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Old 04-17-2013, 10:46 AM   #1
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Tire / Back spacing Help

I posted this in the tire/wheel thread and got nothing so ill try here.

So here is the deal. I have 2013 Unlimited Rubicon which has a 2 1/2 lift, but will be changing out to a 3 1/2 inch lift next week. I will be purchasing a set of AEV Savegre Wheels in Argent. Now from what ive read I need a wheel with 4.5 inch backspacing to not run spacers. however the AEV specs say 5.2" backspacing with a +10mm offset. Im wanting to run a 315/70/17 KM2 or GY MTR's or something similar but I prefer to leave the spacers off. Is this possible to do and not encounter rubbing while off-road and retain full steer,flex, and stuff in the wheel well.

also, using the math in the largest tire on a JK thread
Take offset, divide by 25.4, then add the overall rim width (rim width +1) divided by 2
so 10/25.4 + 8.5 +1 / 2 = 4.94 So this should be the back spacing.

Why is this so hard for me? Am I missing something?

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Old 04-17-2013, 11:08 AM   #2
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When I do the math, I get BS=5.14", which is a bit closer to the AEV value of 5.2".

I suspect you're gonna rub at least some...

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Old 04-17-2013, 02:07 PM   #3
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It's going to depend on who your lift is as well. If you're going with an AEV lift or a Metal Cloak lift for example you'll be fine with the exception of possibly some rubbing on the air dam or a fender liner. If you go with something like Rock Krawler where their control arms do not have the factory bend, then yeah you need the much lower backspacing to not hit those. FWIW I talked to Metal Cloak to find out what backspacing I really needed to not hit anything with 12.5" wide tires on my lift and they said minimum of 5" or less. I'm planning to just go with a 4.5" backspacing so I have plenty of clearance to run v-bar chains if I go snow-wheeling again.
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Old 04-17-2013, 03:04 PM   #4
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Quote:
Originally Posted by flyinion View Post
It's going to depend on who your lift is as well. If you're going with an AEV lift or a Metal Cloak lift for example you'll be fine with the exception of possibly some rubbing on the air dam or a fender liner. If you go with something like Rock Krawler where their control arms do not have the factory bend, then yeah you need the much lower backspacing to not hit those. FWIW I talked to Metal Cloak to find out what backspacing I really needed to not hit anything with 12.5" wide tires on my lift and they said minimum of 5" or less. I'm planning to just go with a 4.5" backspacing so I have plenty of clearance to run v-bar chains if I go snow-wheeling again.

I have a teraflex 2.5 coil now, with TF adjustable lower control arms. Im removing the TF springs and shocks and adding RK springs and fox shocks, and jks quick discos
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Old 04-17-2013, 04:46 PM   #5
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Backspacing is a poor measurement due to it's ties to the width of the wheel. Wider wheels can get by with more bs'ing then more narrow wheels.

Offset is a much better measurement. Offset sets the tire in then same place no matter how wide the wheel is. For the most part, the standards most use here is 0 offset for 17"s and up, -12 for 16's, and -19 for 15's. This is due to the smaller wheels by height need less offset to clear the calipers.

Saying that, +10mm offset should be alright for 12.5" or 315's on 17" and up wheels. It will be close but should not hit. 0 offset is used to cover people that go up to 37's which are normally wider tires. Now if you go to 37's that are 13.5" wide in most cases, then you will probably rub at full turn.
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Old 04-17-2013, 05:34 PM   #6
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Originally Posted by rics1997 View Post
Backspacing is a poor measurement due to it's ties to the width of the wheel. Wider wheels can get by with more bs'ing then more narrow wheels.
Ok now I'm confused. You're saying a wider wheel can somehow get by with more backspacing (i.e. sitting closer in to the frame)? For reference, for 4.5" of backspacing, on an 8" wheel that is 0 offset, 8.5" is -6 (sticks farther out of the fender) and 9" is -12 (even farther out).

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