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FrankCrank
12-07-2014, 11:38 PM
....since completing the mk2 trike ages ago, it's only recently I've had a chance to get out there and do some proper rides. One annoying thing is it has a shimmy, and since I'd got the centre point steering spot on and used decent headset bearings, I was a little disappointed.

On the mk1 the shimmy sorted itself out after a few months as the cheapo bearings quickly became notched and indexed - neither one is desirable, but learned to live with it.

Did a bit more reading on shimmy, and always seems inconclusive as to cause, and how to fix the problem. One suggestion was adding O-rings under the headset top cap, thus creating a certain amount of stiction, and hopefully stopping the shimmy. One thing that will stop the shimmy is applying a lot of pre-load to the bearings, but this will only hasten the notch y steering effect, so not really a viable option.

The idea of adding some stiction made sense to me, so I tried a variation on this (too lazy to get o-rings). Put some rubber washers on the steering ball joints, went for a long test ride, and success - shimmy has dissapeared. The theory of adding some stiction seems to be a good one. The steering is only a tad heavier than before, hardly noticeable really, and I'm a happy bunny again.

Anyways, may be of use to others, and here's a pic:

http://s29.postimg.org/4okm2unnn/IMG_1390.jpg (http://postimg.org/image/4okm2unnn/)

sandman
12-08-2014, 04:27 PM
Hi Frank,
Are you sure its real shimmy or just the way you roll your "R's" haha

DannyC
12-08-2014, 06:06 PM
Hi Frank,

Interesting!
The Canon-ball express has developed a shimmy (that it never had before) ever since our Zombie-fest in the late Summer.
On some fast stretches of routes I find it really disconcerting if not dangerous.
I shall try your tip(s) as above) to see if they help.

Thanks! :-)

Twinkle
12-08-2014, 06:08 PM
Frank

That is an interesting way to build in a steering damper , I will try it out on mine and report back once the washers have arrived .


regards emma

FrankCrank
12-08-2014, 08:01 PM
...worth noting here, Catrike had shimmy issues on their trikes some time back, and resorted to teflon bushings replacing the upper headset bearings. This cured the problem, and again I think the key thing is adding some resistance/stiction into the steering system....

FrankCrank
12-08-2014, 08:11 PM
Danny, I suspect that as your headset bearings have bedded in over time they've loosened up enough to allow a shimmy to develop. Applying more preload will no doubt stop the shimmy in the short term, but notching/indexing will be evident after a while.

Better to play safe I think, and leave the bearings with a light preload, and add in some resistance to counter the shimmy. Anyways, we're not alone - quick look on google shows it's a fairly common occurrence on tadpole trikes.....

Twinkle
12-09-2014, 04:25 AM
Over the past little while I think that some of this shimmying is due to out of balance front wheels , I experienced it since the change of front tyres .

It is mild at low speed but hands off at 15 -20 mph the front wheels will develop a real shake but will stop immediately a finger is placed on the bars .

Balancing the front wheels would be another option as I think this could really be the problem .

The damper is only a means to an end !!!! ..:confused:

regards emma

Ticktock
12-09-2014, 07:37 PM
Based on car experience, the first thing I do with any front end shake or vibration is to balance the wheels--so I don't see why it should be any different with a trike, as the wheel revs are about the same . Most car problems develop around 60 to 80kph on much larger wheels.

Steve G

FrankCrank
12-09-2014, 08:23 PM
....agreed, a damper is not actually fixing the problem, only masking it. The wheels out of balance idea is a good one, but how do you go about balancing a bicycle wheel? - would like to give it a try.....

FrankCrank
12-09-2014, 09:29 PM
....just done a google to try and answer my own question - easy enough to balance a bike wheel - add some solder wire round a spoke as counter weight until the wheel stops randomly, rather than just in one spot (valve stem down).

Suspect this would remedy a high speed wobble, but as I'm a plodder and get shimmy at very low speeds, might not be the cure - but worth elimination.

One theory I have is that it's more of a pendulum effect. The stem and bars point rearwards, and the Akerman arms and connecting rods also. All this one-sided weight may be causing the wobble to set in as soon as it receives the nudge it needs start if off.

So, what if the Akerman steering stuff was all pointing forward instead, would that balance things up and stop the shimmy?

My brain aches now - must have a cuppa and think about something else .............