JulianEdgar

Yesterday while rolling quickly down long empty hills I experimented with taking my hands off the steering. As others have reported, when this is done the front wheel of the Birdy instantly starts to shimmy very badly.

The movement doesn't build up - it just immediately happens. It's weird because when being controlled by two hands, the bike's front end feels immensely stable. Even with one hand off the steering, at speed the stability feels marginal.

Has anyone ever fitted a steering damper to a folding bike?

I have seen them available for normal bikes, and many motorcycles use them.

snafu21

They were a fad on motorbikes, and may still be, but on my moto, a steering damper just foobared the slow speed handing. You can try an inertial steering damper by hanging a bag of shopping from each bar end. It gives much the same result. An experiment for you.

But of course we've had this discussion before. Why would an otherwise sane bicyclist want to ride down a hill without access to brakes and steeering?

My 1990 MTB had a slightly gunked-up set of head tube bearings when I picked it up. Riding it was unpredictable at slow speeds and imprecise at faster ones. It was impossible to push the bike along with the saddle, steering by moving the bike sideways.

This was only 20 year-old grease in the bearings, nothing was too tight or loose. 26" wheels.

JulianEdgar

I think describing them as a fad on motorcycles is overstating the case. It's not my area (which is cars) but a great many very quick current motorcycles appear to have steering dampers.

snafu21

"Appear?" Based on what quantative evidence?

Au contraire: The great majority of retail sports road motorbikes of the fast 600cc and above class in the UK don't have steering dampers, though aftermarket ones are often fitted for no good reason. Harley riders in the UK add them to tuned nitrous injected Sportsters, with little effect at road speeds, as I did. My tuned Suzuki Bandit 1250 with a top speed of +140 mph didn't need a steering damper. But then I never did 140 MPH on it. My ZZR600 would hit 140 mph at Snetterton race track, with me on it, without a steering damper. The current range of road BMW, Suzuki, Yamaha and Honda motorcycles are mostly not fitted with steering dampers in the UK although some of the early heavyweight K series BMW motorbikes were. Honda have been fitting electronic steering dampers on competition-style bikes and heavyweights and they are creeping into trail-adventure and dirt bikes. but they're a still minority on the roads here. There was a fad-ish enthusiasm for retro-fitting them in the late '90's.

For normal road use, at legal speeds, most sports motorbikes are designed NOT to need one. You've got steering oscillations at typical road speeds of 80 mph, you've got a problem bike or a race geometry set up for extremely fast cornering. Race bikes are different.

Back at the bicycle factory

Why do you want to ride your bicycle downhill without hands, brakes and steering? This perhaps, is a more interesting debate. Is there a fault with the Birdy design, or are you hitting 140 mph?

JulianEdgar

Ah well, as to current (motor) bikes, you probably have got me - it's not my area. I buy ex-Yamaha R1 steering dampers and modify them to become suspension dampers on my recumbent trikes, and my eBay searches for motorbike steering dampers pop up with lots of steering dampers from late model hi-po bikes. But I am quite happy to defer to greater knowledge in this area.

Cars? Yes, well then I could argue a case. (But, perhaps agreeing with your argument's thrust, not too many steering dampers on high performance cars.)

I wonder about the Birdy's steering. I think the front suspension an excellent design but I am yet to be convinced about the steering geometry. Perhaps a steering damper would be a band-aid to cope with some intrinsic deficiency, but it would be interesting if it works. I don't ride around no-hands but it was disconcerting to see such a sudden change in steering behavior when I took my hands off.

[Footnote: do you have a link for the Honda electronic dampers?]

snafu21

I don't know about the Birdy, of course, I've never ridden one. There was a thread on here about the effects on the preffered sex when riding past no-handed.

The HESD stuff is here. Steering dampers, as far as my limited knowledge is concerned, are Prozac for aggressive steering geometry. Have you contacted Birdy?

The other notion is that riding no hands moves mass and therefore the CoG slightly rearwards. The grip of a tyre on a road surface is only Mu x R, where Mu is the co-efficient of friction between the tyre and the surface, and R is the downforce. Tyre contact area and tread design is of no concern. So, you'll see that a change in R will be, er, noticable, and less downforce = less grip. The steering geometry will also change slightly but trying to think this through with the complex Birdy front end is quite beyond the capacity of my slide rule this morning.
Armed with this, a taller tyre on the rear, pumped up to the max, might help but that would decrease the caster angle.

Taller tyre on the front?

jur

In the Birdy thread I described what I thought is the reason/mechanism for the Birdy's catastrophic instability... but It seems not worth the effort to damp the steering...

While on tour with 2 loads on the front, the steering became unstable enough that I could not exceed certain speeds or the front would oscillate slowly, with me unable to stop it except by slowing down.

PS I am glad you wrote "dampers" and not "dampeners." We wouldn't want to get wet.

snafu21

Aha! With more weight on the front, the problem gets worse.


Aha!

<scratches head>