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Wheel widening math/opinion needed

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Old 07-19-2007, 08:01 AM
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Default Wheel widening math/opinion needed

I recently bought a set of 17x9.5 aftermarket zo6 wheels. They say they're 54mm offset, but there was no specification on the backspacing (I can measure this). I'm wanting to have 2 of them widened to run a 315 tire on the rears. Weldcraft can widen in 1" increments. Would it be safe to widen them 2" and make them 11.5" wide? I recently saw a post in the appearance section where someone widened a stock 17x9 chrome 10 spoke to a 17x11 and ran a 1.25" wheel adapter spacer on it. They stuck out kinda far though. How wide should I go and what width spacer should I run with them?

OR

Should I save the cash and just keep the 9.5" width, run a 275 MT radial on them with a 1" width wheel adapter to push the rears out to create the look of wider rears?

I want the tire to align near flush to the fender (like a 315 would look on a 17x11 ZR1 wheel), but I want the car to hook. I don't think I'll see much difference in hooking between the 275 and the 315, but I thought I'd ask about that as well.
Old 07-19-2007, 09:25 AM
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I would widen them to 10.5" width, not 11.5" unless you want a tire wider than 315. 315 works well on 10.5" to 11" wheels.

If the wheel were a 54 mm offset 9.5" wide wheel. You are adding 1" to the rear of the wheel, so the center line of the wheel moves 1/2" or 12.7 mm. The offset changes by that much, so now the actual offset would be 66.7 mm. A good offset for a 10.5" wide wheel is around 44 mm. Therefore 66.7 mm - 44 mm = 22.7 mm or ~ 7/8" spacer.

Make sence?
Old 07-19-2007, 09:30 AM
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Awesome man, yeah makes perfect sense. I'm not a math person and didn't think about the mm to inch conversion like that. I knew it was being added to the rear of the face, adding depth...and was thinking 1" adapter would work, but I wanted to be sure. Thanks for verifying!

Do you think keeping them 9.5 wide and running a 1" adapter to bring them flush to the fender would look dumb with a wider 275 tire? Like a MT or BFG DR?
Old 07-19-2007, 01:49 PM
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1" adapter is too much.

The wheels are 54 mm, 9.5" wide wheels. My 9.5" wide wheels have 38 mm offset and I really like the look, so:

Mathmatically, 54 mm - 38 mm = 16 mm or ~ 5/8". Any thicker the wheels will start to stick out and cause other problems.
Old 07-19-2007, 02:00 PM
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Ah, gotcha. So for that look I'd need a hubcentric .625 spacer and ARP longer studs? Do you have any pics of your setup? Thanks for the help
Old 07-20-2007, 05:26 AM
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please, whatever you do, don't stick a spacer on the 9.5'' wheels to make them look wider. At night time, it might look alright, but in the day time it will look like crap... a buddy of mine did that and it looked horrible
Old 07-20-2007, 07:18 AM
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I'm not sure what I'm going to do, just asking for examples and thoughts. Thanks for the insight...last thing I wanna do is look cheesy. So far I'm thinking I will have them widened to a 10.5, just gotta save my pennies to do it.

BTW, after searching I've found several firebirds/ta's on the site that run .5" spacers to push the wheels out in the rear, and it didn't look that bad.
Old 07-20-2007, 08:45 AM
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Originally Posted by 99FormulaM6
please, whatever you do, don't stick a spacer on the 9.5'' wheels to make them look wider. At night time, it might look alright, but in the day time it will look like crap... a buddy of mine did that and it looked horrible

Sorry, that makes no sence at all . . . . spacers aren't used to make the wheels look wider . . . they are used to place the wheel in the wheel well better, and improve the looks of the car . . .
Old 07-20-2007, 08:57 AM
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Originally Posted by Xsta Z 28
Sorry, that makes no sence at all . . . . spacers aren't used to make the wheels look wider . . . they are used to place the wheel in the wheel well better, and improve the looks of the car . . .
That's what I'm going for. So got any pics of your 38mm offset?
Old 07-20-2007, 04:21 PM
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Gives a good idea of how the wheel and trie fill the rear wheel well nicer.

Old 07-20-2007, 05:49 PM
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Originally Posted by Xsta Z 28
Sorry, that makes no sence at all . . . . spacers aren't used to make the wheels look wider . . . they are used to place the wheel in the wheel well better, and improve the looks of the car . . .
i realize it doesnt make sense...thats why i said dont do it...

Originally Posted by 02EBZO6
Should I save the cash and just keep the 9.5" width, run a 275 MT radial on them with a 1" width wheel adapter to push the rears out to create the look of wider rears?
Old 07-20-2007, 08:26 PM
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Mine 17" WS6 rear rims is widened from 9.5" to 11" and i had to run 1/2" spacers and ARP studs 1/2" longer ,Ive broke four sets of gears and two sets of stock axles with no problems at all with the studs or rims ,went with the 8.8" rear with Mosser 31 spline axles and stop breaking axles and gears but only carriers now ,going full spool

Old 07-20-2007, 09:12 PM
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I did it on my car.. used a 1" spacer/adapter to push the rear wheels so they are more flush with the 1/4 panels. Looks better than stock with the fronts at the fenders and rears tucked way into the wells.






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