Steering wheel shake

[diegokid]

When driving my Cobra I get a steering wheel shake at 50 to about 57 MPH. If speeding up or down it goes away. The tires have been balanced over and over to no end. I even used an old fashioned bubble balancer to check the balance.

While in storage the car was on jackstands on the lift unless it was being moved and this shimmy was an issue before the last teardown so it hasn't been sitting on the tires for a few years.

I started checking the tires for being out of round and found one of the front tires to be out by .090 and the other front to be at .045 both are BFGs. In comparision the Kumhos on the rear are out less then .010.

[souzape]

I've had this problem with every set of Radial TA's I've ever owned. Currently run Yokohama S/Ts and have been told by a very reliable source that Cooper Cobras are exactly the same tire. The BFG experience covers at least 4 sets of tires on Vettes and my Cobra.

[spd4me]

My BFG's do the same but at 60 to 65. This was a discussion some years ago on this forum and we all decided it was due the what's called harmonic balance of objects and materials. At a certain vibration or wave lenght, materials will begin to vibrate more radically. If you've ever sat in the back of a jet plane that has the engines mounted against the rear fuselage, you can hear a distinch pattern to the vibration.
Bob

[diegokid]

Guy at church has a road force balancer, I'm taking the two in question to him tomorrow. If that fails I'm changing them.

I read the old posts on this subject.

After 23 years of flying for the USAF I can tell you this. Jet engines are a lot like tires, if there noticeabily vibrating there's something wrong, call the crew chief!

[Aggressor]

Diego - Here's a copy of a response I made in 2005 to a shimmy problem.

"My car exhibited a severe shimmy when I drove to the Unique Homecoming (2002). It occurred at around 45 MPH and got worse at speed. I had the wheels balanced only two days prior to the event so it seemed likely that balance was my problem. In Gadsden I went to a Ford quick service shop and was lucky to find a person very skilled in balancing to close tolerance. Evidently there is a spring within the centering cone on spin balance machines and if it is not removed for the larger rim/tires it will offset your balance. My wheels were tape/weight balanced on the inside as close to centerline as possible."

The tires were BFG TA's and everything was fine after that. The tires wore evenly until there was very little tread left with no balance issues.

- Aggressor

[Naumoff]

Don't drive at those speeds