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Discussion Starter #1
I took my C5 on a track day at Silverstone recently - for the first time. I had a very strange problem and am interested to know whether this is a known issue.

I have the optional Magnesium rims - and after the first 5 or 6 laps I came into the pits and checked the car over to find loose lug nuts. They were all checked with a torque-wrench before I went out. It appears that heat from the brakes is causing this and I expect it's to do with expansion of the different metals involved.

Has anybody ever experienced this with this type of rims on a C5?
 

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DC Crew
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Are they the stock OEM lugs? Are you SURE they were torqued right? What do you mean "loose" ... how loose?

The heat from the brakes won't loosen lugs. I can do 20 laps (240 turns) at balls out speed and foot to the floor braking, never a lug issue even remotely.

Vaporized brake pads and bald tires... you betcha... but the lugs are still there and tight.
 

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Discussion Starter #3
Patrick

Have you got the same Magnesium rims? They're quite diffrerent from aluminium one-piece rims. They have an insert that the lug nut bears against which sits in the Magnesium rim. The insert appears to have loosened - I still can't work out exactly how, but the lug nuts were at least half a turn off. I have a calibrated Snap-on torque-wrench and had them set at 100lbft. I was slowing on the limit - ABS had some work to do. In 20 years of racing and track-driving I've never had this sort of problem. I backed them off and re-torqued and 5 laps later - the same thing.
 

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DC Crew
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Patrick

Have you got the same Magnesium rims? They're quite diffrerent from aluminium one-piece rims. They have an insert that the lug nut bears against which sits in the Magnesium rim. The insert appears to have loosened - I still can't work out exactly how, but the lug nuts were at least half a turn off. I have a calibrated Snap-on torque-wrench and had them set at 100lbft. I was slowing on the limit - ABS had some work to do. In 20 years of racing and track-driving I've never had this sort of problem. I backed them off and re-torqued and 5 laps later - the same thing.
No, I have the '02 speedline Z06 wheels. But, this is the first I've heard of lugs coming loose on stock Magnesium wheels. But, throw racing into the mix and the variables change.

I know they are lighter, and flex a little more... and leak a little more air... but I didn't know there were inserts. I think those are there possibly to keep the holes from elongating because magnesium isn't as strong as aluminum. Loose lug nuts can elongate the holes... and maybe you are past the point of no return and it's just going to get worse.

Maybe the long term solution (if you want to keep these wheels) is re-machining your wheels bolt circle to accept precision machined steel bushing inserts. That might do the trick.
 

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Discussion Starter #6
Thanks guys - so no history there.

The Magnesiun rims have 5 inserts (I assume it's a steel alloy of some sort) that the lug nuts tighten onto and a rear flange of the same metal that bears against the hub, presumably because the Mag is to soft. When I got the car home and took the lug nuts off, one of them was stuck to the insert and it came out with the nut. Strangely this problem was only on 3 of the 4 rims. The back left (Silverstone is a right turn circuit) was totally unaffected. Tyre pressures rose from 30 to 44 psi on this rim and similarly on the other three rims.

If anybody ever has this problem, I'd be interested to discuss this further.
 
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