why are my steer tires cupping?

could be shocks, probably alignment. check your kingpins and wheel bearings for slack, if no slack then I would put 2 steer shocks on and get a good 3axle align. what pressures are you running and when are you checking them?

 

Always good, would that be 85 psi, 90, 100, 110. Low air pressure along with alignment, mostly alignment but the low pressure will cause it to show faster.

I run my steers at 100 psi for 75,000 miles then move them to the trailers.

 

If one tire is cupped on the inside, and the other is cupped on the outside, you need a three axle alignment.

 

Make sure that when you get the alignment done, They check the caster. Mine was cupping badly and I was getting around 45,000 miles from a set of steers and the front end shop kept saying that everything was fine...They weren't checking the caster.

Then I went to a different front end shop!

I now have over 100,000 miles on my steers and have no sign of cupping.

 

caster is NOT a tire wearing alignment angle....... camber is....... as is toe but caster is NOT. are you pulling the same trailer? or different trailers???? also is your 5th wheel greased properly?

 

Camber has to be way off to cause tire wear on a radial its more likely to cause the truck to pull. Sounds like shocks or suspension trouble. I agree with Country29

 

All of the above are valid points. The other area you might need to look at is your trailer alignment. If you pull the same trailer all of the time it might cause be the problem. However if you pull different trailers then that might not be a problem.

 

Cupping is rarely alignment related. Alignment will effect the whole circumference of the tire, not spots here and there. Cupping is caused by inconsistent contact with the road surface. You are looking at tire balance, tire out of round(bad mounting), shocks, springs, pressure or tire quality. Alignments will not fix cupping. If you are running tires made in Japan or Asia, sorry to say, but they never seem to wear properly no matter how good you keep your truck maintained.