Originally Posted by
sd5782
32s on my other bikes mostly, so not a great difference. The Miyata has a soft “trunk” bag on the rear rack and a small one on a front rack so obviously not aerodynamic. I do like the explanation about slowing down and speeding up causing losses. Even with those explanations I would still bet the added weight is a factor. Take a car that weighs X and gets a certain mpg. Wouldn’t it still take a bit more power to propel with 500 extra pounds in the trunk and everything else is equal?
it takes more power to accelerate that weight to a certain speed - but it does not take noticeably more power to sustain that speed. the forces acting against you once you're in motion are wind resistance (a heavy object of the exact same size, shape, and surface texture as a lighter one has the same wind resistance) and friction from your bike's contact surfaces (chain, bearings, etc) and the contact of your tires with the road. those latter frictional forces are marginally higher with a heavy bike, but the difference is very tiny compared to wind at any significant speed.