This is one person’s opinion about tires, but the opinion is shared by many owners.
I have used Michelin LT tires on several vehicles in 30 years of RVing. They have never given me any trouble. They can last for 60,000 miles. I would not consider any other brand.
The size used for the E450 is 225/75R/16 Load range E.
I like the LTX M/S, an all weather tire with the best fuel economy and comfort rating of any tire in the class. Some folks want more sidewall protection and get the ribbed version, but ride comfort drops.
Most people consider 5 years the max life for a tire, no matter how much tread is left.
Your tires will last longer if you weigh your rig and follow the Michelin inflation pressure for the weight on each axle. The max inflation pressure stamped on your tire is NOT the correct pressure – unless your axle weigh requires it.