How many miles do you get out of your good tires?

My tires are closing in on 4 years old and might have 10k on them and I had a blowout yesterday. They have a ton of tread on them. Not a huge load, no water or fuel, only our Rhino in it. These tires have lasted longer than any of the others i have had, they are E rated, i have not heard of G rated before. Can you get those in a ST225/75/15? Even though these have been good I am tired of blowouts, this one tore up my trailer a bit...