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  #1  
Old 02-24-2006
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Trying to find the right backspacing

I'm gonna get 33x12.5 bfg a/t, and new 15x8 wheels, i want the tire to stick out slightly, nothing to major. What would be the right backspacing?
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Old 02-24-2006
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everyone seems to like 3.75, I'm sure you could go a little bit more tucked into the truck like 4"....4.5" is stock
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Old 02-25-2006
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yea, a 3.75 should be good and keep things from rubbing on the inside.
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Old 02-25-2006
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^^ Good job guys yes 3.75 is a good alround BS... if you dont have fender flares i would recommened a 3.25 for a really wide stance
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Old 02-25-2006
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Actually 3.75 is about the stock backspacing on a 15x7" wheel, so on a 15x8 w/ 3.75" of backspacing, theoutside lip of the rim would be about 1" further out than stock (and there'd be no fear of rubbing on the suspension, at least not as far as the rim is concerned.. too wide or too tall a tire can always find somewhere to rub.)

My 17x8 rims have 4.25" of backspacing (after factoring in the 1" adapter) so they are .5" further out at the lip, and .5" further in towards the frame, so the centerline of the wheel stayed the same (what I wanted to minimize bearing wear.)
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Old 02-25-2006
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Quote:
Originally Posted by Wowak
Actually 3.75 is about the stock backspacing on a 15x7" wheel, so on a 15x8 w/ 3.75" of backspacing, theoutside lip of the rim would be about 1" further out than stock (and there'd be no fear of rubbing on the suspension, at least not as far as the rim is concerned.. too wide or too tall a tire can always find somewhere to rub.)

My 17x8 rims have 4.25" of backspacing (after factoring in the 1" adapter) so they are .5" further out at the lip, and .5" further in towards the frame, so the centerline of the wheel stayed the same (what I wanted to minimize bearing wear.)
wowak the stock BS on stock wheels from ford is 4.5.....it also matters the offset for a wheel which i do not know...
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Old 02-25-2006
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Quote:
Originally Posted by Redneckstone
wowak the stock BS on stock wheels from ford is 4.5.....it also matters the offset for a wheel which i do not know...
I never measured, but John Griggs told me it was 3.75 (on Edge Plus 15" aluminum wheels, anyway.)

Offset and backspacing measure the same thing, but backspacing measures from the inside lip, offset measures from the imaginary center-line of the wheel.

examples:

a 15x7" wheel with 0 offset has 3.5" of backspacing
a 15x8" wheel with 0 offset has 4" of backspacing
a 15x10" wheel with 0 offset has 5" of backspacing!

thats why I prefer to talk in terms of backspacing rather than offset.. its a real, usable number when it comes to deciding what will fit on your truck without rubbing/clearance issues.
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Old 02-25-2006
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Actually, Brian, those numbers are incorrect.

Backspacing with zero offset:
7" wheel width -> 4" BS
8" wheel width -> 4.5" BS
10" wheel width -> 5.5" BS

It is confusing because the width and backspacing measurements are taken at two different locations on the wheel.

The width is measured between the inside of the rim flanges where the tire beads seat.

The backspacing is measured from the wheel's mounting surface to the innermost part of the wheel which is the other side of the rim flange.

Since the flange is about 1/2" wide on most wheels, that accounts for the apparent discrepancy.

So, a 7" nominal width inside the flanges translates to about 8" overall width. Split it in half to find the backspacing at zero offset and that is 4". The positive offset of 12mm adds about 1/2" for a total of 4.5" on all 15x7 or 16x7 factory Ranger wheels.



Almost all recent factory Ranger wheels, whether they are 15" or 16" diameter, steel or aluminum, have the same common dimensions:

Width 7"
Offset +12mm
Backspacing 4.5


The only exception in recent years are the base XL steel wheels:

Width 6"
Offset +12mm
Backspacing 4"



Here are my factory 15x7 wheels:






This diagram shows where the measurements are taken:




This is a good cross reference for offset, width and BS:

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Old 02-25-2006
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good explanation Bob like always also here is another good diagram for referance


pip pip cheero good day guys
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  #10  
Old 02-26-2006
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Quote:
Originally Posted by rwenzing
Since the flange is about 1/2" wide on most wheels, that accounts for the apparent discrepancy.

In the back of my head I knew that, but my statement stands true that backspacing is the more usable measurement when it comes to fitament to a vehicle.
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