Wheel upgrades

[Johan Bornman]

 

Cut cut cut cut 

 

Without proclaiming to be an expert on the forces at play with a rotating wheel' date=' my only comment would be that if the wheel is rotating fast and you are trying to steer more than a fraction of a degree, I think that you should then be more worried about a couple of other forces which will suddenly become relevant:

 

1 - Gravitational force which will accelerate your body towards the ground, followed soon thereafter by...

2 - Frictional force between your body and the ground.  Note - this force will be affected by the roughness of the tar

3 - if you are really unfortunate there may be an additional impact resulting in extreme deceleration.

 

Of course, none of these forces depend in the slightest on which wheels you are using.....

 

The "gyroscopic" force I would think is largely responsible for the fact that the bicycle tends to stay upright when travelling in a straight line (note that it is generally easier to ride "hands-free" at faster speeds), but any significant "steering" at high speed is a recipe for disaster. 

 

 

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Mark, convensional wisdom and lore isn't always the truth, as this case proves.

 

Gyroscopic forces play no role in bicycle balance.  A rider balances on his bicycle like a cleaner balances a broom on the palm of his hand - by riding into the fall so that the centre of gravity is restored to the position directly underneath it.

 

Go away from your PC for a minute and go balance a broom.

 

Notice how you push the base of the broom (in your hand) to the point directly underneath its centre of gravity. It falls left, you move left, it falls forward, you push forward and the same for the other two "dimensions".

 

On a bicycle the problem is simpler, since you only have to worry about on plane , the left right-place. You cant fall forwards or backwards unless your's is a unicycle.

 

As you ride and you start to overbalance to the left, you steer left and whoopee, your CoG is underneath your head again.

 

OK, now for gyro forces. For a moment, consider a bicycle with very, very little gyro forces playing on it. Your son's bike has less gyro than your MTB because it is smaller. It is also slower. Your son's mall scooter with Rollerblade wheels have very little gyro forces, yet he zips through the traffic without thinking about gyro forces. Your rollerblades and finally, for the ultimate zero-gyro vehicle, your ice scates! All of these balance with balance.

 

Back to the gyro. Only a fool wil say there's no gyro force on a spinning wheel. The mere fact that you can hold a skewer in your hand, spin the wheel and release your grip on the skewer so that it merely rests in your hand, yet the wheel still hangs there, proves there is a gyro force on the wheel. Further confirmation is that you have to slowly turn in order to prevent the wheel from turning on the skewer and hitting your arm or torso, is further proof.

 

Note how the gyro force operates: you apply an upwards force to the skewer (wheel spinning clockwise) and the wheel turns (as in around a corner) to the right.

 

Now try and envisage this force on the bicycle itself and you'll see that it doesn't contribute to balance but to the wheel's tendency to straighten itself after being leaned into a turn.

 

I hope R2D2??the rocket scientist) will this time join in this discussion. Please do.