My point is exactly what I wrote! I know it’s a lot, I overcompensated.

Or are you saying they do this for the feeling only and regen is a byproduct

Yes. I said it’s designed this way to feel like a normal car. But it’s a very elegant solution! Far better to do it that way and re-capture some of the energy than let it leave the system, like heat from brake pads.

I’d say applying a little drag to regen on an ebike going downhill will be more beneficial than allowing the riders to go as fast as possible downhill

That “drag” is braking!

They could still turn it off

Like letting go of the brake lever! Far simpler than adding a new always-on brake that you have to manage separately.

but why would I do that?

Because sometimes you want to go full speed down a hill because it’s the most efficient way of moving forward! If you slow down, you have to pedal more later. If you slow down and save some of the energy, you still have to pedal more later, because you can’t save all of the energy from the hill, you can only save part of the energy.

There’s a maximum speed you feel comfortable going on steeper descents, and you manually brake to manage it. That’s the only time regen makes sense on a bike.

Also, because we’re not talking about drag that only exists on the hill. This system exists at all times in a hybrid, and if you implement it on a bike, you’ll be coasting less on flat ground too any time you stop pedaling! Why would we want that? Would you brake in a hybrid when you’re on flat ground to “save it for later”? No! Braking, and engine braking, slow you down.

Well, I knew I’d leave too many loose ends explaining something before bed.

Not quite.

When you coast in a car with an internal combustion engine, you go further when you’re in neutral. Why? Engine braking. When you take your foot fully off the pedal, you restrict airflow to the engine and create a partial vacuum that the cylinders have to work against.

I’m not saying to coast in neutral for higher fuel efficiency. It’s quite the opposite with modern engines that cut off fuel injection when it’s not needed while in gear—and it can lead to increased wear and tear on the engine as well as your brakes fading on long descents. But now you have me covering my ass on every little point, ha. You could look up hypermiling and learn about more efficient driving techniques that way!

Now obviously hybrids have traditional internal combustion engines on board that behave the way we’ve just described. The engineers have also added a level of regenerative braking that is variably applied, even when the engine is not on, so that you scrub speed at a consistent pace. Without this, descending with the engine on or off would feel drastically different, and the car wouldn’t behave as expected at all times. It’s similar to how engineers for fully electric cars have added the “crawl” mode that makes a car idle forward when the brakes are off, even though there is no actual “idle” occurring. It makes the car handle the way you expect it to, and that makes you safer.

It is nice to recapture some energy that is used during the braking process. But only if you need to brake. Otherwise, you’re stealing energy you could be using right now and turning into less energy for later. The process of converting energy into various forms is inefficient, so you will always end up with less than you started, and the more conversions you do the more you lose. Potential gravitational energy to kinetic motion energy is more efficient than potential gravitational>potential chemical>kinetic motion, plus that last step is oversimplified because having the chemical energy turn a driveshaft is actually another kinetic energy conversion compared to gravity turning the wheels directly.

Thus e-bikes could benefit from regenerative braking if the system is efficient enough to overcome the loss of efficiency it introduces via weight and drag, but not from the constant low level capture of energy that would be better used now. Because you don’t get to fuel up an e-bike when the tank’s nearly empty—any toll you pay in inefficiency comes outta your legs and your lungs.

I am not an expert and I am sure I glossed over some nuances.

That’s not really how regenerative hybrids work. Turning linear motion into stored energy produces drag, aka braking, so when you hit the brakes, why not store some of that energy that would otherwise just be lost as heat in the brake pads. They’re not just finding extra energy to store for later while you travel downhill unless you have cruise control on (which is to say, unless the car is braking).

Not really, even in this hypothetically perfect scenario. Either the hill isn’t steep enough to generate any real excess energy from rolling down it (too much drag and you’ll stop rolling) or it’s steep enough that what you collect is offset by how much energy the ride home requires. The more potential energy you save for later, the slower you’re traveling now. And you can never cross the threshold to where it’s helpful. You’re trying to steal energy from a closed loop. It’s the “bowling ball dropped from face level” problem all over again. It can never get enough potential energy from its trip away to come all the way back.

Storing pedaled energy is pointless too.

Let’s say one regular old pedal rotation propels you 10 feet.

Let’s instead store 20% of that energy for later. You now only travel 8 feet.

While we’re converting that energy, we lose a quarter of it due to inefficiencies in the process. So now we’ve traveled 8 feet and stored 1.5 potential feet.

Pedal 1000 times. We go 8000 feet and store 1500 potential feet. Stop pedaling, turn on battery support, we go 1500 feet, we get 9500 total. 500 less than an unmodified bike. That’s excluding additional system inefficiencies like the added weight of the modifications and the mechanical efficiency of the pedal assist. It’s more efficient to just pedal.

It’s a band-aid measure that makes cars behave more like buses, trains, or any other form of transit that takes the mental strain off of the individual. Yet it still uses cars, so we all still get those sweet sweet carbon emissions and ridiculously outsized infrastructure degradation. It’s a step in the right direction but we’re still on the wrong path.