Help me stop my Catrike Shimmy!

[legrandfromage]

My first Expedition was a disaster. The frame was replaced with a redesigned steering geometry, which improved the handling from dangerous to annoying. My Exp shimmies quite a bit, which is not only irritating, but puts a lot of stress on the front end.

So, if I can't sort out the shimmy this summer I'm going to get rid of the trike. Here's my plan:

1. Fit 16" wheels. From the crude measurements I am able to make, it looks to me that 16" wheels will bring the steering geometry closer to centre-point.

2. Get some friction into the headsets. I might just superglue the bearings!

3. If the above two steps are a success, then have some metal plates welded onto the kingpins to bring the steering closer to true Ackerman compensation.

Any other ideas would be much appreciated!

legrandfromage

[devious56]

It has been proven that in some instances, the 16 inch wheels makes a big improvement with a shimmying Expedition, but keep in mind that it may not.  It will certainly improve the handling.  I ran 16's on my Expedition for over a year, and we very happy with them.

You mentioned super glueing your headsets, so I'm assuming you have bearings.  Do you know about the teflon bushings that Catrike is now putting in the headsets in place of the upper bearings?  THAT is supposed to be the solution for a shimmy.

David

[John Rooker]

Make sure that your toe in is set correctly.

If your shimmy is such that it shimmies with hands off and goes away with a relatively light touch on the bars, the Teflon bushing will pretty much eliminate it.  If it is shaking with hands on the bars, the problem may be more serious. 

[legrandfromage]

My Exp shimmies quite badly. The shaking is violent enough and frequent enough to make me worried for the longevity of my wheels even when I'm holding on tight and struggling to damp it out.

It's good news about the teflon bearing replacements. A much better way of getting some friction into the steering than glue! I will definitely be getting those! It seems that others have found that 16" wheels work well. It's a pity the trike wasn't manufactured with centre-point geometry in the first place. If these two measures work, then I may not have to fix the Ackerman compensation!

Thanks for the advice!

[John Rooker]

Are you running the OEM tires or have you made a tire change?  The Expedition seems to be more sensitive to any changes than other Catrike models.  It's interesting that some examples of the Expedition handle just fine and others act like yours is acting. 

My impression is that you know what you are doing, so here's a list of things to check..from my memory of the Catrike Expeditions wars of 2008..

Check Toe in adjustment
Check headsets for any play
Tire inflation
Stock tires? or aftermarket skinny or fat?
Check tie rod ends for any play


I think that's about it.

Good luck!

[devious56]

John gave you some very good advice, and other than what he said, I'd suggestest dropping Bruce Bunch (Trikebldr) a PM and see if you can get him involved.  He probably has more involvement, and experience with the shimmy problem than anyone, including the factory.

David

[John Rooker]

John gave you some very good advice, and other than what he said, I'd suggestest dropping Bruce Bunch (Trikebldr) a PM and see if you can get him involved.  He probably has more involvement, and experience with the shimmy problem than anyone, including the factory.

David

I second this suggestion!

Bruce made me aware of the effect of tire width on handling and they proved to be very true on my Expedition.  I had moved to 406X1.3 Conti Sport Contact tires on the front and was not happy with the overall handling.  Bruce explained why so I went back to the stock Marathon Racer 1.5's and things improved. 

[jimali]

what's the history of what's been done so far to cure your shimmy?
What year is your EXP?

John's pretty well covered the drill here:
Check Toe in adjustment
Check headsets for any play
Tire inflation
Stock tires? or aftermarket skinny or fat?
Check tie rod ends for any play

with the addition of the Teflon bushings I haven't heard of a shimmy, yet, that wasn't cured by these.

[legrandfromage]

As I mentioned, my first Exp was dangerous. Extreme shimmy and reverse brake steer! It wasn't fun at all. It was EXP 094 if I recall correctly.

After a great deal of complaining, I was sent a second frame/kingpins, which I put together myself.  This was an improvement, but the fundamental flaws remain just to a lesser degree. These are that the steering is not centre-point and is over-Ackerman compensated. Catrike clearly were aware of the problems with their early Exps, but in updating their design they  were more concerned with brake steer than shimmy. I also think they use the same kingpins throughout their range to keep costs down.

Perhaps I'd better try adding friction to the steering first and get some of those teflon bushings. Unfortunately that means dealing with Catrike...

[John Rooker]

As I mentioned, my first Exp was dangerous. Extreme shimmy and reverse brake steer! It wasn't fun at all. It was EXP 094 if I recall correctly.

After a great deal of complaining, I was sent a second frame/kingpins, which I put together myself.  This was an improvement, but the fundamental flaws remain just to a lesser degree. These are that the steering is not centre-point and is over-Ackerman compensated. Catrike clearly were aware of the problems with their early Exps, but in updating their design they  were more concerned with brake steer than shimmy. I also think they use the same kingpins throughout their range to keep costs down.

Perhaps I'd better try adding friction to the steering first and get some of those teflon bushings. Unfortunately that means dealing with Catrike...

There may be someone on this forum who has tried the Teflon bushing and gone back to the stock bearings. Maybe a set laying around anyone?

[Hipster]

I've a 2006 Expedition CTE137 ... Follow the advice above & look to your tires:

I've cured my shimmy by taking that advice, running the Teflon top bearings & installing slicks on front. My favorite is Schwalbe Kojak 1.35" x 20" - 2nd choice is Primo Comet 1.5" x 20"
3rd choice is Greenspeed Scorcher 1.5" x 20"

(I have run Schwalbe Marathon Racers & tried Big Apples - my Expedition really does not like to run with a front tire that has tread.) I think Duranos would probably work fine. (I do love Big Apples on a couple of my bikes & they work fine on my two Roads ... just not on the front of the Expedition.)

I also run 16" wheels with Schwalbe Stelvio 1.1" x 16" or Marathon 1.38" x 16" on occasion.

DO NOT RUN FAT LOWER PRESSURE TIRES ON THE FRONT OF AN EXPEDITION; That includes Schwalbe Big Apples! 

Oh yeah ... I now set toe-in at zero, with no weight on the seat.

[jimali]

In some cases the shimmy can be cured with correct toe-in and sufficient torque in the headsets.
While toe-in is generally stated as 1/16" toe-in, not all trikes like this and you need to feel out the best setting by venturing small amounts in either direction from that 1/16".
With "normal" bearings in the headsets I found that 45 to 65 inch pounds of torque was needed to cure shimmy.
Ultimately, everything needs to be "right" to cure shimmy.
The Teflon bushings are a huge step in curing chronic shimmy.
If I understand it correctly, Ackerman compensation only comes into play during turns, to reduce scrubbing, and has no affect on "straight line".

[John Rooker]

Ackerman compensation allows the inside wheel to run through a smaller arc than the outside wheel during a turn, right? 

[legrandfromage]

Just checked - I've got 051 and 084, the former is just the bare frame.

Fixing the Ackerman compensation really is just fine tuning. The main problem is the steering not being centre-point. This causes coupling of the steering with external forces in 3 ways:

1. When a wheel hits a bump it steers.
2. During steering, there is an additional displacement of the boom relative to the ground. ie. displacing the boom causes steering.
    (If the trike is steered while stationary, you can see the boom move from side to side. Alternatively, you can move the
     steering by moving the boom from side to side while stationary). This provides a good pendulum!
3. During steering the wheels actually move closer together. This was very pronounced on my first frame. What this does is store elastic energy in the tyres/wheels/frame which adds to the force due to trail that try to turn the wheels straight.


The whole system is primed to shimmy, particularly if you use an extra long boom as I do. You've got a massive pendulum which is coupled to the steering, which is coupled to road surface irregularities. The only way to stop the shimmy is with centre-point steering (which decouples the steering from bumps etc) and/or adding in enough friction to damp it out, as the bushings may do.

[John Rooker]

Does your 084 frame have the gusset on the bottom of the cruciform? I would guess that it does not.  My Expedition was 213, early 2008 and it had the gusset and supposedly had a geometry change.  It never really shimmied but the steering was relatively heavy on that trike when compared to my wife's Trail.