JL Offset & Backspacing Finally Answered!

[Discount Tire]

@Muskoka Minute if this is what you are trying to achieve. You are in essence just trying to decide where the extra inch and a half will go.

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[Muskoka Minute]

Actually I'm trying to figure out what the offset should be to keep my scrub radius the same.

 

[GATORB8]

So if I have a 286/70R17 (33" tire) with a 17x7.5" rim with 37 Offset.
And I go with a 35/12.5R17 (35" tire) with a 17x9" I would have to go with a 42 Offset to keep my scrub radius?

Is this correct ?

You're going the wrong direction to maintain scrub radius.

Increasing tire radius moves the intersection of the steering axis and the ground outward. Increasing positive offset moves the center of the tire inward.

Stock offset is ~44.5mm

Assuming 12 degree steering axis, adding 1" (25.4 mm) of tire radius, you would need to reduce offset by Tan(12)*25.4=5.4mm. So around a 39mm offset.

Or you can use @AnnDee4444 's spreadsheet here, he's got it calc'd out in one of the tabs:
https://www.jlwranglerforums.com/fo...gs-suspension-information-chart-matrix.66591/

 

[Kreepin1]

So if I have a 286/70R17 (33" tire) with a 17x7.5" rim with 37 Offset.
And I go with a 35/12.5R17 (35" tire) with a 17x9" I would have to go with a 42 Offset to keep my scrub radius?

Is this correct ?

Sorry about that, you would need to subtract 5 to maintain stock scrub radius. @GATORB8 nailed it in his post.

But @Discount Tire is pointing out the tire you've picked is physically an inch or more wider. Let's call it 1.5 inches. Half goes inward and half goes outward, so call it .75 inch. Moving the tire out 5mm (by subtracting from stock offset) is less than a quarter inch. So the edge of the tire will move up an inch and also inward .5 inch. Do you have that much clearance?

 

[Muskoka Minute]

Sorry about that, you would need to subtract 5 to maintain stock scrub radius. @GATORB8 nailed it in his post.

But @Discount Tire is pointing out the tire you've picked is physically an inch or more wider. Let's call it 1.5 inches. Half goes inward and half goes outward, so call it .75 inch. Moving the tire out 5mm (by subtracting from stock offset) is less than a quarter inch. So the edge of the tire will move up an inch and also inward .5 inch. Do you have that much clearance?

I have a 2019 Rubicon with 285/70R17 on it now so as far as I know the 35" should fit.
They mentioned the offset was 44. I thought it was 37.

So assuming it is a 44 offset what would the new offset be with 35" tires on a 17x9 rim.
On that same note what would the new offset be if the original offset was 37

On a side note what should the bump stops be with the new 35" tires?

 

[Kreepin1]

I have a 2019 Rubicon with 285/70R17 on it now so as far as I know the 35" should fit.
They mentioned the offset was 44. I thought it was 37.

So assuming it is a 44 offset what would the new offset be with 35" tires on a 17x9 rim.
On that same note what would the new offset be if the original offset was 37

On a side note what should the bump stops be with the new 35" tires?

Most JL wheels are 17x7.5 with a +44.45 offset. So a wheel with a +39mm offset will return scrub radius to stock. FYI, Gladiator Mohave wheels are 17x7.5 with a +37.17 offset.

How much bump stop you need to prevent rubbing depends on how much weight you carry and whether or not you go offroad. There are a number of threads on this. Personally, I'm running 11.5" wide tires on +44 wheels and they rub slightly offroad.

 

[AnnDee4444]

 

[GrayWolf.Overland]

[*]JL Model: JLUR
[*]Wheel: gfx tr 10
[*]Offset: +12
[*]Backspacing: ~5.5
[*]Tire Make: mastercraft courser mxt
[*]Tire Size: 37 12.5 17
[*]Lift: mopar 2.5-3
[*]Rubbing: super mild on inner fenders when off roading. Not enough to be bothersome
[*]Pictures:

@Jerrybizzle - I love this setup and I was looking to get either the AEV JL spec wheels or an aftermarket 17x9 +12 wheel for 37s KO2 C-rated (on my 24 JLUR 4xe)

Did you have any suspension component (LCA, sway bar) rub off-road on 37s on these wheels? The AEV JL spec wheels are 5.7 backspace and there is mixed opinions on it rubbing on some tires and not on others. Wondering what your experience was and if you had to adjust steering stops to prevent rub on the control arms at full turn when sway bar disconnected?

 

[GATORB8]

@Jerrybizzle - I love this setup and I was looking to get either the AEV JL spec wheels or an aftermarket 17x9 +12 wheel for 37s KO2 C-rated (on my 24 JLUR 4xe)

Did you have any suspension component (LCA, sway bar) rub off-road on 37s on these wheels? The AEV JL spec wheels are 5.7 backspace and there is mixed opinions on it rubbing on some tires and not on others. Wondering what your experience was and if you had to adjust steering stops to prevent rub on the control arms at full turn when sway bar disconnected?

I have +18mms with 37" KO2s. Clears all the MC parts, except I can scrub the sway bar end links in the perfect flex/lock situation.

 

[GrayWolf.Overland]

I have +18mms with 37" KO2s. Clears all the MC parts, except I can scrub the sway bar end links in the perfect flex/lock situation.

is that 17x8.5 +18 or 17x9 +18?

 

[GATORB8]

is that 17x8.5 +18 or 17x9 +18?

8.5, but your tire should be in the same place on 9.

 

[GrayWolf.Overland]

8.5, but your tire should be in the same place on 9.

perfect! yeah 17x9 +12 should be exactly the same deal. I also have a similar front full width bumper where there will be some rub at extreme off-camber flex at full lock.. that is ok and manageable if we are aware of it..
Super excited that there is no LCA or sway bar rub with this setup!!! I really hate running negative offset with high poke factor.. I will go ahead with the +12 wheel instead of -12

BTW - I am going with C-rated 37s KO2.. they run a bit narrow and short. I wanted the tallest true to size 35s with lightest weight.

 

[Jerrybizzle]

@Jerrybizzle - I love this setup and I was looking to get either the AEV JL spec wheels or an aftermarket 17x9 +12 wheel for 37s KO2 C-rated (on my 24 JLUR 4xe)

Did you have any suspension component (LCA, sway bar) rub off-road on 37s on these wheels? The AEV JL spec wheels are 5.7 backspace and there is mixed opinions on it rubbing on some tires and not on others. Wondering what your experience was and if you had to adjust steering stops to prevent rub on the control arms at full turn when sway bar disconnected?

On my second set of +12 9 wide wheels (rocktrix) now and still have no issues. Running a different lift that is more flexy (rk springs and shocks) than the mopar and I do rub the front inner fender wells at times, but nothing bad enough to be concerning. I need to change my front bump stops, as when fully stuffed I hit my fenders, but the offset is not the issue there. Good luck with your decision.

 

[Kreepin1]

8.5, but your tire should be in the same place on 9.

To be precise, the 9" wheel will move the tread outboard 0.25" and the inside sidewall about half as much, call it an eighth of an inch.

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