Biking 101: Turning corners

Believe it or not, riding a motorbike and knowing how one turns are two different things.  Professional rider training organisations will introduce you to the concept of “counter-steering” and some may even attempt to explain how this phenomenon works, but, you don’t have to understand it to ride a bike.  Here’s the briefest summary I can give you on what counter-steering is:

If you want to turn left, you turn the front wheel to the right. 
If you want to turn right, you turn the front wheel to the left.

After you’ve read that, I think you’ll understand why the technique is called “counter-steering”.  What’s more is, it actually works!  Here’s my attempt at something between a layman’s explanation and the physics nerd’s explanation.  The explanation given is based off my understanding and what I’ve observed first hand.  I promise I won’t go close to using mathematics in my explanation!

The gyroscopic effect of the turning wheels is what holds a motorcycle up once it is moving at any sort of speed.  (Say around 20kph / 12mph).  The two wheels on the bike have different roles to play.  If we discount the effect of suspension travel, the rear wheel remains with its axis fixed relative to the rest of the motorcycle, whilst the front wheel allows its axis to pivot left and right (when viewed from the rider’s perspective). 

The rear wheel is responsible for keeping the motorcycle moving in the same direction of travel.  The front wheel is responsible for changing this direction of travel.

Lets look at the rear wheel effect first:
If you spin a gyroscope where the top of the wheel is not centred above the bottom, it will maintain this angle, providing the gyroscope does not lose momentum.  Given the freedom of being able to move, it will circle in the direction matching the side the top leans to.  Therefore, once a motorcycle is leaning, it will move in an arc in the direction of the lean. 

Figure 1: Trajectory of leaning wheel 

Once the rear wheel is spinning with a fair degree of velocity, the weight of the rider and motorcycle become insignificant compared to the gyroscopic effect of the rear wheel.  Although you can use your body-weight to lean the motorcycle into a corner, it’s a slow and arduous process unless you can influence the direction the front wheel is pointing.

Here’s where the front wheel comes in:
Forcefully altering a gyroscope’s orientation will cause it to behave in strange ways.  This is best demonstrated with a loose pushbike wheel.  Spin the wheel up whilst holding the ends of the axle. 

A badly drawn arrow indicating a spinning wheel

Push the left end of the axle “forward” and pull the right end toward you.

Oh look, now there are dodgy green arrows as well! 

You will feel the wheel “react” to this movement and the wheel will lean to the left. 

Dodgy red arrow removed to make blue arrow easier to spot

The easiest way to return the wheel to the vertical plane, is to reverse the action you just did.  That is: pull the left hand toward you and push away with the right.

Putting it all together:
With our increased understanding of what is going on, we’re ready to “hit the road”.  (That should be taken as a “figure of speech”, rather than a “literal interpretation”)

  1. Travelling forward on the bike we push the left handlebar away from us.  As explained above, this will cause the front wheel to lean to the left.  The rest of the motorcycle will follow, resulting in both wheels now leaning to the left.
  2. We stop pushing the left handlebar, allowing it to resume a “neutral” position.  It requires some force on our part to remain at this current lean angle, as the gyroscopic effect of the front wheel will now make it “want to” turn in more.
  3. Because the wheels are leaning, the bike travels in an arc.
  4. Once the joy of turning left has worn thin, we need to stand the bike back up.  So, we reverse the process and push the right handlebar forward.

And that’s the simplified version of turning corners on a bike!  I will leave “turning right” as “an exercise for the reader”. 

Some points in closing:

  • I’ve heard it claimed that the Wright brothers (as in the bicycle makers who forgot that push-bikes weren’t meant to fly) noted that you counter-steer bikes.  Later observations (such as “look, my brother is flying”) seem to occupy most text that you see written on the duo.
  • Whilst counter-steering works for push-bikes, the relative weight of the rider compared with the bike means it is much harder to observe the effect.  Body weight / balance play a bigger role.
  • Rider training will teach you to push  the bars, not pull  on the opposite bar.*  I believe this is taught to stop you gripping the bars too tightly.  A loose relaxed grip with your hands is a safer way to ride.
  • Throttle control also plays a large part to how well you can ride around a corner, but that is a story for another day. 

* Personally, I find it easier to feel the gyroscopic effect of the front wheel by pulling on the bars, probably because my arms are tense when doing so.  From changing between the two techniques, I find pushing the bars easier to control.

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