17.5 Tire Upgrade Help! Speed Rating J?

I am in the process of purchasing a 40 ft flatbed trailer ( bigtex 22 gn) and the dealership talked me into the beefer 17.5 tire upgrade, with a load rating of h. sounded good to me at the time, but.......

from what i have found online, all of the st 17.5 tires have a j speed rating or slower, does that mean that i am limited to 62 miles per hour???

are j speed rated tires even worth having considering most highway speeds are70, 75 miles per hour?

is it even allowed by dot?

or should i have gone with a g load rated tire for otr trucking??

please help!!!!

This probably isn't the best place to ask such questions because it's a forum mostly for beginner drivers who drive company equipment. That said, I think you are confusing "speed rating" with "load range" because they both use some of the same letters. Search for info on load range h and j. As for max speed, one article I found says that all north american tires are at least L speed range which is 75mph. I think by getting tires with a higher load range you have increased the weigh you can have on those axles (as far as tire rating anyway, you still have to comply with any load limits for roads you drive on of course).