Originally Posted by
ItsJustMe
I don't think it's physically possible that an ebike is more efficient than a normal bike. You take two otherwise identical bikes, one is operated physically, directly from the energy source (legs). The other is operated by a motor that's less efficient than the muscles in the legs, run from a battery that loses energy (in the form of heat)
Muscles are about 20% efficient. Good quality electric motors peak at around 95% efficient (but their efficiency suffers somewhat when they're not run in exactly the right way.) Your muscles lose energy in the form of heat too ... you have noticed that you sweat when riding hard, right?
If you're going to count all the losses in the entire supply chain for electricity, you should also count all the losses in the supply chain for food -- and they're a lot worse than the electrical grid. And it gets so much worse if you eat meat.
The efficiency measurement of the muscles gets an unfair but unavoidable advantage from the fact that most of the base maintenance level of inefficiency is going to be paid anyway, because the person is alive whether they're riding a bike or riding an ebike.
The 20% I quoted is just for actively used muscles -- not keeping them alive or keeping you alive. If you include that, the efficiency drops (but of course, an athlete becomes more efficient than somebody else, as they can produce more mechanical energy while using more food/energy to power their muscles and the same energy to keep them alive.)
Add in the fact that the more you ride, the more efficient you become, because your body becomes more and more efficient at using fuel the more fit it becomes.
I don't think becoming fit changes the efficiency (i.e. converting chemical energy into motion) of your muscles significantly, but of course losing weight will make you require less food to keep you alive and indeed less energy to move you from place A to B.
Measurements based on how much Big Macs cost per calorie versus gasoline are kind of bogus IMO, we're talking about efficiency of movement versus calorie input here.
Well, if we are, then the electric bike beats human powered bikes hands down -- 85% efficient (real world) vs. 20% efficient.
Big Macs aren't a very efficient form of energy -- transport of the food and the meat really lowers the efficiency. Some sort of vegetable -- potatoes? -- would give nicer values, and even that is really really low if you look at the entire chain.
I'd guess peak efficiency is probably at around 12 to 15 MPH on a diamond frame bike, probably higher in more aerodynamic setups.
It depends on how you're measuring efficiency. Are you including the energy needed to keep the human alive? If not, the speed for peak efficiency (looking only at energy used per mile) is a good deal lower than that, probably as slow as you can go without having problems balancing. The only reason humans like 12-15 mph so much is that that is about as fast as most can easily maintain. To put this in perspective ... if 15 mph requires 100 watts on flat ground with no wind, 7.5 mph probably requires less than 20 watts (air resistance is proportional to speed cubed, and rolling resistance is proportional to speed.)
I stand by my original statement ... it depends on how you define efficiency, on what you're measuring. In some situations, the bike wins. In others, walking. In others (especially if time is factored in somehow) ... motorized transport will win. I think in most cases when somebody says "bikes are the most efficient!" -- they haven't even really fully thought about what they're saying.