Do I need longer wheel studs?
 

1970 911t, no spacers, just got 15x6 ATS classic wheels (from PP classifieds), aftermarket cone seat lug nuts. Rear wheels studs look nearly flush but fronts (image) are sunken in. Mostly street car with plans to autocross. Do I need longer wheel studs?

Thanks. http://forums.pelicanparts.com/uploa...1537043293.jpg

Need may not be the right term. I have about as much grab on the studs as your photo and I AX/track the car with no ill effects.

Want may be what you are asking, but be prepared to spend time and effort into swapping studs.

Cheers,
Ryan

Yes.

General rule of thumb is total thread engagement is equal to the diameter of the stud. In any case, you could only get about one more turn before you got complete engagement of the threads. I doubt that getting longer studs would actually increase strength by any meaningful amount.

Torque them on, and do not over or under torque them.

FWIW, there are people who will tell you that it is OK to run them if you get 8 full turns. I am not one of those people.

id say no. you obviously are at the edge there, but for street and AX usage that will suffice. if you were to track the car generating significant heat in the brakes I might be more concerned. you are likely if AX'ing checking the torque more than the average customer anyhow so that's good.

do you run spacers or are those wheels unusually thick?

Thank you for all the great responses. No spacers. I guess wheels are just unusually thick.

Those would meet the thread requirements for PCA club racing. I ran that way for many years club racing. They are fine.

Phew. Because I didn't want to change them unless I had to.

If you are really concerned there is a shanked lug nut made that goes deeper inside the wheel with more threads but sometimes the wheel lug hole has to be drilled out a little for the larger OD. I have done this in a few cars with good results.

SAE standards used to be 50% of the diameter of the bolt should extend past the nut. So yes, you 'should' replace. Those look like stylized nuts, so YMMV. I'm sure the tech inspectors at an HPDE would have a fit about your fit.

Those SAE standards never made sense to me. Not sure what the extended material does to effect the clamping force of the fastener. Can someone explain? Maybe just an engineer's rule of thumb (their humble opinion)?

Sherwood

The extended material is just along for the ride and doesn't matter to the clamping load, it's just a factor of safety in case the not backs off. In practice the OP's set up may be fine, the first three threads carry most of the load, but racing groups are likely to have a rule like this one from the POC regulations:

Wheel nuts or bolts must fully engage the threads on the stud, or hub, for a length at least equal to the outside diameter of the stud or bolt. Steel lug nuts are required for all Racing classes and recommended for all others.

So measure the engaged thread length, you may be okay as is.

No issue there,if you look closely the nuts are recessed inwards towards the actual thread no issue there,properly torqued and clean lubed threads you will be fine.

These two have it right. Listen to them!!

Grind the nuts back so there is no exposed threads.

I, personally, would change the studs. Not based on anything scientific, just me.