Kinda figured all that in and to me, trailer tires take more abuse and what not. Seems like to me, when you make a sharp turn at slow speed, they are getting a lot of side loading on them. I have a buddy that has a triple axle rig and is always killing his tires (shreds them) but I'm thinking that since he has a small area to park it in, he's jack knifing the trailer a lot. Matter of fact, I know he's jack knifing it. I have plenty of room and don't put my trailers in turns where it's more than 45 degrees truck to trailer. Now I've run passenger car tires on my open flat bed with excellent results but at the most, the weight doesn't exceed 4200 lbs loaded. My enclosed trailer weighs 4500 lbs empty! On the speed deal, the trailer sees what the truck sees so if the speed limit is 75, that's what it's going to go....at least that's what I've been doing for years with my open trailer but may have to slow down a bit with the heavier enclosed rig when I start pulling it....