Backspace and Offset | How do they relate?

[Discount Tire]

We've had a few questions come up recently regarding this topic so we'd thought this may be useful.

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 millimetres 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.

Check out our TIPS & GUIDES Section at discounttire.com for more helpful write-ups!


Here's an offset/backspace reference chart for quick reference:

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[trust]

Thanks!

 

[Discount Tire]

Thanks!

I'm glad you found this helpful.

 

[trust]

So I'm clear, a 0 offset 5" backspace 17x9 should have a slight dish and keep the tire within the fenders, more or less?*

 

[Discount Tire]

trust, Thank you for your question. We are showing your Rubicon came with 17x7.5 +45 offset wheels so if you go with a 17x9 +0 it will push the front lip of the wheel outward 64 mm which is 1.66 inches. It will have a somewhat deep dish and be a bit outside the fender but a common fit.

 

[trust]

Oh ok. I hadn't thought to compare to existing stock. Duh! Thanks for the clarification

 

[Discount Tire]

I'm glad we could be of assistance. Please let us know if you have any other questions.

 

[trust]

Thanks I will

 

[Chick33]

trust, Thank you for your question. We are showing your Rubicon came with 17x7.5 +45 offset wheels so if you go with a 17x9 +0 it will push the front lip of the wheel outward 64 mm which is 1.66 inches. It will have a somewhat deep dish and be a bit outside the fender but a common fit.

Looking for some clarification. I currently have 2020 Gladiator Rubicon. I’d like the tire to poke out a little beyond the wheel well. I currently have the stock 285/70 with the stock 17” wheels. I’d like a wider tire not necessarily taller. I found a set of 305/65/17 bf’s on a 17x9 wheel. -12 offset and 4.5 backspacing. I’m having trouble trying to figure out how much reveal I’ll have beyond the wheel well???? Thoughts....

 

[Discount Tire]

@Chick33, PM headed your way.

 

[trust]

Custom offsets has a pretty good set of tutorials on their website.

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