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Old 01-01-2013, 07:14 PM   #1
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Back space and off set

I know there is a lot of posts irt to this subject, but every situation seems to be different so, I thought I'd ask. I want to order new wheels for my 05 tj that currently has stock 15x7 wheels, no lift and 31x10.5x15 tires. I am looking at pro comps 15x7 152 series. They have 3.75 back spacing, and
-3.00 MM off set.

What differences will a wheel of these specs make compared to the stock wheel with the same tire?

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Old 01-01-2013, 07:37 PM   #2
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Ill be nice a say your in jk forum might want to ask the tj peps!

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Old 01-01-2013, 07:59 PM   #3
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Moving over to TJ area.
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Old 01-01-2013, 08:15 PM   #4
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Forget you ever heard the offset term which is really meant more for car wheels. The offset dimension is basically the difference from the center of the wheel mounting surface to the wheel's mounting flange. But for all intents and purposes, you can forget needing to know a wheel's offset for Jeep wheels.

The backspace dimension is that distance between the wheel's mounting surface and its rear-most (inner most) wheel edge, as is being measured by the yellow tape measure in the below photo.

3.75" of backpace means that an aftermarket 15x7 wheel with 3.75" of backspacing will protrude out of the wheel well 1.75" further than the factory 15x7 wheel that typically has 5.5" of backspacing. That isn't very much backspacing for a tire that is only 10.5" wide. If it were me, I'd want a little more backspacing, like 4.5" or so, so the wheel won't stick out so far.

So basically, the less backspacing, the further out a wheel will protrude. A 15x7 wheel with 4.5" of backspacing will protrude out 1" further than a factory 15x7 wheel with 5.5" of backspacing will.
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Old 01-02-2013, 04:06 AM   #5
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thanks Jerry for answering my question even though I made the mistake of posting it in the wrong section.
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Old 01-03-2013, 10:01 PM   #6
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i was wondering if i could get some advice or help whether what i want to buy for rims and tires will fit my 06 tj. I am going to put a 3" suspension lift and I want to put a 305r70 17 tire on a 17x9 rim with 4.5 backspacing and -12mm offset, I was just wondering if anyone knew if that would work and another quick question, that I have been wondering if it says 4.5 back space and -12mm offset is the 4.5 + the -12mm offset or 4.5 after the offset. Any advice or input would be a big help.
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Old 01-03-2013, 10:31 PM   #7
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Originally Posted by Maysel View Post
i was wondering if i could get some advice or help whether what i want to buy for rims and tires will fit my 06 tj. I am going to put a 3" suspension lift and I want to put a 305r70 17 tire on a 17x9 rim with 4.5 backspacing and -12mm offset, I was just wondering if anyone knew if that would work and another quick question, that I have been wondering if it says 4.5 back space and -12mm offset is the 4.5 + the -12mm offset or 4.5 after the offset. Any advice or input would be a big help.
My advice is to read Jerry's post again and look at the picture it is a couple above^^^^
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Old 09-19-2013, 12:00 AM   #8
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Quote:
Originally Posted by Jerry Bransford View Post
Forget you ever heard the offset term which is really meant more for car wheels. The offset dimension is basically the difference from the center of the wheel mounting surface to the wheel's mounting flange. But for all intents and purposes, you can forget needing to know a wheel's offset for Jeep wheels.

The backspace dimension is that distance between the wheel's mounting surface and its rear-most (inner most) wheel edge, as is being measured by the yellow tape measure in the below photo.

3.75" of backpace means that an aftermarket 15x7 wheel with 3.75" of backspacing will protrude out of the wheel well 1.75" further than the factory 15x7 wheel that typically has 5.5" of backspacing. That isn't very much backspacing for a tire that is only 10.5" wide. If it were me, I'd want a little more backspacing, like 4.5" or so, so the wheel won't stick out so far.

So basically, the less backspacing, the further out a wheel will protrude. A 15x7 wheel with 4.5" of backspacing will protrude out 1" further than a factory 15x7 wheel with 5.5" of backspacing will.
That isn't how Mopar measures backspacing. They measure from the 1/2" wide ledge just below where you are measuring from. Doing it your way will give a BS of 5 7/8" on a Ravine wheel, instead of 5 1/2" as the factory says. I thought your way was correct until today at a wheel shop which had Gambler, Ravine, Ecco, etc takeoffs. I measured the Gamblers your way and they were 5 5/8" instead of the 5 1/4" specified by the factory, and then the wheel shop supervisor showed me the correct way to measure.
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Old 09-19-2013, 06:34 AM   #9
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JerryB's way is the only way I have seen it done.




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Old 09-19-2013, 07:24 AM   #10
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This is the a very comprehensive site on the subject with great reference charts and diagrams...

https://www.rsracing.com/tech-wheel.html#backspace
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Old 09-19-2013, 10:32 AM   #11
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Originally Posted by Wattapunk View Post
JerryB's way is the only way I have seen it done.




That's what I thought also. But take any factory wheel, like a Ravine or any of the others with 5.5" BS and use that method, and the measurement will be about 5 7/8". Then measure from the shelf just inside the outer edge and it will be 5.5", which is 3/8" less.
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Old 09-19-2013, 10:54 AM   #12
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Measuring from the mounting flange to the point where a straight edge rests on the wheel is the only correct way to measure backspacing.
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Old 09-19-2013, 02:31 PM   #13
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Originally Posted by Jerry Bransford View Post
Measuring from the mounting flange to the point where a straight edge rests on the wheel is the only correct way to measure backspacing.
Why would Jeep do it incorrectly? Have you actually measured a factory 5.5" BS wheel your way? I measured Gamblers(5.25") and Ravines(5.5") and they were 3/8" more than the factory spec at 5 5/8" and 5 7/8" respectively. When measured from the top of the shelf just under the outer lip, just as the wheel shop advised, they were right on the factory spec.
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Old 09-19-2013, 03:53 PM   #14
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Why would Jeep do it incorrectly? Have you actually measured a factory 5.5" BS wheel your way? I measured Gamblers(5.25") and Ravines(5.5") and they were 3/8" more than the factory spec at 5 5/8" and 5 7/8" respectively. When measured from the top of the shelf just under the outer lip, just as the wheel shop advised, they were right on the factory spec.
Your description of the backspacing measurement I and others described as "your way" isn't "my" way at all. Do a little research on how backspacing is calculated instead of arguing based on your measurements and you'll quickly learn our descriptions of the measurement are in fact correct.

Perhaps you should contact Jeep with your claims that they are not measuring correctly.

Click on how to measure backspacing - Google Search to learn how since you disagree with us.
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Old 09-19-2013, 10:47 PM   #15
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Originally Posted by Jerry Bransford View Post
Your description of the backspacing measurement I and others described as "your way" isn't "my" way at all. Do a little research on how backspacing is calculated instead of arguing based on your measurements and you'll quickly learn our descriptions of the measurement are in fact correct.

Perhaps you should contact Jeep with your claims that they are not measuring correctly.

Click on how to measure backspacing - Google Search to learn how since you disagree with us.
It's not me that claims they are measuring incorrectly, just differently. You are the one inferring they are incorrect, because using your one and only method doesn't match their numbers. I'm sitting here with 5 unmounted Ravine wheels, and according to your one and only method, the measurement is 5 13/16". Using the bead flange, it's 5.5". Why are you afraid to actually measure a factory wheel, instead of posting links? Are you afraid of what you might learn?
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Old 09-19-2013, 11:41 PM   #16
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It's not me that claims they are measuring incorrectly, just differently. You are the one inferring they are incorrect, because using your one and only method doesn't match their numbers. I'm sitting here with 5 unmounted Ravine wheels, and according to your one and only method, the measurement is 5 13/16". Using the bead flange, it's 5.5". Why are you afraid to actually measure a factory wheel, instead of posting links? Are you afraid of what you might learn?
Years ago, there were standard desk heights of 30". If you bought a desk you could assume it was 30" tall. Then some engineer in some factory decided that 29" was a nice fit for some people, and they started making some desks 29" tall...these were also called a standard height. Just because one company comes out with something sideways, doesn't somehow automatically change the standard that has been done the same for years and years.
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Old 09-20-2013, 06:44 AM   #17
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Jeep also gave us the specification to use GL5 gear lube in our manual transmissions....we know how well that worked out.

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