blue911rsr

Does anybody have any data how rim widh affects a tire. Within the recommended size by the manufacturer.

ExMB

Have you looked on the tirerack site?

993fvr

Recommend article on motoiq.com called " How to Properly Select and Size Tires for Performance" by Billy Johnson

993fvr

Quick addendum: it's under the " Columns " heading and you click on Fast Laps with Billy Johnson

ProCoach

Also, the manufacturer specification page lists min and max recommended rim widths for each tire.

This can vary because the construction of the tires differ, so one size does not fit all.

Joe Weinstein

In autocross we generally find that tires work better at the widest wheel in its recommended range, so much so that multiple tests have shown that a somewhat narrower tire on a wheel so described is faster than a somewhat wider tire of the same type, on the same rim.

ProCoach

Improves transient response, too. Particularly important for autocross.

NYC993

Wider rim, stretches the sidewall making it stiffer and reducing tire roll. I agree on widest rim for the tire (within range).

i run 225 tire on 8 inch wide rim and 275 on 11, which is an inch wider then stock rims front and rear.

on street it makes it easy to get curb rush or crack the rim, so I only run this on track.

EDIT: run 225 on 9 inch rim (stock is 8).

ExMB

IMHO your argument is opposite. Wider rim within the tire/rim actually pinches the sidewall less which is not the same as stretching it. Stretching is going wider than manufacturer's rim recommendation similar to those "stance show cars".

NYC993

? If the rim is on wider side, it's wider than the tire stretching the tire (rim sticks out). If rim is on narrower side, the sidewall "bulges" out.

ExMB

You got it. Sidewall on a wider rim is stretched since its passed its normal angle. On a narrower its being pinched; again because it goes byond its design limits.

Bill Verburg

stretch/pinch is more a matter of symantics

for every .5" increase in wheel width there will be ~.2" increase in tire section width. There is also a slight decrease in OD. The tread width of course doesn't change

here is an example take any tire, lets say RE71R 235/40 x18
it has a design wheel width range of 8.0" to 9.5". If this tire is mounted on an 8.5" wheel it measures 9.5" section width & 25.4" OD(real #s not made up) mount the same tire on a 9" wheel and it measures ~9.7" section width an a tad less than 25.4" OD, mounted on a 9.5" wheel section width goes to ~9.9"

It also changes the nominal spec
ie the 235/40 x18 measures 241/45 x18 on an 8.5 or 246/44 x18 on a 9

actual specs can be all over the place, I used to use the older version RE71
205/55 x16 nominal when mounted on a 7 became a 219/40 x16 and 245/45 x16 on a 9 became a 260/34 x16

KOAN

So Bill, for road racing, do you recommend a wheel with a width at the narrower or wider end of the recommended spectrum for a given tire? Also, do you recommend a shorter or a taller sidewall, all other things being equal? Or is it tire compound and suspension dependent?

Thanks

Bill Verburg

You'll get the best performance from the widest wheel for which a tire is spec'd

Shorter sidewall runs at lower slip angles for the same side force and will run cooler, so yes shorter sidewalls will generally provide the best performance but as always there will be exceptions, for example a ca w/ a really poor camber pattern likely won't see the full benefit of lower profile


Of course compound and suspension characteristics influence grip levels

NYC993

+1 and very happy with how car handles even with compromised street/track alignment. I'm sure part of it is stiffer NT01 sidewalls, but it feels like my suspension is stiffer and more reactive when I put by track wheels/tires on.