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Discussion Starter #1 (Edited)
Yes motorcycles do lean into the wind by themselves I know that experentially.

I knew that gyroscopic precession was involved but didn't understand what frame geometry had to do with it. I found this explanation most helpful.

"Yes, most bikes are self-correcting. A gust causes the steering axis to translate away from the wind side. (The gyro effect of the rear wheel tends to restrain the bike's rolling more than it prevents the frame from yawing, because of the leverages involved. The frame yaws, and the steering head translates.) The contact patch, due to trail, is behind the extension of the steering axis. Therefore, in a crosswind from the left, the steering axis moves slightly to the right. The contact patch is then slightly to the left of the steering axis, meaning that the bike is steering itself to the right. This banks the bike to the left, into the crosswind.

You can take your hands off the bars entirely, and this feature works just fine."

This makes sense to me as I think about what happens in a crosswind. There is an initial slight movement downwind followed by the bike leaning into the wind. Basically the bike is counterstreering itself.

"Here's an interesting photo showing how a bike automatically leans into a 50 mph side wind blast coming out of the fans in the building at the left"

 

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I'm not sure the bike does it by itself. Ride input to compensate for the wind may come into play, otherwise the bike would accept the input and head for what ever way the wind blew.
At least that's my experience and I'm sticking to it!
I've had winds blow me and the sidecar across lanes of traffic. Without rider input, I don't think it would have compensated worth a dang. Bar Ditch time!
 

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FORUM GODFATHER.....R.I.P. PAT
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Gyroscopic precession can best be seen when stunt riders and motocrossers cross up a bike in mid air. With wheels on the ground, lean is controlled by countersteering and to a much smaller extent, side wind and body weighting. Even then it's rake and trail influencing steering when the hands are off the bars that keeps a bike stable to a much greater degree than gyroscopic precession or weight shift. The weight of the bike is much greater than the weight of the wheels. Put vertical forks on a motorcycle and you'll have a hell of a time riding it, even though the gyroscopic forces from the wheels would be unchanged.

A snow ski bike works just fine, steering like any bicycle or motorcycle without wheels.

 

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Thanks Spec! It's what I've been saying for quite a while and I think I just posted essentially the same thing the other day (but real nice to see the line
Is confirming what I've thought!

..Tom
 

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FORUM GODFATHER.....R.I.P. PAT
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The bike will right itself if an outside force hits the side, but it's mostly because the side push creates a handlebar movement so the bike countersteers itself. At about 2:45 in this video, the rider uses weight shift to create a small force to the side like a side wind might and the bike countersteers itself as a result.

 

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Discussion Starter #6 (Edited)
The bike will right itself if an outside force hits the side, but it's mostly because the side push creates a handlebar movement so the bike countersteers itself. At about 2:45 in this video, the rider uses weight shift to create a small force to the side like a side wind might and the bike countersteers itself as a result.

No.

The bike doesn't right itself if a force (wind) hits the bike. Just the opposite. The bike leans into the wind as explained.

If you think that weight shift is turning the bike in that Keith Code video uhh...
Keith goes to great lengths to prove that counter-steering is the only way a motorcycle turns at speed. He even built a bike to demonstrate that.

Motorcycle Countersteering and the No BS Bike

Why do you have to counter-steer after a certain speed? The frame geometry hasn't changed. It's the spinning wheels. They generate enough force that the rider can't turn the tire into the turn.

BTW - The ski bike turns on the ski's edges, no gyro action involved.
 

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FORUM GODFATHER.....R.I.P. PAT
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I think I'm going to leave it at the disagreement. I see doing otherwise a waste of energy for no good result.
 

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The only time a bike of mine has leaned into the wind is a dirt bike in the air when a side wind tends to push the bike away from beneath you. Next time around I would ride to the upwind side of the track, knowing that the wind will move me and the bike in the air in the direction that the wind is blowing.
On the road it always blows me in the direction the wind is going and rider input is required to counter its effect. Some of you guys must be smoking really good stuff.
and p.s. you quote an Adventure Rider forum opinion as scientific proof of your theory?:confused:
 

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The right itself force I mean is that the wind won't blow the bike over, the steering will compensate itself to keep the bike from falling over but turn in the direction of the wind induced lean as a result. I didn't mean it would compensate by keeping its line. Rider input is required to do that.
 

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Discussion Starter #11
The only time a bike of mine has leaned into the wind is a dirt bike in the air when a side wind tends to push the bike away from beneath you. Next time around I would ride to the upwind side of the track, knowing that the wind will move me and the bike in the air in the direction that the wind is blowing.
On the road it always blows me in the direction the wind is going and rider input is required to counter its effect. Some of you guys must be smoking really good stuff.
and p.s. you quote an Adventure Rider forum opinion as scientific proof of your theory?:confused:

The bike leans into the wind (by itself) and mostly goes straight if you let it.

Next time you're getting blown around in the wind try taking your left hand of the bar, right hand just resting on the grip. Bike calms right down huh? Hmm...

Both hands off the bar (in the wind) will demonstrate that the bike is indeed self correcting. Yea the bike will wander off line and need a bar input but it mostly goes straight.

I used the AVD quote because it was succinct without math! Plenty of arm chair physics students claim this and that about motorcycle behavior. Theory has to line up with reality though.
 

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Discussion Starter #12
The right itself force I mean is that the wind won't blow the bike over, the steering will compensate itself to keep the bike from falling over but turn in the direction of the wind induced lean as a result. I didn't mean it would compensate by keeping its line. Rider input is required to do that.

The faster the bike goes the more stable it is because of the spinning wheels. If you can fall off a bike without upsetting it too much it will continue to go (mostly) straight until the wheels slow to a point that the gyroscopic effect no longer comes into play. Then it falls over.

The wheel doesn't turn into the direction of the wind just the opposite. The bike counter steers itself in the wind.
 

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Spec and Pat: I think you guys are basically saying the same thing. It a combination of the steering geometry and a bit of precession going on that tries to steer the bike upright. I think it doesn't actually try and steer it upright but rather to an attitude where there is no change in yaw or roll. (On a bike yaw and roll are pretty much coupled together.) Any change in yaw or roll causes the steering geometry to try to move the wheel in a way that reduces or eliminates the yaw or roll. I suspect gyroscopic precession serves to magnify the effect, perhaps like power steering.


Do the ski-bikes will stay upright at speed if the rider gets off?
(I suspect they will.)

..Tom
 
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