Troubleshooting Trailer Tire Cupping on Inside of Tire

Updated 04/29/2016 | Published 04/27/2016

Question:

I have a 2 axle 16foot Carson flatbed trailer, #3,500 Dexter axles with electric brakes on all 4 wheels. Trailer is often loaded to max weight and tires are kept at max PSI per the tire sidewall. When new tires are purchased and mounted they are balanced before mounting. On the front axle left side, the tire is experiencing cupping on the inside of the tire. All three other tires have a normal wear pattern. The rocker arm shackle straps were replaced about 18 months ago when severe wear was found in the original ones. They are now the double thick ones forged straps rather than the original pressed thinner straps. There are nylon bushings on the equalizer holes for the shackle straps. About 9-10 months ago, while being pulled, the nut on the bolt on the shackle strap on the left front axle came off and the bolt worked loosed causing the suspension to drop. It was repaired roadside and inspected by a mechanic at that time. Since then, no other abnormal wear patterns or problems have been seen in any part of the suspension, but this is now the second tire on the left front that has exhibited cupping on the inside. Any thoughts or guidance is appreciated.

asked by: John T

Helpful Expert Reply:

Cupping is usually caused by a bad alignment or suspension that is worn out and bouncing its way down the highway.

Since you had suspension components go out while traveling I would be willing to bed that something got bent or pulled out of alignment during that incident.

Best option will be to take the trailer to a shop that can do trailer alignments and have them get you straightened out (pun intended).

expert reply by: Jameson C