I have about 30K on a set of Michelin X Radials that I keep inflated to 35psi.
I drive smooth roads and just had the tires rotated for the second time since I bought them (just because they have no signs of wear on them). I drove to Daytona Beach (2 hr drive) on I-95 and noticed that between 70 and 75 mph there was somewhat of a severe vibration at the steering wheel that would make my hands numb after about 5 minutes. Above 75 it was much less, below 70, it was better. Of course, my right foot wanted to be at the vibration speed. At all other speeds all is well. Any suggestions as to what may be causing this?

Thanks
--
'86 sedan with 425,000 miles on the original engine and automatic transmission

Youve solved it but I'll add this comment in case someone else reads:

last year by 91 started doing this at 55-60. I rotated and balanced tires, greased the carrier bearing, checked all bushings, .... same thing. And it was intermittent & inconsistent: not driving time, temp, .... dependent.

Turned out that one caliper piston was sticking, heating the rotor and causing a shimmy. I replaced the caliper and that was it.

It wasn't associated with braking, turning, speed, ... so I assumed that if I braked in certain conditions (on a bump, while turning, who knows) the caliper would stick and hold the pad against the rotor in one spot. Then perhaps bumps would jar it back.
--
240s: 2 drivers and some parts cars

I took the car back to have the tires rebalanced again and the technician said all looked good. When I got up on the interstate this morning, I got it up to 80mph and all was nice and smooth. So I'm ready for another long trip without my hands going numb.
--
'86 sedan with 425,000 miles on the original engine and automatic transmission

Usually a tire balancing problem or internal tire flaw. Could be a minor "flat" spot on a rim where you hit a major pothole in the past. If this tire was always on the back before you may not have noticed. Seems the front amplifies either of these problems.
Could also be a bad suspension bushing or engine mount - but I would think either of these would show up a lower speeds.

Mark