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Discussion Starter #1
I can't seem to grasp the concept of backspacing and offset. What values would make a 16" wheel have the equivalent spacing to a 1.25" wheel spacer? Do I need the width of the wheel to calculate?
 

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You need the wheel before deciding on spacers.

An 8' wide rim with 4" backspacing has zero offset. The hub mounting surface is in the middle of the rim.

Move the mounting point in or out and you have more or less backspacing, and then a positive or negative offset.

What are trying to do with your rim and tire setup?
 

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Discussion Starter #3
I'm trying to decide what kind of wheels to get. I'd like to avoid spacers if possible just because I've heard they can potentially cause some issues over time. I've got an 02 Tacoma with adjustable coilovers and I just got a set of 285/75/16 tires that are sitting in the garage. I'm pretty sure without getting some new wheels or wheel spacers they'll rub the UCAs a little bit. I've got a friend running 1.25" inch wheel spacers with the same setup and it seems to work out pretty well for him on the stock wheels, so I think that's what I'm going for. Any suggestions? Thanks for the clarification on the backspacing / offset it makes sense when you put it that way. I tried reading some other explanations that were just overly complicated.
 

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Discussion Starter #4
So just to confirm, I'm looking for something with -1.25" offset if I want the same effect as a 1.25" wheel spacer?
 

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So just to confirm, I'm looking for something with -1.25" offset if I want the same effect as a 1.25" wheel spacer?
If your rim now needs a 1.25 spacer, then a rim with that additional offset would eliminate the need for the spacer.

Do your wheels and rims not fit? A spacer or rim that puts the tire farther out will help it to not hit the UCA. It may then rub the fender.


What truck, what lift, and what tire/rim combo? And what is the issue you're trying to solve?
 

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Discussion Starter #6
02 tacoma, adjustable coilovers, stock wheels, 285/75 R16. Trying to eliminate UCA rub. I'm thinking if I trim the front bumper a bit, crank the coilovers 3/4's the way up, and get some wheels with some negative offset I should be solid? What tires / wheels are you running on your truck?
 

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2000 Tacoma, Icon C/O at 2.5"

Two sets: 31x10.5 on stock 15x7s - I think they're 4.75 backspace
32.11.5 on aftermarket 15x8s - I think 3" backspace

NO rubbing on the UCA. The 32s with wider rims rubbed at the back of the fender well. I did the pinchweld mod. Now they only slighty rub there when fully stuffed and turned hard over.
 

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I'm running 285 75 16's on 16x8 with 4" backspacing, tires have never made contact with the uca's. Stock backspacing is 4.5", so 4" bs s only .5" farther out. 3.25" bs would be the same as stock rims with 1.25" spacers. That much bs isn't needed and I would guess it would actually cause rubbing issues elsewhere.
 

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You need the wheel before deciding on spacers.

An 8' wide rim with 4" backspacing has zero offset. The hub mounting surface is in the middle of the rim.

Move the mounting point in or out and you have more or less backspacing, and then a positive or negative offset.

What are trying to do with your rim and tire setup?
I want to see your 8 foot wide rims! :D

Joking aside, with an 8" wide rim, 4.5" backspacing is 0 offset, 4" backspacing is -12 offset.


I'm running 285 75 16's on 16x8 with 4" backspacing, tires have never made contact with the uca's. Stock backspacing is 4.5", so 4" bs s only .5" farther out. 3.25" bs would be the same as stock rims with 1.25" spacers. That much bs isn't needed and I would guess it would actually cause rubbing issues elsewhere.
Agreed.I ran 285/75/16s with 4.5" backspacing, no problems. That was with coilovers.


You'll be fine with a 4" backspace.
 

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oops 8' ha.

I forgot about the mounting flange thickness, duh. I should just keep quiet.
 

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The offset amount is determined by the width of the rim. The wider the rim, the greater the offset to maintain the same rim mounting position.

Backspacing is the distance from the rear edge of the rim to the WMS.

Basically they both tell you the WMS of the rim as long as you know the width of the rim. For truck and offroad rims, backspacing is more widely used and offset is used more for passenger car wheels.

 

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Rim Width / Tire Size...Adding to the confusion

One other thing to consider is rim width / tire size. I have 265/75/17 on Sequoia Rims on my 02 Tundra (4.75" BS) and they clear by very little, but they do clear. If you put a wider tire on a narrower rim you get more sidewall bulge. Make the tire a taller one and it may hit. Go to a wider wheel with the same BS and it may clear. So you need to consider all of the above to get a setup that clears. Pushing the wheel out (less BS) may clear the UCA but then cause issues with fender clearance etc. As to wheel spacers causing issues, if you get well made spacers they should work OK. I have 1.5" on my 69 FJ40 running 15 x 10 wheels that have 3" BS so lots of torque on the spacers. Have wheeled it hard for lots of years with never an issue and the rig is driven to most locations (OK, trailer to Moab as it be to far to drive a 40). They have stayed tight (locktite on the spacer lugs) and nary an issue.
 
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