Tag Archives: countersteering

Speed 101: Motorcycle Racing as Real-World Physics Lab at edutopia

The number of errors in this article by Owen Edwards, apparently aimed at educators, helps explain perhaps why so many misconceptions persist in the public mind.

The first misconception is that forward motion somehow causes a bike to resist turning:

In fast turns, lean angle and forward motion counteract the powerful pull toward the outer edge of the track.

and

the initial physics lesson to be learned watching a racing bike hurtle into a tight turn is Newton’s first law of motion: “Every object persists in its state of rest or uniform motion in a straight line unless it is compelled to change that state by forces impressed on it,” explains Falco. To a rider, this means that the faster a motorcycle is going, the less it wants to turn.

The truth is that a a bike’s inertia, the property which does resist acceleration according to Newton’s 1st law, is constant, and a lateral force, such as friction between the tires and pavement, will cause the exact same lateral acceleration when the bike is racing down the track as when it is stationary at the start line.

Mr. Edwards follows up immediately with another common misconception that countersteering works because of gyroscopic precession:

Because the wheels act as gyroscopes, this countersteering leans the bike in the opposite direction (into the turn).

As already discussed repeatedly here, Professor Cossalter in his excellent Motorcycle Dynamics, on page 304 of the second edition, calculates the roll moment generated by gyroscopic effect for a motorcycle traveling at 22 m/s (79 km/h or 49 mph) to be 3.5 N-m (2.6 lb-ft) and compares it to the roll moment generated by the accelerating contact patches of 30 N-m (22 lb-ft), which is 8.6 times larger. He concludes with the note that the gyroscopic effect is present from the instant torque is applied at the handlebars, and the roll moment generated by the lateral force of the tires can take some time, ~0.1 seconds in this example, to build up.

There’s a little more mumbo-jumbo about contact patches:

the tires at an angle, narrowing what engineers call the contact patch and making the bike easier to turn.

But there really isn’t even enough information there to decide what is wrong with it.

The article subtitle is

Isaac Newton hops aboard a two-wheeled teaching tool,

but it appears Mr. Edwards was left standing at the starting line.

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