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Wheel question.

1K views 16 replies 4 participants last post by  V8Square 
#1 ·
OK. Today's dumb question. On wheels. I need to have my rear wheels out further. I am very stupid on wheels(pretty stupid on everything). Do I look for a wheel with a higher or lower number on the backspace to do this?:confused:
 
#2 ·
The first thing you need to understand is the difference between backspace and offset. What you want is a wheel with more negative offset. Backspace is dependent on wheel width and a wheel with less backspace may or may not stick out further, depending on width.

 
#4 ·
The better ones do. Most vendors and catalogs only list backspace because it's easy to measure, if not the most useful information. The bottom line is, for wheels with the same width, less backspace pushes the tire outboard. If the width is different, all bets are off.
 
#5 ·
So Joe,am I correct in assuming that to measure backspace, I take a straight edge, lay it across the back, inside of the rim, and measure from the point of the straight edge, bottom, and then to the wheel surface that mounts to axle/hub for my BS measurement? What about offset measuring?
 
#10 · (Edited)
To calculate offset look at the pics Joe posted. Measure your rim from inside the beads (as illustrated in the pics) and divide by two. Now subtract your BS measurement from that dimension. That number is your offset.
Example:
If your rim measures 10 inches wide and the back space measures 4", 10/2=5"-4" equals 1". This number will generally be listed as 25mm's on most rim charts.
Another interesting fact is that 10" number, measured between the beads, is the ADVERTISED rim width on the wheel charts. What most people don't realize is the ACTUAL width of the wheel will be about an inch wider when measured on the outside of the beads. this can come into play when setting up narrowed rearends or simply trying to stuff as much wheel/tire into a stock wheel well as you can.
Mark
 
#11 ·
To calculate offset look at the pics Joe posted. Measure your rim from inside the beads (as illustrated in the pics) and divide by two. Now subtract your BS measurement from that dimension. That number is your offset.
Almost. As you point out, the width is the inside-to-inside dimension, but backspace is the outside-to-wheel mounting flange dimension. You need to also subtract the wheel lip. This can be 1/4" to 1/2" on most wheels.
 
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