This is topic Wheel question: offset VS. backspacing? in forum Tech Talk at Northern California Ford Owners  .


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Posted by iceman302 (Member # 7180) on :
 
I just ordered some 17x9 Bullit reproduction wheels for my 5 lug conversion I'm doing on my '92 LX. I'm using '94/'95 spindles and then all the rest is typical SN95 stuff.

My question is this: when I ordered the wheels, they told me that they were a +24mm offset which translates into about 1.4mm less than an inch, so that would be about an inch from the wheel center at 4.5" which equals 5.5" of backspacing and not the 5.95" that others tell me a +24mm offset equates to. What's the deal? Am I calculating it incorrectly? I'm concerned b/c the wheels will be a tight fit @ 5.95" and won't work @ 5.5" so someone please clarify. Thanks.
 
Posted by racercosmo (Member # 1864) on :
 
Offset is the offset from the center of the wheel. so yes, 24 is just under an inch and you would think that the backspace is roughly 5.5". Backspace is the distance from the hub to the outer rim of the wheel, which is about 1/2" more.
If you ever measure your wheels outside to outside, you will notice that a 9" wheel is really about 10" total width. 9" is the measurement inside where the tire bead sits.
 
Posted by iceman302 (Member # 7180) on :
 
quote:
Originally posted by racercosmo:
Offset is the offset from the center of the wheel. so yes, 24 is just under an inch and you would think that the backspace is roughly 5.5". Backspace is the distance from the hub to the outer rim of the wheel, which is about 1/2" more.
If you ever measure your wheels outside to outside, you will notice that a 9" wheel is really about 10" total width. 9" is the measurement inside where the tire bead sits.
Thanks for the clarification. I was more than a bit confused, but after hearing your explanation it makes perfect sense. I knew that backspacing measured all the way out to the edge of the wheel, but the I was getting mixed up by using the center of the wheel as a reference point.
 
Posted by Luke87GT (Member # 21) on :
 
racecosmo is exactly right.

Your 9 inch wheel really measures 10inches from lip to lip and you have to account for that. Most Ford rims have 1/2" of lip on each side of the rim. Thus:

centerline: 10/2 = 5"

offset 24mm = 0.95"

Backspacing = centerline + offset = 5.95"

Good luck!
 
Posted by iceman302 (Member # 7180) on :
 
quote:
Originally posted by Luke87GT:
racecosmo is exactly right.

Your 9 inch wheel really measures 10inches from lip to lip and you have to account for that. Most Ford rims have 1/2" of lip on each side of the rim. Thus:

centerline: 10/2 = 5"

offset 24mm = 0.95"

Backspacing = centerline + offset = 5.95"

Good luck!
It's even easier to see it when you put it like that. I wonder why nobody at any of the wheel distributors (including the Tirerack) could explain that one to me. Thanks.
 
Posted by CLEEN 50 (Member # 5867) on :
 
quote:
Originally posted by Luke87GT:
racecosmo is exactly right.

Your 9 inch wheel really measures 10inches from lip to lip and you have to account for that. Most Ford rims have 1/2" of lip on each side of the rim. Thus:

centerline: 10/2 = 5"

offset 24mm = 0.95"

Backspacing = centerline + offset = 5.95"

Good luck!
Very good explanation [patriot] .
 




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