Thursday, 15 April 2010

Does weight matter?

The basic phisycal equations for the forces on a bicycle rider show that weight has almost proportional effect on the power required for cycling. That is: the required power is greater by the same percent as the percent weight increase of the rider+bike+luggage combination. Interestingly, this fact is the basis for the conclusion that weight doesn't really matter that much: if I weigh 75 kg, my bike 15 kg and my touring luggage 20 kg (a total of 110 kg), then even if I manage to reduce my luggage by 50% (10 kg less - a very difficult task indeed), it would still mean just 9% gain in power. Why then bother with it at all? Well, there are several reasons why light weight might be prefered. I can think of the following:

- The fatigue life.
- The simplicity.
- The effort.
- The lifestyle.
- The elegance.

The fatigue life. Weight has large influence on the material of the bike and other equipment. Metals fatigue roughly with 3rd power of stress - and stress is proportional to weight. 5% decrease in weight, for example, results in 16 % increase in fatigue life of the equipment. 20 % decrease in weight = 73 % increase in fatigue life. By reducing the weight one then considerably reduces the likelyhood of equipment breakage. This is the primary benefit and the one that made me go the light way. The stories about cracked rims and broken racks are almost without exception told by 4-panniered heavy-duty tourers. By the way, it seems logical that the weight has similar effect to the body fatigue. The body can heal, of course, but it requires energy to do so.

The simplicity. Simplicity is freedom. And freedom means simplicity. They are the same thing. With each thing less you are more carefree. I remember one occasion when I bought a wooden carving in Zimbabwe. From the moment when I purchased an, otherwise outstanding sculpure, I was in a constant worry. How will I transport it on a bike? How will I protect it from the rain? What if they stole it from my tent? How will I take it on the plane trip back home? Will they accept it as hand luggage? And if not how will I package it? These worries made for some miserable nights until the return trip and a 2 kg statue on the the rear rack resulted in a couple of broken spokes (on otherwise already weakened back wheel).

The effort. As said above, you need more power to cycle with heavier setup. 9 % more power may seem negligible with respect to the comfort that you're supposedly throwing away. It is a matter of preference: is it important to you to make 10 or 15 km more each day? Or you can cycle the same distance, feel much less tired and have more time in enjoing your rest. Far more effort (in terms of percentage) is saved when you have to carry or push your bike: in this situation your body weight doesn't enter the equation and the effort is proportional just to luggage (and bike) weight. In fact, body weight should not have the same impact as luggage and bike weight. Heavier people are usualy stronger and can produce more power. It is somewhat misleading or "unfair" to compare lugguage weight of differently strong people. But if we take out the body weight from the above equations, then reducing the luggage weight by 50% makes a 29% gain in power, instead of 9%. The real percent gain is somewhere in between.

The lifestyle Cyclists like to think of themselves as ecologicaly superior to motorists. By the same line of reasoning lightweight touring is superior to loaded touring. A couple of years involved in reducing the luggage weight had changed my view on many things, unrelated to cycling. I became aware of many redundancies in our everyday procedures and behaviour.

The elegance Obviously this is a subjective thing, but a light setup on an elegant bike, preferably set in some spectacular natural environment, is a real pleasure to my eye.