Backspacing and Offset

pontiacgp

blank
Mar 31, 2006
29,389
113
Kitchener, Ontario
Norrisboy79 said:
I want to go with a 10 inch rear wheel on my 79 cutlass what bc do I need to make it clear everything and not stick out of the wheel well I'm talking about weld prostars by the way. Can anybody help me????

what rear end do you have?
 

GbodyJay

n00b
Feb 16, 2014
3
0
http://www.srtforums.com/forums/att...re-rim-width-backspace-offset-calculation.jpg
just thought i would add my 2 cents

28620d1145043186-how-measure-rim-width-backspace-offset-calculation.jpg
 

83StreetMachine

Master Mechanic
Dec 16, 2011
371
93
Central NJ
Last edited:

565bbchevy

Geezer
Aug 8, 2011
8,447
113
Michigan
That's much better.
I think everyone is over thinking this. Here's a simple example:
You have an 8" wide rim with a 4" backspace
That is a 0 offset rim. This is because the centerline of the rim is 4" (centerline = rim width/2) and the backspace is 4".
Don't let the metric conversion to mm trip you up.

An 8" rim with 0 offset would about 4.5" of backspace.
 
Last edited:
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350Cutty

Apprentice
Dec 20, 2018
51
18
Miami, FL
I don't know if it has been mentioned, but for offset, the smaller the number (or more negative), the further out they stick out. Like the wheels on my truck have a -11 offset and I can see them clearly in my mirrors because they stick out a lot. +15 is more of a factory wheel offset and would sit inside the fenders.
 

Doug Chahoy

Comic Book Super Hero
Nov 21, 2016
2,550
113
I don't know if it has been mentioned, but for offset, the smaller the number (or more negative), the further out they stick out. Like the wheels on my truck have a -11 offset and I can see them clearly in my mirrors because they stick out a lot. +15 is more of a factory wheel offset and would sit inside the fenders.
I have to say after reading this entire thread INFO OVERLOAD! When the factories started making the wheels more like hubcaps (like a new Camaro) they can't in my understanding be centered. The whole wheel seems to be all B/S the way it sits over the brakes toward the frame.
 
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BOXCARS

Master Mechanic
Apr 29, 2017
337
63
Well, I just read the last few comments. My question would be, why don't they just reveal the backspace measurement, eg 5", 4.5", 4" etc.? What good is zero offset, or some other figure that describes offset? Many wheel ads only mention offset. Why would they want to confuse their customers? Wouldn't it be easier to understand to just use the backspace measurement? Inquiring minds need to know.

thinking.png
 

rafael martinez jr

Not-quite-so-new-guy
Dec 13, 2017
47
18
new jersey
hi i have an 80 malibu with a ford 9in ive been looking to run a 15-10 with a 4.5 backspace looking to fit a fat tire in the back everyone is telling me that i have to notch the frame and roll the lip on the quarters any ideas would help thx
 
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