Wheel backspace/offset

[CATMdude45]

I know there is a thread with folks showing off their rims/tires but very few people talk about what offset they have. My issue is the 1952 3100 I bought has a chevelle rear end installed and the tires that are on it are terrible, the rims were modified to fit the 5 bolt by 4.75 lugs. It has 14 x 7 in the front and 15 x 8 in the rear but the two rear rims do not even match. I am looking to get new wheels and tires. I am not a fan of low profile tires so I am going to stick with 15 or 16 inch rims. So here is my question.....what offset should I be ussing, I am thinking of sticking to the 235/75/15 tire.

[dwcsr]

Originally Posted by CATMdude45

I know there is a thread with folks showing off their rims/tires but very few people talk about what offset they have. My issue is the 1952 3100 I bought has a chevelle rear end installed and the tires that are on it are terrible, the rims were modified to fit the 5 bolt by 4.75 lugs. It has 14 x 7 in the front and 15 x 8 in the rear but the two rear rims do not even match. I am looking to get new wheels and tires. I am not a fan of low profile tires so I am going to stick with 15 or 16 inch rims. So here is my question.....what offset should I be ussing, I am thinking of sticking to the 235/75/15 tire.

Off Set is the distance of the mounting surface of the wheel to the centerline of the wheel

Back Space is the distance of the in side edge of the wheel to the mounting surface of the wheel

Offset comes into play when you have a defined space ( wheel Well) that a wheel will fit in and a defined axle width that may or may not drop the wheel mount flange in the center of that space

Lets say you have a 10" wheel well and want to run a 8" wide wheel with 1" clearance on each side. The outside wheel well measurement is 75", subtract 20 (the two wheel wells) and you have the inside wheel well measurement of 55" , you have an axle that is 61.5" which ends up at 1/2" off center line of the wheel well and the wheel. but leaves you with a back space of 4.5". if you have a 7" wheel and all other measurements are the same except you have a two inch clearance on the inside well then you end up with a back space of 3.5" and the same offset

[mr48chev]

Well you could set the rear axle on stands, pull the rear wheels or one of them and lay a straight edge across the bolt mount surface and measure from there to the bed side. That would give you how much room you have on the inside after you deduct a decent amount of tire clearance room.

Then measure from the mount surface to the inner lip of the fender to see how much clearance you have there.

I went out and looked at my 15x8 Enkie 32 rear wheel and it had a 3-1/2 inch back space which I would say is the max back space without mini tubs. Running a 255-60-15 tire I only had about 1/2 inch clearance at most. A 235 tire should give you more room and if you go 70 or taller rather than 60 that would help a bit too.

On the outside I had just enough room to get my fingers between the tire and the fender but not any more than that. Those tires really fill the space

[mphudak]

What year chevelle rear? I have an abody cutlass 12 bolt (69 i believe) and is likely close to what you have. I'm running 15x7 w/4.125" BS w/235/75r15's and have atleast an inch clearance on the inside. Note I have suburban and not sure if the bed sides of a truck are different, but believe the clearance is the same.

[CATMdude45]

Originally Posted by mphudak

What year chevelle rear? I have an abody cutlass 12 bolt (69 i believe) and is likely close to what you have. I'm running 15x7 w/4.125" BS w/235/75r15's and have atleast an inch clearance on the inside. Note I have suburban and not sure if the bed sides of a truck are different, but believe the clearance is the same.

It is a 1968 chevelle I believe. The front spindals were swaped as Well so that the front and rear would have the same bolt pattern.