheel than a smaller one, at least that's how I see it.

Others will tell you that larger tires spin more easily, some function of sidewall aspect ratio. Hard for me to argue since I haven't tried 'em, but I'm sticking to my ferris wheels.

 

[Vipera Russelli]

Here is an email from my good friend Hans on the matter. Good food for thought:

"lots of thoughts

First, rim size is not the same as tire size. If the outside diameter is the same then there is no change in horsepower or torque (mostly, read further). Second, tire sidewall height. This is a prime consideration for cornering. Generally the smaller the sidewall, the better the cornering due to less flex. But, too small of a side wall and the heat build up degrades the tire performance (caused by side wall flexing on every revolution, why proper air pressure is even MORE critical for tire life on performance small sidewall tires).

The kicker is, larger rims make for more rotational mass which severely (ok maybe slightly hurts) degrades performance. Therefore, larger rims may or may not increase overall car performance. The classic trade of better handling versus quicker acceleration.

http://www.sportcompactcarweb.com/editors/technobabble/0209scc_techno/"

 

[CHAD]

The chassis dyno is almost completely unaffected by tire diameter and gearing in general. There are very small changes in efficiency but for the most part, if you dyno with a 25" diameter tire or a 27" diameter tire, the numbers will be the same given no slippage. The same is true for rear end gears. 4.10's or 3.07's will show very similar numbers.