Thou Shalt Calculate Backspacing - JKowners.com : Jeep Wrangler JK Forum
 
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post #1 of 4 Old 03-16-2016, 02:43 PM Thread Starter
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Thou Shalt Calculate Backspacing

Looking to confirm my math on calculating backspacing. I'm ordering a 2016 JKU sport and I am going to add new wheels/Duratrac 315/70/R17s and a 3" BDS lift.

I believe that the backspacing on stock wheels is 6.5", and they generally run 255 tires which are 10" wide. So for my new Duractrac tires that are 12.5" wide, I will need a wheel that has less backspacing to accommodate the wider tires and fit properly in the wheelwell. So going from 6.5" of backspacing to 4" of backspacing "allows" for the additional 2.5" of width in the tire.

How'd I do?
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post #2 of 4 Old 03-16-2016, 04:05 PM
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Yip most people recommend 4 to 4 1/2 for 35's and 3 1/2 to 4 for 37's.

'11 JKUR, 3" Full-Traction w/5100's, 37x17 Trail Graps on Slabs, 10 Fact Axles, Adams front DS, TF44 front, PSC Hydro Assist. Home made sliders, bumpers, tire carrier. Warn XD9000i w/Smitty Synth line.
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post #3 of 4 Old 03-16-2016, 04:52 PM
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Quote:
Originally Posted by estark573 View Post
Looking to confirm my math on calculating backspacing. I'm ordering a 2016 JKU sport and I am going to add new wheels/Duratrac 315/70/R17s and a 3" BDS lift.
Hope you research the BDS lift thoroughly before buying. I don't know anything about 'em, hopefully you do.

I believe that the backspacing on stock wheels is 6.5",
Stock alloys on my JK had 6.25" back spacing.
and they generally run 255 tires which are 10" wide. So for my new Duractrac tires that are 12.5" wide, I will need a wheel that has less backspacing to accommodate the wider tires and fit properly in the wheelwell.
So far, so good . . . but then:
So going from 6.5" of backspacing to 4" of backspacing "allows" for the additional 2.5" of width in the tire.
Only 1/2 of the additional tire width is going toward the Jeep to interfere.
However, the added diameter also (or more so) requires reduced back spacing to keep from rubbing.


How'd I do?
Close. See notes above.

Quote:
Originally Posted by Robnoxious1 View Post
Yip most people recommend 4 to 4 1/2 for 35's and 3 1/2 to 4 for 37's.
Pretty much that ^^^ (those are good, safe numbers).
With angled front lower control arms (like TF, Synergy, and ?), you can run 35s on 4.75" of B.S. and 37s on 4" of B.S.
On kits that have straight front lower control arms, you need less back spacing to keep from rubbing on the arms.

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post #4 of 4 Old 03-16-2016, 04:55 PM
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That additional 2.5" of tire isn't all on one side.

<edit> Nevermind...covered.

Last edited by funfred; 03-16-2016 at 04:57 PM.
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