Rim Width vs. Contact Patch

[SgtRauksauff]

Just found a pic that shows how much rim width actually changes overall contact patch of the tire....

13x10's on the left, 13x8's on the right. Same tire, 255/40-13 Hoosier A6.
http://img.photobucket.com/albums/v234/Vanimaniac/Dans%20Car%20Pics/Picture116.jpg

What the 13x10's look like on the car. mine'll be like this when I get the doolers for the rims and tires....
http://img.photobucket.com/albums/v234/Vanimaniac/Dans%20Car%20Pics/Picture120.jpg

--sarge

[devlish]

doesn't change the contact patch hardley at all really... just the sidewalls are stretched out on the 10's versus straight on the 8's.

not to mention that the roll factor will SUCK with the 10" wide rims. instead of the sidewall holding the car straight like the 8's will, the 10s are already leaned over and will offer nothing as far as sideways grip goes.

get the correct tire for the rim and be happy. Personally, i think that picture just shows you that 10"wide rims will look badass on the car, but don't really offer you anything "grip-wise". and probably weigh more than the 8's

[Dizmm]

not to mention that the roll factor will SUCK with the 10" wide rims. instead of the sidewall holding the car straight like the 8's will, the 10s are already leaned over and will offer nothing as far as sideways grip goes.s

I think you got that backwords devlish. Your better off having a slightly wider rim than your tire. Not the tire wider than the rim.

[SgtRauksauff]

You want the suspension doing the work, not the tire. 10" rim is within the tire's recommended size, btw. 8.5" to 10". so an 8" rim would actually be pinching the tire too much. Extra wear on the outside corners when it rolls, resulting in what Dizmm has already experienced a couple weeks ago....

The contact patch does change, but not as much as the picture would indicate. instead of the tire being pinched and the tread cross-section being slightly rounded with the tread shoulders slightly off the ground, the shoulders are actually ON the ground, where they should be. More consistent contact, better grip, better feedback, better handling.

The guy running that setup on his AE68 is actually going to SCCA Nationals in a couple weeks, whenever they are. I'd say the system works pretty well...

--sarge

[devlish]

I think you got that backwords devlish. Your better off having a slightly wider rim than your tire. Not the tire wider than the rim.

to some extent... but the 10" wide rims look too wide for those rubber.

SLIGHTLY being your key word there.

[Dizmm]

for reference, you should have a 225 on an 8in wide rim.

[devlish]

^ weak.

[SgtRauksauff]

oh, the rim's guy's running are spinwerkes rims, about 10lbs each. actually lighter than his 13x8s., which are rota RB's, if I remember correctly, weighing in around 15-ish lbs. That's a major difference! Which I may actually be buying, as spending 1200 bucks for a set of rims is kinda crazy. 225/45-13's were what he was running before he went to the 255's.

Or, I could say screw 13's, and go 15's, and run the 275/35-15.... :)

--sarge

[ragdoll]

doesn't change the contact patch hardley at all really... just the sidewalls are stretched out on the 10's versus straight on the 8's.



Truth. Over extending the tire onto a rim which is too wide(10" rim is too wide for 255's) is of no benefit for performance, and visually it looks silly. In this case, the 8" rim is more appropriate but still not the optimal size for that size tire.

Dunlop knows a thing or two about tires. Learn: http://www.dunloptires.com/care/widthRatio.html

[SgtRauksauff]

10" is within Hoosier's recommended range for the tire. https://www.hoosiertire.com/rrtire.htm Don't forget, hoosier's tend to be rather larger than what they're stamped as. My 205's measured 223-ish. so either 225 or 220, which is quite a bit larger. if they keep a similar ratio, the 255's would be closer to 270....

[Dizmm]

10in is a bit wide for a 255, a 9inch would be about perfect. But i'd rather have a wider rim than one thats too narrow. Larger contact patch will always provide more grip.

[Dizmm]

Wider rims may offer some performance advantages over narrow rims. A wider rim increases the distance between the beads, which results in a straighter sidewall, which stiffens it. This results in quicker steering response and higher cornering forces.

Negatively, the straightened sidewall transmits more road shock to the wheel and suspension, placing greater stress on chassis and suspension parts and delivering a harsher ride. The straighter sidewall exposes the rim, making the wheel more susceptible to damage.

At a performance standpoint, you want a wider rim.

[devlish]

or just run 165-70 all seasons like VPT and be done with it.

[Dizmm]

VPT, what tires exactly are you running again?!?!

[SgtRauksauff]

I just got a set of Hankook Z214, in the C51 compound. same size as the hoosier A6, 225/50-14. As soon as I get'em mounted on a rim, I'll measure the difference. There's no way the hoosier is a real 225, though.

--sarge

[VPT]

VPT, what tires exactly are you running again?!?!



BFG touring. 185/60/14 or they could be 70, not sure.

[benben84]

Yep a slightly stretched tire will perform better than a a tire that is slightly too wide for the rim, the stretched sidewall allows the suspension to do the work as opposed to the sidewall giving.

I'm not really going to performance when I get my wheels but I will be getting an 18x9 wheel and hoping to fit a 245/40/18 on them. Should look just about right, not too stretched.

[VPT]

http://www.stephenmason.com/cars/rotationalinertia.html