Recumbent Trike - Shimmy

Commuter_2000

Hi,

I've got a Catrike Expedition recumbent trike with the long boom, and I'm finding that when I approach 20-25 MPH that I get a really bad shimmy and have to slow down.

When I purchased the trike nearly a year ago I discussed the problem that I experienced on a demonstrator, and so the front tyres were replaced with low-profile tyres prior to delivery (Schwalbe Marathon rather than Big Apple), which did help, but the problem appears to still exist.

I'm quite tall (6ft 4") which apparently doesn't help this situation.

What causes this phenomena, and what can I do to alieviate it? It is mainly a problem when riding down hill or have a good tail wind as I can get moving. I find I can only average around 10-12 MPH on the flat and I don't find the shimmy to be a problem at this speed.

I did wonder - do the wheels need balancing like on a car? Is it vibration-induced, hence why it occurs at higher speeds??

Anyone know how to check the toe-in on these trikes, too? I think I need to spend a couple of hours and just go over it to make sure everything is OK!

Best regards,
Commuter_2000.

Cunobelin

Much discussion on his subject here:

http://p073.ezboard.com/bcatrike

Causes are attributed from loose spokes, untrue wheels, differing tyre pressures, tyres, loose headset, pedalling style, and a host of other reasons. There is even a suspicion that the headset angles on the Expedition have been tweaked to solve this problem.

Catrike have actually introduced a tool for this dark art of toeing in. (http://www.catrike.com/calibro.html) A self built version from a cheap telescopic washin line support will work as well I think. Full instructions on altering toe-in are on this page.



There is some controversy over the level of toe-in or whether in fact toe-out is the answer.


Mine was terrible for this when I first bought it, but in my case Ian made a few modifications including the tyre change you mentioned and cured the problem. I have now been in excess of 45 mph with no shimmy. Given the care which Ian takes with etting u p these trikes, this would give some credence to the rider size and pedalling style being a factor.


! have also tightened up the headsets a couple of times as the star fangled washer seems to be slipping.

My Expedition runs on highly inflated Marathon Plus (balanced pressure) and a monthly check on play in the headsets - I am about to replace the headset washer with a Hope Head Doctor to see if this improves things.

Where are you geographically - it may be worth ringing Ian to have a chat.[/img]

Commuter_2000

Hi,

Thanks for the reply!

I talked with Ian regarding the Shimmy prior to purchase, and he could only really attribute it to my height and the tyres (hence the Marathon slicks on the front).

Do you find a higher or lower tyre pressure helps to reduce shimmy?

Is there a specific torque the headset wants tightening to? I'm concerned I might break something.

Toe-in or toe-out? Great question!! Trial and error??? I certainly don't want to alter this unless I really have to.

Best regards,
Commuter_2000.

Cunobelin

I run mine at 90 PSI all round, and always check that the front are "matched.

One thing I still find though is surface is a cause. On my commute there is one road where hands on is essential and another where hands off at full acceleration is possible.

Might be worthwhile either posting on the Catrike board where the expertise lies.

Tdr1nka

I found I'd get anything from a shimmy to a fish tail in the first month on my KMX.

As I got used to the ride I soon found it was all in the pedalling and riding position.
Now I sit up a bit more and I'm used to holding my legs and knees straight,(my knees did some funny things with no cross bar to stop them getting at each other!)and the shimmy has now gone!

T x