Tires: Tire Pressure, gross axle weight, rockwood travel trailer

I have a 2002 GMC Safari van and pull a 2004 Rockwood travel trailer that weighs in dry at 3550 pounds. The van specs call for P215R75 15 tires. I had a set of Micelin tires on the van and they were very squirmy feeling at 35 psi when pulling the trailer and the sidewalls were showing extreme cracking. I have all the necessary towing equipment such as weight distributing hitch, sway bars etc. I now have a set of LT215R75 15 tires on the van as recommended by several towing experts to get a stiffer sidewall, these tires have a max of 50 psi and I currently have them set at 35 psi. Do I need to up the tire pressure to get the advantage of the firmer sidewall ?



First, most of the stiffness in the sidewall is due to inflation pressure - so the "experts" you consulted are wrong about this fixing the problem..

The second thing is that your "experts" should have been able to tell you that LT tires should use 15 psi more than the same size P metric.

But I think part of your problem may be the towing capacity of the vehicle.  Check with GM to see what it is, and I'll bet you are exceeding the rear GAWR (Gross Axle Weight Rating) - the load on the tires, which would include the tongue weight plus what you put in the van.

I would also check the alignment - of both the van and the trailer.