Confirmed: Offset and backspace of stock JL Rubicon wheel

WXman

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What do you mean by a positive offset can you give me example please.
Every wheel has a centerline. This is 0 offset.

You can buy wheels with positive offsets or negative offsets. A negative offset will push the wheel itself out. This gives you more tire outside the fender. A positive offset wheel pulls the wheel in. The factory wheels have high positive offset (+44.45mm) in order to meet crash test requirements, fuel economy requirements, etc. and to prevent debris from flying out of the tires and damaging other motorists' vehicles.

Most guys stick with positive offset for these reasons, but go with less offset. Maybe a +10mm like I did, or a +18 or +25. Something along those lines. That way you're still pushing the tire out farther than stock, but you're not going nuts with it.

Some states like PA have strict laws regarding how your tread fits inside your fenders so everyone should be familiar with local laws.





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ocrejects

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Every wheel has a centerline. This is 0 offset.

You can buy wheels with positive offsets or negative offsets. A negative offset will push the wheel itself out. This gives you more tire outside the fender. A positive offset wheel pulls the wheel in. The factory wheels have high positive offset (+44.45mm) in order to meet crash test requirements, fuel economy requirements, etc. and to prevent debris from flying out of the tires and damaging other motorists' vehicles.

Most guys stick with positive offset for these reasons, but go with less offset. Maybe a +10mm like I did, or a +18 or +25. Something along those lines. That way you're still pushing the tire out farther than stock, but you're not going nuts with it.

Some states like PA have strict laws regarding how your tread fits inside your fenders so everyone should be familiar with local laws.
Thank you so much for the explanation! At least now when I go looking for wheels I know what to look for. Thanks again !
 

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I didn't want to start a new thread, but I wanted to ask the question... Does anyone have experience with the what the maximum backspace on a jl Rubicon with a 12.0 or 13.50 wide tires.

I do understand the diff between offset and backspace.

Offset is helpful when considering purchasing wheels, but IMHO backspace is the critical factor when considering if a wheel will bind with suspension or steering components.

Again IMHO a 9" wheel is about as wide a wheel that you would want on a jeep that is regularly driven on the streets.
So you basically have a range between 8-9" which seems to limit the options for keeping the tire 2" or less from the sticking out from the fenders on a jl Rubicon.
 

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Hey @tmakaro or @WXman , could you help me out please. I'm looking at the rim with the specs below and I'm not getting the math on how this will look. I'd like the wheel/tire to slightly extend beyond the fenders, but not far. Could you give me your thoughts on this setup? If it had a offset of -12, would that be more tucked in or pushed further out?
  • Wheel Size: 17x9
  • Bolt Pattern: 5 on 5
  • Offset: -6
  • Backspace: 4.75
Really appreciate your help, Don
 
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The formula is: so - no + (ntw - otw)/2 * 27.5
So = stock offset
No = new offset
Ntw = new tire width
Otw = old tire width

Example:
45 - -6 + (12.5 - 11.5)/2 * 27.5
45 - -6 + .5 * 27.5
45 - -6 + 13.75
51 + 13.75
64.75mm further out than stock
Divide by 27.5 to get it back to inches and you get
2.36 inches further out than stock

Or just google wheel offset calculator. There are some great graphical ones out there :)
 

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Hey @tmakaro or @WXman , could you help me out please. I'm looking at the rim with the specs below and I'm not getting the math on how this will look. I'd like the wheel/tire to slightly extend beyond the fenders, but not far. Could you give me your thoughts on this setup? If it had a offset of -12, would that be more tucked in or pushed further out?
  • Wheel Size: 17x9
  • Bolt Pattern: 5 on 5
  • Offset: -6
  • Backspace: 4.75
Really appreciate your help, Don

In a nutshell, that's going to stick WAY out. You're adding 1.5" of width PLUS 51mm of offset away from the hub which is another 2".

Take a ruler and butt it up against the lip of your wheels and look at where 3.5" puts you. That's WAY out there, and that doesn't even include the bulge of the tires you'll be using.

I recommend +10 to +25 range for aftermarket wheels.
 

GhostDivers

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In a nutshell, that's going to stick WAY out. You're adding 1.5" of width PLUS 51mm of offset away from the hub which is another 2".

Take a ruler and butt it up against the lip of your wheels and look at where 3.5" puts you. That's WAY out there, and that doesn't even include the bulge of the tires you'll be using.

I recommend +10 to +25 range for aftermarket wheels.
I am soo glad I asked and thankful you let me know! I like the look of JIMBOX's Jeep...a little old school. But, I'm not looking for the paddle wheel look. Kind of a bummer as I was set to order these.

Thank you again for getting back to me!

Pro Comp Wheels.jpg
 

Hold24

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So far its been real diffcult to find a wheel manucfacture thats making the correct backspacing. They all stick out way to far.. I waiting on the Aev... Until then I'll run the oem rubi wheels..
 
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In a nutshell, that's going to stick WAY out. You're adding 1.5" of width PLUS 51mm of offset away from the hub which is another 2".

Take a ruler and butt it up against the lip of your wheels and look at where 3.5" puts you. That's WAY out there, and that doesn't even include the bulge of the tires you'll be using.

I recommend +10 to +25 range for aftermarket wheels.
Hi @WXman, I believe 3.5" + bulge incorrect. It should be 2.36" plus bulge.
edit: assumes a 1" wider tire too.

for example, If you have a stock wheel with 45mm offset and 11.5" wide tire and then get an aftermarket 9" wheel with a 45mm offset. That top of the tire tread will be in the EXACT SAME position as it was before. This is regardless of wheel width. However as you mention the tire will have much more side bulge on the wider tire. The bulge should be less that 3/4" inches on each side. I suspect more like 3/8" on each side for the bulge. The reason being is the top tread of the tire doesn't bulge at all.

I like your recommendation. 25mm is okay for a Rubicon but might cause an issue if your aftermarket control arms are straight unlike the bent factory control arms.
 
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TroyBoy

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So far its been real diffcult to find a wheel manucfacture thats making the correct backspacing. They all stick out way to far.. I waiting on the Aev... Until then I'll run the oem rubi wheels..
I agree. I am waiting for the AEV Borah for the JL with the 25mm offset. By my calculations that will put my tires 20mm out further than what I have.
 

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Hi @WXman, I believe 3.5" + bulge incorrect. It should be 2.36" plus bulge.
edit: assumes a 1" wider tire too.

for example, If you have a stock wheel with 45mm offset and 11.5" wide tire and then get an aftermarket 9" wheel with a 45mm offset. That top of the tire tread will be in the EXACT SAME position as it was before. This is regardless of wheel width. However as you mention the tire will have much more side bulge on the wider tire. The bulge should be less that 3/4" inches on each side. I suspect more like 3/8" on each side for the bulge. The reason being is the top tread of the tire doesn't bulge at all.

I like your recommendation. 25mm is okay for a Rubicon but might cause an issue if your aftermarket control arms are straight unlike the bent factory control arms.

You're right. It's actually 2.75", not 3.50".

9 inch wheel has a centerline of 5 inches. -6mm is 0.25" which is where the 4.75" backspace comes from. That's 1.25" less than stock.

Then the 9" wheel itself is 1.5" wider.

So the total is 2.75, not 3.5". I just threw that first number out there quickly because I was in a rush. My bad.

In any case, if the guy wants to keep most of his tread inside the fenders a negative offset wheel ain't gonna' work.

Cheers.
 
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rizej

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Here is a really cool visual calculator:
https://tiresize.com/wheel-offset-calculator/
tire.jpg
This is a great tool to visually compare wheel specs and different sizes quickly. The basic thing to look for and avoid would be the case where the new wheel & tire combination is closer to the hub than the original correct? As long as the new wheel & tire combo put the inner edge of the tire further away from the hub, then all should be well
 

GhostDivers

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While I'm asking for help...I hear you on the offset of +10 to +20 would be the preferred range, but does backspacing come into play or does just focusing on the offset provide the simplest way to gauge?
 

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