Correct axle misalignment - HOW?

[DaveW]

...Once that pressure passes the MAX inflation pressure stated on the tire sidewall while on the road, the tire is GOING TO FAIL in a relatively short time.

All tires are designed to account for the tire pressure going up from the max nominal inflation pressure as they are used. That is NOT a tire failure mode unless something else is seriously wrong with the tire, its loading, etc. Tires are designed to be OK at nominally 50% over-inflation.

If tire pressures are going up enough to cause failure, something is generating heat, or there was a lot of water in the tire that condensed overnight and evaporated as it got hot.

[Steve Davis]

Dave,
My tire failures (when I was having them.... on my previous trailer .. not this one) were all over the place. I remember specifically one time I stopped for fuel and when I went back to check on the trailer it "looked funny", but I didn't pick up on it right away. I checked inside to make sure that all was OK, then closed it back up. As I was walking back towards the tow vehicle (which at that time, I think was a Ford Van), I decided to take another look .. then I walked to the other side and looked and it looked OK. Went back and FINALLY realized that one of the tires was significantly LARGER than the other. Closer inspection showed that the tire/belt had TOTALLY SEPARATED .. and it was like a NASCAR tire with an inner liner .. except it wasn't flat. The outer belt must have been only minutes away from leaving the carcass. Thankfully, I had noticed it and was able to change the tire before that happened. I didn't think to check the pressure in that tire, but willing to bet it was over 100 PSI. Hard as a rock and hot as a pistol.

My long term analysis was as stated in my post above. When the tire was operating significantly in excess of the stated sidewall stamp, something happened inside that started the belts to separate. That was the ONLY one I ever caught 'in time' - all the rest were a ragged pile of rubber and steel by the time I got to the side of the road. I once had a DOUBLE as the gator from one tire slung around and took the valve stem out of the tire behind it (or in front .. I forget which was first). Fortunately, I started carrying 2 spares before that failure (Return from Savannah on I-16 .. temps near 100 degrees). All those first years, I was maxing out the tire pressure since the sidewall said 'set tire pressure COLD'. So it would normally be running near 100 PSI on an LRE tire which started at 80#. At the same time as I made the decision to lower the tire pressures, I added the TPMS so I could MONITOR what was going on. I found that if I inflated the tires to 60 PSI, I got a higher gain in pressure than I did starting at 45 PSI - so from then on, I was SOLD. I was never able to weigh the tires separately on that trailer fully loaded but I did weigh the entire trailer at about 7100# (3500# axles). I then ramped up to 5200# axles and still had the problem until I then lowered the pressure and finally got everything under control.

My new trailer has started off with 5200 axles and only LRC tires .. and it weighs very nearly the same. But with the lower pressures (~50 PSI cold on Max 65 PSI ST tires) I've never exceeded the 65 PSI and have yet to have a 'running flat' in, I guess it's now something over 10 years of towing including years with the previous trailer. I will add that I DON'T tow at the speed that some of you do. My motorhome likes to do about 60-65 and that's what we normally run. I will also add that I HAVE run through some REALLY BAD roads with horrible potholes and bumps - up and down - but it's mostly the SAME roads that I used to run when I had so much trouble and now I don't (other than the cabinets trying to climb off the walls of my motorhome). I have also lowered the pressure in my motorhome tires to soften the blows from the roads. Having the TPMS has given me the confidence to run lower pressures since I can SEE what is going on. After 5 years or so on my new Michelins on the RV at the lower pressures, I'm now seeing some odd wear patterns (ribs are not wearing evenly) due to the low pressures, but since RV tires generally AGE out rather than mileage out, I'm not too concerned about it.

Steve

[DaveW]

... I will also add that I HAVE run through some REALLY BAD roads with horrible potholes and bumps - up and down - but it's mostly the SAME roads that I used to run when I had so much trouble and now I don't (other than the cabinets trying to climb off the walls of my motorhome). I have also lowered the pressure in my motorhome tires to soften the blows from the roads...

With this additional info, I am convinced that with the higher pressures you were suffering from carcass impact failure, i.e., the "stone," "X," or "impact" break that I described due to the crappy roads. Lower pressure absolutely helps minimize that type of failure by allowing more overall tire flex. It is also likely that the damage would not immediately be obvious since the carcass damage would have to grow (like a fatigue crack gradually growing) until the damage got large enough to cause failure.

This sort of thing is one of the reasons that serious off-roaders use large balloon tires at low pressures.

[Daryl DeArman]

All those first years, I was maxing out the tire pressure since the sidewall said 'set tire pressure COLD'. So it would normally be running near 100 PSI on an LRE tire which started at 80#.

25% PSI increase? I've never experienced such pressure increase from cold. But then, I'm usually towing from home to some place that is rarely hotter ambient than home by more than a few degrees. The only difference would be in temp from operation. Maybe the alignment is really building heat in your tires.

I had a class C RV that had a number of failures on the rear duals. I now carry an infrared pyrometer with me and when I stop at gas stations I check all tire temps at sidewall and trailer brake temps just to make sure nothing is odd. Class A hasn't had a single tire failure---knock wood.