Backspacing

[87Chief]

I'm looking for some new rims for my truck. I'm going to stick with 31x10.50x15's for now and was planning to get some 15x8 black cragar steel wheels or pacers but I'm stuck on the backspacing

 

I'm not sure which way sticks out more or sticks in more.. like 3.75" compared to 4.25" ..

 

I want a little wider stance.. any suggestions?

 

Thanks

[johnnyc]

3.75 would stick out more than 4.25.

[skidoo_j]

Wheel Technical Information

[mvusse]

Even the 4.25 will stand out more than the stock rims.

[Keyav8r]

Skiddo_j - thanks for posting the link. I've been wondering about back spacing and that also answers some questions I didn't know I had!

[jpnjim]

I didn't read the link, but going with an 8" wide vs 7" wide wheel has a big effect on this as well.

 

Factory XJ,YJ & TJ 15x7's were 5.25" BS

Factory TJ & YJ 15x8's were 5.5"BS to try to compensate for the added wheel width.

 

For every inch under those BS numbers, your tire will stick out 1" more one per side than the factory wheels.

 

Don't forget to take into consideration the added tire width.

 

A 31x10.5 on a 4"BS 15x8 will stick out about 2" more than a stock TJ 30x9.5 on a TJ 15x8 w/5.5"BS.

(1.5" more due to back spacing +.5" more due to 1" wider tire)

 

Put the 31x10.5 on a 4"BS 15x7 and it will tuck back in 1/2-3/4" (assuming the tire width also shrinks about 1/2" overall with the 1" narrower wheel).

 

 

 

 

 

If I'm looking for a little more track width compared with Stock Wheels,

I really like 15x7's with 3.75-4" BS for narrow tire XJ/MJs.

Tread usually it comes out even, or just past the front flare lip.

 

4.5"BS 15x7's or 4.75BS 15x8's if I'm trying to tuck them in a little more.

 

Wide tires will edge past the flares even with 4.5-4.75" BS.

[Eagle]

A key point to remember is that 31x10.50-15s on factory 15x7 rims with 5-1/4" backspacing, will tuck up inside the wheelwells when the suspension is compressed, which is why we can run 31x10.50s on stock rims with no trimming of the sheet metal or flares.

 

ANYTHING that moves the tires farther out (less backspacing and/or wider rims) results in the outer shoulder of the tire (or the tread itself) making contact with the bodywork when the suspension compresses, thus requiring trimming.

 

There are no aftermarket rims offering 5-1/4" backspacing. Even in 15x7, a rim with 4-1/4" backspacing puts the tires 1 inch farther outboard. Then add another inch for 15x8 rims, and now the outer sidewall and shoulder will ride 2 inches farther out than stock. In states that require the fenders to cover the tread of the tires (which, I think, is just about every state), that 2 inches is enough to make your new tires and wheels illegal.

[skidoo_j]

http://www.rimsntires.com/specs.jsp

 

 

You can use this one to see the difference different wheels/tires will produce.

[jpnjim]

A key point to remember is that 31x10.50-15s on factory 15x7 rims with 5-1/4" backspacing, will tuck up inside the wheelwells when the suspension is compressed, which is why we can run 31x10.50s on stock rims with no trimming of the sheet metal or flares.

 

ANYTHING that moves the tires farther out (less backspacing and/or wider rims) results in the outer shoulder of the tire (or the tread itself) making contact with the bodywork when the suspension compresses, thus requiring trimming.

 

There are no aftermarket rims offering 5-1/4" backspacing. Even in 15x7, a rim with 4-1/4" backspacing puts the tires 1 inch farther outboard. Then add another inch for 15x8 rims, and now the outer sidewall and shoulder will ride 2 inches farther out than stock. In states that require the fenders to cover the tread of the tires (which, I think, is just about every state), that 2 inches is enough to make your new tires and wheels illegal.

 

Agreed that its tougher to stuff tires in when they stick out too far.

 

When I went from 33x12.5's on 4.75"BS 15x8's to 3.75"BS 15x8's I had to move my ft flares up 4" or so to get the same amount of flex.

 

If you look around enough, you can find a limited number of aftermarket wheels with XJ friendly 4.5-5.5" BS.

I had some American Racing Aluminum wheels in 15x8's w/5.25"BS.

Nice with 31x10.5's

 

side view doesn't show stick out well,

but you can see how shallow the wheels were on their front side,

(AR Wheels; 15x8/5.25bs w/31x10.5 TrXus's on a friends Jeep)

 

[jpnjim]

Sorry for so many pics....

just better to tell the story with.

 

Not all are 31's,

but they do show 9.5",10.5",11.5"&12.5" wide tires on different bs wheels and how far they stick out:

 

 

 

 

30x9.5" on TJ 15x8's 5.5"bs

31x10.5 on 15x8's 5.25"bs

 

same, on ZJ:

 

 

32x11.5 on factory 15x7's 5.25"bs

 

32x11.5 on Eagle 15x7's 4"bs (did NOT stick out as much as I thought they would)

 

 

 

35x12.5 on steel 15x8's 4.75"bs (borderline legal around here, rears tuck in pretty good, so no one really ever said anything to me)