Alan B
100 GW
Recently a friend considering an ebike asked me some questions that I thought would be worth sharing here. What follows is fairly abbreviated, whole books have been written on this topic. Here I will boil it down.
Prospective User Question:
Take a look at this web page, which is very hard on mid drives ! I'm interested in your comments.
http://www.pedegoelectricbikes.com/faq/#hub
My Summary of Pedego's page:
Hubmotors are best for most people.
Most mid drives are 250W, Pedego humbotors are 500W.
You pay more and get less with mid drives.
Maintenance is higher with a mid drive than a hubmotor.
Mid drives are complicated and you have to shift.
Hub motored bikes are more pleasant and easier to ride.
My response to my friend:
So far I've built all the types, medium size DD (direct drive) hubmotor, large DD hubmotor, geared hubmotor and now mid drive. They all have their advantages, and I am not throwing any of them away, they all have their use cases. You should pick what you want to do based on your needs. What follows is based on my experience building a small fleet of ebikes and using them for commuting, transportation, exercise and fun.
Now Pedego is in business to sell and support a lot of ebikes, and they have their own issues to deal with. The biggest bike manufacturers are going mid drive. Bosh is one example, and there are a number of others. Why is that? Mid drive ebikes are the lightest and have the widest range of application, and are the most bike-like system. In countries with low power limits (most of the world), mid-drives make the most of low power. However hubmotors are also useful ebikes.
What bike are you going to convert? What are you going to do with it? That matters and guides what is the best choice for you.
Direct Drive (DD) hubmotors are best for high mileage commuting. They make a heavier bike, and if you have steep hills you need a BIG hubmotor. You can't beat DD hubmotors for simple reliability. But it takes a lot of copper and magnet material to have adequate torque, making a hubmotor heavy and if you get on a really steep hill it may overheat, burn up or just fail to get up the hill. The DD's regen capability is wonderful for those big downhills, especially if it is variable regen (which depends on the controller). Large DD hubmotor equipped bikes tend to be heavy and more Moped-like machines. Some folks are annoyed by the poor coasting of the DD hubmotors, as there is a little bit of magnetic resistance to rolling in the motor. A large DD hubmotor can handle a lot of power.
Geared hubmotors are smaller and lighter, but the gears are fixed (*). They have a clutch and coast like a regular bike. And you lose regen. Which means the brakes have to work much harder. They are more limited in motor power (due to a smaller motor with a more difficult heat dissipation path), require more maintenance (than DD hubmotors), and climb hills a little better than a low power DD hubmotor (but not as well as a high power DD hubmotor
). They keep the bike fairly light, but not as light as a mid drive. They are fairly expensive and require periodic maintenance inside the hubmotor of the gearing and clutch system. If you have some steep hills you'll probably need either a large DD hubmotor or a geared hubmotor to give enough assist to be useful. The large DD hubmotor will reduce the room you have available for gearing, so the geared hubmotor may be a better choice if you still want a wide range of pedal gears. Geared hubmotors can't handle quite as much power (as DD hubmotors) due to their size and to the heat conduction path.
With either type of hubmotor you have to deal with absorbing the reaction torque, which can be quite tricky on some bike frames. You have to make or buy a new wheel and fit a big flatted axle into the bike's dropouts. Not all frames are easy to fit this big axle into, and you may have to hack the frame and file the dropouts (or make custom units) to make it work. Not a problem for a manufacturer, but for you and me, a lot of fiddling to get it all together. If you put the hubmotor in the rear (the best place for a motor) then you also have to deal with the gearing, and the width of the motor, and the brakes. Disc brakes are problematic with alignment and clearance issues to sort out. Rim brakes not so much, though the new rim has to match and have rim braking surfaces. And if you make the wheel yourself you have to deal with spokes of special lengths, and difficulty getting the offsets right, etc. If you put the hubmotor in the front wheel you need to be concerned about torque reaction, fitting the front fork lips, and the loss of front suspension effectiveness if you have that. The safety implications of front wheel fork, dropout or mounting failures are significant, an ugly crash and a pair of broken collarbones may result from a problem here.
With either hubmotor you have to deal with changing tires. It is MUCH harder to get a motor wheel off and back on, and it is HEAVY to work with. Not something you want to do on the side of the road. Not at all like changing a tire on a regular bike wheel.
Hubmotors do have one big plus - chains last a lot longer. I just measured the chain on my Borg, a hubmotor bike with getting toward 10k miles on it, and the chain wear has not reached the 0.75% chain replacement point. Nice for a commuter, just charge and ride, and replace the occasional worn out rear tire. I did find that the freewheel wore out at about the same rate as the rear tire, but they aren't expensive. Lubing it did seem to help, and just replacing it when the tire was off since it is not that fun to remove the motored wheel.
Mid drives come in many flavors. Some require special frames and batteries like Bosch, a very expensive proprietary setup. Fine for a big manufacturer, but small manufacturer's (perhaps like Pedego) can't deal with all that easily. The particular mid drive that I'm working with here is designed to be a drop-in system for regular bikes. It is easier to put on a bike than a hubmotor. There are very few problems to solve, providing that the bottom bracket shell is one of the standard types that the Bafang drives are made for, and providing that there is space for the motor to ride in front of the downtube. Some new frames are not a good fit, but most older (and many new) frames are fine. If the downtube curves and comes into the front of the bottom bracket shell it can force the motor to ride lower than I'd like, for example.
You get to keep all your rear gears, and it gives the handy option of a rear internal hub (a sturdy one is required however). I have nine on my new bike, a huge range from 36 to 12 teeth. I had to give up the triple chainring in front, as the BBSHD only has one ring, but I still have a very large range, enough that I can still ride the bike without the motor running. It has no regen though. So I picked a frame with dual hydraulic brakes and put bigger discs on, so I have plenty of braking there. Some mid drives do support more than one chainring, so if that is important to you look for it. Chain wear is greater on small cogs, best to use 14 or more teeth and keep the chain speed high and tension low (and keep it clean and well lubricated).
The mid drive puts more wear and tear on the chain and cogs. Not much of a problem, but you do have more drivetrain maintenance if you ride a lot. For daily commuting I would go with a DD hubmotor. Just like I built initially. But for occasional use you can just buy a new chain every 2000 miles or so (I have 1300 miles on mine now and I don't see much wear, according to the chain wear gauge). How many miles are you going to ride? Pedal bike chains generally wear out in 2000-3000 miles, though folks often ride them much longer and then are faced with a more expensive replacement of not just the chain but also the cogset and perhaps even the chainring(s). Get a chain wear gauge and replace the chain before the worn chain ruins the other elements in the drivetrain.
The power handling of a mid drive varies over a wide range, depending on the design. The small mid drives such as Bosh don't handle a lot of power, but they take advantage of the gearing and produce a lot of torque at low speeds. Larger mid drives like the BBSHD with higher power produce a lot of torque at higher speeds. The most powerful mid drives (such as Zero motorcycle motors) produce too much torque for bicycle chains and gears and need to use a motorcycle type left hand drive chain that is much tougher than bike chain. High power mid drives that drive through the bike chain can produce wear and rapid failure of bike chain and gearing. Bike gearing is designed to handle a couple of kilowatts peak and a few hundred watts average. Exceeding that increases wear and chances of short term failures.
There are also some gears inside the BBS, pretty similar to what is inside the geared hubmotor. They don't require much maintenance, but might require some grease every 5000 miles or so.
As I have experienced, the mid drive will easily handle the STEEP stuff. The bike is light, like a bike. Pick up a hubmotor ebike. They are not very light. Hubmotors are heavy (or the light ones have little torque). The geared hubmotors are lighter, but you still end up with a lot of weight in the motor wheel which is not a good thing for balance and inertia. Mid drives are balanced, and you can put one into a dual suspension bike and really handle rough terrain. All the major bike manufacturers are going mid drive with their electrics. The manufacturers that are making hubmotor bikes are the ones who didn't make bikes before. There will always be exceptions, but this is generally the case.
The mid drive is much easier to install (assuming we are talking about a good bolt-on kit like the BBS02 or BBSHD). Take the old crank out, Clamp on the new crank/motor, Mount a battery, display and plug in the wires. You can do a throttle, or not with the BBS02 or BBSHD and just the pedal assist controls. No wheel to build or pay for. No fat axles to fit. No torque arms to figure out. No new gearing and disc brake clearances to sort. No brakes to match up. Changing a tire is quick and easy, QR axles still work. Buy some chain lube and a chain wear gauge, keep it clean and lubed, and replace it before it wears out your cogs.
Hubmotors are simpler to operate. Just mash the throttle and go. With a mid drive you get to think about shifting again. But consider this - If you have a hubmotor and a mid drive that are both using the same power, and reaching the same top speed, and if your bike has a 12-36 tooth range sprocket, then in the lowest gear the mid-drive will generate THREE TIMES the torque that the hubmotor can generate, at the same power level. The difference is, on the really steep stuff, the hubmotor will be straining and getting hot, and the mid drive will be loafing and staying cool. I find if I put my BBSHD on this bike into third gear and leave it there, I can ride it like a hubmotor with a 20mph top speed, and lift the front wheel if I'm not not careful with the strong torque. If I need to climb steeper, I still have two gears to downshift into. If I need to go faster I have six gears to shift up into. But I can ride it without shifting, and the motor doesn't get hot.
The riding experience is different. Riding with a hubmotor is like driving an automatic transmission. Just twist the throttle and go (or pedal for pedal assist systems). The mid drive is more like driving a manual transmission. Shift up, shift down, think about shifting before you stop, (with an internal geared hub you can shift while stopped), letting off the throttle, reducing pedaling, or using a brake or gear shift sensor to reduce power while shifting. I can simulate the hubmotor driving experience with the BBSHD by putting it in the appropriate gear and leaving it there. But shifting is normally part of the mid drive experience that is less important with the hub motor. Plus the small motor mid drives really need to be shifted to have adequate torque. So they are busier to ride.
And whatever you choose, have fun! Let's go ride!
(*) There is at least one small hubmotor that has two speeds internally. This allows the small motor to stay cool while slowly climbing steep hills, however it still has hubmotor disadvantages like torque arms, building a wheel, changing flat tires and difficulty of fitting the disc brake, but for some users it could be a good choice with a fairly light bike and low chain wear.
Prospective User Question:
Take a look at this web page, which is very hard on mid drives ! I'm interested in your comments.
http://www.pedegoelectricbikes.com/faq/#hub
My Summary of Pedego's page:
Hubmotors are best for most people.
Most mid drives are 250W, Pedego humbotors are 500W.
You pay more and get less with mid drives.
Maintenance is higher with a mid drive than a hubmotor.
Mid drives are complicated and you have to shift.
Hub motored bikes are more pleasant and easier to ride.
My response to my friend:
So far I've built all the types, medium size DD (direct drive) hubmotor, large DD hubmotor, geared hubmotor and now mid drive. They all have their advantages, and I am not throwing any of them away, they all have their use cases. You should pick what you want to do based on your needs. What follows is based on my experience building a small fleet of ebikes and using them for commuting, transportation, exercise and fun.
Now Pedego is in business to sell and support a lot of ebikes, and they have their own issues to deal with. The biggest bike manufacturers are going mid drive. Bosh is one example, and there are a number of others. Why is that? Mid drive ebikes are the lightest and have the widest range of application, and are the most bike-like system. In countries with low power limits (most of the world), mid-drives make the most of low power. However hubmotors are also useful ebikes.
What bike are you going to convert? What are you going to do with it? That matters and guides what is the best choice for you.
Direct Drive (DD) hubmotors are best for high mileage commuting. They make a heavier bike, and if you have steep hills you need a BIG hubmotor. You can't beat DD hubmotors for simple reliability. But it takes a lot of copper and magnet material to have adequate torque, making a hubmotor heavy and if you get on a really steep hill it may overheat, burn up or just fail to get up the hill. The DD's regen capability is wonderful for those big downhills, especially if it is variable regen (which depends on the controller). Large DD hubmotor equipped bikes tend to be heavy and more Moped-like machines. Some folks are annoyed by the poor coasting of the DD hubmotors, as there is a little bit of magnetic resistance to rolling in the motor. A large DD hubmotor can handle a lot of power.
Geared hubmotors are smaller and lighter, but the gears are fixed (*). They have a clutch and coast like a regular bike. And you lose regen. Which means the brakes have to work much harder. They are more limited in motor power (due to a smaller motor with a more difficult heat dissipation path), require more maintenance (than DD hubmotors), and climb hills a little better than a low power DD hubmotor (but not as well as a high power DD hubmotor
). They keep the bike fairly light, but not as light as a mid drive. They are fairly expensive and require periodic maintenance inside the hubmotor of the gearing and clutch system. If you have some steep hills you'll probably need either a large DD hubmotor or a geared hubmotor to give enough assist to be useful. The large DD hubmotor will reduce the room you have available for gearing, so the geared hubmotor may be a better choice if you still want a wide range of pedal gears. Geared hubmotors can't handle quite as much power (as DD hubmotors) due to their size and to the heat conduction path.With either type of hubmotor you have to deal with absorbing the reaction torque, which can be quite tricky on some bike frames. You have to make or buy a new wheel and fit a big flatted axle into the bike's dropouts. Not all frames are easy to fit this big axle into, and you may have to hack the frame and file the dropouts (or make custom units) to make it work. Not a problem for a manufacturer, but for you and me, a lot of fiddling to get it all together. If you put the hubmotor in the rear (the best place for a motor) then you also have to deal with the gearing, and the width of the motor, and the brakes. Disc brakes are problematic with alignment and clearance issues to sort out. Rim brakes not so much, though the new rim has to match and have rim braking surfaces. And if you make the wheel yourself you have to deal with spokes of special lengths, and difficulty getting the offsets right, etc. If you put the hubmotor in the front wheel you need to be concerned about torque reaction, fitting the front fork lips, and the loss of front suspension effectiveness if you have that. The safety implications of front wheel fork, dropout or mounting failures are significant, an ugly crash and a pair of broken collarbones may result from a problem here.
With either hubmotor you have to deal with changing tires. It is MUCH harder to get a motor wheel off and back on, and it is HEAVY to work with. Not something you want to do on the side of the road. Not at all like changing a tire on a regular bike wheel.
Hubmotors do have one big plus - chains last a lot longer. I just measured the chain on my Borg, a hubmotor bike with getting toward 10k miles on it, and the chain wear has not reached the 0.75% chain replacement point. Nice for a commuter, just charge and ride, and replace the occasional worn out rear tire. I did find that the freewheel wore out at about the same rate as the rear tire, but they aren't expensive. Lubing it did seem to help, and just replacing it when the tire was off since it is not that fun to remove the motored wheel.
Mid drives come in many flavors. Some require special frames and batteries like Bosch, a very expensive proprietary setup. Fine for a big manufacturer, but small manufacturer's (perhaps like Pedego) can't deal with all that easily. The particular mid drive that I'm working with here is designed to be a drop-in system for regular bikes. It is easier to put on a bike than a hubmotor. There are very few problems to solve, providing that the bottom bracket shell is one of the standard types that the Bafang drives are made for, and providing that there is space for the motor to ride in front of the downtube. Some new frames are not a good fit, but most older (and many new) frames are fine. If the downtube curves and comes into the front of the bottom bracket shell it can force the motor to ride lower than I'd like, for example.
You get to keep all your rear gears, and it gives the handy option of a rear internal hub (a sturdy one is required however). I have nine on my new bike, a huge range from 36 to 12 teeth. I had to give up the triple chainring in front, as the BBSHD only has one ring, but I still have a very large range, enough that I can still ride the bike without the motor running. It has no regen though. So I picked a frame with dual hydraulic brakes and put bigger discs on, so I have plenty of braking there. Some mid drives do support more than one chainring, so if that is important to you look for it. Chain wear is greater on small cogs, best to use 14 or more teeth and keep the chain speed high and tension low (and keep it clean and well lubricated).
The mid drive puts more wear and tear on the chain and cogs. Not much of a problem, but you do have more drivetrain maintenance if you ride a lot. For daily commuting I would go with a DD hubmotor. Just like I built initially. But for occasional use you can just buy a new chain every 2000 miles or so (I have 1300 miles on mine now and I don't see much wear, according to the chain wear gauge). How many miles are you going to ride? Pedal bike chains generally wear out in 2000-3000 miles, though folks often ride them much longer and then are faced with a more expensive replacement of not just the chain but also the cogset and perhaps even the chainring(s). Get a chain wear gauge and replace the chain before the worn chain ruins the other elements in the drivetrain.
The power handling of a mid drive varies over a wide range, depending on the design. The small mid drives such as Bosh don't handle a lot of power, but they take advantage of the gearing and produce a lot of torque at low speeds. Larger mid drives like the BBSHD with higher power produce a lot of torque at higher speeds. The most powerful mid drives (such as Zero motorcycle motors) produce too much torque for bicycle chains and gears and need to use a motorcycle type left hand drive chain that is much tougher than bike chain. High power mid drives that drive through the bike chain can produce wear and rapid failure of bike chain and gearing. Bike gearing is designed to handle a couple of kilowatts peak and a few hundred watts average. Exceeding that increases wear and chances of short term failures.
There are also some gears inside the BBS, pretty similar to what is inside the geared hubmotor. They don't require much maintenance, but might require some grease every 5000 miles or so.
As I have experienced, the mid drive will easily handle the STEEP stuff. The bike is light, like a bike. Pick up a hubmotor ebike. They are not very light. Hubmotors are heavy (or the light ones have little torque). The geared hubmotors are lighter, but you still end up with a lot of weight in the motor wheel which is not a good thing for balance and inertia. Mid drives are balanced, and you can put one into a dual suspension bike and really handle rough terrain. All the major bike manufacturers are going mid drive with their electrics. The manufacturers that are making hubmotor bikes are the ones who didn't make bikes before. There will always be exceptions, but this is generally the case.
The mid drive is much easier to install (assuming we are talking about a good bolt-on kit like the BBS02 or BBSHD). Take the old crank out, Clamp on the new crank/motor, Mount a battery, display and plug in the wires. You can do a throttle, or not with the BBS02 or BBSHD and just the pedal assist controls. No wheel to build or pay for. No fat axles to fit. No torque arms to figure out. No new gearing and disc brake clearances to sort. No brakes to match up. Changing a tire is quick and easy, QR axles still work. Buy some chain lube and a chain wear gauge, keep it clean and lubed, and replace it before it wears out your cogs.
Hubmotors are simpler to operate. Just mash the throttle and go. With a mid drive you get to think about shifting again. But consider this - If you have a hubmotor and a mid drive that are both using the same power, and reaching the same top speed, and if your bike has a 12-36 tooth range sprocket, then in the lowest gear the mid-drive will generate THREE TIMES the torque that the hubmotor can generate, at the same power level. The difference is, on the really steep stuff, the hubmotor will be straining and getting hot, and the mid drive will be loafing and staying cool. I find if I put my BBSHD on this bike into third gear and leave it there, I can ride it like a hubmotor with a 20mph top speed, and lift the front wheel if I'm not not careful with the strong torque. If I need to climb steeper, I still have two gears to downshift into. If I need to go faster I have six gears to shift up into. But I can ride it without shifting, and the motor doesn't get hot.
The riding experience is different. Riding with a hubmotor is like driving an automatic transmission. Just twist the throttle and go (or pedal for pedal assist systems). The mid drive is more like driving a manual transmission. Shift up, shift down, think about shifting before you stop, (with an internal geared hub you can shift while stopped), letting off the throttle, reducing pedaling, or using a brake or gear shift sensor to reduce power while shifting. I can simulate the hubmotor driving experience with the BBSHD by putting it in the appropriate gear and leaving it there. But shifting is normally part of the mid drive experience that is less important with the hub motor. Plus the small motor mid drives really need to be shifted to have adequate torque. So they are busier to ride.
And whatever you choose, have fun! Let's go ride!
(*) There is at least one small hubmotor that has two speeds internally. This allows the small motor to stay cool while slowly climbing steep hills, however it still has hubmotor disadvantages like torque arms, building a wheel, changing flat tires and difficulty of fitting the disc brake, but for some users it could be a good choice with a fairly light bike and low chain wear.
