Total Motorcycle Community Forums

I'm thinking about starting motorcycling next spring, and I've been reading up on the subject, particularly the beginners guide on this site. I spotted a problem in the counter-steering article. Namely, the idea that gyroscopic effects are what keep a bike stable. Most of the research in this area seems to have been done on pedal bikes, but the theory should apply to motorcycles as well.

What that research says is that the gyroscopic effects of the wheels are too small compared to the total weight. This is confirmed in a paper by David E. H. Jones (PDF link), who attached a counter-rotating wheel on the front of a pedal bike, which would nullify any gyroscopic forces. He found the bike was a bit tricky to ride, but was still stable enough to be ridden with no hands. Thus, gyroscopic forces play a minor role.

It was found that the most important aspect to stability was "trail". Draw a line through the steering axis to the tip of the front wheel. Then note the point where the wheel actually touches the ground. The distance between these two points is called "trail". The larger the trail, the more stable it is. Bikes with negative trail (the steering axis hits a point behind the contact point) are very difficult to ride.

More info and references are available on Wikipedia: http://en.wikipedia.org/wiki/Bicycle_an ... e_dynamics

The counter-rotating wheel on the front of a pedal bike theory for a motorcycle has been talked about in the past and has even been tried out on a motorcycle last year as well. It does work, infact, BOTH work. The counter rotating wheel was found to be a little heavy as it's unsprung weight. But the gyroscopic effect of a motorcycle's wheels is what keeps the bike stable at speed theory is just as correct and universally accepted... but that doesn't mean we can't debate it here.

Mike

Ugh, you're thinking about it too much. Keith Code used to tell people that if you truly understand it, you can break it down to the simplest terms... in this case, that would be

push right, go right... more than that and you're over-thinking it

hi-side,

push right, go right... more than that and you're over-thinking it

You could think yourself right out of a motorcycle because by some thinking a motorcycle is not logical.

The rake and trail on a motorcycle has much more to do with "flickibility" than "stability." Now a bike with a longer trail might seem more stable to some, but that is only because it takes more control input to get an equivalent lean angle than a shorter raked bike. Conversely, a short raked bike will be able to "flick" into corners faster, but might be harder to keep perfectly upright at slower speeds.

Basic explanation but there ya go

Kellan

hi-side wrote:Ugh, you're thinking about it too much. Keith Code used to tell people that if you truly understand it, you can break it down to the simplest terms... in this case, that would be

push right, go right... more than that and you're over-thinking it

I know am I about to kill the spelling but this relates directly to Acumens razor.

Patrick

Patrick wrote:

hi-side wrote:Ugh, you're thinking about it too much. Keith Code used to tell people that if you truly understand it, you can break it down to the simplest terms... in this case, that would be

push right, go right... more than that and you're over-thinking it

I know am I about to kill the spelling but this relates directly to Acumens razor.

Patrick

You done killed it good. Occam’s Razor

..and who says ya can't learn things on the internet? Now I know what Occam's razor is ..... (I had to go look it up)

Here's a good way to actually feel the gyroscopic effect:

Remove the front wheel from a bicycle. Hold it out in front of you by the ends of the axle. Have a friend spin the wheel while you hold it. Once you get it up to a pretty spin, try to change the wheel's axis of rotation. (Tilt it side to side.)

What you'll find is that even a bicycle wheel has a good deal of stability at relatively low speeds. Now imagine how gyroscopic effect a mtorcycle wheel has - which weighs much more and rotates faster.

(An even more interesting experiment is to stand on a turntable or Lazy Susan while doiing this.)

frezik wrote:

It was found that the most important aspect to stability was "trail". Draw a line through the steering axis to the tip of the front wheel. Then note the point where the wheel actually touches the ground. The distance between these two points is called "trail". The larger the trail, the more stable it is. Bikes with negative trail (the steering axis hits a point behind the contact point) are very difficult to ride.

More info and references are available on Wikipedia: http://en.wikipedia.org/wiki/Bicycle_an ... e_dynamics

Hi frezik

The gyroscopic effect is, indeed, very small, but it is crucial to keeping the bike's centre of gravity over its contact patches and therefore to its stability.

The idea that trail is responsible for stability defies logic and experience.

Think about it.

The gyroscopic effect is created by a turning wheel. When you are rolling along on a bike with the wheels turning the bike stays easily upright because the gyroscopic effect is in play. When you come to a stop, the wheels stop turning, the gyroscopic effect ceases, and the bike becomes much less stable.

Trail is just trail; it doesn't depend on the motion of any parts. If trail were responsible for a bike's stability the bike would stay upright whether it were moving or not.

I think you just need to trust the evidence of your own eyes (not Wikipedia writers) to decide this one.

[Edit: erm... having thought about this, frezik, my comments don't make a lot of sense either. I think I missed the point about the dynamic elements of steering geometry. I've read your main article more thoroughly and think he's probably on to something. Hmmmm! Interesting.]

The Wikipedia article though, is misleading on this point and in several of the other things it says as well.

But I agree with hi-side. As interesting as it is, you'd better forget it as soon as you get on a bike. You'll never learn to ride if you have a head full of this stuff.