Curious, but I wonder what the condition is of the steering headset bearings in the tank slappers at lower speeds? I drive 70mph no problem on our local hwys. I rebuilt the steering bearings the first thing I did to this bike when i got it and have never had that 'sloppy' feeling you get just before a tank slapper. I've had this bike up to 90mph and feels pretty steady but that is straight line only.
I guess my point is before installing a steering damper maybe install new bearings first? If it is still a problem then install the damper. But really why are any of us going that fast on public roads anyway? (flame on)
No, that's a good point, and I'm glad you made it. If your steering head bearings are shot (and I'd recommend converting the old balls to tapered rollers on any old bikes) or if your swingarm bushes or wheel bearings are clagged, tires knackered, pressures low etc, this can exacerbate the situation and bring on a speed wobble. (tank slapper, etc)
My 1979 BMW R100RS was absolutely rock stable at high speed (100 MPH +) with the standard fairing and panniers, but as soon as I took the big fairing off and mounted a BMW R90S handlebar fairing, it went into the most violent tank slapper, not helped by the short flat handlebars.
The afore-mentioned items were all in good condition, and I surmised that the change to the airflow over the bike, along with the big Krauser panniers sticking out like dogs balls caused it. I took the panniers off and tried again, and the wobble was gone. The BMW had a steering damper fitted as standard (as many European bikes of the era did also) but the damping was non-existant, so I replaced the damper and never experienced another "slapper" in the 12 years that I owned that bike.
If anyone here has a damper fitted that's been there awhile, make sure you check that the damping is still good, a statue of a steering damper won't help you if everything turns to mud............ Cheers, Terry.