105 mph shimmy

[Daiku]

Greetings mates,  I was on a small road trip over Labor Holiday here in the US and found myself with open highway going through Tennessee.  I had my 06 Girly loaded up with gear in the oem bags and my 47 litre Givi top case with some extras.  As I crossed over the ton the bike began to develop a very predictable shimmy on the open highway.  It would snake down the road weaving ever so slightly from left to right.  I took it up to a constant 105 mph indicated and it did the same.  I took it up to 110 mph and it started to get less predictable in its behaviour so I backed it back down to 90 and it tracked straight once again.  I'm running a tall and wide CBailey windscreen for what its worth with relatively new Michellin Pilot Road tires.

Curious as to anyone's opinions on why this happened?

Luggage?
Aerodynamics?
Alignment?

[Timbox2]

There could be any number of things contributing to what your describing but the main thing will be that you have overloaded the bike and the shock cant handle it. Have you got the shock on max preload and damping?  I would ditch the panniers anyway if you are regularly wanting to do those sort of speeds and get a decent shock built to your weight etc. My old Cast wheel Tiger and my current spoke wheel would do exactly the same as yours until I put a Wilbers on them. I still wouldnt be trying to do 3 figure speeds with panniers anyway.

PS: as an aside Triumph say not to exceed 80 with luggage, they also found out the hard way

[Chris Canning]

What he said you could bet your house on it 

In laymans term your down at the back and up at the front hence you are on a Triumph Tiger Chopper

[Sin_Tiger]

  tail wagging the dog.

[Nick Calne]

tail wagging the dog.

Tail wagging the cat...

[Daiku]

Thanks all.  The "shimmy" was like a perfect and predictable sine wave running down the highway.  I make sure the oem rear shock was fully adjusted for maximum load prior to departing on the trip.  Being one who likes to travel on my bike and do so at open speeds on open roads, a Wilbur shock and RaceTech front fork kit may be coming my way sooner rather than later.

I took six hours of country roads to arrive at my destination (and enjoyed every minute) and was returning on open highway racing sunset.  A dose of patience on my behalf (when travelling) doesn't cost nearly as much as a well tuned suspension but is a lot less fun.

Also, H/T to Timbox2 re: Triumph's own warning to top out at 80 mph with panniers.  I should've known better, fully loaded.