Dear Matthew Alice: Please settle a disagreement between me and my mate. He just bought a brand new state-of-the-art bicycle that weighs about seven pounds less than my older, less expensive bike. I say his bike takes less effort to ride (i.e., up hills) than mine because it weighs less. He says if I just lose seven pounds, it will be the same as if my bike weighed seven pounds less and our expended effort will be the same. I totally disagree. The bike still weighs the same and that is the object you’re moving. Please set him straight. — Megan Christopherson, Mission Beach
Sounds to me like he’s just weaseling out of buying you a new bike, Megan. True, in some vague, theoretical way, it will take less effort for the slimmed-down you to ride up that hill, since you’ll be moving less weight. But as a practical matter, he’s missing a few spokes. Without knowing any of the details of this situation, I’d have to guess that the percentage gain in riding efficiency he acquired when he bought his new bike is greater than what you’ll gain by shedding seven pounds. But he can take some comfort in the fact that your explanation of why he’s wrong isn’t quite right either.
What you’re really moving when you pedal a bike are the wheels. You and the frame follow along out of necessity. A seven-pound weight loss from you or from the frame of your bike theoretically will amount to about the same thing. But in the real world of bike physics, the combined mass of you and the frame is much less important than the mass of the wheels. For ever)' unit of mass lost in the wheels, you’d have to lose from two to four units (some say even more) from your hips to get the same benefit. The lighter the wheels and the smaller the point of contact with the road surface, the less effort it will take to accelerate your bike. Every push of the pedal is overcoming not so much the weight being moved but the resistance of the road surface at the point of contact with the tire. So it’s really impossible to ignore the fact that his “state-of-the-art” cycle is probably designed for maximum efficiency where it counts — where the rubber meets the road. Literally. You may note, however, that on downhills you look like a champ, since there your greater mass helps your momentum.
The real world of biking includes other significant variables like the efficiency of the drive mechanism, the flex in the frame, and especially the amount of drag produced by your biking posture and the clothing you wear. And speed is a big factor, too. The slower you’re riding, the less difference there will be in relative energy output between you and your mate, regardless of bike design. So I hope this gives you enough information to keep the spat going until he finally gets sick of it and buys you a new bike. If he spent thousands for his pride and joy but only gained in efficiency what you would gain by losing seven pounds, well, it’s the salesman who took him for the best ride of all.