Interesting study: Bike weight and commuting time

[Danneaux]

Hi All!

I recently came across an interesting study comparing commute times between a lightweight (carbon) bike and a heavier, steel-framed bicycle: http://www.bmj.com/content/341/bmj.c6801.long

Methodologically, I was left with a number of questions -- what about differences in tire size and pressures? Aerodynamics? The steel bike has full fenders. The bikes were ridden on an unequal number of journeys. Weather was a variable, but clothing might not have held constant. There's myriad differences, so the results must be taken with a generous grain of salt. If measuring differences due purely to weight, it would have been better to use the same bike but add weight to it.

He does make the point that in terms of total weight (bike and rider) the 4kg difference between bikes didn't amount to much.

Still, it is a fun look at trying to compare two different bikes, speed, and a single rider.

I was really intrigued by the conclusion: The author prefers his older, steel-framed bike, so much that he would not replace his carbon bike if it were stolen(!), saying, "...A new lightweight bicycle may have many attractions, but if the bicycle is used to commute, a reduction in the weight of the cyclist rather than that of the bicycle may deliver greater benefit and at reduced cost".

Best,

Dan.

[mickeg]

I think that there is a detectable time difference, depends on tires, tire pressure, hills, frequency of stops, road surface, gearing, etc.  Each route would have a different time differential.

When I am coming home after a 20 mile exercise ride, when I start from the next to last stop light from home, if I am on my Nomad with 2.25 width knobby tires, when I get about 200 feet (roughly 65 meters) from the last light, it turns red and I have to wait about two minutes for it to turn green.  But if I am on my old Columbus Tubing Italian bike that weighs 15 pounds less and has 25mm tires pumped up to high pressure, I can usually just barely make it through that last light without having to stop.  My bike computer that only records moving time will usually say that the Nomad takes a bit over 5 percent more time for that 20 mile ride, but just that last light by itself adds two minutes of stopped time if I am on the Nomad.

I have two sets of wheels for my Long Haul Trucker.  One set has robust 37mm wide touring tires with stiff casing, the other set I had 25mm wide supple high pressure tires.  When I rode that bike for exercise, I usually found that the 25mm tires would get me home in about 3 percent less time than the wheel set with heavier tires.  In this case the only difference was tires and slightly different weights for the wheels because it was always the same bike for comparison.

Hill climbing by itself is an interesting study.  I have had people pass me with fast carbon bikes, then when the hill gets steep, they slow down and because they do not have the low gearing that I have they have to stand on the pedals at very low cadence just to make any headway, while I might start passing them because I can gear way down and stay seated.

[David Simpson]

To me, an important factor in riding is the comfort and enjoyment of the ride. I don't ride to win a race. I ride for pleasure. I don't mind it if my heavy bike requires a slightly longer (+10%?) time to ride my commute, if my ride is that much more comfortable. In fact, a slightly longer ride on a comfortable bike can feel faster than a shorter, less comfortable ride.

Besides, I like riding, so maybe I don't want to get there sooner.

One impression that I get from hearing these kinds of stories is that while a heavier bike makes the ride slower, it doesn't make it as slow as we expect. There is less of a difference in overall ride-time between a lightweight bike and a heavier bike than what we would expect there to be, provided that the heavier bike is not unfairly slow (e.g. due to cheap tires).

- Dave

[Andre Jute]

I'm with Dave: I ride for pleasure. But I do take a certain pleasure in technical enquiries too.

When I replaced my Gazelle Toulouse with the Trek Smover (you can see both at
http://coolmainpress.com/BICYCLING.html )
these were two very similar bikes, and I reengineered the Trek to be exactly similar to the very pleasing Gazelle, the only significant difference being that the Shimano Nexus 8-speed gearbox on the Trek was automatic. There was a ride I did several times a week, timed by my bike computer/HRM, with the records transferred to my computer. The automatic bike, by putting me in the correct gear every time, was measurably and significantly faster for what to me felt like less effort. Of course, it was only one rider, and I soon fell to taking that saved ten per cent, and a quarter hour more, for lying on my back on a bridge wall and daydreaming...

Does my study tick all the boxes of ivory tower statistical probity? Nah. But then the art of statistics, for those of use who've risen above the drudgery of chi-squares, isn't perfection but a usable answer from inadequate data. So I am not inclined to condemn that study for falling short of 3000 respondents. After all, it arrived at a credible answer: the respondent prefers the steel bike, which experience tells us is the correct answer.

[jags]

my new carbon bike is a joy to ride light fast climbs like a dream.
if i were to compare it to the sherpa there no contest thats a fact, but when it comes to comfort and solid ride with panniers the sherpa wins hands down.
you cant compair a donkey to a racehorse 

anto

[il padrone]

Hill climbing by itself is an interesting study.  I have had people pass me with fast carbon bikes, then when the hill gets steep, they slow down and because they do not have the low gearing that I have they have to stand on the pedals at very low cadence just to make any headway, while I might start passing them because I can gear way down and stay seated.

*cough*

Those carbon wunder-boys must have been really out of form or rank newbies, as a higher gear being pedalled half-well will always get you up the hill faster than a low gear spinning. I have done rides on my single speed in hill country with friends on geared touring bikes and what happens is that a fit rider can just stand and push the gear (assuming the gear is appropriate and the hill not excessive) while those on  multi-geared, heavier bikes will tend to gear down. It is easier for them to climb the hill, but also notably slower.