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Comment by conradev | Hacker News Reader

The one thing about e-bikes that I don't get is: why the chain?

https://www.voromotors.com/products/emove-roadrunner-v3-seat...

This thing has 500W hub motors, no expensive derailleur, no chain to maintain, just tires and brakes. The hub motors have internal gearing. I love mine for getting around LA.

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That isn't a bicycle. It's a scooter.

So the difference is having pedals? Even if said pedals are just acting as a throttle and not actually making you put in any effort?

Almost all ebikes use a torque sensor in the bottom bracket, meaning you do have to put out some effort to get full power from the motor.

Bicycles have pedals that can propel the vehicle forward by pedaling, yes.

That thing you linked to is not a bike, it's a motorcycle. It should be licensed, taxed and insured like one.

The chain is to connect the pedals to the rear wheel as you might expect, assuming you want to be able to pedal.

I see the rivan thing has a toothed belt rather than chain.

If I understood the article correctly in this case the pedals are not physically connected to the wheel, it states the pedals run a generator that charges the batteries. So for this specific bike it would actually be possible to remove the belt (save for the other disadvantages of a hub motor).

This Rivian bike is bizarrely "pedal by wire" - there is no physical connection between the pedals and the rear wheel.

Instead the pedals work as a throttle to set the speed of the motor and to charge the battery while you ride, reducing depletion speed. It also harvests energy when braking.

If the battery in this bike dies completely, or is removed, you cannot pedal to move it at all. The "toothed belt" (gates drive) connects to the motor, with no link to the pedals.

In theory this design could have been done with no chain/gates drive using hub motors and still work much the same, given all the pedals are really doing is turning a dynamo-contraption to charge a battery.

I think the chain makes sense you want to let the rider pedal. If you don't, hub motors are the obvious way to go.

"The rider pedals a generator, which replenishes the battery, "

The chain is probably to keep unsprung weight low. Hub motors are not the best for comfort.

Why is that? Do you want sprung mass to be heavier or unsprung mass lighter?

I see how lower unsprung mass could be easier on the tyres but I have no idea how it could impact a rider who's isolated by full suspension.

Sort of both, lower unsprung mass means the wheel moves more easily up and down without the rest of the vehicle doing the same.

Torque, electric motors need gearboxes just like everything else

This doesn't address the question "why a chain" though.

Many motorcycles have grunty torque, gearboxes, and no chain: https://en.wikipedia.org/wiki/Category:Shaft_drive_motorcycl...

The BMW R 100GS Paris Dakar was the bee's knees for crossing the Tanimi Desert: https://www.motorcyclespecs.co.za/model/bmw/bmw-r100gs-pd-89...

Yes, the gear reduction is done in the "gearbox" in those. Some bikes use chains to do the same.

If you have elecreic hub motors there is no room for these between the hub motor and wheel.

So, we appear to agree, there could be a shaft or a chain between the gearbox and the wheel.

Ergo, the existence of an off hub gearbox neither forces nor requires a chain to be used to transfer power.

The arguments for why use a chain Vs why use a shaft are not predicated on the existence of a gearbox.

Shaft drives are less efficient than (clean) chain drives. Chains are just really, really good (outside of extremely dirty conditions).

Chains wear down, as do gear wheels.

They both have their pro's and cons, I've a few hundred thousand km's across the globe each with both shaft's and chain's.

Thank you for expressing your personal opinion though.

Everything wears down.

Chains are objectively more efficient than shaft drives -- it's not my personal opinion.

The two major downsides for chains are maintenance and longevity.

The main benefits to shaft drive are longevity and ease of maintenance.

That's objectively more efficient to those that travel a lot in harsh conditions.

Opinions are almost always personal.

Shaft drive is more expensive to produce, tends to be a little heavier, and usually has more friction loss.

Shaft drive delivers power better, wears less than a chain, easier to maintain.

Swings, roundabouts, and tangential from answering why "Torque, electric motors need gearboxes" doesn't answer the progenitor question "why chain".

My bike vendor likes chains. They wear more easily, but are easy enough to maintain and change. Basically everything old school bike like has maintenance/repair advantages.

I'm not sure I agree, but more when compared with belt drive and internally geared hub. But then again, I believe him that those are hard to repair when they fail (even if they are sturdy until then).

I also prefer shaft drive over a chain. Much less hassle and if not punished, can be almost maintenance free. A chain is easily worn and can even rust away just sitting there.

Not really if you just keep it lubed. I have a BMW shaft drive bike, and I have to change the rear end oil, the driveshaft oil, the transmission oil and the engine oil every year. My Honda just needs the chain lubed, adjusted, and engine oil changed. You check it every 600-1000 miles or so, but I can adjust and lube the chain in about 5 minutes.

Unsprung weight.

Almost all bicycles and ebikes don't have suspension -- all of the weight is unsprung.

The answer I was looking for! I was looking for the trade-off

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