Different size steer tires?
 

I was running across I-10 into Texas yesterday with a friend. We fueled up in Orange, TX and I noticed his left steer tire was so low that it was nearly on the rim. The thing had gone from 110 to 35 PSI in less than a few hours. Called the company, they told him to take it into the Petro in Beaumont, TX. We get there, and they don't have another tire in the same size, which is a 275/80R22.5. So they put an 11R22.5 on there, and insist that it's the same thing...but the truck doesn't sit level anymore.

So I get on Michelin's website, and discover there's a 1.5" difference in overall diameter between the new tire and the right side tire. I know this isn't good, and I told him he should make sure that gets corrected ASAP.

Would this be a DOT violation if discovered? I know they will wear horribly unevenly, but is it likely to affect handling?

They should have replaced both. I'm not sure about the US dot regs but here in Canada mismatched sizes on the steer are not allowed. I'm digging around trying to find it in the US regs but haven't yet.