Roubaix shimmy

[PJ520]

My Specialized Roubaix, 2007 or so, vintage is bog standard with a Cane Creek headset. It develops a severe shimmy when coasting downhill at about 40 mph, I can feel it starting from 33 mph or so. An article in the latest Bicycle Quarterly (p. 80) on a bike they are testing mentions that Chris King headsets are prone to shimmy and this can be fixed by using a needle bearing headset. Would it be worth trying a different headset on my bike? For all I know Cane Creek may be needle bearing but I'm sure it isn't top of the line kit.

I can tame the shimmy by clamping the top tube with my knees but they first time it happened I had the heebyjeebies. And it would be nice not to have shimmy at all.

[reohn2]

It would be worth regeasing or replacing the headset bearings,if the races have become brindled that could cause it.
Front wheel bearings?
I'd also check the front tyre and experiment with a different one and or different tyre pressures,I once had a bike that would shimmy on a certain tyre a change of tyre sortied it.

[Brucey]

your cane creek headset is likely to have industry standard quality ball bearings in it, like 99% of decent quality bikes these days. I very much doubt that your headset is contributing to the shimmy in any way. The shimmy is most likely arising because of some problem in the frame, the fork, the wheels, the weight distribution.

Sometimes using a roller bearing headset can reduce a shimmy, regardless of its cause. It does this by damping the steering motion. I personally dislike the feel of roller bearing headsets for this same reason. IME they need an excessive preload in order not to rattle on bad roads and if there is the slightest problem with the bearings they start to bind somewhat if the preload is enough to prevent rattles. Other folk say they don't notice these things or don't mind them.

You may not even be able to source a roller bearing headset to fit your bike, so don't get too excited about the prospect of fitting one.

in any event I'd be inclined to check the rest of the parts for faults first, check with other owners if they have experienced the same thing or not, try different wheels, that kind of thing.

cheers

[NATURAL ANKLING]

Hi,
Tank Slap on motorcycles, scary at that speed and you cant physically keep your hands on the bars
Normally above case is worn rear tyre / badly set up suspension AND wheels out of line

As suggested tyres, worth checking wheels are in line.

[Samuel D]

Does Bicycle Quarterly say why Chris King headsets may be prone to shimmy?

[Valbrona]

Are you riding with a few inches of spacers under your stem?

[PJ520]

Does Bicycle Quarterly say why Chris King headsets may be prone to shimmy?

"For this test I assembled the Mule with a Chris King headset which in our experience exacerbates any tendency to shimmy. (We have "cured" the shimmy on many bikes simply by replacing Chris King headset with a needle bearing headset)"

Is all Jan Heine says on the subject. The quotes around "cured" are Heine's. No mention of a brand of needle roller bearing headset. I'm going to put mudguards on which may change the dynamics for the better (or not).

[mig]

the bike has always done this? or just started?

[PJ520]

the bike has always done this? or just started?

Hard to say; it's done it for quite some time. I don't often get up to 40 mph and after my experience when I did I've avoided high speeds. I took it to my LBS after the bad shimmy and he could find nothing wrong.

I usually ride my trusty Trek 520 which did require a new headset after 45K miles. But after getting left behind on a club ride I'd like to start riding the Roubaix on such rides. The Trek at 38 lbs is a bit on the heavy side for keeping up on the hilly terrain round here. The R has about 6K on it. I think I'll try different tyres.

Thanks everyone for your replies

[gregoryoftours]

What type of ck headset do you have? I wonder if the chris king issue happens with only the old type of ck headset where the steerer is held centrally in the bearing cap with an o-ring, or if it also happens with the newer griplock split ring design that everyone else uses in their headsets. There were threads about steerers becoming quite deeply scored when the old type of headset had been used for a while, suggesting that the steerer moved about a bit not just turned, if this was the case maybe the unusual movement/vibration of the steerer could contribute to speed shimmy. If you do have the old type you can buy a griplock bearing cap to convert it, might be worth a try although not cheap, of course.

http://www.winstanleysbikes.co.uk/produ ... tAod520AqA

[Brucey]

OP does not have a CK headset.

BQ's use of one in their tests is little more than coincidence in that a CK headset (in good condition) works very much like lots of others, perhaps with less seal drag than some. In fact if I wrote for BQ there is no way I'd ever publish a statement like 'exacerbates shimmy' in relation to a specific type of headset not least because I wouldn't want to be sued by the makers of that headset....

I'd choose words like 'no intrinsic friction/damping' instead. This is a neutral statement. On most decent bikes (that don't shimmy in normal use) you don't want any friction/damping in the steering; if you have any, it just makes the steering feel terrible (all the time) and makes riding no-hands somewhat fraught too.

IMHO if you take a bike that shimmys badly in normal use and 'fix it' using a roller bearing headset then it is a case of two wrongs (sort of) making a right.

Note that any bike will have a critical speed at which it can be provoked to shimmy but this normally requires that you unload the steering and take your hands off the bars etc to allow it to start. If it starts during normal riding (i.e. hands on) I'd argue that there is a serious fault of some kind; normally the hands supply more than enough damping. A favourite cause for unprovoked shimmy is a wheel/tyre (usually front but can be rear) that has swash in it, and/or simply isn't laterally stiff enough for some reason.

cheers

[gregoryoftours]

OP does not have a CK headset.

Oh yes, I didn't read that properly at all!
I'm not familiar with 'swash' - If a wheel has swash does it mean that it's laterally out of true ie laterally uneven, or can it also be a wheel that's true but dished incorrectly so isn't running in a line with the other wheel?

[Brucey]

By 'swash' do you mean the wheel/tyre being laterally out of true?

yep. Possibly this is a poor use of English on my part!

BTW I meant to say before but I have had a bike that shook enough to cause shimmy all because one of the tyres was badly manufactured; the tyre looked fine until you rode on it, and whenever the bad part of the tyre saw a load, it deformed sideways. Very odd indeed; it felt like a really badly buckled wheel to ride on, but when you spun the wheel round, there was nothing to see.

cheers

[gregoryoftours]

Ah you already answered my question, thank you. That tyre deformation sounds pretty alarming. I am pretty sure I had an experience with shimmy induced by my hands once - I'm not quite sure I'm remembering right but I think it happened when I was gripping the bars quite tight, and it was some butterfly bars which in conjunction with a too short stem made the effective stem length 0, so the steering was really twitchy. I had to really loosen my grip to let the bike calm itself back down. I think I've remembered that right.