What is Rim Offset and Backspacing? How Do They Affect Fitment?

Have you been told your Honda needs a high offset wheel or that your new Jeep wheels must have the right backspacing?

Many drivers are familiar with rim diameter, bolt pattern and centerbore, but not offset and backspacing.

Offset is the distance between the mounting pad and rim's midpoint. The diagram to the right shows a wheel with a positive offset. Every contemporary Original Equipment wheel has a positive offset, however O.E. offset varies. For example, my old Honda Prelude SH has 16x6.5 wide, 55mm offset wheels while a 2013 Jeep Wrangler Sport comes with 16x7 44 mm offset wheels.

What happens when you get a new wheel with a different offset?  A higher offset results in the wheel and tire moving more in (towards the hub). A lower offset causes the wheel and tire to move out (towards the fender). 

What happens when you replace the 2013 Jeep Wrangler Sport's 16x7 44 mm offset wheels with the 17x8 6 mm offset MAMBA MR1X wheels? The 38 mm offset difference pushes the outside edge 38 mm out towards the fender and the additional width adds another 12.7 mm. Therefore, compared to Original Equipment, the outside edge is 50.7 mm further out towards the fender. Relative to the O.E. wheel, the MAMBA MR1X provides 25.3 mm additional inside clearance.

Backspacing is the distance between the mounting pad and the back of the wheel. Offset and wheel width will be marked on the back of the original and aftermarket wheels, but backspacing needs to be measured.

What does this all mean to you? Since we have already checked to see what fits your vehicle, all listed wheels have a compatible offset and backspacing specification. If you've lowered your car or you're running an oversized custom fit tire size, a higher offset wheel will allow for better fender clearance and a lower offset wheel will create additional inside clearance.

Shop by vehicle to view the wheels that are available for your application.

Comments

Wednesday, December 31, 2014 by Phil Rivers

I quote "A higher offset results in the wheel and tire moving more in (towards the hub). A lower offset causes the wheel and tire to move out (towards the fender)", though in your Diagram, that would appear to be exaclty opposite to the truth. PLEASE explain this in terms I will understanjd, Thank you.
Monday, August 17, 2015 by Don McFeely

will DECOY CUV 18"X8 - 35mm off set - 5.866 backspace
5-127 bolt pattern fit on a 2016 jeep wrangler sahara 255/70/18
tires
Wednesday, August 19, 2015 by cy

Don, the Ultra Decoy definitely fits the 2015 Jeep Wrangler Sahara but we haven't had 2016's here to test fit.

No substantive changes have been planned for 2016 so the Decoy should fit your 2016 Jeep but ask your dealer to verify there's no fit difference between the 2015's & 2016's.

255/70-18 will fit on fine on an 18x8 (8" wide) wheel.
Thanks. Cy.
Monday, August 31, 2015 by jeff

So I am looking at a wheel that is 17X9
it says it has a -12mm offset and a 4.5" backspacing
well 4.5 is cl of rim and -12mm offset should leave a backspacing of 4"
so how does it have a -12mm offset and a backspacing of 4.5 on a 9" wheel?
Wednesday, September 2, 2015 by cy

Jeff,

While the wheel flange is not included in a wheel’s published width, the widths of both wheel flanges are approximately the same so that a “9-inch wheel” actually measures approximately 10” wide when laid flat.

When you physically measure the backspacing of the wheel you’ll ending up including the ½” of the rear wheel flange. So in order to calculate offset from the backspacing measurement you have subtract ½” from whatever you measure.

For the 17x9” 4.5” backspacing wheel that 1/2” adjustment puts the mounting pad ½” (about 12 mm) “in” relative to the centerline so that your offset is -12 mm.

Thanks. Cy
Friday, April 15, 2016 by Chris

Based upon your description of how offset works (larger offest = wheel coming inward) compared to your image ( as Offset gets bigger the outer lip of the wheel would logically get further from the hub). Which would be correct? This is very important to me as I am setting up a vehicle for autocross and would like to keep a factory track width if not greater.
Friday, April 15, 2016 by cy

Chris,

With a higher offset wheel the entire wheel & tire assembly will move in. With a lower offset wheel, the entire wheel & tire assembly will move out.

Let’s look at a specific example. We shipped wheels for your 2011 WRX that came with Original Equipment (OE) 17x8 ET 53 wheels. You purchased 17x8 ET 45. So we’re changing to a new wheel with same width but 8 mm lower offset. Compared to your OE wheel, the outside edge of your new wheel will be 8 mm (approximately 1/3” ) further “out” towards the fender. Since the entire wheel & tire assembly is moving out, there will be 8 mm additional clearance between inside edge of the wheel and inner wheel well.

Thanks. Cy.
Thursday, May 5, 2016 by Peter

My current aftermarket rims with a 10 mm positve offset rub badly on my OE mudflaps. If I go to new rims with a -12mm offset, will ti move my tires roughly one inch further in toward the vehicle center line and help to alleviate the rub when the steering is sharply turned? i.e., does more negative offset help to cure oversized tire rubbing inside the fender?
Thursday, May 5, 2016 by cy

Peter, assuming both your old and new rim are the same width, then your new rim will be 22 mm (.87 inches) out towards the fender. So you'll have 22 mm more inside clearance. Will that be enough? Check how bad the current rub problem is by turning the wheel all the way and visualizing whether or not 22 mm will fix the issue. Thanks. Cy.
Thursday, May 19, 2016 by Mike

I have a 2003 Infiniti G35 coupe with 8"x18" OEM rims at a 30mm offset. I have opportunity to purchase G37 rims at a good price which are also 8"x18" but with a 43mm offset. I understand this will bring the wheel 13mm inside the fender compared to OEM. Will this be a noticeable difference or would I require a spacer to keep the same/similar look? I am hesitant to use a spacer. Any thoughts or opinions?
Friday, May 20, 2016 by Cy

Mike, we don't sell Original Equipment wheels so we don't have detailed fitment information on those wheels. Obviously there will be less clearance so there will be a risk of rubbing on the inner wheel well, suspension, brake calipers and brake rotors.
The best resource if you're looking to use Infiniti Original Equipment wheels on a different chassis or generation is the feedback from other G35 drivers at the G35 owners' sites we sponsor such as:

http://g35driver.com/forums/

Thanks.

Cy
Tuesday, June 28, 2016 by Robert Smale

Phil- You are getting confused because offset isn't just spacing (that is what wheel spacers do.) The offset of a rim is decreased by making the rim more concave or "deeper", so the rest of the rim moves outward toward the fender relative to the mounting pad. An increased offset makes face of the rim more "flat", so the rim and tire have to move deeper into the wheelwell before the mounting surfaces mate. Hope that helps.

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