Ruined brand-new ProStars on 03 Cobra.....

phil a

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Hello

Long-time lurker, hoping you guys will be able to share some of your expertise on a frustrating situation I'm trying to work out. I have an 03 Cobra, bought some wheels/tires for the drag strip as spring/summer are finally here

This car had had 15" Weld's previously, though Alumastar rather than Prostar. The knuckle and banjo bolt were clearanced by the prior owner and the car has run on 15" rear wheels w/o issue previously. FTBR tierods were added as well to ensure nothing touched/rubbed. Prior wheel size was 15x10 w 6.5" backspacing; I put on a pair of 15x9 w/ 5.5" backspacing. Here's the question: I had clearance when the car was up in the air on jackstands.....I had clearance once the car was lowered to the ground.

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When I went to drive the car out of the garage, I could tell pretty quickly something was wrong - it seemed like it was stuck and unwilling to move. I backed it into the garage, put it back up on the jackstands, and found two huge gashes in the inside of both barrels. Hmmmmm..... I took the wheels to a local shop, who quickly assured me they were toast and would be very dangerous to consider running them. I called and talked with tech guys at both Weld and at Jegs; I understand the barrel design differs between the ProStars and the Alumastars from a few conversations I've had with Weld and with Jegs. What I can't figure out is what happened to the clearance? I've been told "It's probably your suspension deflecting," which I can't make sense of, as once the wheel is torqued to the hub, nothing is capable of moving per my understanding of the suspension. I've also been told "Those wheels aren't recommended for your car," despite me telling them they'd be been clearanced and I had clearance after installing them.

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(yes, that's a giant chunk of aluminum that was gouged out!)

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When I put the car back up, I spun each wheel by hand and noticed I do have clearance .... but only at some points! The wheels appear to be off-center(?) if that's even possible, as the knuckles rub at the same grooves, even when up in the air, but once it gets beyond those grooves in the barrel, there is plenty of clearance (per Weld, 2mm is considered OK). I can't imagine this is an acceptable amount of (in)tolerance, especially if they're OK with just a mm or two of clearance.

I'm out two new wheels and not sure which direction to head

Thanks for taking the time to read through this - any thoughts/opinions appreciated!

Phil
 

olympic

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A few possiblilities:

-wheels are out-of-round (not likely.)
-wheel bearings are worn and have play in them. (most likely)
-hubs are bent
 

CobraBob

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That sucks! That is some serious gashing there. Sorry you lost the wheels. Had you noticed any vibrations or noise (even faint) from the front end when driving (before swapping wheels)?
 

phil a

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Thanks for the replies

lol @ custom clearanced....

Bob, these are on the rear but no, hadn’t felt/heard anything unusual. Hadn’t considered wheel bearings....could bad bearings contribute that much? Wouldn’t I have heard noises or felt a shimmy from the IRS? Also, why would it cause only half of the barrel to be affected rather than the entire circumference if it was bearings?

Keep anything coming guys I really appreciate it!
 

hotcobra03

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Bolt pattern?
Hub of rim?

It should center on hub before tightening.

Only way I can see wheel rubbing tie rod is if this isn’t achieved
 

01yellercobra

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I wouldn't have run it with as close as that tie rod mount is. The ones I've seen usually have more material removed.
 

gt347mustang

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First rule of running small diameter wheels on an IRS cobra is spin the wheel over several times to ensure clearance. Many wheel manufactures nowadays can't machine a barrel perfectly straight.
 

phil a

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Well, maybe I'm just hard-headed, but I bought another set of Prostars with same dimensions, same width/backspace/diameter

Bolted up a bare wheel to L halfshaft and what do you know, not only was there no interference throughout the entire revolution of the wheel, but the clearance between knuckle/tierod was constant while I spun the wheel. Hard to believe it isn't a wheel-problem at this point, as another wheel of same EVERYTHING is fine. Now to figure out how to check for runout, off-center hub, or however you'd call it

Thanks again guys
 

01yellercobra

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You'll need a micrometer with a magnetic base to check run out. I picked up a decent kit off Amazon when I rebuilt my rear end. It's not high end like a Starrett, but it works good for someone that might use it a couple times a year.
 

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