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If you’ve found yourself asking what the difference is between wheel offset and backspacing, you’re not alone! We field this question often and wanted to share this write-up to provide insight on the topic.
Please note that this is a high level overview and the examples shown are not specific to Bronco Sport fitments.
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Typically speaking, 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 very back edge of the wheel.
Generally 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 a visual, orange is the 17x9 +12mm offset and blue is the 17x9 -12mm offset. In this example you see the lower offset extends further out both with the inside lip of the wheel as well as the outside lip of the wheel.
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.
Here's an offset/backspace chart for quick reference:
Lastly, we want to call out that if the offset or backspace is the same when comparing wheels, the overall fit will change based on the width of the wheel.
Take a 17x9 with -12mm offset and a 17x10 with -12mm offset for example. Although the offsets are the same, the front lip of the 17x10 with -12mm offset extends further out by just over 1/2-inch and the inside lip extends 1/2-inch closer inwards.
Same goes for backspace. Take a a 17x8 with 4.5-inches of backspace (0 offset) and a 17x9 with 4.5-inches of backspace (-12mm offset) for example. Although the backspace is the same between each wheel, the front lip of the 17x9 with 4.5-inches of backspace extends 1-inch further out, however the inside lip of both wheels mirror each other.
If you have any questions, would like fitment assistance, or need a price quote, please shoot us a private message here on the forum (link in signature). We are happy to help and will make sure you are taken care of!
Also, check out our TIPS & GUIDES Section at discounttire.com for more helpful write-ups!
Please note that this is a high level overview and the examples shown are not specific to Bronco Sport fitments.
_______________________________________
Typically speaking, 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 very back edge of the wheel.
Generally 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 a visual, orange is the 17x9 +12mm offset and blue is the 17x9 -12mm offset. In this example you see the lower offset extends further out both with the inside lip of the wheel as well as the outside lip of the wheel.
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.
Here's an offset/backspace chart for quick reference:
Lastly, we want to call out that if the offset or backspace is the same when comparing wheels, the overall fit will change based on the width of the wheel.
Take a 17x9 with -12mm offset and a 17x10 with -12mm offset for example. Although the offsets are the same, the front lip of the 17x10 with -12mm offset extends further out by just over 1/2-inch and the inside lip extends 1/2-inch closer inwards.
Same goes for backspace. Take a a 17x8 with 4.5-inches of backspace (0 offset) and a 17x9 with 4.5-inches of backspace (-12mm offset) for example. Although the backspace is the same between each wheel, the front lip of the 17x9 with 4.5-inches of backspace extends 1-inch further out, however the inside lip of both wheels mirror each other.
If you have any questions, would like fitment assistance, or need a price quote, please shoot us a private message here on the forum (link in signature). We are happy to help and will make sure you are taken care of!
Also, check out our TIPS & GUIDES Section at discounttire.com for more helpful write-ups!
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