Rim/tire width

[CapriRacer]

Originally Posted by skyking

Thanks for that. I have a question to pose:
I am building a 5th wheel trailer with (2) 2000 pound rated axles, and the common tire size in that situation is ST175/80R-13, with a 24.1" dia. 23.2" loaded height, 1360 LB capacity. I have planned around the ~23.2" loaded height. Other design factors require that I keep the diameter around this value.
I can't find any resistance data on these tires.......

And you won't. Aside from the fact that finding RR on regular passenger car tires is difficult and complicated, ST tires (like LT tires) are largely exempt from the regulations that apply to passenger car tires - so they are proportionally ignored by the folks that are interested in such things.

Originally Posted by skyking

.........The super low crr bridgestone b381's are available in a 185/70R14 with a similar diameter and a 1200 pound capacity.
The trailer's planned load values are closer to 900 pounds per tire, about a 10% cushion below axle rating.
So this tire is slightly wider, but has a lower aspect ratio. Any thoughts? Are trailer tires low crr to begin with?

One quirk that you are not aware of is that Passenger car tires have to be derated 10% if used on a truck or a trailer. So the load carrying capacity would be 1200/1.1 = 1090 (or about a 21% reserve capacity)

But be careful. These things have a way of growing out of hand. I wouldn't be surprised if that 900# load turns into a 1,00# load pretty quickly.

[skyking]

Thanks. I'll not derail the thread further, but I am weighing the trailer as I build it. The torsion half axle sizes jump from 2000 to 3500. torsion axles perform best when loaded near design capacity; a lightly loaded torsion axle is a rough riding one.