Going straight – why riding in a straight line isn’t as straightforward as it sounds.

 

Some of my favourite cycling anecdotes feature Roger de Vlaeminck.  He was famous not only for winning Paris Roubaix (he still holds the record with four victories) but for his riding style and his skill.  One story is that he never had a puncture in Paris Roubaix*, but the one that I like is that he could ride in the tramlines.  That’s to say that he could ride into them, ride along and then ride back out.  He could ride in a straight line.  I don’t know how true the story is, but I’m pretty sure that professional racing cyclists used to ride straighter than they do now.

roganded

I’ve written before about the number of crashes that happen on straight pieces of road.  If you’re watching the Tour de France just look at how the riders weave around.  Watch the paths that their wheels take.  It’s scary.  And that’s for me, watching from the sofa.  I’m not surprised that it’s stressful in the peloton.

I’ve written before that I think this is largely a consequence of modern bike setups.  Today’s riders are every bit as skilled as their predecessors (maybe not all as skilled as RdV), but their bikes are set up like fly-by-wire fighters.

In the early days of triathlon triathletes quickly earned themselves a reputation for being dodgy bike handlers.  This was mainly because triathlon bikes, with their steep seat tubes, were very difficult to handle and the triathletes riding them, being new to cycling, didn’t know anything else.

So what is it that makes a bike, or a setup, difficult to keep in a straight line?

It helps to understand a little of the physics of steering and stability.  The easy bit to understand is centre of gravity.  One of the amazing things about riding a bike is that you can actually stay upright at all.  Imagine a line on the ground between the points where the wheels touch it.  It’s the width of a tightrope and your centre of gravity has to stay vertically above it, otherwise you’ll topple to the side!  In fact, you only stay upright because you steer those two points on the ground to keep that ‘line’ underneath you.  If the two points are fixed it’s very difficult to stay upright – you have to do what tightrope walkers do to shift your centre of gravity.

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So to ride in a ‘straight’ line you actually weave very slightly from side to side.  If the amplitude of your weave is sufficiently small you can ride in the tramlines, if it’s too wide you can’t.  

What affects the size of the weave?  The other day I put my bike onto my rollers and found that the front wheel was turning much more slowly than the back one (because the band had perished and stretched).  It made the bike incredibly difficult to ride.  Not impossible, because I could still keep the line between the wheels underneath me, but difficult because there was no gyroscope effect from the front wheel.  

If centre of gravity is easy to explain and understand the gyroscope effect is anything but.  However, it’s easy to feel it for yourself.  Find a wheel and try the experiment below… .

Hopefully the experiment shows that turning the handlebars generates a stabilising force, though it feels like very destabilising wobble if you do it quickly,  and leaning the bike generates a gentle turn.  I normally use this demo when I’m teaching people how to ride round corners fast as it illustrates why you must lean the bike rather than turn the handlebars.  However it also illustrates why you can control and steer your bike with no hands (if the handlebars turn on their own the bike self centres, but if you lean the bike with your hips it turns) and why leaning heavily on the handlebars makes the bike unstable (because any body movement puts weight onto one side of the handlebars and causes the front wheel to lean).

If your riding position is ‘forward’, like so many of today’s professionals, your bike is inherently unstable.  The act of pushing the pedals slides you to the front of the saddle.  It’s a double whammy.  Not only is more of your body weight on the handlebars but the only thing that stops you going right off the front of the saddle is you pushing on the handlebars.  

In fact it’s not just a double whammy.  The whams keep coming…  sore hands, neck and shoulder pain, lower back pain, perineal pain, nervous descending…

 


 

*Actually he punctured three times in the fourteen P-R that he rode.

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