Discount Tire

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.
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.

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.

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


I hope this helps.

-Matt

ahmad

So, the less the backspacing, the more the wheel will go out, right?
for example, a 10'' rime with 3'' backspace means that the rim will be out 7''?

ronjenx

The answer I get is 8".

Matt,

Nice presentation.
Thanks!

Discount Tire

I'm not sure what you mean by "be out" but I think you might be referring to the front spacing of the wheel. Like ronjenx said, a 10" wide wheel with a 3" BS (-64mm offset) would have 8" of front spacing. Typically speaking, the lower the offset/backspace, the more the wheel will push out towards the fenders or away from the suspension. It all depends on the rim width and offset.


Thank you


-Matt

mjolnir

This should be a sticky, or at least included in the faq section for newbies. Seems to be something that comes up every week or two.

Great explanation

Discount Tire

Thank you

BoggerSwap

A sticking point that took me a while to get my head around, (which Matt correctly touched upon) was that there is a 1/2" flange (or shoulder) running around the outside of the rim. The mounting point of the tire is on the inside of the flange, but the backspacing is measured to the outside of the flange. Thus, An '8 inch' rim is 8" between the inside edges of the flange, but the wheel is really 9" wide. Thus an 8" wheel with 0 offset (has the wheel mount dead center in the wheel), has a 4 1/2" backspacing, NOT 4". When calculating or converting any other offsets, you need to account for this extra 1/2".

You'd be surprised how many tire / wheel vendors don't understand this.

Brashanic

Is the net effect of backspacing the same whether it is the rim or the rim plus spacers?This is from my phone so I hope you understand what I am asking

jeeperaf

if you are talking about wheel spacers, they will "decrease" backspacing you have on a rim as they will "push out" the center line of the rim away from the vehicle's body.

make sense?

Brashanic

yeah. i was wondering if the leverage on primarily spindle components , knows the difference between spacers or backspacing. i have never understood completely if offset comes into play as to leverage. am i making any sense yet?