Tech FAQ: Does bike weight matter?
Editor’s Note: Lennard Zinn’s regular column is devoted to addressing readers’ technical questions about bikes, their care and feeding and how we as riders can use them as comfortably and efficiently as possible. Readers can send brief technical questions directly to Zinn.
Does bike weight really matter?
I’m about to invest in a better bike now that I’m taking riding more seriously, and I’m looking at the different options depending on the frame materials.
I happen to be an engineer, so I wondered how much bike weight actually matters when climbing. Say that I’m going up a climb that can be as steep as 20 percent in a given moment, the role weight plays can be calculated using basic math (see the graph, where w= bike weight and d= weight drag, as if someone is pulling you from behind the bike).
The actual weight drag difference between a heavy steel bike (like mine, at 29 pounds) and a top of the line “lightweight” carbon fiber bike (say 17 pounds?) is actually just a couple pounds, and in a very steep climb. In lower grade climbs the weight drag is just a fraction of a pound.
So… unless a rider is planning to lift the bike over his/her shoulders, I don’t see the extra $2K investment justified in the bike weight alone. (I can just carry less water when climbing.) I guess inertia plays a role in competitive situations (a lighter bike helps provide faster acceleration… I guess we can calculate if this actually matters as well!!).
Every place I look recommends “getting a lighter bike if you live in a mountainous area.” Is this a myth or am I overlooking anything?
The lighter bike will climb faster if you put out the same power. Whether the amount faster it is matters enough to you to spend the big dollars is the question.
Here’s an experimental measurement of the effect of adding 1/3 as much weight as you’re talking about (four pounds vs. 12 pounds) to a bike and riding up a big climb, namely l’Alpe d’Huez. In this experiment, the extra four pounds added one minute to the rider’s time, which was around 50 minutes, so it made him about two percent slower. So tripling that to get your 12-pound heavier bike would be six percent slower.
Here’s another one. On a hilly loop course, a 20-pound weight difference in bikes yielded a 13.6-percent drop in speed. Extrapolating that to your 12-pound weight difference, you’d be looking at an eight-percent speed loss.
Personally, I would find a six-percent or eight-percent speed loss to be rather unbearable, but if you don’t care about that, then no need to spend the extra money.
I have to tell you that you really dropped the ball on your stack and reach article. There are so many flaws in it I just don’t know where to start, but the biggest flaw (other than the fact that the article is written by a clueless idiot that hasn’t got a prayer) is that bikes are not identical. Your so-called reference point of backing a bike up to a wall works fine if you are measuring identical bikes like a Madone 5.0 to a Madone 5.0, but when you start to measure between brands or even different bikes from the same maker your theory falls completely apart. Things like rim height, tire height, and chainstay/seatstay length can and do vary from bike-to-bike, especially between brands, and that variance can be between one-to-two centimeters, which tosses consistency (and your entire method) right out the window.
For someone who is so hot and such an authority on all things cycling I am really surprised that you would put your name on such a fairy tale, but maybe you have become a victim of your own publicity and you think that being Leonard Zinn of Velo Snooze [sic] makes you immune to mistakes. Guess what? It doesn’t.
I think at the very least you owe the readers of Velo Snooze [sic] a printed and public apology for you screwing the pooch on this one. In the future if you ever want to verify one of your half-baked pipe dreams before you go publishing it and making a fool of yourself, run it by me first, I’ll help you out.
Boy, I’m going to hightail it right down the Sarasota to take advantage of your kind and thoughtful offer; no telling what I could learn from you! Bikes of different brands are different and have different measurements? Well, I’ll be…
Apparently, the point of taking X-Y measurements this way escaped you. I’ll attempt to clarify it, if for no other reason than that other readers less endowed with your eloquence might have also misunderstood.
The point of the whole stack and reach measurement exercise is to set up a two-dimensional coordinate system within which you can compare different bikes (yes, even bikes of different brands!). The origin of that coordinate system is the center of the bottom bracket. When you take a vertical measurement up from the floor, it does not become a stack (Y) measurement until you subtract off the bottom bracket height (floor to center of bottom bracket measurement). Similarly, when you take a horizontal measurement from the wall, it does not become a reach (X) measurement until you have subtracted off the horizontal measurement from the wall to the center of the bottom bracket.
Believe it or not, David, subtracting the distance to the bottom bracket from the wall and from the floor actually allows you to compare bikes that do vary in all of those things you mentioned, “like rim height, tire height, and chainstay/seatstay length.” Creating this X-Y coordinate system with the bottom bracket as the origin allows you to ensure that the two bikes you are comparing have the saddle and handlebar in the identical position relative to the center of the crank.