Front/Rear wheel/tires different.

[THAWA]

I'm fairly sure we all know that you want the circumfernce of the tires to be the same on all four wheels, but what about the width? If you have two different sized tires (of the model/brand/etc to keep treadwear similar) but the circumference was still within spec, would this be safe for your center diff? For example, 16x6.5 or 16x7 wheels in the front with 205/50-16 tires, and 17x7 or 17x7.5 wheels in the rear with 225/40-17 tires. The circumference should be 75.6 in and 75.7 in respectively, so it should still be within spec, so shouldn't this not worry the center diff? Or is there something I'm overlooking?

[Splinter]

Most muscle cars have wider rears than fronts, I dont think there's a problem with it..

[skid542]

I can't see anything where it would make a difference. Maybe if your backs were 20" and your front 6" then during tight turns you would cause some wear to the center diff but a 20mm difference shouldn't be a problem, or that's my semi-educated guess.

[THAWA]

Most muscle cars have wider rears than fronts, I dont think there's a problem with it..

Most muscle cars are 2wd.

I can't see anything where it would make a difference. Maybe if your backs were 20" and your front 6" then during tight turns you would cause some wear to the center diff but a 20mm difference shouldn't be a problem, or that's my semi-educated guess.

Why would 20/6 cause a problem?

[skid542]

Hmm... well I was thinking that the inside wheel is going to turn at a rate according to where, width wise, the tire is following the path. Some of the wheel will obviously need to slip some but I would think that the location of on the tire, again width wise, that determines the rate would be different for two differnt sized tires and if the difference was great enough it'd cause problems. But I don't know enough about how the rear diff works so maybe that'd get cancelled out by the equal effect of the other side going faster? That was my thinking at least.

[BAC5.2]

What would be the advantage of this?

Are you attempting to counter over-steer by inducing understeer with a narrower front tire? Or do you like the raked out look?

I guess you COULD do this. The diameter of the tires is almost identical (4-tenths of a mm over for the 225/40/17).

You also need to take into account rim width. A 205/50 width tire on a 7" rim is going to have a shape FAR different than a 225/40 on a 7.5" rim. The tire sans rim will be perfectly within spec, but the tire on the rim will be differently shaped, and that could lead to a difference in actual diameter.

My 205/55's on 6.5" WRX rims are shaped VASTLY differently than my 225/45's on 7.5" rims.

[Legacy777]

I agree with Phil.

[THAWA]

Hmm... well I was thinking that the inside wheel is going to turn at a rate according to where, width wise, the tire is following the path. Some of the wheel will obviously need to slip some but I would think that the location of on the tire, again width wise, that determines the rate would be different for two differnt sized tires and if the difference was great enough it'd cause problems. But I don't know enough about how the rear diff works so maybe that'd get cancelled out by the equal effect of the other side going faster? That was my thinking at least.

I think I understand what you're saying. Are you thinking that the rear tires being wider will slip less and cause more power to be sent to the rear whenever you turn? That might pose a problem.

[THAWA]

What would be the advantage of this?

Are you attempting to counter over-steer by inducing understeer with a narrower front tire? Or do you like the raked out look?

I guess you COULD do this. The diameter of the tires is almost identical (4-tenths of a mm over for the 225/40/17).

You also need to take into account rim width. A 205/50 width tire on a 7" rim is going to have a shape FAR different than a 225/40 on a 7.5" rim. The tire sans rim will be perfectly within spec, but the tire on the rim will be differently shaped, and that could lead to a difference in actual diameter.

My 205/55's on 6.5" WRX rims are shaped VASTLY differently than my 225/45's on 7.5" rims.

I'm not sure what advantages or disadvantages there are.

I'm personally not planning on doing this at all. I'm just trying to get more information about our cars going. Plus there aren't any wheels I want that come in two different sizes.

The width thing makes sense. I wasn't too sure which would equate to having generally the same shape between the two axles. It might be better to find the measurement of the tire on the wheel, and the sizes that are within spec might change. Also aren't your 205/55-16's an entrie different brand from your 225/45-17's? That could equate to the difference in the way they are shaped. Aren't most tires that are the same brand and model usually physically similar? Like if you used two pairs of RE92's or something, they should hold about the same shape on different wheels (that are the correct size for the tire)?

[skid542]

Yeah, I don't know if 'slip less' is quite the right wording, think of it like a wagon with really narrow wheels with the rear set sticking further out from the centerline than the fronts, but the end result is the same.
I would think that front and rear LSD's can handle a slight mismatch, one side on the inside of the turn and the other being on the outside, so I would think that center could handle a slight mismatch. Now what quantitatively constitutes a slight mismatch, I don't know.

[BAC5.2]

They are the same brand (bridgestone), but different model (RE92 vs. RE070).

Exact dimensions of tire diameter and section width, and rim width, the tire SHOULD be similar, but also more weight will be in different parts of the wheel.