JohnLZ7W

A couple of weeks ago I had another instance of broken lugs on my car. One sheared completely while torquing it, one with hairline cracks and two more that were hanging on by a single thread. The first time this occurred a couple of years ago it was also 3 broken lugs. It's worth noting that another TTRS owner has had the exact same failure, the broken lugs looked identical to mine. Has anyone else seen this problem?

Install history of 034 C5 RS6 rear rotor upgrade on my car:

3-23-2014, 30000 miles, installed 034 C5 RS6 upgrade
4-30-2014, 31000 miles, installed motorsporthardware.com studs
10-6-2016, 56000 miles, discovered multiple sheared studs, replaced with factory lug bolts
3-10-2018, 69000 miles, JHM C5 RS6 rear rotors installed
2-26-2019, 78000 miles, discovered sheared factory lug bolts

Time and mileage between failures... Note this is just when I noticed the broken lugs, I have no way to verify when they actually broke. The first time seemed to have been broken for some time before discovery given oxidation on the exposed metal. This more recent time only one lug had broken all the way and the metal was cleaner. Two other lugs were hanging on by a single thread and another was showing hairline cracks so I believe I caught it closer to the actual failure point.

873 days, 25k miles between installing C5 RS6 rotor upgrade and discovering broken studs
890 days, 23k miles between replacing studs with bolts and finding broken bolts

This failure has happened with OEM C5 RS6 rotors as well as JHM manufactured C5 RS6 replacement rotors. The failure has occurred with aftermarket studs as well as the factory provided lug bolts. After the first time I assumed it was due to poor quality aftermarket studs but with the factory bolts also shearing I can only presume this is an issue with the fitment of the C5 RS6 rotors on the 8J hubs. In 78000 miles I've never had a single issue with the studs or lug bolts on the front axle.

I tend to be very careful about torquing lugs on my car since my summer Neuspeed wheels require hub-centering rings and I am used to having spacers installed (although never on my TTRS). For those reasons I torque my wheels to ~70ft lb with effectively no weight on the wheel and then follow with a second pass to 90 ft lb. I rarely use an impact gun to remove and never to install. If a shop works on my car and removes the wheels during service I always retorque lugs once I get the car home. I do not believe that any of the lug failures I have had are related to a material defect in the lugs or a result of over torquing.

After examining the differences between the OEM RS6 rotors, the JHM replacements and the Girodisc equivalent (I no longer have my factory TTRS rotors) my theory is that the C5 RS6 hub must be slightly smaller in diameter than the 8J TTRS hub. The TTRS hub comes in contact with either the ridge on the hat (OEM RS6 rotor) or the angled part of the hat (JHM) and in either case the hat does not sit flush against the hub allowing for some movement which over time is compromising the lugs. The Girodisc hat has a flat inner face which should allow it to seat properly across the entire area of the hub surface which I am hoping fixes the problem. I guess I will know for sure in about 880 days.

The JHM rotors seem much worse in fitment but the time and mileage between failures was incredibly similar to the OEM RS6 rotors. Maybe the factory lugs are built to higher spec? In any event I believe the OEM C5 RS6 rotors are not a proper fit for the TTRS and the JHM replacements are potentially even more dangerous.

I've shared all of the above with 034 and they're looking into the issue too but they have only heard of mine and the one other failure.

Lots of pics of the lugs and rotors with some annotations on the pictures