Friday, 19 November 2010

"Does my bum look big on this bike?" -The weight debate-you or the bike?

Bicycle weight seems to be something of an obsession and I have to wonder sometimes if the male of the species has taken leave of their collective senses? I realise this subject has probably been done to death, but here goes my ten penneth……

Many make it clear that to be with the cycling "In-crowd" you must have the very lightest bicycle and do everything you  can to make your bike light. If you don't, not only is the bicycle you ride a joke.... but you must be too.

In the world of the cycle cognoscenti  Light = Good; Heavy = bad.

I should know dear readers for I ride a Pashley Gents Roadster (and by God I love it!) yet the distain of some for that small admission needs to be seen to be believed…..the bike and yours truly weighing in at 100kgs. So spare me any tourette's like blurtings all you modern racing chaps! In any case, at the risk of bringing down a storm of choice remarks upon my head I thought I’d dare to try to prop up my argument with evidence.

First of all let me make it clear, weight is important. If it weren't, I would be enjoying pleasant 200mile rides on a 100kilo road bike equipped with a chaise longues. So despite my reservations on the issue, I accept that we should all ride modern, well-made, well equipped bikes.

BUT! truth what we are debating is nothing more than a few kilos here and there. Bikes range from “commuter bikes” like my all-steel Pashley, to a super-light barely strong enough to negotiate a pot hole single speeder.  Given the usual rider and bike coming close to a combined weight of say 82 kilos, the difference in performance between bikes of differing weights may surprise you.

James Martin, Ph.D. an assistant professor of exercise and sport science at the University of Utah provides some interesting calculations that makes the issues of weight very clear.

He took a 5 kilometer hill of 7% grade as an example, which is a good stiff climb. He further assumed a 73kg rider who can produce 250 watts on a 10 kg bike. Given those circumstances it would take 19 minutes and 21 seconds for the rider to get up the hill. Now comes the interesting bit. For every 2kgs added the trip up the hill would take 30 seconds longer. So even on my Pashley on a really tough climb it would only take 22 minutes and 21seconds (a mere 3 minutes longer).

That means that even on a heavy old clunker like mine, I’d only be three minutes late for the jolly picnic at the top of the 20 minute climb. Just in time for the weight watchers to get the sandwiches and tea out!

The performance advantage of a light bike is clearest when the hill is steepest. When the road flattens out, those 30 seconds per kilo grow smaller and smaller and make no real difference on the level because as the speed of the bike increases, the greater resistance comes from the wind, tire rolling resistance, bearing drag, clothing….. less and less on the weight (on a downhill stretch it’s a slight advantage to have a heavier bike). 

Variations in peoples body weight are much greater than the weight of their bikes ever could be and make a much bigger difference. If that same 73kg, 250 watt rider on the bike indicated in the first instance were to be 100kgs in weight he would reach the top 6 minutes and 10 seconds later……..that is 3 minutes after me on the jolly old Pash….and I’d then have to ask my butler to have the “Bolly” chilled!

So don’t stress about bike weight my dear velocipedal chums…….lose weight off yourself!

Bottoms up!...heads down!

1 comment:

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