[ggggbmw]

While chatting with people at my last HPDE, one of them mentioned he would have to replace his lug bolts soon. They were nearing their cycle life. He stated that he was told by a BMW rep to replace his lug bolts after every 30 wheel changes. (I think he said 30. Might have been 20.)

I'd never heard of this. Assuming that you don't over-torque them, or they have some other damage, I would think that lug bolts would have a near infinite life. They are a very high grade hard metal, and frankly, I would think the hub threads would wear quicker.

Then again, most cars are unlikely to see 30 changes in their whole lives. Even if you swap summer/winter every year. But for those of us who are constantly taking track wheels/tires on and off several weekends a year, you could see 30 cycles in a year or three.

He was driving a newer M3, so maybe this is some M thing? Or possibly a hard-core race/time-attack/HPDE thing? Some googling didn't bring up any big results, but I didn't search hard.

Or, was the BMW rep just shining him on for a nice routine sale?

[hwntime]

I've never heard of that before. As long as they were always torqued to spec and there's no worn threading or rust/damage, I would think they should last for the life of the car

[B58togo]

Apex recommends annual replacement of their studs if you track your car. I don’t recall any reference from BMW indicating stock bolts as having any type of maintenance cycle.

https://www.apexraceparts.com/media/...structions.pdf

[aerobod]

The M14x1.25 10.9 bolts BMW uses on most cars now has a high safety margin when torqued to the correct value (140Nm). The tensile proof load (the axial load below which all bolt deformation is elastic) for these bolts is 109kN. A torque of 140Nm on a dry thread will produce an axial load of approximately 50kN (0.2 K assumed for friction), leaving a 118% safety factor. As long as the thread is not damaged in anyway, and the bolt has never been over torqued by any significant amount, there should be no lifecycle limit due to bolt stresses.

When BMW used M12x1.5 10.9 bolts torqued to 120Nm, the safety margin was a lot less, with a proof load of 74kN and an axial load of 50kN at 120Nm, there was only 48% margin which could easily be exceeded by using thread lubrication or inaccurately calibrated air tools on the bolts, leading to bolt deformation.

[dradernh]

Originally Posted by B58togo

Apex recommends annual replacement of their studs if you track your car. I don’t recall any reference from BMW indicating stock bolts as having any type of maintenance cycle.

That's interesting. With no apparent ill effects, I ran Bimmerworld's race studs on an E36 M3 race car for 104 days and ~3,000 laps during 2010-2013. No air tools were used; all lug nut removals and reinstalls were done by hand. The only time studs were removed was when new hubs were installed, and the used studs were installed in the new hubs (I'm not 100% sure that was always the case, though).

I never discussed this subject with other drivers, but I wouldn't be surprised if some were changing studs out every year. I know that other drivers occasionally had a stud break.

Some drivers considered wheels to be wear items and changed them out each year or two. I traveled with seven sets of wheels with mounted tires (four drys, three wets), and never had an issue requiring a wheel to be replaced. I suspect some drivers were either overly cautious and/or there was a wide range of experiences with equipment.

As always, my 2¢, and YMMV.