DFC4S

Noticed something similar, but mine was due to tire flat spots due to the car sitting,not driven for a few weeks. Went away after ten miles on the freeway.

geolab

IMO it would be better, and sometimes cheaper, to be more talkative on the situation you are having. It should be frustrating for you not to find the solution from
the first try. If you read the answers you got, it is a variety of similar situations members
got and were given to you as alternatives. If you follow all the advices, you would change:
control arm bushings
wheel bearings
flat spot tires
wheel imbalance
"rotor vents and/or holes are clogged with dust"
Tie rods
etc.
If you could tell us more of what was it like before, how the change came, after something done
on the car or not.
In my case, I had vibration at exactly 60 mph as well. 58 mph nothing, 62mph neither.
But I had sent my wheels for full refurbish several weeks before, and had had new tires fitted.
I balanced the wheels and tires like 5 times, and nothing solved the problem.
I tied my problem to the wheels/tires because that was the only thing changed.
Finally found residual sandblast material in the hollow part of the rear wheels.
the hollow wheels are so well balanced from factory, that if you balance the wheels WITHOUT the tires, you would need a 20 grams weight exactly opposite the valve inlet. anything else, there is something in the wheels.
So from my personal experience, at exactly 100 km/h, my solution was with the rear wheels.

Academictech

This was the case on my first '97 C2S, steering wheel chatter exactly at 60 mph nothing above or below. Mentioned it to the wrench when upgrading the 17" wheels to 18", he said if it's still there after the change, probably control arm bushings but it disappeared with the new rims (996 TT's with Pilot Sports). Driving a low mile '98 C2S across the country, had it intermittently from 55mph to 65mph, always seemed to be during the first 50-60 miles or so of driving each day, that one proved to be an air imbalance. On my current '97 C2S, had it exactly at 60 mph. Changed out the Sumitomo II's that were on the car with Bridgestone Pole Positions, now she's as smooth as a baby's *** at all speeds.

trophy

Don't do 60! do 70 no more shaking

mcipseric

+1

fixedgame

Thanks all for your reply. Will look into the bushings this weekend. I vaguely remember my mechanic mentioned the deteriorating bushings when I went in for the 60k service. Need to confirm the inspection report.
I drive my car regularly so no flat spots for sure.
Tire pressures are checked also.

black ice

Slightly out of true wheels can show up as a vibration at a narrow band of speed that goes away whey you exceed it.

Just another possibility.

dave

David Schiff

once again Geolab, superbe.
ds