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Tightening the head bearings could be just adding resistance to movement, or the same as adding in some damping, as in a friction damper. THAT is the wrong approach. The head bearings should be adjusted to where they aren't loose, or too tight.

I can't type all of the comments that I would make to ME-109 here. Far better to do it in person. I think that it would be a very interesting discussion.

The steering on my modified /6 is smooth as can be at all speeds except very high ones. I opened her up the other day during some spirited riding with a friend with a 90S.
Not trying to brag ....I passed him easily on a long straight, he was topping out at 92 and I whizzed by him at about 110mph. OK, spare me the speeches and sermons. When I reached around 114 she began to shake violently and didn't stop until I got the speed below 90.
My bags were empty, tires,forks and shocks are in good shape. My guess is tire inflation. I don't intend to drive those speeds on a regular basis, but obviously vintage racers must encounter these issues. What's the optimal inflation for high speed riding of an airhead using modern tires?

Matt, before trying anything mechanical, try riding without those "empty" bags. I've ridden the same bike both with and without bags and the aerodynamic difference was stunning, especially in a crosswind.

+1 on Tim's comments. Also, one may test for stability at a much lower speed.

On the tyre front, using modern stable tyres, I find that around 36 psi is good. High speed instability is not fun.

mattcfish wrote:The steering on my modified /6 is smooth as can be at all speeds except very high ones. I opened her up the other day during some spirited riding with a friend with a 90S.
Not trying to brag ....I passed him easily on a long straight, he was topping out at 92 and I whizzed by him at about 110mph. OK, spare me the speeches and sermons. When I reached around 114 she began to shake violently and didn't stop until I got the speed below 90.
My bags were empty, tires,forks and shocks are in good shape. My guess is tire inflation. I don't intend to drive those speeds on a regular basis, but obviously vintage racers must encounter these issues. What's the optimal inflation for high speed riding of an airhead using modern tires?

Yikes! The guy with the real crisis in this situation is the 90S "original superbike" owner whose machine tops out at 92mph. Better keep that on the down low for the benefit all of the 5-figure sellers out there . . .

khittner1 wrote:Yikes! The guy with the real crisis in this situation is the 90S "original superbike" owner whose machine tops out at 92mph. Better keep that on the down low for the benefit all of the 5-figure sellers out there . . .

Maybe it isn't tuned up properly, seems like it oughtta be able to go faster than that.

Steve in Golden wrote:

khittner1 wrote:Yikes! The guy with the real crisis in this situation is the 90S "original superbike" owner whose machine tops out at 92mph. Better keep that on the down low for the benefit all of the 5-figure sellers out there . . .

Maybe it isn't tuned up properly, seems like it oughtta be able to go faster than that.

Maybe the R90S guy has got an accurate speedo!

chasbmw wrote:

Maybe the R90S guy has got an accurate speedo!

He does. He's got a Trail Tech gauge. I think mine reads a bit slow. At his 92mph, I blew past him (mine reading 100 at that point, pulling hard and driving smooth).
I'm running 30/32 psi right now Macadams. Is the consensus to run higher for high speed stability?
I had this happen once before with full bags. Like I said, I don't run it to full speed (never reached because of shake) too often. I put some braces on the bags and I've since added a custom full fairing off a Yamaha Race bike. You'd think that would have changed thing. I do believe my previous shake was at a lower speed, so maybe I've made some progress. Will need to try without bags when the mood suits me.

mattcfish wrote:

chasbmw wrote: Maybe the R90S guy has got an accurate speedo!

He does. He's got a Trail Tech gauge. I think mine reads a bit slow. At his 92mph, I blew past him (mine reading 100 at that point, pulling hard and driving smooth).

I thought most MC speedos are optimistic and say you are going faster than you really are. Though I've noticed the one on my GS is pretty close to what the GPS says I'm doing - it usually reads 2 or 3 MPH faster than the GPS says which ain't bad.