Thought about my offset and backspacing...problem? - Ranger-Forums - The Ultimate Ford Ranger Resource


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Old 08-20-2005
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Thought about my offset and backspacing...problem?

Here we go with an exhaustive read...

I want to run 17x9 wheels on the Ranger. I have them already, the wheels I was going to use on the Mustang. Anyhow, here is a calculated guess to as WHY they won't work.

The stock Ranger wheel is either a 15x7 or [I think] 16x7.

The stock offset is .472 inches positive offset, 12mm.

The wheels I have now, have 2.88 inches of offset, with a 6.12" backspace.

Here we go with my spheil.

That's alot of weight out toward the edge of the tire/wheel!

You can imagine a bar-bell used for bench-presses.

You have the weight [suspension components/GVW] in toward the center [less offset] and the bar [front rear suspension/driveline] is under little stress.

When you move the weight out toward the end of the bar, the bar will bend and bow [in theory] under the stress of the weight being out to the edge.

Does that make sense, to you engineering folk, or just plain old folk that might know?

This is an educated guess, but I am a "CT", and I tend to over think things.

I have been looking online at some new 17x8 wheels with the correct offset, and just thinking about having the correct 'numbers' make's me feel better, not to mention they'd fit easier.

Right?
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Old 08-20-2005
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6.12" of backspacing is a whole helluva lot. Isn't that # why some mustang rims you have to run spacers? Seems like way too much backspacing. I'd look at keeping it around 4-4.5".
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Old 08-20-2005
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For the most part, the original offset is chosen to work with the steering geometry and optimize wheel bearing loading. The aftermarket wheels that you own appear to have the more "modern" offset first seen on FWD but now common on many RWD, 4WD and AWD, too. The Ranger geometry and offset are definitely old school - that doesn't mean good or bad, just old school.

What you're saying is true: the wheel bearings would be loaded differently with the greater offset than with the factory offset. There is also the possibility of rubbing on the inside of the tire because you would be adding more backspacing.

Cosmetically, the center of the wheel would be pulled toward the center of the truck. This would be partially offset by the wider width. Still, the overall effect would be of the wheels/tires being pulled slightly into the wheel well.

I'd stay close to the factory offset, if possible.

~~~~~~~~~~~~~~~~~~~~~~

Side note:
There's something that doesn't quite add up in the offset/backspacing/width combination that you gave for the wheels you have now.



Backspacing on a 7" wheel with +12mm offset is ~4.5 (factory Ranger)
Backspacing on a 9" wheel with +12mm offset is ~5.5

Backspacing on a 9" wheel with +2.88" offset would be ~7.9".
Backspacing on a 9" wheel with -2.88" offset would be ~2.1".
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Old 08-20-2005
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Thanks Bob. I went by what the website said for the backspacing, and figured out the rest from there. If their 6.12" is incorrect, it'll throw off ALL the numbers.

I am considering 17x8 for the new wheel choice, but I do not want the typical Cobra wheels, but there doesn't seem to be much else out there that sparks my interest..ugh.
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Old 08-20-2005
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Quote:
Originally Posted by Swoop1156
Thanks Bob. I went by what the website said for the backspacing, and figured out the rest from there. If their 6.12" is incorrect, it'll throw off ALL the numbers.
I would sooner believe that the 2.88" offset is what's wrong. It's hard to imagine a 9" wheel with almost 8" of backspacing.

On a 17x9 wheel, the 9" number is the width inside the flanges where the tire mounts. The overall width of a 9" wheel is usually about 10", making the center at about 5".

The backspacing is the distance from the mounting surface to the innermost wheel lip. So, for a wheel with its center at 5" and an offset of 2.88", that gives a backspacing of about 7.88"

Working it the other way, from the given backspacing number of 6.12", you would have an offset of 6.12"-5"=1.12" or about 28mm. This is a more realistic number.
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Old 08-20-2005
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'Eh, it's 1am here and too many numbers!

Either way, I don't think I should run them, right?

Thanks for the tech help, Bob. We all really appreciate it.
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Old 08-20-2005
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Quote:
Originally Posted by Swoop1156
Either way, I don't think I should run them, right?
I think staying close to the factory offset is the best idea but lots of owners run a variety of Mustang wheels on their Rangers. There are so many variables that the only real way to know about clearance and appearance is a test fit. Or maybe somebody on one of the Ranger sites can supply a photo and their experiences doing the same swap.
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Old 08-20-2005
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Yeah, true. I don't know. I can't test fit them until I get home or my Dad does one for me. I think I'd rather shy away from 9" anyhow. I had it all dialed in for the Mustang, not the Ranger.

I like to do things right the first time.
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