Tires of different sizes have different aspect ratio, i.e. a 50 series tire vs a 70 series tire which is the ratio of the tire height to the tire width. Based on a given wheel rim diameter, a 70 seies tire is taller and will have a larger rolling circumference or more inches around the tire than a 50 series.
What I'm saying is you really need to look at the rolling circumference of a given tire to see what is going to happen. The tire with the smaller circumference will have an effective "lower" axle ratio or make a better towing choice than a tire with a larger circumference. The circumference of a tire is Pi x the diameter. Pi is 3.14 and the diameter is the diameter of the thread, not the wheel.
If nothing else, you can jack up a wheel and use a cloth tape to mesure the circumference of the tire thread.
On another note, a 5000# 5er may be a bit much for a 1/2 ton truck. The pin weight of a typical 5er will run close to 20% of the trailer GVWR. In the case of your 5000# trailer, this is about 1000# in the bed of the truck. Do you have 1000# of cargo carrying capacity when loaded?
My company provided vehicle is a 2006 Ram 1500 with the 4.7L engine, 3.55 axle and 5 speed aautomatic. According to the data on the truck, it is rated to pull something like 6500#. I have pulled a utility trailer that was between 3500 and 4000# and the poor truck was suffering on the highway between San Antonio and Houston, Texas. I-10 through here is fairly flat. I managed to get a whopping 8 MPG trying to maintain between 65 and 70 MPH.
My brother had a 1500 with the 5.9L gas engine and he has a 21' TT which it is hard pressed to pull in east Texas. SInce he is looking for a larger trailer, he sold it and got a 3/4 ton Dodge diesel.
In short, you need to weigh the truck loaded fro travel (add 150# for the 5er hitch) and work with the trucks GVWR and GCWR to see what you have left over for towing.
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