Wobble Testing

Thanks for doing this web site all these years. Every so often I think about selling my 87 VR, but my wife objects strongly, so we keep on mainatining it. It has all the usual problems, cracked plastic parts, spongy brakes, and a wobble that lurks in the realm of possibility.  I read with interest the articles on speed wobbles, and found that several people did more or less what I have done, fork brace, the best and newest tire possible on the rear (and front), correct tire and suspension pressures, properly torqued swing arm.
I had 3 separate rounds adjusting the steering head bearings, and found that for my bike and me (230 lbs.) and sometimes my wife, when setting the tension on the head bearings, it's better to err on the tightish side. A very small tweak on the nut made all the difference. The wobble has disappeared for many thousands of miles. One must be careful here, as others have noted, not to overtighten, because that can damage the races.
During the "wobbling" period, I researched the Engineering library at the Univ. of Tx. for technical descriptions of the dynamics of single track vehicles, finding little information in this country, and more in European publications, particularly in the Netherlands. One research team went so far as to instrument a robot-driven motorcycle. It was supported in a frame while at rest. The whole rig was towed behind a truck which carried the instrument field. As the rig got up to a stable speed, the bike was released from constraint inside the cage, so it was dynamically on its own, and travelling the same speed as the rig.
By varying loads, bearing tensions, tires, and terrain, the team developed an a priori theory of oscillations for that machine (a BMW boxer c. 1968). What's interesting is that it never goes away entirely, just changes the place where it occurs. As another engineer friend of mine put it, "all single track vehicles have modal resonance points where the oscillations will tend to strengthen rather than weaken, unless some force is applied to damp them out."
Whatever I did to the machine, the "wobbling" type of oscillation appears to reside in a speed regime where I never go, and that's fine with me.....Frank Ray

Last update: 03:30 PM Sunday, September 26, 2004

• Adding Grease Zerks to Early 1st Gen Ventures
• FORK REBUILDING FOR DUMMIES
• SuperBrace Discussion
• Progressive Fork Spring Replacement
• 83-85 Shop Manual Misprint - AntiDive Adjustment
• Loose Damping Bars
• Anti-dive Systems Clarified
• Changing Fork Seals
• Upgrading Rear Shocks
• Progressive Suspension Rear Shock Part No.
• Get That Superbrace!
• CLASS System Overhaul
• Removing The CLASS System
• Suspension Controller Fix
• Air Suspension Woes
• Poor Handling
• Fixing The Wobble