Why Does Everyone Talk About Backspace Instead of Offset? - JeepForum.com
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Unread 07-25-2015, 09:21 PM   #1
christensent
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Why Does Everyone Talk About Backspace Instead of Offset?

Quick question, is there a reason the jeep community generally talks about backspace? Offset is based on the center of the rim, so two people can perfectly duplicate a tire position regardless of the rim width. But backspace is based on the edge of the rim, so one person saying "I run this tire with 4 inch backspace and it doesn't rub" means absolutely nothing unless they give their rim width and then people would have to do some math to compare that backspace to their own on a different rim width...

So, why is offset something that is practically never discussed on this forum, everyone is talking about backspace?

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Unread 07-26-2015, 05:25 PM   #2
jadmt
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Originally Posted by christensent View Post
Quick question, is there a reason the jeep community generally talks about backspace? Offset is based on the center of the rim, so two people can perfectly duplicate a tire position regardless of the rim width. But backspace is based on the edge of the rim, so one person saying "I run this tire with 4 inch backspace and it doesn't rub" means absolutely nothing unless they give their rim width and then people would have to do some math to compare that backspace to their own on a different rim width...

So, why is offset something that is practically never discussed on this forum, everyone is talking about backspace?
simple backspacing is standard ie 4.5" or 5" etc offset is metric ie 12mm or 20mm etc and freaks everybody out lol. Pretty easy to figure backspacing if you now the offset but nobody wants to wrap their head around it.
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Unread 07-26-2015, 09:28 PM   #3
christensent
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Originally Posted by jadmt View Post
simple backspacing is standard ie 4.5" or 5" etc offset is metric ie 12mm or 20mm etc and freaks everybody out lol. Pretty easy to figure backspacing if you now the offset but nobody wants to wrap their head around it.
But if two people have 4.5" backspace, one on a 8" wide rim and one on a 10" wide rim, their tires will be in different places with respect to the axle/frame...

Now if two people have 20mm offset, one on 8" wide rim and one on a 10" rim, their tires will be in precisely the same place with respect to the axle/frame

That is true, right?
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Unread 07-27-2015, 06:15 AM   #4
WXman
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Quote:
Originally Posted by christensent View Post
But if two people have 4.5" backspace, one on a 8" wide rim and one on a 10" wide rim, their tires will be in different places with respect to the axle/frame...

Now if two people have 20mm offset, one on 8" wide rim and one on a 10" rim, their tires will be in precisely the same place with respect to the axle/frame

That is true, right?
No. With respect to the frame/inside of wheel well no. Backspacing is a fixed number. It's the distance between the mounting flange and the inner lip of the wheel. It's a simple measurement and it's the one that makes the biggest difference in being able to run wider tires. That's why I think it's the most commonly referred to figure.

Offset is a step farther to calculate and it honestly doesn't really matter most of the time. Backspacing is what matters. You can figure anything you want to figure about fitting new tires and you can even mock up where new tires will sit in the wheel housing of the vehicle by simply knowing the wheel width and backspacing.
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Unread 07-27-2015, 09:52 AM   #5
mike_dippert
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Quote:
Originally Posted by christensent View Post
But if two people have 4.5" backspace, one on a 8" wide rim and one on a 10" wide rim, their tires will be in different places with respect to the axle/frame...

Now if two people have 20mm offset, one on 8" wide rim and one on a 10" rim, their tires will be in precisely the same place with respect to the axle/frame

That is true, right?
Backspacing is the measurement between the wheel mounting surface and the inside edge of the wheel.

Offset is the distance from the mounting surface to the middle of the wheel.

IMO, backspacing is easier to work with when working with clearance (real world stuff). If you're doing suspension theory/design, offset would probably be better.
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Unread 07-28-2015, 07:35 PM   #6
CJ7nvrstk
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What Mike D said.

IMO, offset is more important in the car world when you are tying to keep tires inside fenders. On a lifted Jeep that you are slapping big tires on, that is rarely a concern.
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Unread 07-28-2015, 07:48 PM   #7
wilson1010
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Backspace is more important because one is trying to keep the tires and rims off of the frame.
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Unread Yesterday, 09:24 PM   #8
sardog12
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It is a method to measure something in two different ways. In this case, backspacing is just an easier concept to understand and calculate which is the only reason that it is considered "more important".
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