i2imca Cone Effect 1

Another rambling on my weekend with i2imca, this time a bit harder for me to explain. A big part of motorcycle stability is down to the gyroscopic effect of the two wheels – at even lowish speeds their spin helps keep the bike upright. There is also stuff that goes on because there are two wheels acting as seperate gyroscopes.

Anyway, as biker types know the way you turn is to use something called countersteering, which is a counter-intuitive thing that involves moving the bars the wrong way and making the bike tip the way you want. Otherwise providing the bike is going along fast enough (20mph ish) it will go in a straight line. Once you start leaning a thing called the cone effect comes in to play. Motorcycle tyres are not square in profile like car tyres, which never move from the vertical. Bike tyres have quite a round profile that helps the bike lean. And because of this the tyre walls (the bit between the rim of the wheel and the edge of a tyre) are only part of the rolling circumference of a tyre on a motorbike (doesn’t quite sound right that bit). Anyway, because the radius of the tyre shortens off towards the rim, the more you lean over the smaller the radius – sound familiar? Half the cross section of a tyre looks like part of a cone. One thing cones do when you roll them is go round in circles, and providing you can lean far enough over you can get a bike to turn – albeit very very slowly, not enough to turn most corners.

For a proper techie explanation go look at Motorcycle Handling and Chassis Design by Tony Foale over on google.

The cone effect is important to understanding how much you need to countersteer when leant over.