Recommended Backspacing?

RockyMtnHigh

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A lot of lifts have a "recommended backspacing" usually around 4.5". Is that a minimum, maximum, or exact? As I understand it, 0" backspacing would essentially mean that the inside wall of the tire is on the same plane as the axle hub. In that case, there would be plenty of room between the inside of the tire and the shocks/coils/control arms. So I assume that means that less backspacing is better (i.e., more clearance.) Therefore 4.5" would be the MAXIMUM backspacing, otherwise the tire would collide with the shocks/coils/control arms. I've read that the stock Rubicon rims have 6.5" backspacing, which would not work with a lift that recommends 4.5" backspacing. Am I correct, or do I have this backwards?





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A lot of lifts have a "recommended backspacing" usually around 4.5". Is that a minimum, maximum, or exact? As I understand it, 0" backspacing would essentially mean that the inside wall of the tire is on the same plane as the axle hub. In that case, there would be plenty of room between the inside of the tire and the shocks/coils/control arms. So I assume that means that less backspacing is better (i.e., more clearance.) Therefore 4.5" would be the MAXIMUM backspacing, otherwise the tire would collide with the shocks/coils/control arms. I've read that the stock Rubicon rims have 6.5" backspacing, which would not work with a lift that recommends 4.5" backspacing. Am I correct, or do I have this backwards?
It's usually the max that is listed, although you can usually go 0.25" more without issue. You can go less, but it pushes your wheels out, increasing your scrub radius, and can cause interference elsewhere at full steering stops.
 

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My wheels are 17x8.5 +12 offset/5.25 back space. They stick out prob 2.75" more.
I think my stock rims were 7.5" wide vice 8.5 and my 305 tires are about 2.5 wider than the stock 245's.
So i got a 1" wider rim and 2.5" wider tire. So going to a 5.25 vice 6.25 backspace gives an inch more space from the inside lip of the rim to the shock/spring/fender liner. The 12" wide tire then is 3.5" wider than the rim, so it likely sticks out 1.75" more on each side of the wheel. So the inside clearance =1" - 1.75" = .75" closer inside. On the outside the Wheel sticks out 1" + 1.75" more tire = 2.75". So the tire is .75" closer inside and sticks out 2.75". The 1" wheel width increase is all on the outside.
My front tires would likely hit the control arms if not moved out. Smaller back space # moves the wheel out.
https://www.discounttiredirect.com/learn/offset-backspace

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Factory wheels are +44.45mm offset, which is 6.1" backspacing.

There are numerous people running larger tires on stock wheels. So you do not need 4.5" backspacing to clear tires necessarily.

Personally, I think the sweet spot is around 5" backspacing. My wheels are 5.16" backspacing and 8.5" wide and I just barely stick out past the fenders. It's perfect.
 
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RockyMtnHigh

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Factory wheels are +44.45mm offset, which is 6.1" backspacing.

There are numerous people running larger tires on stock wheels. So you do not need 4.5" backspacing to clear tires necessarily.

Personally, I think the sweet spot is around 5" backspacing. My wheels are 5.16" backspacing and 8.5" wide and I just barely stick out past the fenders. It's perfect.
I'm not concerned about tire size, but rather lift kit recommendations. For example, RockKrawler recommends 4.5" backspacing on rims for their lift kits. In that case I couldn't use my stock rims which are 6.1" backspacing
 

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I'm not concerned about tire size, but rather lift kit recommendations. For example, RockKrawler recommends 4.5" backspacing on rims for their lift kits. In that case I couldn't use my stock rims which are 6.1" backspacing
You have to factor in tire size when considering backspacing. The BS requirements to clear everything at full turn and travel will be different if one is running an 11.5 inch tire vs a 13.5 inch wide tire for example.
 

WXman

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That's true. It can get kind of complex if you really break it down. For example, a wheel with 4.5" backspacing is going to swing in a much larger arc than a wheel of the same width with 6" backspacing. That's why a lot of guys find that less backspacing actually creates more clearance issues with tires.

There's a fine line to walk. But yep, it does matter which specific size tire you will be using. Obviously most guys are doing 35x12.50 or 37x12.50. Those seem to be the more common sizes. I still think something around 5" backspacing is the sweet spot. But 4.5" would certainly work.
 

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Is anyone running no lift -6mm offset with 35"s on a JLU rubicon and 2" bumpstops, any rubbing issues, does it fit?
 

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I'm not concerned about tire size, but rather lift kit recommendations. For example, RockKrawler recommends 4.5" backspacing on rims for their lift kits. In that case I couldn't use my stock rims which are 6.1" backspacing
Rancho also recommends 4.5 back spacing with their kits. When back space is discussed you also have to take in to consideration do you plan to air down as that changes the equations as well. 4.5-4.7 basically future proofs you. You could go a + offset and alway add spacers if needed, however many tire shops will not work with spacers (when I was considering 3 tire shops turned me down)
 

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I think you'll rub with 13.50's (38+) with only 4.5 backspace at full lock/offroad. Need 3.5 was my understanding.
 

Village Idiot

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After researching this and having some experience... I would stick between 4.75 and 5.5” of backspace.

Don’t get a wheel wider than 8.5” unless running bigger than 37” tires. Don’t get the 13.5” wide 37s, get the 12.5”. The jl steering is sensitive and keeping that scrub radius to a minimum is very important. Cheers. .
 

AnnDee4444

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After researching this and having some experience... I would stick between 4.75 and 5.5” of backspace.

Don’t get a wheel wider than 8.5” unless running bigger than 37” tires. Don’t get the 13.5” wide 37s, get the 12.5”. The jl steering is sensitive and keeping that scrub radius to a minimum is very important. Cheers. .
FWIW: The scrub radius is effected by the tire diameter.

Scrub Radius vs. OEM.png
 

Sdmeyer11

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Like a lot of people, I'm driving myself insane with this decision. I think I've read every wheel offset thread at least 3 times. My lift calls for -12 or 4.5 backspacing. The wheels I want (17x9) come in -12 and +12 offset. I'm leaning towards the +12 because I don't want the tires sticking out past the fenders too much. But I don't want to rub. My Jeep 80th will probably never go off-road, not sure if that makes a difference. I'm also buying Toyo ATIII tires in 315/70/17. Would I be better off going with 285/75/17 if I go with the +12?
 

Village Idiot

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Like a lot of people, I'm driving myself insane with this decision. I think I've read every wheel offset thread at least 3 times. My lift calls for -12 or 4.5 backspacing. The wheels I want (17x9) come in -12 and +12 offset. I'm leaning towards the +12 because I don't want the tires sticking out past the fenders too much. But I don't want to rub. My Jeep 80th will probably never go off-road, not sure if that makes a difference. I'm also buying Toyo ATIII tires in 315/70/17. Would I be better off going with 285/75/17 if I go with the +12?
I think a 9” wheel is wider than ideal for a sub 35” tire size. That being said, the benefits of the +12 offset at high speeds especially should be noticeable.
 

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