Mickey thompson sportsman

[Blown66]

I have a set of Mickey Thompson Sportsman's (29x18.5x15) and through street use I have had to replace 3 tubes in the last three months...two in the past week...all with valve stem breaks.

Anyone else have this problem...everything checks out (wheel) rear end supports etc...

Today...the guys that mounted them put 14 lbs in, I went down and added 4 more ...drove a total of 16 miles, no abuse...pop.

Any ideas?

Thanks in advance.