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Old 10-08-2010, 11:38 AM   #1
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Backspace and Offset - How do they relate?

Offset and backspace are essentially two different ways of looking at the same thing. They determine the location of the wheel and tire assembly when bolted to the vehicles hub.

Offset is the measured distance between the hub mounting surface and the wheels center line.
With X being the determined offset, the hub mounting surface on positive offset wheels is X amount forward from the wheel center line. The hub mounting surface on negative offset wheels is X amount backwards from the wheel center line. The hub mounting surface on 0 offset wheels is the wheel center line.
Backspacing is the measurement from the hub mounting surface to the back edge of the wheel.

***Typically speaking, the higher the offset/backspace, the more the wheel will tuck inwards towards the suspension or away from the fender. The lower the offset/backspace, the more the wheel will push out away from the suspension or towards the fender.
For Example:

*If the offset on a 9" wide wheel is +12mm, the hub mounting surface will be 12mm forward from the wheels center line. Measuring from the hub mounting surface to the back edge of the wheel, the backspacing is 5.5"

*If the offset on a 9" wide wheel is -12mm, the hub mounting surface would be 12mm towards the back of the wheel from the wheels center line. Measuring from the hub mounting surface to the back edge of the wheel, the backspacing is 4.5"

Here's how to calculate the backspacing using the rim width and offset:

First - add 1" to the rim width and then divide by 2 to find the wheels center line (you have to account for the wheel flange which is why you add 1" to the rim width) . Second - convert the offset which is in millimeters into inches. There is 25.4mm in 1 inch so divide the offset by 25.4. Lastly - add the converted offset to the wheels center line if the offset is positive for the correct backspacing. Subtract the converted offset to the wheels center line if the offset is negative for the correct backspacing.
For Example:

17x9 +12mm offset

*9" rim width + 1" = 10"
*10"/2 = 5" (wheels center line)
*+12mm offset/25.4 = 0.47" (0.50" rounded up)
*0.50" + 5" = 5.50" Backspace


17x9 -12mm offset

*9" rim width + 1" = 10"
*10"/2 = 5" (wheels center line)
*-12mm offset/25.4 = 0.47" (0.50" rounded up)
*0.50" - 5" = 4.50" Backspace

***Please note that the wheels center line is the backspacing for 0 offset wheels.


I hope this helps.

-Matt

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Old 10-17-2010, 04:39 PM   #2
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Holy crap my head is spinning. I was thinking about getting a set of rims that are 15 x 10 with a a 4 inch backspace. My jeep is a 97 sport with no lift and I have 30x9.5x15 tires on it now. Will the tires fit the rims and will the fit my jeep? I suck at math and got a headache reading the above post.

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Old 10-18-2010, 10:58 AM   #3
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A 10" wide wheel that has 4"s of backspacing has around a -38mm offset. This is very aggressive for your 97 without a large lift as the extra wheel width will stick outside of the fender a good amount. Also, the recommended rim width range for tire size 30x9.50-15 is 6.5" to 8.5". Mounting this tire size on a 10" wide wheel will stretch the casing a good amount which can cause multiple issues.

With this tire size, I recommend finding a wheel that is 7" or 8" wide with an offset around 0mm.

15x7 ET0 = 4" BS
15x8 ET0 = 4.5" BS

-Matt
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Old 03-07-2011, 06:44 PM   #4
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Bump!
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Old 03-13-2011, 07:10 PM   #5
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So to help us JK guys and girls. Say we wanted to run 315/70/17 on our JK's What kind of Backspace or offset would we be looking for. I own an Auto Parts store and i'm very familiar with the auto industry but not wheels and tires as I do not sell them. I have recently got the opportunity to maybe get into this field but im very lost. like I said 315/70/17 no rub ??
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Old 03-14-2011, 03:35 PM   #6
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Originally Posted by John412 View Post
So to help us JK guys and girls. Say we wanted to run 315/70/17 on our JK's What kind of Backspace or offset would we be looking for. I own an Auto Parts store and i'm very familiar with the auto industry but not wheels and tires as I do not sell them. I have recently got the opportunity to maybe get into this field but im very lost. like I said 315/70/17 no rub ??
With the correct lift ,2.5" or higher, the ideal backspace for tire size 315/70-17 (35") is 4.5". The most popular wheels size in this backspace is 7x9 ET-12.
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Old 03-27-2011, 11:45 AM   #7
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What tire would you recommend for a 2011 JK that has mostly pavement driving. I have a farm and do get into the mud and cross ditches for duck and turkey hunting. I want a "beefier" look to my Jeep and may eventually add a small spacer lift at a later date. I like the wider tire look as well so if I could safely go as wide as 33/305s I would...I also want to see more tire and less wheel so maybe 17 inch wheels?...Help? I've been trying to understand the whole backspacing issue and this thread was helpful with respect to that but didn't answer my question about how to pick a tire for my vehicle and avoid rubbing or damage.
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Old 03-28-2011, 12:29 PM   #8
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For more tire and less wheel, I suggest going 15". Without any lift, you can fit 33" tires with ease. Any excellent tire size to run is 33x12.50-15 and based on what you are looking for out of your tires, I suggest the Goodyear Wrangler DuraTrac. Wheel wise, the 15x8 3.75" BS MB72 would be sweet. Here are the links with more details.

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Old 03-28-2011, 07:38 PM   #9
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thanks for the advice. I like the wheel choice. Its very simple and black...with very little silver...just what I have been looking for but haven't been able to settle on.
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Old 11-29-2011, 01:31 AM   #10
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Originally Posted by Discount Tire View Post
For more tire and less wheel, I suggest going 15". Without any lift, you can fit 33" tires with ease. Any excellent tire size to run is 33x12.50-15 and based on what you are looking for out of your tires, I suggest the Goodyear Wrangler DuraTrac. Wheel wise, the 15x8 3.75" BS MB72 would be sweet. Here are the links with more details.

Tire Details - Discount Tire Direct

Ok This spoke to me. I have a Stock (No Lift) Rubicon 2010 2Dr. Not interested in a lift but would like a slightly bigger tire.

If the 33x12.5-15 on the MB72 werre next to the Stock BFG M/T 255/70/17 (I thnk?)

How much taller is that 33 than my stock set up?
How much wider?
How much further does is stick out (towrads the fenders?)

No lift needed?

What are the con to having less rim and more rubber?
What are the pro's?

It would seem that even in the 33" were equal to the Stock wheel they would look bigger (more balloony) due to the smaller rim... Sound right?

Thanks... My stock tires are getting low and I am on the prowl for new tires. Wanna do it right. Like the DuraTrac - looks good. What is the expected tread life?

Lots of questions.
Thanks
RubiDub
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Old 11-29-2011, 11:08 AM   #11
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Quote:
Originally Posted by RubiDubiDoo View Post
Ok This spoke to me. I have a Stock (No Lift) Rubicon 2010 2Dr. Not interested in a lift but would like a slightly bigger tire.

If the 33x12.5-15 on the MB72 werre next to the Stock BFG M/T 255/70/17 (I thnk?)

How much taller is that 33 than my stock set up?
How much wider?
How much further does is stick out (towrads the fenders?)

No lift needed?

What are the con to having less rim and more rubber?
What are the pro's?

It would seem that even in the 33" were equal to the Stock wheel they would look bigger (more balloony) due to the smaller rim... Sound right?

Thanks... My stock tires are getting low and I am on the prowl for new tires. Wanna do it right. Like the DuraTrac - looks good. What is the expected tread life?

Lots of questions.
Thanks
RubiDub
A couple members replied to this post over in the 33x12.50-15 DuraTrac thread. We added our comments as well.

http://www.wranglerforum.com/f33/33x...o-96568-6.html
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Old 12-03-2011, 11:12 PM   #12
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Ok, I'm a newbie. Ive read a lot and have gotten confused. I have a 2010 4dr rubicon with 255/75 r17. I have been told by to different local places that a 15" wheel will not work? My jeep is stock for now, may do a leveling kit. But I'm definitely going to need new tires. I do some off road trails at Superlift here in Arkansas but nothing to hard core. Any advice would be appreciated.
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Old 12-04-2011, 08:42 AM   #13
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So will my stock P255/75R17 tires that came with 2012 Jeep Unlimited work with these Wheels Ultra Wheel Gauntlet 17x9 12 offset 5-127 bolt pattern? I really dont want to swap out my original tires just yet. No lift yet completely stock.
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Old 12-04-2011, 04:41 PM   #14
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For those considering Goodyear Duratracs.....I had some and I loved them. They are more aggressive than most all terrain tires yet they ride quiet and smooth compared to mud terrains and the prices were not too far out there!
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Old 12-05-2011, 10:41 AM   #15
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Quote:
Originally Posted by Doc3613 View Post
Ok, I'm a newbie. Ive read a lot and have gotten confused. I have a 2010 4dr rubicon with 255/75 r17. I have been told by to different local places that a 15" wheel will not work? My jeep is stock for now, may do a leveling kit. But I'm definitely going to need new tires. I do some off road trails at Superlift here in Arkansas but nothing to hard core. Any advice would be appreciated.
Not all 15" wheels will clear the brakes on the JK. 15" aftermarket steel wheels won't but there are some 15" alloy wheels that do. Here are all the 15" wheel models we offer that will work

Wheel Details - Discount Tire Direct

Wheel Details - Discount Tire Direct

Wheel Details - Discount Tire Direct

Wheel Details - Discount Tire Direct

Wheel Details - Discount Tire Direct

Wheel Details - Discount Tire Direct

Wheel Details - Discount Tire Direct

Wheel Details - Discount Tire Direct

Wheel Details - Discount Tire Direct

Quote:
Originally Posted by Hexonx View Post
So will my stock P255/75R17 tires that came with 2012 Jeep Unlimited work with these Wheels Ultra Wheel Gauntlet 17x9 12 offset 5-127 bolt pattern? I really dont want to swap out my original tires just yet. No lift yet completely stock.
The 255/75-17 size is too narrow for a 9" wide wheel and is not recommended. If you want to run the stock tires then you'll want to find a wheel that is 8" wide.
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Old 12-05-2011, 11:25 AM   #16
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Originally Posted by Discount Tire View Post
Not all 15" wheels will clear the brakes on the JK. 15" aftermarket steel wheels won't but there are some 15" alloy wheels that do. Here are all the 15" wheel models we offer that will work

Wheel Details - Discount Tire Direct

Wheel Details - Discount Tire Direct

Wheel Details - Discount Tire Direct

Wheel Details - Discount Tire Direct

Wheel Details - Discount Tire Direct

Wheel Details - Discount Tire Direct

Wheel Details - Discount Tire Direct

Wheel Details - Discount Tire Direct

Wheel Details - Discount Tire Direct



The 255/75-17 size is too narrow for a 9" wide wheel and is not recommended. If you want to run the stock tires then you'll want to find a wheel that is 8" wide.
Thank you for the response. I guess I should look into just doing a tire and wheel package then, and go with 16" wheels and a bigger tire. I really don't want to put a lift on just yet.
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Old 12-05-2011, 04:29 PM   #17
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Thank you for the response. I guess I should look into just doing a tire and wheel package then, and go with 16" wheels and a bigger tire. I really don't want to put a lift on just yet.
Let us know if we can help you with a combination
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Old 12-05-2011, 04:52 PM   #18
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I might stop by my local Discount Tire, uggh so frustrating that there is a lot of wheels for my stock tires. Not a whole lot that I like =/
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Old 12-05-2011, 05:30 PM   #19
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I think the Level 8 ZX would be a good pick.

Here they are on our JK (no rock rings)



With rock rings

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Old 12-10-2012, 07:06 PM   #20
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What are the specs on the Level 8 ZX and do you carry those?I have a 2013 JWUS and am looking to go with a 15" wheel.I like a few of the ones you have shown but these look sweeeeet!Also one of the members"Kramer2K" used silver Black Rock Vipers from Discount Tires and they also look good,any info on these that might help would be great!
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Old 12-10-2012, 07:13 PM   #21
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