rehash of an old topic / tire pressure

[working on it]

After finally putting my finished trailer on the road for a weigh-in and roadtest session, I also tested tongue weight scenarios and "tire pressure" theory. Since I posted this under the latter subject, here's my summary of what I suspected to be true, not only on this trailer, but on others I have used. Trailer tires, "ST", are not the same as car and truck tires. They act as a suspension component (shock absorber substitute), sway control (in some small part), and as a load bearer. BIAS PLY vs RADIAL On this trailer, I use bias ply tires (ST205-75Dx14) rated for 1760 lbs, load range C; I inflated the tires to their max load pressure rating- 50 psi - and drove to the scales. I drove quickly, on some bumpy, all twisty back roads and a Farm to Market Highway (speeds from 20-40-60mph). Even with only a 4% tongue weight and the tongue 6" nose-up (testing a worse case load situation, also) it pulled beautifully...followed the truck perfectly (even on switchbacks, over bumps) and minimal jumps over a pothole or two. I had expected it to jump around a lot; it didn't. When I got the weight, I saw why it hugged the road so well. It was 1280lbs (should become 1438 when loaded for camping). Or 73% of the tire's max load. When fully loaded, at 1438lbs, that will become 82% of max rated load for the tires. Discount Tire recommends 20% load margin as a safety factor http://www.discounttire.com/dtcs/infoTrailerTireFacts.dos. I feel that I'm fortunate to have picked the right size tire to build around (the original 8" wheels wouldn't have been enough!). As I left the scales, I adjusted the tire pressure down (proportionately) to 73% of the 50 psi, to test the theory of pressure to load. At 36 psi, I returned home, again on the same roads. This time, the trailer didn't track as well, exhibiting a slight tendency to go wide on the switchbacks. I returned home, and promptly re-inflated to the recommended 50 psi. Mind you, this is what I've found to be true for BIAS PLY ST tires. I've also had RADIAL PLY trailer tires. Though I've seen tables posted here promoting the proportionate adjustment for them, I've also experienced the same sidesway when doing just that. I keep my radial trailer tires at max recommended (cold inflation) psi now too. I even run a pair of radials on the rear axle of my car trailer, behind a pair of bias plys. Handles great (for an 18 foot racecar on an 18 foot dovetail). This post is just my input to a good, but now locked, thread. http://www.tnttt.com/viewtopic.php?f=2&t=55770&p=1013626&hilit=tire+pressure#p1013626