« on: December 06, 2010, 12:49:10 pm »
At the very great risk of confusing this perfectly good argument with facts, let me add some data.
I looked up the weight (mass) of Sun CR-18 rims, as I know these are available in both sizes. 26”, 440 g. 700C, 484 g. Add to these the mass of some Schwalbe Marathon tires (available in many sizes, and popular with tourists): 559x40 (26x1.50”), 600 g; 622x32, 580 g; 622x40, 720. I think the 700Cx40 is much wider than many road tourists, use, but it’s there if you want to get picky about equivalent widths. Making a few simplifying assumptions (like massless hubs and spokes), I calculated the energy, in Joules, required to accelerate these components to 10 mph: 26”, 10.39 J; 622x32, 10.63 J; 622x40, 12.03 J. So to accelerate these wheels to 10 mph, you’d need 2.3% more energy for the 32 width wheels, and 15.7% more for the 40 wheels, over the 26” wheels.
Of course, you’ll need to accelerate yourself, the bike, and the luggage if you don’t want to watch the wheels rolling off down the road. If everything else weighs 250 pounds, that’s 1133 J. Total energy to accelerate you and your loaded bike is remarkably similar across the wheel differences: 0.02% more for the 32 wheels, and 1.4% more for the 40 wheels, again compared to the 26” wheels.
I’d call that 0.02% negligible.