CD Drive Motor Superior?

[Andy88]

I would like to hear your comments on this passage, agree? disagree? Taken from a bike builder.

With a CD Drive eBike solution, the bikes’ complete crank set is replaced by a motor drive unit with its own chain-set incorporated in the assembly. The motor unit will directly drive the bike’s chain as you would have done previously

By using the motor to drive the crank, it enables youto use the bike’s transmission as the motor’s gears similar to a car. By using the bikes’ gears, the electric motor can run in its optimum RPM range in each gear. This translates to a more efficient motor and a lighter better balanced e-bike. Why a lighter bike? When going through the gears, you don’t need as heavy a motor to propel you up hills, you don’t need as much capacity in your battery because a crank drive is considerably more efficient than a hub motor especially when climbing.

We believe that the Crank Drives are far more superior than Hub Drives overall.

 

[flecc]

If legal pedelecs had a wide speed range there could be more truth in that, but since they only cover a speed range of about 5 to 15 mph and electric motor low end torque is so strong, so many gears are far too many for the motor. Two at most would be sufficient for that 10 mph speed span, and for that reason there are now a few two speed hub motors.

There are also some high torque single gear hub motors that compare very favourably with the crank drives for most riders and terrains.
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[Andy88]

If legal pedelecs had a wide speed range there could be more truth in that, but since they only cover a speed range of about 5 to 15 mph and electric motor low end torque is so strong, so many gears are far too many for the motor. Two at most would be sufficient for that 10 mph speed span, and for that reason there are now a few two speed hub motors.

There are also some high torque single hub motors that compare very favourably with the crank drives for most riders and terrains.
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Very good input, valid points much appreciated.

If you were buying a legal new style hub kit, which brand would you opt for?

 

[Kinninvie]

I have both hub and crank drive bikes and agree with the above.
I shpuld point out though that my hub drives are all direct drive and I have no experience of a geared hub.
As an example,on a local 10 mile hilly route, my 1000W hub uses 1Ah per mile and struggles up the steeper hills whereas my 750W crank drive uses just under 0.5Ah on the same route and goes up the steepest hills with mimimum effort required by me.

 

[Andy88]

I have both hub and crank drive bikes and agree with the above.
I shpuld point out though that my hub drives are all direct drive and I have no experience of a geared hub.
As an example,on a local 10 mile hilly route, my 1000W hub uses 1Ah per mile and struggles up the steeper hills whereas my 750W crank drive uses just under 0.5Ah on the same route and goes up the steepest hills with mimimum effort required by me.

Interesting, thank you.

 

[Andy88]

Here is a Summary from the same people.

Hub Drive Basics
All the e-bikes that have a “hub-motor” ( or “hub wheel”, which is basically the electric motor inside the rear or front wheel ) are operating at one fix gear, which is usually designed to have an optimum running speed near the eBike’ top speed. In these conditions the hub motor needs to generate a very high torque during acceleration or going uphill which has a negative effect on the e-bikes’ battery & components by drawing large amounts of current. High peak currents should be ok for very short amounts of time, but prolonged high current will cause overheating of the motor and controller, possibly resulting in a component failure.

Most manufacturers that are looking to make a cheap eBike, will go with a hub motor solution. But, lets not be all negative about them, Hub motors do have a place in the market. If you’re looking to buy an eBike on a small budget and you just to do shorter journeys on the flat, then they’re ideal. But if you want an eBike that’s better at hill climbing, less likely to overheat and more efficient for longer journeys, then mid-drives are in our opinion, the best option.
Hub Drive Pros – Cheaper than Mid Drives and a good option if the terrain is flat
Hub Drive Cons – Draws high loads at low speeds and when climbing hills, can only deliver its full power at one speed, to remove the wheel you need to disconnect a motor
Bafang ThumbMid Drive Basics
With a Mid Drive eBike solution, the bikes’ complete crank set is replaced by a motor drive unit with its own chain-set incorporated in the assembly. The motor unit will directly drive the bike’s chain as you would have done previously
By using the motor to drive the crank, it enables youto use the bike’s transmission as the motor’s gears similar to a car. By using the bikes’ gears, the electric motor can run in its optimum RPM range in each gear. This translates to a more efficient motor and a lighter better balanced e-bike. Why a lighter bike? When going through the gears, you don’t need as heavy a motor to propel you up hills, you don’t need as much capacity in your battery because a mid drive is considerably more efficient than a hub motor especially when climbing.
We believe that the Mid Drives are far more superior.

Mid Drive Pros – Good for hill climbing, more efficient, motor draw less current, motor is central and low aiding the bikes centre of gravity
Mid Drive Cons – More expensive than the hub drive and you may lose your front derailleur for a single chainring.

In Summary
Each drive type has its advantages and disadvantages over the other, so its really up to the user to decide which to choose. But, our recommendation is that if you have a limited budget, want an eBike for around town, don’t plan on tackling many hills or plan to go off road, then a hub drive should suit you fine. However, if you are planning on tackling more hills or are planning on going off the tarmac, then we would suggest looking at a Mid Drive eBike.

 

[flecc]

If you were buying a legal new style hub kit, which brand would you opt for?

Having had good service from eZee bikes, first choice the eZee kit. It's one of the most powerful internally geared single speed hubs.

Kits using the BPM and CST motors are about equal to the eZee one, I believe Woosh do those.

On the economy issue, the use of torque sensors by the crank drive motors somewhat forces more effort from the rider to get the power wanted, making for a false comparison. I've owned both CD and hub bikes at the same time, and the hub motor bikes have given me the lazier ride but at the cost of higher current consumption.
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[Andy88]

Having had good service from eZee bikes, first choice the eZee kit. It's one of the most powerful internally geared single speed hubs.

Kits using the BPM and CST motors are about equal to the eZee one, I believe Woosh do those.

On the economy issue, the use of torque sensors by the crank drive motors somewhat forces more effort from the rider to get the power wanted, making for a false comparison. I've owned both CD and hub bikes at the same time, and the hub motor bikes have given me the lazier ride but at the cost of higher current consumption.
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Thanks once again, so useful in the decision making process.

 

[flecc]

mid-drives are in our opinion, the best option.

Mid Drive Pros – Good for hill climbing, more efficient, motor draw less current, motor is central and low aiding the bikes centre of gravity
Mid Drive Cons – More expensive than the hub drive and you may lose your front derailleur for a single chainring.

Their view is far too simplistic and carefully misses out the con of high transmission wear when all the rider and motor effort goes through it. Many CD users suffer short sprocket and chain lives.

And their idea that hub motors are only a cheap bike option is wrong, there are a number of excellent high end hub motors, I particularly like Panasonic's high torque rear hub motor. They are a noted CD maker so they must think them worthwhile.
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[Andy88]

Thank you once again.

 

[anotherkiwi]

A mid-motor can be easier to mount to an aluminium frame, no mucking about with filing dropouts and fitting torque arms.

You use a normal rear wheel which gives a wider range of choice in gearing - hub gears, any size cassette, freewheel if you have a wheel with one of those. Easier to fix a puncture. Negatives: chain line can be a problem.

My mid-drive is a PAS sensor mid-drive but the sine wave torque simulation controller does a very good job of making it behave very smoothly - there is no transition felt when passing from powered to un-powered riding and vice versa.

I can turn up the assistance and just turn the pedals
I can turn down the assistance and provide more effort
With my new gearing I can go far with little effort - assistance level 2 up steep (>13%) hills in bottom gear only draws 250-300 Watts compared to over 500 in assistance level 5. The sacrifice is of course top speed in this case.

Early next year I will be a two bike garage and put my hub back into service, it will be easier for me to compare because this time it will go into a bike that is the right size for me. My judgement is much kinder with the mid-drive bike because it is just so much more comfortable than the last hub powered one.

 

[Andy88]

Again another great contribution from real user experience, especially on the fitting. Thank you.

 

[Deleted member 4366]

I've done side by side tests with a hub motor and crank motor running with the same voltage, current and the same rider weight. There was no significant difference in battery consumption, It's a myth that crank-drives are more efficient. They have the potential to be more efficient, but that potential isn't realised in practice. The proviso for both being similar efficiency is that the hub-motor isn't used a long way outside it's comfortable operating range, e.g. using a 500 rpm DD motor to climb hills at 12 mph (180 rpm), which will be very inefficient. What little efficiency the CD might gain must be lost by the inefficiency in the drive train.

The hub-motor will always give you a more comfortable ride because there's no requirement to be in the right gear and there's no stress on the chain when you change gear. CDs gain on very steep hills because you can use low power to climb slowly when a HD will stall out, so CDs can be advantageous if you have a lot of steep hills.

People often forget that you can get hub-motors in a range of winding speeds. A 160 rpm hub-motor will climb as efficiently as any CD, but it won't help you much past 10 mph. If your really want to stick to the 25 km/h limit, even a 201 rpm hub-motor can climb pretty well. ASFACS, most ebikes with hub-motors use a speed of around 230 rpm, which means you get good power at 15 mph at the expense of the torque needed to climb steep hills.

All the above speeds and RPMs are with reference to 26" wheels. Obviously, speeds and efficiencies change with wheel size, so a tiny low power 328 rpm hub-motor can be very efficient climbing very steep hills if it's in a 16" wheel.

 

[Andy88]

D8VEH you are an absolute star! Do you know how much the BigBear has improved since you did your test ride and group review in 2014?

 

[Deleted member 4366]

D8VEH you are an absolute star! Do you know how much the BigBear has improved since you did your test ride and group review in 2014?

Good question. I'm not sue whether mine had the 15A or 20A controller, probably the former. I tested the crossbar version a couple of months before. There's a review of that somewhere. The stepthrough that I tried at Redbridge had the same power, so it should be a bit more now. That stepthrough version was the most comfortable electric bike I've ridden. I'm pretty sure that it's a very suitable bike for what you want - probably the most suitable out of the legal bikes. Russ, one of the forum admin, rode round the whole Redbridge circuit without pedalling, and there's some moderate hills on that. He's a bit lighter than us though.

 

[Andy88]

Thanks

 

[Andy88]

Good question. I'm not sue whether mine had the 15A or 20A controller, probably the former. I tested the crossbar version a couple of months before. There's a review of that somewhere. The stepthrough that I tried at Redbridge had the same power, so it should be a bit more now. That stepthrough version was the most comfortable electric bike I've ridden. I'm pretty sure that it's a very suitable bike for what you want - probably the most suitable out of the legal bikes. Russ, one of the forum admin, rode round the whole Redbridge circuit without pedalling, and there's some moderate hills on that. He's a bit lighter than us though.

How much difference would a 20A controller make vs 15A?

Sorry so many questions

 

[KirstinS]

How much difference would a 20A controller make vs 15A?

Sorry so many questions

On. the basis that amps = torque and voltage = speed

Id say about 30% increase in torque but maybe this is too simplistic a view

 

[Deleted member 4366]

Yes, 33% more power at low speed. I can only guess at which point the controller stops limiting power, but probably somewhere around12 mph.