Steering dampers

My Commando has TT100s on, standard 19 inch wheels, and shakes its bars at 30 mph and weaves over white lines at 80 mph.

Dave,

you need to establish that the swingarm axis is square in two planes to the steering head axis. When the swingarm is angled away from 90 deg to the steering head and there is suspension movement, the rear wheel travels through an arc which constantly changes the degree of alignment between rear wheel and frame centrelines.

It's this that causes many problems with handling. It can be a similar feeling to worn swingarm bearings. The isolastics usually get the blame but the problem is frame geometry.

I've found with 100/90 19 Road Riders on 2.5 inch rims, front and rear, the front needs changing approx. at 3,000 miles to maintain wobble free steering hands off. They then get used at the rear, which can be worn down to the wear limit with only a slight shimmy over white lines - no movement with good tread. Steering damper helps if the front tyres worn past 3,000 and also when the forks bang into mini pot holes in the road when cornering at speed.

Had similar front wheel shimmy problem at certain speeds and rates of accelerationon my Mk 3 when I had it outin Kenya even with new tyres (TT100 4.10 X 19)fittedback and front. Fitted a Norton / Triumphsteering damper which cured everything and made handling rock solid atall speeds / acceleration rates -and only needed the mildest of settings.

After shipping back to UK and a total rebuild bike handled well from the outset without trace ofweave or wobble. Possibly a properly refurbed swinging arm did the trick.

Assuming all bearings new tyres etc are good and you've still got handling problems then the frame geometry is out. Steering dampers only mask the problem. Due to production methods/quality control, some bikes are going to be worse than others.

The isolastics are not the cause of weaves and wobbles otherwise how would Peter Williams achieve what he did on the monocoque, which he states was the best handling bike he'd ridden.

As your bike weaves in a straight line then I can't see how the handling can be good around the bends, especially at 80mph. If centre of gravity is to blame then an Interstate would exhibit the same symptoms as your Fastback, as the riders mass is further back. My Interstate steers and handles fine around corners and even in a straight line.

I don't see how a steering damper is going to alter the machines centre of gravity. Not that I think centre of gravity is the problem, it's the frame geometry. Checking before assembly started is the way to go. If accurate measurements aren't made how do you know?