Steve-
There are 3 aspects to vibration with rear mounts.
The first one, actual engine vibration, is negligible, the axle mounted brace really absorbs any vibration, and the noise is behind you.
The second part involves the front strap. In the Ozarks I hit a pothole and the brace snapped at the hole where it curves and attaches to the fender support. GEBE started using a heavier gauge metal for the straps this year, and as "insurance" I put a long, heavy duty zip tie from the engine bracket to the fender support.
When I started last year, the first bikes I used were those $100 Wal-Mart Avalons, where the front strap attached under the shock. I'd tap a hole, use a little lock-tite, I never had a problem with that set up.
The third type of vibration involves the belt
IF the ring is not "true and centered". Once I switched to 12 gauge Workman wheels, broken and bent spokes were a thing of the past, PLUS when I snapped the ring on, the thing WILL NOT MOVE.
The trick is put a little liquid soap or vegetable oil in the notches, snap in the 12 o'clock and 6 o'clock positions, MEASURE. Then snap in 3 and 9 o'clock, MEASURE.
If you have these 4 spots equal (use a caliper, protractor, or I made some plastic gap wedges), THE TENSION ARM WILL BARELY MOVE. That prevents the tension arm from springing open, or seldom anyway. It adds to the belt performance to make sure the ring snaps on true.
BTW- before this forum, the only place I found talking about rear mounts was here:
http://lee.org/blog/archives/2005/08/10/motorized-bicycle
The discussion really deteriorates at the end, it's pretty funny when they talk about the death trap this kid built for $25.
