Broken Wheel Studs

Charlie Smith · **Posted:** Thu Jun 16, 2005 10:45 pm

I broke a wheel stud this past weekend when putting my street tires back on the car. I did not cross thread it. It hand tightened fine most of the way. Anyway, it seems like this is a common occurence with autocrossers.

After thinking about it this week, I have a theory. Both the stud and lugnut expand under the extreme heat during a run. I believe that the lugnut cools faster than the stud, making it very tight around the stud. When I removed it after my last run, I believe that it damaged the lugnut's threads. Any comments on my theory or have one of your own?

Also, replacing wheel studs on Integras is NOT an easy task. At first I thought I could bang the old one out and put the new one in without removing the hub assembly. WRONG! I banged it out of the hub, but could not remove it from the assembly due to clearance issues. I had to take it to the dealership to get them to pull the hub assembly and replace studs and wheel bearing.

I have got to find a solution to this problem. I think I will let the car cool down for a while before removing the lugnuts. I may also try anti-sieze eventually too.

Charlie

Keith Vail · **Posted:** Thu Jun 16, 2005 10:48 pm

Charlie, I busted a stud on my civic a couple years back. Ever since then I put anti-sieze on the studs and have never had a problem since. You just have to re-apply the anti-sieze every so often when it appear to be worn off. Hope this helps.

Gordon Taylor · **Joined:** Fri Aug 29, 2003 9:19 am **Posts:** 51

I take my wheels off once I'm home, so run heat isn't the problem. I was breaking one every couple of months. Asked Carl at Sports & Compacts what to do, and he said to (1) torque to minimum value (66 ft-lbs on NB Miata) and put one drop of light oil (Miracle Mystery Oil, etc.) on the end of the stud before putting on the nut.

I haven't had to replace a stud since I started doing this. YMMV.

Rich Anderson · **Posted:** Fri Jun 17, 2005 9:02 am

Please note that applying anti-seize, oil or any other fluid changes the clamp load for a given torque value.

While not wheel studs, this shows what a large impact a different type of lubricant can have on the torque setting. Remember, torque is just a measure of bolt (or stud) stretch. If you reduce the friction of the threads and apply the same torque, the stretch will be greater. Adding oil and using the lowest recommended torque setting might work, but it also might not.

Matthew_Thomson · **Posted:** Fri Jun 17, 2005 9:02 am

whats a lug nut?

Rich Anderson · **Posted:** Fri Jun 17, 2005 9:09 am

Matthew_Thomson wrote:

whats a lug nut?

I can show you a BMW wheel bolt that looks like a Coke bottle if you want! IMO, if you have wheel bolts, get studs. Stripping a hub because of a bad bolt is much worse that dealing with a stripped stud.

MilesBeam · **Joined:** Fri Aug 15, 2003 1:57 pm **Posts:** 427

Charlie Smith wrote:

I broke a wheel stud this past weekend when putting my street tires back on the car. I did not cross thread it. It hand tightened fine most of the way. Anyway, it seems like this is a common occurence with autocrossers.

After thinking about it this week, I have a theory. Both the stud and lugnut expand under the extreme heat during a run. I believe that the lugnut cools faster than the stud, making it very tight around the stud. When I removed it after my last run, I believe that it damaged the lugnut's threads. Any comments on my theory or have one of your own?

[snip]

Charlie

I could be wrong... but Charlie I don't think your theory of the lug nut cooling faster than the stud is the problem. I supect the stud is failing because of excessive tension along the longitudinal axis. In your theory, the cooling lug nut would put some degree of compressive stress on the stud at the point of contact, and may cause a slight effective change in the pitch of the threads.. but since the two objects are in contact with each other, the surfaces in contact should cool at approximately the same rate, making this a bit of a mute point.

Studs can fail for a variety of reasons.
- fatique
- mechanical stresses induced by thermal expansion/contraction
- over tightening or under tightening
- corrosion (requires a long time though.....)
- improper seating of the wheel when lug nuts are initially tightened
- failure to re-torque after an initial install of the wheel each time...

Each of the above is worth a chapter in a book, which I won't write today!

Translated... a few problems autocrossers can have would come from:
- how often you change tires/wheels without changing lugs/studs
- torque wrench out of spec
- putting cold wheels on a very hot car right after an autox and tightening to mfr specs (the studs wiill be forced to stretch some as they cool down)
- adding lubricant to the studs/lugs and still tightening to mfr specs can cause you to overtighten the lugs

I try to let the car cool after my last run some before tightening the lugs down on the street wheels.

It's a good idea to change studs/lug nuts periodically on the car. If you do a lot of track events and or autocross heavily, it's cheap insurance to do it every year. It's easy to take care of in the garage, and a royal pain at an event.

Hope this helps.

Miles

Stephen Westerfield · **Posted:** Fri Jun 17, 2005 12:28 pm

MilesBeam wrote:

It's a good idea to change lugs/nuts periodically on the car. If you do a lot of track events and or autocross heavily, it's cheap insurance to do it every year. It's easy to take care of in the garage, and a royal pain at an event.

Just curious, did you change out all of them while you were in there? or just the bad one. I had one break off a few years back so had them all changed at the same time (bad part about that is, once you pull the hub apart, if you don't do the wheel bearing while you are in there....expect to revisit this excercise in a few months). Looks like you did the wheel bearing, so that is good. I was just going to tell you though, when doing the rears, if you order a new rear wheel bearing, that assembly comes complete with new lug nuts and all (assuming your is like mine, and it looks to be when I checked on www.acuraparts247.com ).

Chuck Frank · **Posted:** Fri Jun 17, 2005 1:37 pm

We had 2 studs break on the Miata early on in our AX career, well before we started using an impact wrench. After that I put one small touch of wheel bearing grease, just enough to only fill the thread valleys in an area ~ 3/8" wide and 1/4" down the stud (one wipe with the tip of a lightly greasy finger) and run the nut up and down the threads a couple times by hand to spread it. Since then we have not lost a stud to breakage in >4 years and a LOT of tire changes (16 times at ONE event once- hot changes between runs) even with using our high powered impact wrench for the last 3 years. I break them loose with the gun and run them down snug with it but hand torque each to 80 ft#, the torque value specified for 12mm studs.
I clean the lugs with solvent and regrease once a year. I think one thing that helps too is on both the Miata and Celica we use lugnuts that are closed on the ends to keep dirt out of the threads. I believe that the torque value on lugs is not based on stretch of the stud, but rather on the interference fit of the taper of the lugnut in the seat of the wheel, therefore is is important to NOT get any lubricant on those tapered surfaces.

Rich Anderson · **Posted:** Fri Jun 17, 2005 1:54 pm

Chuck Frank wrote:

I believe that the torque value on lugs is not based on stretch of the stud, but rather on the interference fit of the taper of the lugnut in the seat of the wheel, therefore is is important to NOT get any lubricant on those tapered surfaces.

I do not believe this is correct. Once the seat of the wheel nut makes 360° with the seat on the wheel, there is unlikely to be any further movement towards the hub face. The compressive strength of metals is far greater than their tensile strength. The friction of the nut turning against the conical seat might indeed be a portion of the overall torque needed, however it is not likely to be a significant contributor.

Note that the Tire Rack's guide (seen here) shows that required torque increase with stud size. If the seat were the critical element, then torque would be rated by seat size, materials and other considerations.

This is not to say that the advice of keeping oil and grease off the seats is not sound. I just don't agree with the statement that torque is not based on stud stretch.

Vincent Keene · **Posted:** Fri Jun 17, 2005 1:58 pm

Rich Anderson wrote:

The friction of the nut turning against the conical seat might indeed be a portion of the overall torque needed, however it is not likely to be a significant contributor.

That friction would make *some* difference in torque and causes damage to seats over time. I use McGuard lugs with a rotating conical seat. Once the cone of the lug makes contact with the wheel seat the cone no longer turns. They are expensive ($80 for a set of 16) but well worth it IMO.

Wes Eargle · **Joined:** Mon Oct 27, 2003 9:47 am **Posts:** 3683

From what I recall about materials science, you don't want to stretch a lug. Doing so fatigues it and makes it prone to fail. It will not "relax" to it's previous form when de-lugnutted either.

Rich Anderson · **Posted:** Fri Jun 17, 2005 2:01 pm

Vincent Keene wrote:

That friction would make *some* difference in torque and causes damage to seats over time. I use McGuard lugs with a rotating conical seat. Once the cone of the lug makes contact with the wheel seat the cone no longer turns. They are expensive ($80 for a set of 16) but well worth it IMO.

Do these wheel nuts come with a notation that a lower torque specification may be required as there is less friction during assembly and therefore force is transfered into wheel stud stretch more easily?

If seat friction is a large contributor to the torque value, one would have to assume that there would need to be such a warning.

Rich Anderson · **Posted:** Fri Jun 17, 2005 2:07 pm

Wes Eargle wrote:

From what I recall about materials science, you don't want to stretch a lug. Doing so fatigues it and makes it prone to fail. It will not "relax" to it's previous form when de-lugnutted either.

Threaded fasteners, by design, are intended to stretch slightly when fully tightened to specification. This creates a preload, which serves to clamp the wheel securely to the hub. If under-tightened, the nut (or bolt) can gradually loosen. If over-tightened, the stud or bolt can exceed its "elastic" range, and be permanently stretched (fatigued), which destroys its ability to provide clamping load. If this happens, the stud or bolt can either loosen on its own or can break during operation.

Check out page 4 (large PDF file).

Vincent Keene · **Posted:** Fri Jun 17, 2005 2:08 pm

Rich Anderson wrote:

If seat friction is a large contributor to the torque value, one would have to assume that there would need to be such a warning.

I said "some" not sure how much.

BTW, when I was in the FRP pipe/tank business, we did pipe pressure testing all the time. Using SS bolts required anti-seize (messy stuff!) if you ever want them to come back apart. Therefore all bolts had torque values listed as "lubricated" which are of course different than "dry".

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