Not sure what you mean "relative to the weight".... I put 34 psi in. The max load is 35. I don't carry that much crap in my car .....YET.... In 3 weeks I'm going from Mobile AL. to Port Angeles WA. In my 89, 244.

The main things I have noticed about these tires are: little to zero road noise. Steering seems smoother. Don't feel the bumps in the road as much,(I have poly's all-around).

Right now ( I've only had them for a week) for the price it is a great tire. I don't think you can go wrong with a Michelin.....except for the Allegro....I haven't heard good things about them.

As far as I know the width of the tire doesn't make your speedometer chance readings. Its the height of the tire from rim to tread. If you have 15 in. wheels then you may want to go with 60 or 65's R15. To Make up for the extra wheel diameter.

There are plenty of people on the board that know a heck of alot more than I on the tire issue. either do a search or post a new question. However everyone likes to talk tires, so get ready for alot of different replies.

Good Luck