why is rim width the issue? - Team Camaro Tech
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post #1 of 11 (permalink) Old Jun 25th, 12, 11:20 PM Thread Starter
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Lyndon
 
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why is rim width the issue?

I can't understand why the rim width is so critical on the back of these cars. What I mean is, most people agree that it is relatively safe to use 275 wide tires in the back without problems, especially if the lips are rolled/trimmed. But at the same time there is much debate over using a 9.5 inch rim vs. a 10 inch rim. Again, 9.5 is agreed as usually safe, while 10 is pushing it, and may not work. I'm confused by this because a 10 inch wide wheel is 254 mm wide, which is still 21mm narrower than the supposedly safe 275mm tire. It looks like if the tire clears than the wheel will clear, since it is narrower than the tire. I know I must be missing something here, or this wouldn't have been debated so much. Could someone explain it to me? It matters to me because a lot of wheels are not available in 9.5 inch widths, but are in 9 or 10. Also when you want the widest lip possible, I'm thinking that requires the widest wheel possible.
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post #2 of 11 (permalink) Old Jun 25th, 12, 11:42 PM
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Re: why is rim width the issue?

It's all in the backspacing... A 9.5" wheel with 5.5" backspacing is about as close to the inner fender as you want to get with a 275 tire and you'll still be triming or rolling the fender lip and I bet the tire still rubs if you go through a steep driveway at an angle to clear the pipes.

Switch to a 10" wheel and your still have to run a 5.5" backspacing which means you are pushing the full extra 1/2" toward the fender lip... Raise the rear so the fender is above the tire and you can run a 10" wheel. I have seen a few show cars that have 10" wheels with 5.75" backspacing and from personal experience I know they rub on the street even though guys say no they don't...

...Dennis

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post #3 of 11 (permalink) Old Jun 26th, 12, 12:17 AM Thread Starter
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Lyndon
 
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Re: why is rim width the issue?

how much clearance between the inner sidewall of the tire and the inner wheel tub do you think is the absolute minimum, if using a four link to hold the differential centered?
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post #4 of 11 (permalink) Old Jun 26th, 12, 04:36 AM
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Re: why is rim width the issue?

What it comes down to is this...

If you want something "plug and play", you need to use one of the size/backspacing combo's that's been used 1000 times before.

If you want to use something wider or with more/less backspacing, you need to be prepared to measure your own car and if needed, get some small spacers or return the wheels as needed to make sure they fit ok. Every one of these cars are different, the rears aren't always centered, the quarters aren't always installed in the same exact position, etc.

Jason
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post #5 of 11 (permalink) Old Jun 26th, 12, 05:28 AM
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Re: why is rim width the issue?

I just went through this issue and had 17 x 9.5 (really 10" rim to rim)made. Well the biggest tire I could get with that wide a rim was a 275 x 40 and it was not tall enough for my tastes, looked like a rubber band tire and too small in the wheel well. Like he said the rear end was close to an inch off center to the drivers side causing the right side to rub. It all started when there was no tire made to fit my 10 x 16 wheel. I am now going to a 8" wheel so I have a better selection of tires and can get the look with proper backspacing. No real reason to have such a wide wheel unless I am going to install drag tires and go racing. At the end of the day my favorite tire wheel combo is the 70's Corvette 8 x 15 with the short center caps. 245x60 on the back and 225x60 on the front . . . .has a wider stance than the 16's and 17's (due to backspacing) I have and just a lot of money for those Billet Specialities and tires, over $2200.
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post #6 of 11 (permalink) Old Jun 26th, 12, 11:36 AM Thread Starter
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Re: why is rim width the issue?

for me it's not as much about the rubber as it is the amount of wheel lip. More dish seems to look more agressive. I knew I should have mini-tubbed. Just always thought I didn't have enough motor to need it. Now I realize it creates the look I like.
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post #7 of 11 (permalink) Old Jun 27th, 12, 05:17 AM
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Re: why is rim width the issue?

The backspace will give you the deep look you want. Select a 2 piece wheel and have the backspace you want for the deep look you want. A 8" wheel with a back space of 3" will give a deep "5 inch" front space. Billet Specialities can make what ever you want. Give them a call and check out their web site.
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post #8 of 11 (permalink) Old Jun 27th, 12, 11:25 AM
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Re: why is rim width the issue?

Lyndon,

You need to consider the section width of the tire in your caculations, for example the BF Goodrich 275/40/17 KDW tire has a section width of 277mm on a 9.5" wheel, the notes on their site say to add 5mm to section width for every 1/2" wider wheel, so now the section is 282mm on a 10" wheel. This senario gets even worse for 15" dia wheels.

Another thing to consider is the wheel width is measured inside the bead lips of the wheel, most wheels have around 1/2" wide lip on both sides so the 10" wheel is actually more like 280mm wide overall not 254.

Perhaps these 2 things is why its not adding up for you?

Mike
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post #9 of 11 (permalink) Old Jun 27th, 12, 12:28 PM
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Re: why is rim width the issue?

Quote:
Originally Posted by The Camaro Guy View Post
The backspace will give you the deep look you want. Select a 2 piece wheel and have the backspace you want for the deep look you want. A 8" wheel with a back space of 3" will give a deep "5 inch" front space. Billet Specialities can make what ever you want. Give them a call and check out their web site.
This will work if you jack the rearend up high enough to clear the tire and don't mind 2-3" of tire sticking out the fender. I've gone to a lot of trouble on my '72 Nova to fit vintage old school 8.5" wheels with about 3 1/4" backspacing so the thing doesn't look like a stink bug. I found some 265/50 tires and that's the best I could do so they don't stick out too far...

...Dennis

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post #10 of 11 (permalink) Old Jun 27th, 12, 07:25 PM
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Re: why is rim width the issue?

You're not only trying to clear the outer 1/4 panel lip, but also the inner wheel well, as well as the lower mount shock bracket. Go look at a correctly back spaced wheel with a fat tire under it, it's a near miss with the lower bracket, and very close between the inner and outer fenders. You're limited to space because of the inner and outer, only way for exceeding the width from factory is mini or full tubing the rear and possibly re locating the shocks. Lots of dish is cool, but wheel rubbing sucks, and leave the jacked up rears and 4" of tire sticking out to the 80's. Even when you have a fat tire sticking out, the traction will still not be as good as a properly backspaced wheel that is smaller because the tire is sooooo far from the axle it can bend to the road!

The only Mustang I'd ever own is a Fender.

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'14 5.0 Mustang
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post #11 of 11 (permalink) Old Jun 27th, 12, 09:57 PM
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Re: why is rim width the issue?

I thought it was tread space, or the rim vs the traed. No, BS must rule..
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