Twitch at 100k(60mph)

Hi All,
I have an 73,850 commando which has an 18 in rear wheel ,19 front but becomes twitchy
at this speeds .
Has had a steering damper on but no improvement.
The engine cradle has a second ISO fitted (welded) to the rear lower section
with lugs welded to the frame but no through bolt fitted.
Any ideas on the twitching and the extra Iso,
Cheers Steve

Have you investigated the iso clearances ?
Checked the swingarm for sideways play ?
Notchy steering bearings. ?
Wheels and tires all pointing straight ahead and in line ?
Rear shock absorbers (dampers) still got good damping ?
All engine and cradle bolts tight and not slopping around. ?

All things that are part of the Commando maintenance routine...

88chips said:

Hi All,
I have an 73,850 commando which has an 18 in rear wheel ,19 front but becomes twitchy
at this speeds .
Has had a steering damper on but no improvement.
The engine cradle has a second ISO fitted (welded) to the rear lower section
with lugs welded to the frame but no through bolt fitted.
Any ideas on the twitching and the extra Iso,
Cheers Steve

Click to expand...

Have you searched 'wobble' and 'weave' in the top RH search box? Could that be the 'twitch' you've experienced?
A photo of the modification/additional iso would be helpful.
Ta.

Bob Trigg once said that any single-track vehicle could be made to wobble. I would suspect tire issues.

I put up with a problem with my 750 for years. I was talking to someone on e day and he asked me what happened when I took one hand of the bars. Did it shake? When I said yes, he said its your front tyre.
I suggest you renew your front tyre, because that fixed my problem..

Actually, can you explain to us what you mean by twitchy., Mine was ok until I was doing 70 mph on big sweeping bends, then it went out of control [ might be called a tank slapper ]
Dereck

Hi 88chips.
If your 'twitch' is my 'weave', I can appreciate your problem as it is at 100kph.
My 'weave' comes in at 125kph and goes at 130kph (choosing above or below that is just fine).
Does the 'twitch' disappear at higher speeds?
Ta.

Have you tried increasing the spring pre-load on the rear shocks ? If the back of the bike is low, that changes the steering geometry (reduces trail) and the way the bike self-steers. Most bikes are set up to be stable under brakes, if you reduce the trail the bike tends to tip into corners quicker and tighten their line coming out under power. In a straight line they can wander and a become bit vague, especially if there is movement in the frame assembly. Tyre shape is another factor which can start a catastrophe if the back of the bike is too low, it sometimes only takes a longitudinal ripple in the road surface to set it off

needing said:

Have you searched 'wobble' and 'weave' in the top RH search box? Could that be the 'twitch' you've experienced?
A photo of the modification/additional iso would be helpful.
Ta.

Click to expand...

Oh no "wobble and weave" where's Hobot...could turn into a long thread.

Please mind your manners dennisgb and help get our terms straight.
A twitch is a single fast event with out repeating in cycles such as weave and wobble do. Many twitches can occur repeatedly with calm interval between them but that is not weave/wobble either. Weave & wobble can also positive feedbackits cycling into one big twitch of snatch down or fly ups but that is not weave and wobble as can easy be done instantly w/o any weavy wobble cycles. Twitchy-ness is an unpredictable series of time separated twitches that have no pattern similar to encountering storm front gusts between sem-truck blasts or rolling across a truck spill of building debris or broken up surface.

I vote with tyres too as first concern as so infamous for causing and solving mysterious disturbing behavior. MIght play with air pressure difference as has cause me twitches on slow leaks in both iso lastic Cdo and fat tire modern sports bikes. Might try 2-3 lb less in front than rear to see if settle down to easy steering some for more tyre clues. Loose or sloppy worn items as mentioned can cause an instant twitch as slack taken up then steady as she goes til another load shift takes of slack the other way then steady as she goes w/o hint of weave wobble, which is always cyclic and never instantly recovering like a twitch or twitches or twitchy-ness.

I only know of one exception to Bob Trigg rule of thumb but does not apply to any thing else, yet.

I didn't say anything...someone else said "Wobble and Weave".

I'm wobbling and weaving myself a little but it could be the Jagermeister

Carry on.

Have the headstock bearings been checked?
& I've often traced a weave down to low tyre pressure, especially at the rear.
The simple solutions are often the ones that work