Wheel Stud / Lug nut engagement

[IowaBen]

I installed the front brakes that came with my complete kit, and my solid axle rear end I got from Fortes.

I noticed the front studs are close to flush with top of the lug nuts, but the rear studs are inset from the top of the lug nuts. Additionally, the last .25" of the studs have no threads (front and rear).

I took some measurements:
Front studs have about .790" of thread engagement
Rear studs have about .630" of thread engagement

IMG_0323.jpg
IMG_0324.jpg

I suspect I should swap the rear studs. Looks like it will be doable if I disassemble all the brakes to make room to hammer them out. Wanted to check with the group in case I'm overthinking it.

Thanks!
Ben

[Bob Cowan]

For any fastener, you want to see about 2-3 threads.

[CraigS]

Bob is 100% correct.

[Jeff Kleiner]

I'm with Bob and Craig.

Jeff

[Inman Lanier]

The statement of 'you need 2-3 threads' is somewhat popular - however the actual absolute minimum (lacking more information) that most engineers espouse is the higher side - 3 threads. Let's, however take that into context - if you have significant consequences of failure, my recommendation is to reconsider such a small amount of engagement. There are many reasons, a significant one of which is cycle limitations. Likely the stress in a joint with that small an engagement is so high on the material properties you are grossly limiting the number of loading cycles. By that I mean fatigue. Cyclical loading on materials ultimately results in fatigue; the limit being linearly correlated to the number of cycles, and logarithmically related to the stress. As you approach the yield stress of a material, a small increase in stress can have a significant impact on the number of cycles.

There are way too many factors to simply come to one simple summary as in xx threads. A much more generally accepted minimum that is espoused by fastener experts is that you want the minimum threads engaged that correspond to the cross-section of the fastener. Assuming you have a 1/2 by 20 stud, then you want 1/2" thread engagement in the nut. 3 threads has very little to no margin and may be of issue depending on the materials involved.

[Bob Cowan]

A much more generally accepted minimum that is espoused by fastener experts is that you want the minimum threads engaged that correspond to the cross-section of the fastener. Assuming you have a 1/2 by 20 stud, then you want 1/2" thread engagement in the nut. 3 threads has very little to no margin and may be of issue depending on the materials involved.

We are not talking about thread engagement. On a critical fastener, I would want to see 100% thread engagement. You could probably get away with less. But my CDO would not allow it.

We are talking about how many threads you see past the top of the nut.

[Jeff Kleiner]

Inman! Good to see you participating again after all of these years! I get together with JOhn & Richard every winter when I make it to PBC---we'll have to try to include you on the meet up next time

Jeff

[Inman Lanier]

We are not talking about thread engagement. On a critical fastener, I would want to see 100% thread engagement. You could probably get away with less. But my CDO would not allow it.

We are talking about how many threads you see past the top of the nut.

Too funny - hear I am reading that thread as if I'm responding to a request from maintenance for a compromised fastener joint. The quotes and phrases were too coincidental. Sorry for my lapse/misunderstanding.

[Inman Lanier]

Inman! Good to see you participating again after all of these years! I get together with JOhn & Richard every winter when I make it to PBC---we'll have to try to include you on the meet up next time

Good to hear from you as well, Jeff. Yes, after mine was laid up for TOO long, the body is off since I had some bent valves to deal with. Go figure - retired for 6 years now and other projects in the way. Now I'm cleaning up the 22 year old car to drive around again. Look forward to seeing you next time down. Please include me in the invite.