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Rim offset question.

bhicks

bhicks

NAXJA Forum User
Location
Forest Falls, CA
I am currently in the process of buying new rims and I thought I understood what the offset was all about. I thought the if a rim has a 4" offset it will stick out further than a rim that has a lesser offset like 2.5". I am currently running 35's and was going with a crager soft 8 15" x 8" riim with a 4" offset. I thought that would be perfect for my 6.5" lifted XJ. A friend of mine told me I should go with a 2.5" offset to push the tires out further and prevent rubbing on my long arms. Won't a 2.5" offset bring the tires in and not out? Someone please clue me in.
 
Oops. I meant to put this in the modified tech forum. Can someone help me transfer this over?
 
Offset is measured from the centerline of the rim - you can calculate it using backspacing and rim width. I've never heard of soft 8s that are 15x8 with a 4" offset, don't think they even make them, are you maybe confusing offset and backspacing? Because they do make them with 4" backspacing, which would be 0" offset in an 8" wide rim. 2.5" of backspacing instead of 4" will push the tires another 1.5" outwards. Stock backspacing is 5.25" on a 7" rim which comes out to 1.75" of positive offset (distance from centerline of wheel to WMS), 2.5" backspacing on an 8" rim would be negative 1.5" offset.

https://www.rsracing.com/tech-wheel.html - more info

PS - I'm running 11.5" wide tires on 8" rims with 4" of backspacing, seems to work great. I have no rubbing lock to lock on one side, and a little rubbing on the other side which should go away or balance out when I properly recenter my axle and deal with my swaybar links.
 
kastein said:
Offset is measured from the centerline of the rim - you can calculate it using backspacing and rim width. I've never heard of soft 8s that are 15x8 with a 4" offset, don't think they even make them, are you maybe confusing offset and backspacing? Because they do make them with 4" backspacing, which would be 0" offset in an 8" wide rim. 2.5" of backspacing instead of 4" will push the tires another 1.5" outwards. Stock backspacing is 5.25" on a 7" rim which comes out to 1.75" of positive offset (distance from centerline of wheel to WMS), 2.5" backspacing on an 8" rim would be negative 1.5" offset.

https://www.rsracing.com/tech-wheel.html - more info

PS - I'm running 11.5" wide tires on 8" rims with 4" of backspacing, seems to work great. I have no rubbing lock to lock on one side, and a little rubbing on the other side which should go away or balance out when I properly recenter my axle and deal with my swaybar links.
Click to expand...


Thank you!! That was excellent info and your right. I AM mixing up backspacing and offset. I didn't realize they were 2 different things. I was using the two words interchangably which is what made everything get all mixed up. It looks like the 15 x 8 with 4" backspacing rim will be the right one for me. I have 3/4" and 1.25" spacers if I need to use them, but I doubt I will. Once again, thanks for the info.
 
Before I go and order these rims, I should take a quick pole. This question goes out to guys with 33" x 12.5" tires or bigger. What backspacing are you running on your rims?
 
Last edited:
Mine are 33s (in my sig, forgot to mention it before.) I was also confusing backspacing and offset before I ordered mine, which is why I knew about that page that describes it... I still don't know why backspacing is measured in inches and offset is usually measured in mm :huh:

Another thing, if you get the Cragar rims, don't worry about it if they come and the centerbore is larger than the hubs on your Jeep. Same thing happened with me, they work fine (XJ acorn style lug nuts make for good lug-centric setup), if you're worried about it you can get adapter rings that make the lug-centric Cragars back into hub-centric rims, they're usually made out of plastic or aluminum though so I figure they're not carrying weight anyways.
 
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