who really understands offset and backspacing? i think most people think they may but still ask the experts.

[AA1mike]

any experts out here? is this correct? i just learned this a shot while back. i am still trying to pic a lift and i have factory 18x8 5 inch backspacing +19 offset rims.
when you add wheel spacers you decrease backspacing.
example..2 inch spacer with a factory wheel with 5 inch backspacing you will end up with a backspacing measurement of 3 inches.
now if the spec is minimum back spacing of 5 inches for the lift kit then this will not work.
now your calipers and or your control arm have interference.

backspacing and offset are different.
offset is the distance from center of the wheel.
backspacing is distance from wheel mounting surface to outer lip of the wheel.

 

[jimothy]

Backspacing, offset, and wheel width are related by this formula:

backspacing = (width + 1) / 2 + offset / 25.4

Backspacing and width are in inches. Offset is in millimeters (25.4 mm = 1 in). 1” is added to the width to account for 0.5” front and back lip on the tire.

To calculate offset from backspacing and width:

offset = 25.4 * (backspacing - (width + 1) / 2)

Or equivalently:

offset = 25.4 * backspacing - 12.7 * width - 12.7

Your 18x8 +19mm wheels have a backspacing of 5.25”.

 

[AA1mike]

Backspacing, offset, and wheel width are related by this formula:

backspacing = (width + 1) / 2 + offset / 25.4

Backspacing and width are in inches. Offset is in millimeters (25.4 mm = 1 in). 1” is added to the width to account for 0.5” front and back lip on the tire.

To calculate offset from backspacing and width:

offset = 25.4 * (backspacing - (width + 1) / 2)

Or equivalently:

offset = 25.4 * backspacing - 12.7 * width - 12.7

Your 18x8 +19mm wheels have a backspacing of 5.25”.

 

[AA1mike]

you are on my list of experts.lol
you are correct my wheel is 5.25 not 5.
is the point i made about the spacers subtraction from the backspacing correct. most big lift kits require at least 5 inch backspacing.

 

[jimothy]

you are on my list of experts.lol
you are correct my wheel is 5.25 not 5.
is the point i made about the spacers subtraction from the backspacing correct. most big lift kits require at least 5 inch backspacing.

I’m not an expert at much of anything, but sometimes, it’s fun to dust off my algebra so it doesn’t seem like my schooling was a complete waste!

Yes, spacers will decrease backspacing as well as offset. They push your wheels outboard, which is equivalent to a reduction in backspacing and offset. A 2” spacer would reduce backspacing by 2” and offset by about 51mm.

What I’m not an expert on at all is whether this is a good idea, or whether it would be a good fit for a lift kit. But what I think is true is that a lift kit is going to say at most a 5” backspace; 5.25” might be too much and your tires may run the UCAs; a spacer could help with that. Too little backspace (too negative offset), and your tires may run the wheel wells; too large a spacer will make that worse.

But there are people better qualified to advise on that than me.

 

[Mountain Whiskey]

You could break out the calculator and play with the buttons for a bit or you could just look at one of the many charts online like the one below from Discount Tire.