Sunday, January 14, 2007

Why do big guys suck at climbing?

OK, so maybe they don’t suck, but they certainly aren’t particularly good.  We’re talking generalities here people...  If you look at cross-section of cyclists, it seems that smaller riders can climb, larger riders can time trial, and sprinters are sort of a mixed-bag.  Why does this seem to be the case?  I had a monumental thought this morning - actually, a number of thoughts - and actually liked some of them.
Let’s address big rider climbing performance.  We can all agree that climbing performance is enhanced with more power and less weight.  Of course there are other factors, but we’re dealing in generalities here, so let’s keep the problem bound to the major factors.   Let’s start with two identical riders with identical body-mass indexes and power outputs.  As one is magically shrunken to a more diminutive size (no, were not talking about going on a diet here), conventional wisdom would indicate he can climb better, as he weighs less.  You see, the less a rider has to carry uphill, the faster he can go.  However, this does not answer the question of why little guys can climb.  You see, as our hypothetical rider gets smaller, he loses weight, but also loses power.  

We are dealing with two factors, weight and power, which are related to each other.  Since we’re dealing with a ratio here, the logical conclusion one has to ask himself is not, “Why do big guys suck at climbing, but why to big guys have a lower power to weight ratio?”   
Here is where the facts tend to complicate things.  The major factors which work against the small rider are bike weight, and wind resistance.    Bike weight is the same between the small and big riders, so the small rider actually has to devote a higher percentage of his power to carrying the bike uphill.  Also, as a rider gets smaller, he also gives some aerodynamic advantage to the larger rider.  True, as his size decreases his area (hence drag) will decrease, but it does so at a slower rate (remember my last blog: area is squared, while volume is cubed).   And, yes, aerodynamics does matter on climbs, I can personally attest to that.  So where does the smaller rider get an advantage?  I am thinking that they have a mechanical advantage.  Not from the bike, but from the body.

Ever notice that in the sport of powerlifting that the larger guys have a higher absolute power, but the smaller guys can lift a higher percentage of their weight?    Well, it’s true.  Of the elite lifters, smaller guys can bench a little over 3 times their body weight, while the larger ones can do “only” 2.7-2.8 times their weight.   (Back when I was lifting, I weighed 125lbs, but was bench pressing 245lbs; just under double my weight.  This was something that none of my peers could do.)  I have heard that this is due to the fact that individuals with shorter limbs have a slight leverage advantage.  It seems that as a percentage of their total bone length, their tendons tend to connect slightly farther from the pivot point of the joint.  I don’t know if that is true, but if so, would translate into less work for the muscle to accomplish the same amount of movement.  This would provide some compensation for the previously mentioned issues.  

I have a supplemental theory.  I think smaller riders tend to be better climbers because of natural selection.  It’s as simple as this:  We already know that smaller riders have a slightly tougher time in the wind. Hence, in order to compete in this venue, a smaller rider must be slightly stronger (relatively speaking) than a larger rider.  Since those small riders tend to stay in the sport, and the ones off the back don’t, once we go riding in the hills, the only small riders that are left tend to exceed the others in a power/weight ratio.  We then generalize that small guys can climb.

Truthfully, I have no idea why big guys suck at climbing.  Obviously, as a rider gets larger, their weight tends to increase faster than their sustainable power increases.  Why that is the case is still up for dispute.