I’ve never seen any studies on this topic but I’ll throw a few theories out there. My personal belief is that most criteriums are run counter-clockwise, therefore most of your cornering is done to the left. Many sports requiring cornering go to the left (e.g. speedskating, track and field, nascar, etc). Cornering is where most crashes happen so it’s natural that the left side will take the brunt of the fall. However, for many years I’ve kept close track of every crash that I’ve ever witnessed outside of criteriums and nearly all of them have been on the left. It’s uncanny. Even during my mountain bike days where left and right corners are just as prevalent, I’d almost always fall to my left. I’d always rationalised it as an instinct to protect my too-expensive-to-replace XTR drivetrain. But I wasn’t the only one.
Could there be an evolutionary, physical or psychological reason for falling to the left? Could it have something to do with 70–90% of the world’s population being right-handed and we have a natural instinct to protect our dominant side as much as possible?
I can’t find much on the topic but one of my favorite blogs, The Cozy Beehive (which I highly recommend) wrote about this topic a few years ago and an interesting discussion took place. A couple theories that were suggested:
One theory came from and article in “The Dominant Leg” (By Simone Kosog in the science section of the ‘Süddeutsche Zeitung Magazin’ 1999):
“…This left twist effect seems to be generally apparent in animals. Circus horses enter traditionally the arena on the right and circle left wards. Foresters know that a wounded deer will always run away left wards, even if the closest forest is to its right. Even bees tend to circle leftwards when they spiral upwards to gain height in the air.
The basic driver behind this phenomenon seems to be the fact that all cells in nature are composed of amino acids which have a left spin. Chemists can manufacture amino acids with a right spin, yet we can’t use them. Apparently both types of amino acids existed in the primordial soup at the beginning of life hundreds of million years ago. Yet life developed only from those with a left spin. The favorite theory is that at that time – when the earth did not yet have the protective ozone shield – radioactive rays from the cosmos did more harm to the amino acids with a right spin. Yet why those with a left spin would be more protected – if at all – is still a mystery.”
People who are lost in the desert tend to walk in circles with a left spin, i.e. counter-clockwise.
Most or our supermarkets are organized the same way: entrance is on the right, the cashier on the left. Studies have shown that customers tend to feel slightly stressed – increased cardiac pulse, elevated blood pressure, slightly faster walking pace – and buy less when they have to walk in the opposite direction.
Same on the sports field: most track and field sports – from the 400 meter distance runner to the hurdle racer, they all run towards their left. Even the everyday jogger tends to run counter clockwise around the field or lake if he has free choice…”
“If you been riding long enough to have some falls, I’ll bet that almost every injury has been on the left side of your body. How do I know this? Because its the same for me and many other riders. If you want to find an old bike racer, look for a guy with scars on his left elbow. There seems to be a physiological reason for this and it is very interesting, though it hasn’t been formally documented as far as I know. It has to do with the location of the heart, the body’s primary organ.
As we know, the heart is to the left of the center in the chest. When the body loses equilibrium, it has a strong tendency to fall toward the heart side. This also explains why most riders find it easier to corner to the left than to the right. And it’s why track races go counterclockwise so that all turning is to the left. The reason it feels more natural is that the distance from the heart to the ground is less when turning left than when turning right. Even though track riders often do fall on their right side, this doesn’t disprove the theory. It just points out the bike’s tendency to slide down the banking.
I have no clue why most crashes (even outside criteriums) seem to happen on the left side and don’t even have any statistical evidence to back this up, but have yourself a great weekend and keep the rubber side down!