Wow, I didn’t realize eMTBs have gotten so popular that manufacturers are partnering with Grammy Award-winning rappers. 😄
In all seriousness, the second chain is a strange idea, considering there are already two-wheeled vehicles with single chains that transmit substantially more power: motorbikes.
Of course, motorbikes shift gears internally – and also have no standardization of the chain being in left or right, although it’s usually left. So what they’ve done here is build two drivetrains – drivechains? – with two sets of sprockets. This just seems… mechanically suspect, since that’s two derailleurs and if they desynchronized, destruction of something is highly likely, be it the rear axle or the chain taking up the full burnt.
It’s a difficult problem, no doubt, as there’s no market for bicycle components that can handle such high power transmission. And whatever they build, it will end up being proprietary. So maybe this is their best option, but it doesn’t seem that good.
Honestly, it’s surprising that normal bicycle components have handled the onslaught of 250W (Euro spec) or 750W (US spec) ebikes without major reports of chains and sprockets exploding into pieces, probably be cause humans can (briefly) produce such outputs. Of course, there is a market for ebike specific parts too, to add mechanical headroom, although they tend to just be made more robustly, rather than totally reengineered.
I don’t ride MTBs, but I understand one of the more frequent issues on trail is to bump the derailleur against a tall rock or taking a fall where the bike lands on the starboard (right) side. Of the components on a bike with the least ground clearance – tires, wheels, pedals, cranks, derailleur, chain – the derailleur is unique in that if it gets damaged, that’s potentially game over for the today. All the others can be banged to kingdom come and you can probably still ride on, or make quick repairs to limp back to the trail head.
The ebike before us doubles the number of failure points: two derailleurs. So now the bike is vulnerable to both port-side and starboard-side impacts. But then there’s also the mechanics of the hub of consider.
To support two sets of sprockets, the hub ostensibly requires both sides to ratchet. I can imagine two ways to do this: 1) the port-side hub transfers torque across the barrel to the convention starboard-side ratchet, or 2) the port-side has its own ratchet.
The challenge with #1 is that the hub barrel may have to be reinforced to accommodate this torque. Yes, disc brake torques might already have reinforced the hub, but we’re talking about substantial amounts of power beyond a normal bike. Moreso, the mismatched torque “path” between port- and starboard-side can cause lag, burdening one side over the other under hard acceleration. Automobiles have a similar issue known as torque steer.
But then we also have to consider if the single ratchet will survive the input power. With the expiration of the DT Swiss patent, the star ratchet is increasing in popularity, in part because its design does not concentrate forces into just three or six pawls and teeth. Pawl breakage is known to happen in acoustic bikes, so it stands to reason it’s a substantial issue for high power ebikes. Supposing this bike uses a star ratchet, the matter of teeth doesn’t disappear: how much teeth engagement is allowed? DT Swiss specifically designs a line of 24t (15 degree engagement) for ebikes because more teeth (eg 36t, 54t) would be too brittle under ebike power conditions. For MTB, fewer than 36t gives a “sloppy” feel when pedaling.
Solution #2 solves the torque and ratchet issues, by dividing power evenly to both sides of the wheel. Or does it? Two unsynchronized ratchets will not engage at the same time, worsened if there are fewer teeth. Under load conditions, very briefly, only one ratchet would transfer power while the other spins into engagement. That, to me, seems like a mechanical issue waiting to happen, if one ratchet dies without notice, causing the other ratchet to take on the full load, and it too dying shortly thereafter.
Finally, how does the rear brake disc attach if there’s a sprocket set in the way?
I want to be clear that I’m not entirely writing off this ebike. It certainly is interesting as a machine, but it seems to have made design choices that either box it into really hard engineering problems or detract from the MTB experience in ways that reduce its appeal. Could they have overcome the mechanical issues? Yes, but great cost, great complexity, or great proprietary would be needed.
Wow, I didn’t realize eMTBs have gotten so popular that manufacturers are partnering with Grammy Award-winning rappers. 😄
In all seriousness, the second chain is a strange idea, considering there are already two-wheeled vehicles with single chains that transmit substantially more power: motorbikes.
Of course, motorbikes shift gears internally – and also have no standardization of the chain being in left or right, although it’s usually left. So what they’ve done here is build two drivetrains – drivechains? – with two sets of sprockets. This just seems… mechanically suspect, since that’s two derailleurs and if they desynchronized, destruction of something is highly likely, be it the rear axle or the chain taking up the full burnt.
It’s a difficult problem, no doubt, as there’s no market for bicycle components that can handle such high power transmission. And whatever they build, it will end up being proprietary. So maybe this is their best option, but it doesn’t seem that good.
Honestly, it’s surprising that normal bicycle components have handled the onslaught of 250W (Euro spec) or 750W (US spec) ebikes without major reports of chains and sprockets exploding into pieces, probably be cause humans can (briefly) produce such outputs. Of course, there is a market for ebike specific parts too, to add mechanical headroom, although they tend to just be made more robustly, rather than totally reengineered.
? What’s mechanically suspect?
What do you consider more suspect in contrast to other eMTBs?
I don’t ride MTBs, but I understand one of the more frequent issues on trail is to bump the derailleur against a tall rock or taking a fall where the bike lands on the starboard (right) side. Of the components on a bike with the least ground clearance – tires, wheels, pedals, cranks, derailleur, chain – the derailleur is unique in that if it gets damaged, that’s potentially game over for the today. All the others can be banged to kingdom come and you can probably still ride on, or make quick repairs to limp back to the trail head.
The ebike before us doubles the number of failure points: two derailleurs. So now the bike is vulnerable to both port-side and starboard-side impacts. But then there’s also the mechanics of the hub of consider.
To support two sets of sprockets, the hub ostensibly requires both sides to ratchet. I can imagine two ways to do this: 1) the port-side hub transfers torque across the barrel to the convention starboard-side ratchet, or 2) the port-side has its own ratchet.
The challenge with #1 is that the hub barrel may have to be reinforced to accommodate this torque. Yes, disc brake torques might already have reinforced the hub, but we’re talking about substantial amounts of power beyond a normal bike. Moreso, the mismatched torque “path” between port- and starboard-side can cause lag, burdening one side over the other under hard acceleration. Automobiles have a similar issue known as torque steer.
But then we also have to consider if the single ratchet will survive the input power. With the expiration of the DT Swiss patent, the star ratchet is increasing in popularity, in part because its design does not concentrate forces into just three or six pawls and teeth. Pawl breakage is known to happen in acoustic bikes, so it stands to reason it’s a substantial issue for high power ebikes. Supposing this bike uses a star ratchet, the matter of teeth doesn’t disappear: how much teeth engagement is allowed? DT Swiss specifically designs a line of 24t (15 degree engagement) for ebikes because more teeth (eg 36t, 54t) would be too brittle under ebike power conditions. For MTB, fewer than 36t gives a “sloppy” feel when pedaling.
Solution #2 solves the torque and ratchet issues, by dividing power evenly to both sides of the wheel. Or does it? Two unsynchronized ratchets will not engage at the same time, worsened if there are fewer teeth. Under load conditions, very briefly, only one ratchet would transfer power while the other spins into engagement. That, to me, seems like a mechanical issue waiting to happen, if one ratchet dies without notice, causing the other ratchet to take on the full load, and it too dying shortly thereafter.
Finally, how does the rear brake disc attach if there’s a sprocket set in the way?
I want to be clear that I’m not entirely writing off this ebike. It certainly is interesting as a machine, but it seems to have made design choices that either box it into really hard engineering problems or detract from the MTB experience in ways that reduce its appeal. Could they have overcome the mechanical issues? Yes, but great cost, great complexity, or great proprietary would be needed.
I’d guess the second chain is for regerative braking
nvm they say in the article the second chain is only for motor power