High speed weave

[AndyM]

Went for a ride this weekend, ~3500 miles in five days, on my 03 Tiger. Bike was loaded to the gills, tankbag, Givi topcase, aux gas tank, Triumph panniers. On the way out it would start to weave at speeds of 95+. Not head shake, felt more like it came from the back. More pronounced if I chopped the throttle to slow back down. Rally scary when it happened.
After I got where I was going I cranked up the settings on the rear shock and that seemed to settle it a bit, at least up to 105 or so. The roads I was riding were perfect for cruising at 100+ and I was limited by the bike.
Any ideas what would cause this?

[Bixxer Bob]

Inadvertently introduced a weave problem on my Blackbird after setting the new rear shock too soft.  Cranked up the pre-load and damping and no more weave.

If it doesn't weave when not loaded to the gills that's a clue - you need more spring compression and more damping when it is, although on the Tigger that's a big call.  Mine's almost at the max with just me on it in order to make it handle the way I like,  and I only weigh 170lbs