5th Wheel Broken Stud Theory
Although we are currently running a Class C, several of my camping buddies are pulling 5th wheels. They keep having problems with broken wheel studs with the aluminum rims. They carry torque wrenches ...
Forum Discussion
One of the characteristics of steel is that it will last forever if the stress applied is kept to less than 50% of yield strength. One you go over 50% it lasts a number of cycles of the stress being applied and removed with life going down as the stress goes up. A bolt stressed at 90% yield strength will last forever if the stress is not relieved and re-applied.
In a proper design a bolt that is properly tightened holds 2 objects together with such force that they will not be pulled apart, thus changing the stress on the bolt. The rigidity of the flat face of the wheel against the flat face of the spindle should far exceed that of the bolts. So, unless there there is a mechanical defect in the flat faces causing them to rock the bolt should not be stretched enough to change the stress on it IF IT IS PROPERLY TIGHTENED. BEING OVERTIGHTENED WILL NOT CAUSE THE BOLTS TO FATIGUE WHILE IN USE or result in a failure while in use. Failure from overtightening should only occur during the tightening process.
Most fatigue failure is caused by bolts not being tightened enough! This allows the wheel to pull away from the hub at times, creating a cyclical stretching/stress increase.
So the failure in use is due to LOW TORQUE, mating surfaces that are not flat or possibly the stretching/shrinking cycle resulting from brakes heating up and cooling off and the different coefficient of expansion of the two metals. Having said that, the aluminum wheels that I just bought have steel inserts in the bolt holes to help prevent this situation.
If my trailer was to have trouble with studs breaking I would make sure that the lug nuts are tightened enough, that the wheel to hub mating surfaces are flat and smooth, that there are steel inserts in the aluminum wheel lug holes and that the brakes are working evenly so that one or two are not getting much hotter than they should.
On edit, one more thing to consider, especially if the trailer did not come with the wheels on it. I changed my trailer from steel to aluminum wheels and had a terrible time finding lug bolts the right length. The lug bolts that came with the steel wheels were too short and all that I could find at the parts houses were too long, in both the unthreaded shank and overall length. I finally found some on Amazon with the right shank but were still too long. I was able to cut them to length. I actually just got that done a couple of weeks ago so it will be a while before I can swear that they are reliable.
In a proper design a bolt that is properly tightened holds 2 objects together with such force that they will not be pulled apart, thus changing the stress on the bolt. The rigidity of the flat face of the wheel against the flat face of the spindle should far exceed that of the bolts. So, unless there there is a mechanical defect in the flat faces causing them to rock the bolt should not be stretched enough to change the stress on it IF IT IS PROPERLY TIGHTENED. BEING OVERTIGHTENED WILL NOT CAUSE THE BOLTS TO FATIGUE WHILE IN USE or result in a failure while in use. Failure from overtightening should only occur during the tightening process.
Most fatigue failure is caused by bolts not being tightened enough! This allows the wheel to pull away from the hub at times, creating a cyclical stretching/stress increase.
So the failure in use is due to LOW TORQUE, mating surfaces that are not flat or possibly the stretching/shrinking cycle resulting from brakes heating up and cooling off and the different coefficient of expansion of the two metals. Having said that, the aluminum wheels that I just bought have steel inserts in the bolt holes to help prevent this situation.
If my trailer was to have trouble with studs breaking I would make sure that the lug nuts are tightened enough, that the wheel to hub mating surfaces are flat and smooth, that there are steel inserts in the aluminum wheel lug holes and that the brakes are working evenly so that one or two are not getting much hotter than they should.
On edit, one more thing to consider, especially if the trailer did not come with the wheels on it. I changed my trailer from steel to aluminum wheels and had a terrible time finding lug bolts the right length. The lug bolts that came with the steel wheels were too short and all that I could find at the parts houses were too long, in both the unthreaded shank and overall length. I finally found some on Amazon with the right shank but were still too long. I was able to cut them to length. I actually just got that done a couple of weeks ago so it will be a while before I can swear that they are reliable.
