The one thing where I suspect mass might matter is in the wheels. It's a huge difference between getting a heavy wheel spinning and a light one, and at least for commuting/recreational usage, most of that will be bled off as heat anyway.
When people say heavier bikes and/or wheels "resist drag better", it sounds like all that extra mass somehow magically makes it so that you need less power on the pedals to maintain speed. That is simply wrong.
True
> and so will require less energy to bring it up to the speed it had before decelerating, because the difference in speed will be less
False
The higher inertia of the heavier object resisted the deceleration, and that same higher inertia will resist acceleration too in exactly the same way. You've gained nothing at all.
> For the same reason, you would not ride while dragging an open umbrella behind yourself, but you'd have no problem putting a metal cube of the same mass on your stem. It's the ratio of cross-section and mass.
Now you're talking about aerodynamics which is a whole different matter. For aerodynamics, cross-section is of course a major factor (not the ratio of cross-section and mass!). That's pretty obvious, but has nothing to do with a discussion about mass.
(Ratio of cross-section and mass is relevant for things in free fall, because there gravity is the relevant force. Completely different from a vehicle on a flat road.)
What does this mean? A downhill gives your legs a rest if you coast but it's not going to restore all the energy you burned going up the hill. And if you're riding sportily (not even a race necessarily), you'll still be pedaling the same amount of watts downhill. You'll just be going faster for the same amount of muscle power.
> Mass doesn't matter as much as people used to think. (Hence no modern bikes being made out of drillium.)
Modern bikes are getting lighter and lighter.
> The one thing where I suspect mass might matter is in the wheels.
Yes, in terms of ROI by unit weight, lighter wheels are the best place to start.
The trend over the last few years have been disk brakes, aerodynamic features and wider tires, all of which come with a weight penalty. Some brands are now starting to converge their aero and lightweight offerings, though.
Not really. Bikes don't have a battery to store reclaimed energy, if that would even be a thing. Maybe you go a bit faster on the downhill; I wouldn't call that reclaiming energy.
> Mass doesn't matter as much as people used to think.
On a flat road at a constant speed, mass doesn't matter (except for the slightly increased rolling resistance). With speed changes (in situations with sharp corners for example, or if you want to accelerate fast to escape from the bunch or to catch someone else) or in hilly/mountainous areas, mass does matter.
For recreational use, spending lots of money for shaving of a few grams here and there is not worth the effort, that's true. But a few kilograms more or less do make a difference.
> Hence no modern bikes being made out of drillium.
Modern top-of-the-line road bikes for climbing are already as light as allowed by the UCI. It makes no sense to drill holes in such a bike: you wouldn't be allowed to use it in a race.
This sort of edge case maximalism feels useless and needlessly contrarian - it seems as though if I were to claim you can pay for things by credit card, you’d claim “that doesn’t work what if the power is out”.
In my experience, hilly rides are just harder and I'm more tired after them. It's actually very surprising that what I would expect to be a common sense viewpoint is being considered the contrarian one! Sure, apply elementary physics and hills are meaningless, but apply real-world physics and maybe they aren't so meaningless. And we aren't even considering the differences in energy efficiency when your body has to work harder, or the major differences in energy loss through air drag at high speeds. There are also concerns about how comfortably and efficiently you are able to convert muscle energy into motion through pedaling (similar to how fast walking gaits are very inefficient) at both the high (downhill) and low ends (uphill) of pedal RPM.
The big hills I can think of near me all have either stop signs at the bottom, or another hill to climb.