I have an 05 MC convertible and a few months ago put on a new set of Yokohama Envigors. At about three thousand miles noticed what seemed to be a balance issue at 50+ mph. Took it in and had tires rotated and balanced. Same problem. Over the past few months the tires have been balanced and rebalanced several times with no difference. Came to realize the shudder seems to only occur while accelerating and only over 50 mph. Let off the gas and no more shudder. Accelerate and there's the shudder. The steering wheel doesn't seem to be effected, but the whole car shudders. My mechanic checked the motor mounts and seemed to be OK.

I'm open to suggestions. Thanks for any insight.

 

I'd check CV joints/ wheel bearings for looseness/wiggles