Gyroscopic effect

Shaun · Likes 'em bent Joined: 17 May 2003 Karma :

I've read a couple of wheelie guides recently and they both said that if you hit the front brake whilst doing a wheelie it has an interesting gyroscopic effect. Is it really that interesting since neither of them mentioned or explained any more of what this effect is and whether it is dangerous or not, anyone care to explain? Thinking

I hope I'm not being really stupid and they just mean the wheel will stop turning.

Smoto Bob · World Chat Champion Joined: 06 Dec 2003 Karma :

i have no idea but..

Gyroscopic effect is from spinning, so whens its spinning it helps keep the bike balanced left-right. And you can use the steering as well for this.

If your doing a tail whip, you have to rev the engine to bring the back into line Wink

same sort of thing.
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Milo · World Chat Champion Joined: 08 Feb 2002 Karma :

With the front wheel spinning it will help you keep the bike on the strait and narrow, if you stop that force then it'll make wheelie's much less stable. I don't wheelie too much myself so can't say how much of a difference it makes, best to wait for one of the other guys/gals to post.

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DukeRed · World Chat Champion Joined: 07 Mar 2004 Karma :

I imagine you'd become unstable because the spinning of the front wheel even in the air gives stability.

Jan
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mr jamez · World Chat Champion Joined: 04 Aug 2003 Karma :

Rally drivers use the gyroscopic effect to stop their cars from nose diving after a jump as well Very Happy

G · The Voice of Reason Joined: 02 Feb 2002 Karma :

Right, firstly you can apparantly counter steer while on one wheel using the gyroscopic effect, it thus also helps to keep the bike straight.

I've never really noticed this, most of my wheelies are pretty slow, so I probably wouldn't notice it anyway even if I was good enough to.

also...

I know that in motocross stunts you can pull the throttle on to make the rear dip (I think). So presumably pulling the brake on could actually help the front to rise a bit?... obviously it's going to have to be going fairly fast in the first place.

Smoto Bob · World Chat Champion Joined: 06 Dec 2003 Karma :

Korn · Admin Joined: 01 Feb 2002 Karma :

I don't completely understand the physics but I can tell you it's a bad idea. At one point one of the calipers on my VTR was binding, meaning that a second or two after clutching it up the front wheel would have stopped spinning, this made it really unstable and it was impossible to correct the bike's heading, not to mention the landings were very violent as the front wheel had to suddenly spin up from 0 to 60 odd mph in a fraction of a second. After a few hairy moments I figured out the problem and fixed it double quick time Shocked

Incidentally the gyroscopic effect of the front wheel is also why the faster you pull wheelies, the easier it is to adjust direction and actually make your wheelie go in a straight line.
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old bob · Two Stroke Sniffer Joined: 28 Sep 2002 Karma :

Please unless you are very skilled and have supberb reactions do not try applying the front brake to the front wheel when off the ground.

The spinning front wheel exerts a strong force due to gyroscopic effects, the forces work at right angles (you can gauge the direction of a reaction by applying the corkscrew rule). Difficult to explain simple to feel with a small gyroscope. When you lift the front wheel with it spinning there is a fairly large force reacting which you naturally balance and compensate for, moving the steering changes the direction of the reaction and gives some feel of control.

The effect reduces as the wheel slows but you naturally compensate. Stop the wheel suddenly and you change the reaction effect rapidly and you won't have had time to adjust you will probably find the bike will react violently.

Apart from which if you touch down with a bit of brake applied you may find the resultant cartwheel over the bars a little embarrassing.

Danny · Ask Me About Stoppie School Joined: 26 Jan 2003 Karma :

hugo-a-gogo · Trackday Trickster Joined: 13 Feb 2004 Karma :

talking bout 'crossers and rally cars using the engine to adjust position in mid-air, isn't that just torque reaction? view the car bike from the left - engine turns anti clockwise, car tries to turn clockwise, rear dips (assuming these rally cars have transverse engines)
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Milo · World Chat Champion Joined: 08 Feb 2002 Karma :

If you spin the rear wheel up or stop it then then using the equals and opposite reaction theory then the bike must turn in the other direction - pitching the front up or down.
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Shaun · Likes 'em bent Joined: 17 May 2003 Karma :

And now I know. Very Happy

Very good explanation bob, I now fully understand that its a terrible idea to do it! Thumbs Up

Adam_P · World Chat Champion Joined: 23 Jan 2004 Karma :

Watching the Motocross and indoor super cross stuff they all use the back brake while in the air to get the back end to come up a bit so they land in a better position.

I'd never thought about what the front would do though. But then, I'm not one for wheelies really (I have a hard enought time staying in control on two Laughing

) so I'll leave it to the talented people. Wink

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