It will be interesting to see how the tires work out. I like the idea of the sidewall height being shorter with the 20" rim since the tire is so narrow.
I ran a set of 325/85/16 Michelin XML's on my Dodge when I 1st built it. They where speed rated at 62mph if I remember right. Even though the weight rating was about 5000lbs per tire if I pushed them to 65-75 the tread wore VERY quickly. After a longer stretch on the highway the tread actually felt a little sticky. I tried a bunch of different air pressures but couldn't find anything that worked well for higher speed highway travel. Lower tire pressure around town seemed to be the best for ride and traction. Overall I was happy enough with them for what I paid, but they did have there limitations.
Just a few notes from a similar(ish) situation.
My experiences varied from yours a little bit, I ran the 11.00 x 20s tube type tires on my M-37 (6500 lbs), at least 4 different brands of tires, and all aggressive off road treads, and cruising on the highway at 75 in az temps. I used to run them at 30 psi (max rating around 90 to 100), they never seemed to get hot or warm, I believe one set was even a max speed of 55 mph IIRC:yikes: Tread life was decent (wonderful compared to the swampers or pitbulls I have run), the only thing lacking was rock crawling traction...
I am personally surprised that more taller but narrower tires aren't being developed again for light trucks, especially with the big rim sizes being so common.
That said, I am worried about the wear, Carlyle wore his quickly, but also had some other issues. Others report decent mileage, even on heavier earthroamers and mogs...so your speed to wear relationship may be right on the money....
Truth be told, I would've run a more traditional 37, but the width was a deal breaker for Mr C, his experiences and his terrain made the narrower width a priority. With the 20 inch beadlocks, it at least gives him some more tire options in the future also. The other thing to consider is that another set of tires is already in the planning stage, for when offroad travel isn't a necessity.
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