Why do ebikes need gears?

[Cyklefanatic]

As more and more electric cars become available it is becoming clear that transmissions are going to become a thing of the past. Only the Porsche Taycan has a transmission and it only has two gears. The argument is that an electric motor can deliver maximum torque over a wide range of RPM with maximum torque available at 0 RPM.
But the ebike industry seems to be going in the opposite direction moving away from single speed hub drives to mid mounted motors using gear reduction. The argument is that it allows more torque over a wider range of wheel speed. If this is true then it should be true for cars too. A smaller motor using a transmission would deliver more torque over a wider range with less weight.
Both cannot be true.
I am hoping someone smarter than me can explain this conundrum.

 

[Gionnirocket]

Because an ebike is also powered by humans... So unless you are Fred Flintstone, we need gears.

 

[J.R.]

The evolution of cycling has been to reduce weight. For me an ebike is a bicycle first and last. A lightweight bicycle performs and just feels better. Gearless motors, typically called direct drive motors are much heavier than geared motors. Magnets are heavy. A direct drive can be twice as heavy as a geared motor, while still not delivering as much torque. A car is designed to carry the load, an ebike, at close to bicycle weight, is not.

The push is for lighter weight ebikes, so the geared motor isn't going away anytime soon.

 

[Cyklefanatic]

OK so the human part of the bike needs gears. But the motor is a separate element that can be attached with or without gears. On a plug-in hybrid car the ICE engine still uses a transmission but the electric motor does not. Electric motorcycles and scooters also do not use gears.

 

[K PierreR]

Because cars don't top out at 1 hp.

I should say that tongue in cheek because of the way the e bike regulations are written. They are written as motor output, not battery draw power. Motor output has to do with rotational speed of the motor. A 3000 watt bike motor is not actually putting out much power at near zero speed even though the battery is putting out 3,000 watts. The bike is putting out a ton of torque but no power the way the regs are written. The regs are written to limit speed through power output but not limit torque per se. Sooner or latter, the e bike industry will start to write closed software to handle this. You might not need a transmission but that will still affect the range.
The problem with an e bike is that it is a bicycle, not a motorcycle. A bicycle has limited weight carrying capacity and electrics eat into useful loads.

 

[Gionnirocket]

OK so the human part of the bike needs gears. But the motor is a separate element that can be attached with or without gears. On a plug-in hybrid car the ICE engine still uses a transmission but the electric motor does not. Electric motorcycles and scooters also do not use gears.

Because of weight that the human will need to be able to propel on his own....it's really not a complicated riddle.
I've seen the comment here more than once that riders say that they hardly ever change gears when relying on the motor... I don't agree with it, but it is done.

 

[Cyklefanatic]

The evolution of cycling has been to reduce weight. For me an ebike is a bicycle first and last. A lightweight bicycle performs and just feels better. Gearless motors, typically called direct drive motors are much heavier than geared motors. Magnets are heavy. A direct drive can be twice as heavy as a geared motor, while still not delivering as much torque. A car is designed to carry the load, an ebike, at close to bicycle weight, is not.

The push is for lighter weight ebikes, so the geared motor isn't going away anytime soon.

But electric cars also struggle with weight. Manufacturers are going to great lengths to reduce their weight by using aluminum everywhere even though it costs more. If adding a transmission to an electric car would allow lower weight I am sure Tesla would be all over it.

 

[Mr. Coffee]

Because some of us ride and pedal their bikes on actual mountains.

 

[theemartymac]

A "wide range" of RPM is completely relative. Even Teslas have carefully tuned torque curves and efficiency ranges. The only reason a Tesla is such as speed monster down low, is that they start out ludicrously overpowered and give up the top end completely. That's not to say they aren't adequately "fast", but given the performance metrics below 100mph, they should be Bugatti-eaters on the track above it, and they are far from it. They are actually VERY slow above 100mph by supercar standards. And the efficiency at both very low and very high speed is quite poor, and the Tesla REQUIRES active battery cooling systems and complex BMS to keep from total nuclear meltdown when driven hard.

Translate that to a tiny bicycle motor and controller at todays level of technology, and that same performance range drops dramatically. We simply cannot add the weight and complexity of the systems that make a Tesla a decent (but still limited) wide-range performer, so we are stuck using traditional gears for the foreseeable future. Bike tech is going to be a long ways behind the best e-vehicles, and the fast charging needs to truly extend our range even farther, so real efficiency is still a long way off. That's not to say the future isn't bright however. It's a pretty cool time to be alive - technologically speaking.

 

[J.R.]

But electric cars also struggle with weight. Manufacturers are going to great lengths to reduce their weight by using aluminum everywhere even though it costs more. If adding a transmission to an electric car would allow lower weight I am sure Tesla would be all over it.

Where would you cut the weight on an ebike? Even the lightest carbon fiber ebike weighs in the mid 30 pounds and those bikes use a lightweight geared motor, with lower than average torque. Cost is 8 to 12 grand. Direct drive motors are too heavy for a bicycle. BTW I have a direct drive ebike and it doesn't come close to my bike using a geared system.

 

[AHicks]

Here's my take, and I've been saying this for a while now, that a mid drive really doesn't need 9-10 speeds - IF - it has sufficient power. Talking bikes, you need to qualify your thoughts with the size of the motor when talking gearing requirements. Clearly the gearing requirements of a 250w motor operating in rolling hills is going to be much different than one rated at 1600w, no? You want to complicate that even further? Add torque sensing to your thoughts.....

Hub drives play by a completely different set of rules. They don't care how many gears they have (one or none). Here, the gears are about YOU!

 

[Mr. Coffee]

Here's my take, and I've been saying this for a while now, that a mid drive really doesn't need 9-10 speeds - IF - it has sufficient power.

That depends a lot on what those speeds are. Most 1x systems have gear ranges of less than 450%, so inevitably either the low gears are too high or the high gears are too low. Even with a spendy Rohloff-equipped ebike I find that the lowest gears are quite a bit higher (usually 25-30 gear-inches) than a decent mountain or gravel bike (where 18-22 gear-inches is more common).

Also, even more than electric motors, humans are maximally efficient in a fairly narrow RPM range. So if you are riding long distances or riding fast that efficiency starts to matter much more than if you are merely riding to the corner store or the park.

There are a lot of different places people e-bike, and one shouldn't assume because X works fine where you live and ride that it will work everywhere.

 

[indianajo]

I pedal my bike unpowered when the wind is not >12 mph in my face or the trip is not over 25 miles. I have 24 speeds & use them all. 3 x 8. Because I have an 8 speed chain instead of 9 or more, it lasts 5000 miles.
DD hub motors burn up the watthours around town and on hills. I had one, my geared hub motor used 1/2 to 1/3 the watthours. My summer commute has >77 hills. DD motors weigh 12 lb too. I had the DD on the back, it was heavy rolling it out of the garage over the step. I have the geared hub motor on the front. balences the bike with the panniers on the back. The geared hub motor doesn't drag unpowered. It weighs about 10 lb with battery, about the same as 3 tubes, tools, 40 oz water & panniers to carry all that.
BTW, one advantage of riding the bike unpowered, when covid19 hit I had plenty of oxygen. I was ill 137 days, but not ill enough to go to a hospital. It would have been quicker in the hospital where I could have remdisavir, but the only medicine authorized for me at home was tylenol. People that can't get vaccines should have seen covid coming and worked out to prepare for it. I've known too many friends that sat around after retirement & were dead in 3 years of heart attack. It's been 12 years since I quit working for money & my heart is fine.

 

[RunForTheHills]

Once you eliminate the gears and add enough power to overcome the need for them, you may as well just call it an eMotorcycle and not an eBicycle.

 

[theemartymac]

Once you eliminate the gears and add enough power to overcome the need for them, you may as well just call it an eMotorcycle and not an eBicycle.

I'm not sure that I would go so far as the emotorcycle line just yet. Even the largest of mid drive motors are still less powerful than a typical corded power drill, and perform at horribly low efficiency when driven in any way like a city commuter motorcycle. As a guy who has and has owned many motorcycles of all size and usage, we're not exactly entering the automotive realm yet. We need at least 4 or 5 times the power to get anywhere near there.

 

[AHicks]

That depends a lot on what those speeds are. Most 1x systems have gear ranges of less than 450%, so inevitably either the low gears are too high or the high gears are too low. Even with a spendy Rohloff-equipped ebike I find that the lowest gears are quite a bit higher (usually 25-30 gear-inches) than a decent mountain or gravel bike (where 18-22 gear-inches is more common).

Also, even more than electric motors, humans are maximally efficient in a fairly narrow RPM range. So if you are riding long distances or riding fast that efficiency starts to matter much more than if you are merely riding to the corner store or the park.

There are a lot of different places people e-bike, and one shouldn't assume because X works fine where you live and ride that it will work everywhere.

Mr. Coffee, clearly our riding styles/needs/conditions differ a great deal. Rather than just blowing my opinion off as nonsense, or pull the direction of the conversation way off topic, let's pick this conversation up when you've spent some time on a bike with more power than you know what to do with.

My point is regarding the idea that the more power you have available, the less need there are for the number of available gear ratios. I doubt that's going to change much no mater where/how you ride....

 

[RunForTheHills]

I'm not sure that I would go so far as the emotorcycle line just yet. Even the largest of mid drive motors are still less powerful than a typical corded power drill, and perform at horribly low efficiency when driven in any way like a city commuter motorcycle. As a guy who has and has owned many motorcycles of all size and usage, we're not exactly entering the automotive realm yet. We need at least 4 or 5 times the power to get anywhere near there.

That is true. But it seemed to me that the OP was suggesting that the eBike industry should change direction towards eliminating gears and adding more power. Maybe I misinterpreted his post. I know there is a lot of disagreement on what the legal definition of an eBike should be, however I don't think many people would call a 10,000 watt fully suspended vehicle with a belly full of batteries an eBike even if it had pedals. And they are out there.

 

[Mr. Coffee]

My point is regarding the idea that the more power you have available, the less need there are for the number of available gear ratios. I doubt that's going to change much no mater where/how you ride....

That again depends on where and how far you intend to ride.

If you have a more powerful bike, obviously for a given battery size you will have less range. So if you are on a super long climb (or even poor road conditions) you are probably forced to run at a lower assist level just to make the trip at all, which brings you back to having lower gears. So unless you pack around a ridiculously large battery that bigger motor does you less good than you'd otherwise think.

Also there are pretty brutal practical limits on how big a battery you can put on a bicycle.

Terrain makes an enormous difference. I can easily run at 10wh/mi (or even less) in gentle terrain and good road surfaces. Change that to steep, rough roads and it is more like 100wh/mi.

 

[theemartymac]

That is true. But it seemed to me that the OP was suggesting that the eBike industry should change direction towards eliminating gears and adding more power. Maybe I misinterpreted his post. I know there is a lot of disagreement on what the legal definition of an eBike should be, however I don't think many people would call a 10,000 watt fully suspended vehicle with a belly full of batteries an eBike even if it had pedals. And they are out there.

I think it's certainly going to be an interesting evolution through the middle ground. We are definitely reaching the limit of the current technology for conventional/traditional bicycle components, and you're right the tolerance for true monsters on the city trails and sidewalks isn't/won't be there, which suggests a couple of routes we can go. One of them involves simplifying the current drivetrain, so we can improve chain lines/beef up remaining components, maybe reduce overall weight, etc. I think the idea of doing this on cargo bikes and certain ebike models makes sense, and would better address the interim needs of the 'heavy-bicycle' community. It does also suggest migrating outside of the current conventional bicycle definition, so there is obviously going to be room for interpretation and redefinition. I could actually see using my mid drive with only 6 wider-range gears instead of the current 9, as I'm really only using the extra gears to reduce cassette wear right now and have my 5 favorites for 99% of my riding. There is also a potential ease of use benefit to fewer gears and simpler systems, especially with the older riding demographic, so I could see that being in our future. Time will tell, but I'm not a gambling man...

 

[RunForTheHills]

I think it's certainly going to be an interesting evolution through the middle ground. We are definitely reaching the limit of the current technology for conventional/traditional bicycle components, and you're right the tolerance for true monsters on the city trails and sidewalks isn't/won't be there, which suggests a couple of routes we can go. One of them involves simplifying the current drivetrain, so we can improve chain lines/beef up remaining components, maybe reduce overall weight, etc. I think the idea of doing this on cargo bikes and certain ebike models makes sense, and would better address the interim needs of the 'heavy-bicycle' community. It does also suggest migrating outside of the current conventional bicycle definition, so there is obviously going to be room for interpretation and redefinition. I could actually see using my mid drive with only 6 wider-range gears instead of the current 9, as I'm really only using the extra gears to reduce cassette wear right now and have my 5 favorites for 99% of my riding. There is also a potential ease of use benefit to fewer gears and simpler systems, especially with the older riding demographic, so I could see that being in our future. Time will tell, but I'm not a gambling man...

I agree. There are some valid use cases for ebikes that aren't well served by the current definition of an ebike. Like cargo bikes and heavy riders. I don't understand the need for speed on a bicycle though. For me, once you move into the 30-50MPH range on flats and uphill you are looking for a motorcycle or scooter. Either allow enough time for your commute, use multi-modal transportation, or buy, register, and insure a motorcycle.