65 MPH vibration 83 911SC euro

I have 225X50X17 bridgestones on Etoile wheels on front and 255X40X17 Bridgestones on back. At 65MPH I get a bad vibration that diminishes at about 75 MPH. Jacked up each front to just clear the ground and spun by hand. Wheels are dead true but the tires are a little out of round. Removed wheels and checked dynamic balance. One needed .25 OZ and the other .5 OZ. But I am using stick on weights. Can anyone put some "spin" on this? What should the max runout of tire be? Should I be using plastic coated weights on rim edge? Car was in storage for 5 years. Also clecked each side for play (bearings, tie rods) and found none. 60,000 miles on car. Thanks
Afterthought: If it was the "flat spots" (which I will measure with a dial indicator to determine if it is a true flat spot or a true out of round) would it not be felt at all speeds as a thumping?

[This message has been edited by machintek (edited 12-22-2000).]

If the car was in storage for 5 years, sitting on those tires without moving for 5 years, I think you need to buy new tires. They are most likely flat spotted, which seems confirmed by your comment that they are "a little out of round"!!

The word "storage" says it all unless the car was on blocks the entire time. The tires may recover somewhat after you put a few miles on them. I had this happen to a street/drag car a few years back. With that car I just set the linelock and roasted them round again! Probably can't do that with your car though.

I too had a car instorage for way too long and had "SQUARE" tires.that dang near bounced me off the road. I bought new ones, and tossed the old. I later heard that I should have tried to run the square ones at low pressure for a while before dumping them. Anyone ever have that experience?

Our 911SC also was stored for 2 years and the Pirelli's were a bit square at first. I agree with the run them a while comment, but think you should use "normal" pressure instead of under-inflating them (which usually causes tires to run hot and can cause damage).

We have stick on weights, too, and there is a slight vibration at around 75. Is it possible this is a harmonic?

If you can put the car up on jack stands for a week or so, I suggest taking the wheels off the car, inflating them to 60 psi, and allowing them to age awhile in a warm room, the warmer the better ... 80-100 degrees F! If it was summer, you could leave them out in the sun for a few days, but winter sun won't do it, I don't think! And, I don't think you should operate them on the car at less than 24 psi, either! Don't forget to lower the pressure before putting them back on the car! You won't need to worry about having to figure out the problem with the ride ... if you happen to forget!

------------------
Warren Hall
1973 911S Targa