6 ms·

Mass matters for the simple reason that if you need to climb a hill, the energy required to lift a mass is proportional to the mass. Granted, barring extremely

Mass matters for the simple reason that if you need to climb a hill, the energy required to lift a mass is proportional to the mass. Granted, barring extremely heavy bikes, ~3/4 of the mass is the rider.

fluoridation 4y ago
The human is more like >80% of the mass of the entire system, not ~75%.
- layer8 4y ago
  Not sure why this is downvoted. A normal bike shouldn’t weigh more than 15 kg (some weigh just half of that), so a human at 75% would only weigh 45 kg at most. Maybe people are thinking of e-bikes, which are a lot heavier.
  - mshroyer 4y ago
    My steel touring/commuter bike (not an e-bike) easily weighs more than that, at least if I count the lock and repair kit I keep attached to the frame.
    - fluoridation 4y ago
      Just how much extra equipment are you carrying? I would expect a bike like that unloaded to be around 12 kg.
    - layer8 4y ago
      Fair enough, but for a human, let's say weighing 70 kg, to be 75% of the total weight, the bike plus whatever is attached to it would have to be above 23 kg. You only reach such a ratio with extra luggage.
kqr 4y ago
Also you reclaim the energy on the downhill. Mass doesn't matter as much as people used to think. (Hence no modern bikes being made out of drillium.) 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.
- rhn_mk1 4y ago
  You reclaim it downhill if you book it. Casual riders seem to brake after reaching a certain speed, so they will send that energy to heat the brakes. Plus, the unfun of getting up the hill is probably more important than the fun going down, as it takes longer :)
  - DangitBobby 4y ago
    Unless you have a stop sign, traffic signal, or sharp curve at the bottom.
- fluoridation 4y ago
  On the other hand, a heavy wheel will also hold more angular momentum and so will better resist drag, at the cost of more difficult acceleration, braking, and stiffer but more stable steering.
  - roelschroeven 4y ago
    A heavier wheel, just like a heavier bike in general, doesn't "better resist drag". Yes, it makes the bike slow down slower, just as it makes it harder to speed up the bike. 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.
    - fluoridation 4y ago
      No, it's not wrong. Given the same cross-section and initial speed, a heavier object moving through a fluid over a certain time will decelerate less than a lighter object, 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. 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.

fluoridation 4y ago

The human is more like >80% of the mass of the entire system, not ~75%.

layer8 4y ago
Not sure why this is downvoted. A normal bike shouldn’t weigh more than 15 kg (some weigh just half of that), so a human at 75% would only weigh 45 kg at most. Maybe people are thinking of e-bikes, which are a lot heavier.
- mshroyer 4y ago
  My steel touring/commuter bike (not an e-bike) easily weighs more than that, at least if I count the lock and repair kit I keep attached to the frame.
  - fluoridation 4y ago
    Just how much extra equipment are you carrying? I would expect a bike like that unloaded to be around 12 kg.
  - layer8 4y ago
    Fair enough, but for a human, let's say weighing 70 kg, to be 75% of the total weight, the bike plus whatever is attached to it would have to be above 23 kg. You only reach such a ratio with extra luggage.

kqr 4y ago

Also you reclaim the energy on the downhill. Mass doesn't matter as much as people used to think. (Hence no modern bikes being made out of drillium.) 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.

rhn_mk1 4y ago
You reclaim it downhill if you book it. Casual riders seem to brake after reaching a certain speed, so they will send that energy to heat the brakes. Plus, the unfun of getting up the hill is probably more important than the fun going down, as it takes longer :)
- DangitBobby 4y ago
  Unless you have a stop sign, traffic signal, or sharp curve at the bottom.
fluoridation 4y ago
On the other hand, a heavy wheel will also hold more angular momentum and so will better resist drag, at the cost of more difficult acceleration, braking, and stiffer but more stable steering.
- roelschroeven 4y ago
  A heavier wheel, just like a heavier bike in general, doesn't "better resist drag". Yes, it makes the bike slow down slower, just as it makes it harder to speed up the bike. 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.
  - fluoridation 4y ago
    No, it's not wrong. Given the same cross-section and initial speed, a heavier object moving through a fluid over a certain time will decelerate less than a lighter object, 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. 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.