Wheel Balancing & Tire issue

[Ed Raabe]

Hi All I have a pronounced shaking at 65 MPH
I have had the wheels road force balanced, the suspension tightened and front wheels aligned with no improvement. The shaking seems to be coming from the wheels not the drivetrain (its not vibration)
I have stock wheels and Firestone replica bias ply tires
The tires' sidewalls seem to be misshaped in and out by about 1/4 in. as the rotate them so they appear to wobble as observed driving down the road. NOT the wheels as they are fine. I hope I have described the issue properly. Ed R

 

[HeadacheGuy]

I am a mechanic but not a tire guy but I have to chase shake and vibration issues on a weekly basis so bear with me. Shake and vibration are pretty closly related so a little more info may be needed. When it shakes does it change AT all when letting off on the gas pedal instantly or does it stay the same until you reduce it to a lower speed gradually? If it changes when the load is taken off instantly you are chasing a drivetrain problem and not the tires or wheels. Choices here are tight or loose u-joint (one sticking in a plane may not be evident unless you pull the driveshaft and feel it), loose pinion in the differential , or something like a bad rear transmission mount. if your problem is the latter and you have to get rid of the shake by reducing to a lower speed and it gradually goes away you are back to wheel, tire OR unbalanced driveshaft. If you jack the car up you want to spin the tires and look for side to side runout and especially up and down runout . if you have it on a hoist (preferable) run it in drive and watch the rear wheels. The catch here is that a tire can be balanced with runout and tire shops miss this. I have seen customers have tries balanced that where badly cupped and the tire guys never said anything to them. Also do you feel it in the steering wheel? If yes or know it gives you a direction if you are chasing backs or fronts. The important point here is little to no up and down runout. The tire needs to be round. Sighting the tread when spinning will tell you side to side runout. Sorry for the long post but I feel for you. These can be hard to chase.

 

[Ed Raabe]

Thanks I will try another test run, but I believe I have tested the Drivetrain using the method you described and discounted it. I took it to the shop and the Mechanic found the front & rear suspension loose! He said he went over everything but could only test drive up to 55mph. This issue starts around 62 and at 67 it is really bad and then smooth out a little over that, but no "fun " to drive.
The tire shop rotated the tries on the rims to reduce the amount of weights on the wheels and told me they are round "true" but I found a 1/4" difference in the sidewall run out when I spin the wheels top to bottom, but the tread seems straight as an arrow! The rims seem OK
3 of the 4 tires look like they wobble going down the road!

 

[paul2748]

Can you get another set of tires and rims to make a test on? If it's ok with the test set, then definitely your rims and/or your tires.

Did you check side run-out on the rims? Are they straight?

Is this for a Concours car? if not, I suggest radials if the rims check out.

 

[Ed Raabe]

Thanks Paul that is the next step I can pull the wheels off my Edsel and take a run with those. The wheel was straight but tire tire sidewall was warped. Will keep you up dated. Ed