Making tight turns - Page 2 - Suzuki Burgman Forum
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post #11 of 20 (permalink) Old 11-12-2015, 07:30 AM
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Does that look like a castor img wheel or like a rock steady gyroscope ?
Do you mean the caster angle? If so my answer will be both of them.
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post #12 of 20 (permalink) Old 11-12-2015, 07:39 AM
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Gyroscopic effects would prevent a tank slapper by holding the front wheel still
Actually the gyroscope is causing it because of rider mistake and make it worse by applying more force on the handle bars or due to lose of traction on the road, for that reason i said it's a side effect.
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post #13 of 20 (permalink) Old 11-12-2015, 07:46 AM
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"Gyroscopic affects have almost no influence, the bikes geometry and having constant smooth inputs are what make feathering the brake work. "

Totally agree at slow speed (the subject of this thread) ... pretty much disagree at higher speed. The primary forces behind the transition from regular steering at slow speed to counter steering at higher speeds are gyroscopic forces. Certainly there are other factors that are in play, including the bike's design, but gyroscopic affects do have a significant influence on how the bike handles as speed increases.

A simple illustration ... take a wheel off anything you have (a bicycle, a wheel barrow, etc.) and put an axle through the hub. Holding both sides of the hub with each hand, it's easy to move the wheel around when it's not spinning. Start the wheel spinning, and you'll see very quickly the effect of gyroscopic forces.
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post #14 of 20 (permalink) Old 11-12-2015, 08:07 AM
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A spinning wheel can even balance itself on one single end of the axle while the other one is free in the air.
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post #15 of 20 (permalink) Old 11-12-2015, 08:11 AM
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A spinning wheel is hard to disturb using the hub, yes - but that is because you only have a 1 inch lever, not because the force is large.
Multiply your lever by 30-40 times and things change dramatically. Its an illustration of levers more than anything else.

I want to point out that I'm not guessing about this stuff - I work on dynamics for vehicle/aircraft manufacturers and the military.

If you calculate the torque from gyroscopic forces on a bike they come out at about 6 NM, that isn't going to hold a bike up.

Bike stability comes from its geometry.
Keep the tyres the same and change the rake of the forks and the bikes stability will change, half a degree will make a significant difference.

A sports bike and a cruiser with exactly the same wheels and tyres have the same gyroscopic forces but the stability will be different. The sports bike will be twitchy and the cruiser will be relaxed because the geometry is different.

The sports bike will be more prone to tank slappers too, again because of its geometry.

Last edited by Bluebottle; 11-12-2015 at 08:18 AM.
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post #16 of 20 (permalink) Old 11-12-2015, 12:38 PM
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There have been made made experiments with counter-rotating discs on the wheels, cancelling out all gyroscopic effects, and they proved that the geometry is the main factor.
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post #17 of 20 (permalink) Old 11-12-2015, 04:30 PM
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Dynamicists have done a lot of empirical work over the years and there is solid maths and physics - but that tends to make people's heads bleed

Feathering the rear brake definitely works
Keep the engine steady and control the speed with the brake. Smoothness is the important thing. Notice that increasing your speed will tend to stand the bike up and reducing it will drop it down - but try to stay constant.

On the tank slappers that have been mentioned but are a bit off topic - the main cause is a feedback oscillation. I'm happy to discuss it if anybody wants to go into it.

Note that to a dynamicists you get "wobble" (oscillation at the front wheel countered by the "normal rake"), "weave" (oscillation around the rear wheel, countered by the wheelbase length) and "capsize" (where there is no oscillation - so it is just falling over). Things get complicated but the larger forces and concepts aren't too bad.
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post #18 of 20 (permalink) Old 11-12-2015, 06:43 PM
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Originally Posted by TNJim View Post
Talked about in this thread:
650 Slow Speed Maneuvering Techniques
This will give you the best answers to your question.
Some of the answers got off track from your question. Nothing wrong with their info just doesn't help you with your problem.

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post #19 of 20 (permalink) Old 11-12-2015, 08:14 PM
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After all the foregoing the only I can say is that when making a U-turn from a stop, turn the handlebar all the way over to lock on the side you want to go, lean over on that side then give it the gas.
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post #20 of 20 (permalink) Old 11-23-2015, 04:53 AM
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And as you start the u turn, most important, "look where you want to go."
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