Backspacing vs Offset

[nondem]

It's pretty aggravating trying to compare wheels when some places tell the backspacing and some don't...some use inches and some metric. Some just don't say it...
Take these wheels from discount tire:

They give a lot of specs but not backspacing:

I need 3.75 or 4" backspacing but neither -13 or -19 come out even close.

How do I tell short of ordering and hoping? You would think a big national tire retailer would give better/less confusing info.

 

[freedom_in_4low]

this isn't perfect because the thickness of the wheel rim outside of the tire bead varies, but on average:

This graphic shows the difference, though I think it's showing backspacing wrong because I'm under the impression backspacing is measured to the outside edge of the rim, not to the bead as shown.

View attachment 343144

 

[Jerry Bransford]

http://www.gtsparkplugs.com/Offset-to-Backspace.html

 

[TheBoogieman]

Backspacing is for Jeep wheels. Offset is a Rapper for the Migos.
Kiari Kendrell Cephus, known professionally as Offset, is an American rapper who has released music both as a solo artist and as part of Migos.

 

[freedom_in_4low]

it's often posted here that offset is a useless measurement for Jeeps, and it is if all you're talking about is clearance, but using offset makes it a LOT easier to talk about changes in scrub radius, especially between wheels of different widths.

 

[tnjeepguy]

While on wheels, what size tire is "best" for a 15 x 7 wheel ?? Does a 11.5 give better off road stay on the rim ?? Or better to go to 15 x 8 with 11.5 tires ??

Off road rule may be different than road performance, huh ??

 

[machoheadgames]

it's often posted here that offset is a useless measurement for Jeeps, and it is if all you're talking about is clearance, but using offset makes it a LOT easier to talk about changes in scrub radius, especially between wheels of different widths.

I still think the "offset is useless for a Jeep, use backspacing only" is a silly argument for any vehicle and doesn't make sense. One is more simple to comprehend in the brain, but other than that they are both measuring the same thing in a different way and I do agree, offset is more accurate for scrub radius considerations since it factors the width of the wheel into it.

 

[TRE3TOP]

Backspacing - distance from lip of wheel

Offset - distance from midline of wheel.

 

[dla]

I need 3.75 or 4" backspacing but neither -13 or -19 come out even close.

How do I tell short of ordering and hoping? You would think a big national tire retailer would give better/less confusing info.

Either of those will work
-13 = 4” BS
-19 = 3.75” BS

 

[nondem]

Ok...that at least clears it up. I need to brush up on my googling because none of my keywords spit out those particular handy charts. Just useless ones that left out key info(as usual).
So, w/3.75 and 4" backspacing being in the acceptable range - which is preferable? I know it's only a quarter-inch but still gotta choose one.

35's on a TJ w/5.25" of lift.

FTR: I just ordered 5 each 35x12.50R15 BFG KM3's.

 

[TRE3TOP]

Ok...that at least clears it up. I need to brush up on my googling because none of my keywords spit out those particular handy charts. Just useless ones that left out key info(as usual).
So, w/3.75 and 4" backspacing being in the acceptable range - which is preferable? I know it's only a quarter-inch but still gotta choose one.

35's on a TJ w/5.25" of lift.

FTR: I just ordered 5 each 35x12.50R15 BFG KM3's.

Yes that will give you a nice stance without sticking out too much.

 

[Jerry Bransford]

I still think the "offset is useless for a Jeep, use backspacing only" is a silly argument for any vehicle and doesn't make sense. One is more simple to comprehend in the brain, but other than that they are both measuring the same thing in a different way

No they're not measuring the same thing, not even in a different way.

Offset is the distance between the wheel's mounting surface and the center of the tire position which does not change no matter the wheel's width. Backspacing is the distance between the wheel's rear/inner-most edge and the wheel's mounting surface and it changes with the wheel's width.

 

[freedom_in_4low]

No they're not measuring the same thing, not even in a different way.

Offset is the distance between the wheel's mounting surface and the center of the tire position which does not change no matter the wheel's width. Backspacing is the distance between the wheel's rear/inner-most edge and the wheel's mounting surface and it changes with the wheel's width.

Gonna disagree with you there. They're both expressions of the relationship between the rim and the mounting surface. One uses the inner edge of the rim and the other uses the centerline.

 

[Jerry Bransford]

Gonna disagree with you there. They're both expressions of the relationship between the rim and the mounting surface. One uses the inner edge of the rim and the other uses the centerline.

They are not measuring the same thing... which is my point. Backspacing tells me how much absolute clearance I have between the inside edge of the wheel and my TJ, the Offset dimension does not.

 

[jjvw]

Either of those will work
-13 = 4” BS
-19 = 3.75” BS

Is this true on both a 7" wide wheel and a 10" wide wheel?

 

[jjvw]

No they're not measuring the same thing, not even in a different way.

Offset is the distance between the wheel's mounting surface and the center of the tire position which does not change no matter the wheel's width. Backspacing is the distance between the wheel's rear/inner-most edge and the wheel's mounting surface and it changes with the wheel's width.

They are the same thing as much as someone saying his gas tank is dead flat empty when engine is still running with 5 gallons left is the same thing as having no gas left.

 

[dla]

Is this true on both a 7" wide wheel and a 10" wide wheel?

No, but it is for the 8” wheels he is interested in.

But you already know this.

 

[machoheadgames]

Offset is the distance between the wheel's mounting surface and the center of the tire position which does not change no matter the wheel's width. Backspacing is the distance between the wheel's rear/inner-most edge and the wheel's mounting surface and it changes with the wheel's width.

I am aware.