Steering theory

[Skyryder]

I post on a number of othe biker forums and came across this.
http://www.soundrider.com/jun04/nobsbike.htm

One of the best I've come across concerning counter steering.

Skyryder

ps

Motorcycle Handling and Collision Avoidance: Anatomy of a Turn, H.H. Hurt, Jr., SAE Paper 73032, Volume I - Motorcycle Safety, Proceedings, Second International Congress on Automotive Safety, 1973.


This was mentioned in the article but have been unable to down load. Maybe someone can find it on the net.

SR

[marty]

ahhh. but HOW does countersteering work? i haven't found a decent explantion of the physics of it (well not in any motorcycling arena anyway)

[Quasievil]

Thats interesting aint it. Body steering is not possible,only counter steering.
Thanks for the link

[FROSTY:Me]

in theoery sounds ok--in practice i don't think theyve thought it through properly

[wkid_one]

ahhh. but HOW does countersteering work? i haven't found a decent explantion of the physics of it (well not in any motorcycling arena anyway)

Simplely put - any moving object will endeavour to continue to travel in the direction it is travelling with. With bikes - given that they have two wheels in perfect alignment with one another - you actually only use the front wheel to control the angle of LEAN not direction at any speed over say 20kph.

What actually happens when you steer a bike at speed is this. You actually push the bars in the opposite direction, as by doing so, the bike falls INTO the direction of the corner - you then use the lean of the bike and the tyres to turn you around the corner. This principal applies on all vehicles of two wheels - and is the main reason we fall off our bikes when the training wheels come off. All the front wheel is actually doing is controlling how far the bike leans - and therefore turns.

Essentially what is happening is the bike is endeavouring to continue to travel in a straight line when you turn the wheel. If you turn the wheel left - the bike will actually tip to the right as physics dictates that it will try to continue in the same direction it was travelling prior to the input.

You CAN'T turn a bike any other way at speed - it is impossible.

[marty]

there is much debate on this subject, but the basic science is that 'countersteer' has 2 parts: the lean into the corner by the rider, and application of force to the handlebar by the rider. it is this application of force that brings discussion, as the lean into the corner is obvious - you lean in.
if, while travelling at speed (say above 70km/h), without the rider leaning AT ALL, rearward force is applied to the right handlebar, the bike will turn to the left. you can muscle the bike to the right, but the bike wants to turn left.
this phenomena is called gyroscopic precession. gyroscopic precession is the term given to the forces acting on a rotating disc. it means that an input to the change of direction of that rotating disc, will be output 90 degrees around it, in the opposite direction.
here's an easy way to see it happen: get a push bike wheel. hold onto the axles, and get someone to spin it up. pull the right axle towards you. the top of the wheel will fall to the left, the bottom will lift to the right. the movement will only stop when the input stops. this is the same as pulling the right handlebar towards you, except the bottom of the wheel is for all intents fixed to the ground, so the top of the wheel receives all of the input, and 'falls' to the left accordingly. different steering rake on different bikes means a different rate of change, but also brings in further issues such as the wheel wanting to 'fall over', such as on a cruiser with a lot of rake, or be really twitchy on a bike with low angles of rake. so the question remains, is how much is leaning off the bike part of countersteering? i don't know. it certainly shifts the c of g, but side car riders do that, and their bikes don't lean. as far as i know (only experience is riding 3 wheel ATV's) gyroscopic precession will only have an effect if the wheel (disc) is allowed to lean, so it probably doesn't work on 3 wheelers. it certainly still works even if the (2 wheeled) rider doesn't lean.
this is a basic rule of helicopter flight control - if you ever get to have a look at the swashplate on a helicopter rotor, you will see that the cyclic control input for forward flight is on the side of the swashplate, and the one for sideways flight is (usually) at the front