However, the researchers’ calculations showed that neither the gyroscopic or castor effect is actually responsible for a bike’s propensity to steer and self-stabilise.
So like a shopping trolley, push your bike forward and the front wheel necessarily tucks in and trails behind the direction of travel. The result is that, like a castor that can move 360° around a vertical axis (imagine your headset is the castor’s bearing and your hub is its axle), your front wheel ‘follows’ your handlebars. But actually the wheel contacts the floor just behind this axis.’ People assume the actual ground contact point of the front wheel is in front of the steering axis because of the head angle and fork rake. The other is that a bike behaves like a castor on a shopping trolley. ‘People naturally think that if something spins fast it becomes rigid due to the gyroscopic effect, so when you turn it, it wants to turn the other way. But taking the rider out of the equation, why does this happen with a bike?
As the vertical broom starts to lean left, the balancer moves their hand to the left also, bringing the bottom of the broom back underneath its falling top, thereby regaining balance. Ruina likens the effect to the balancing of a broom on one’s hand. The bike will quickly fall over in the same way it falls over when it’s stationary.’ We can show this if we lock the steering on a riderless bike, push it along, then let it go. ‘What’s well known is that steering gives you balance. ‘You can only keep a bike upright when it’s moving,’ Ruina says.