Looking at new tires and I know most go with a 12.5 tire on 17s. What are the thoughts of going skinnier like 255x85x17 (35x10x17)?

 

I prefer 13.5 wide in rocks

 

NOT knowing your use; you might benefit from this video:

 

Mainly used on forest service roads. No rock crawling.

 

Very good article on tire witdth!

 

Go with the most narrow with the most height. So 255 with 85 sidewall is a good combo with what you describe as use. Benefits of narrow = may not need offset wheels (think reduced issues of DW and clearance), better fuel mileage, less unsprung weight, taller tires get better pumpkin clearance, and possibly can go C rated tires for better ride. I run 285/75-17 C rated Toyos and so far are not disappointed. But as zimm17 points out for serious rock work the wider tires are better which I agree with.