Advantages of crank drive over hub drive.
- Thread starter Zebb
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Deleted member 4366
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It's not a case of one type of drive being better than the other, because it depends on what bike or motor you're talking about. You need to decide what you want from a bike and then choose accordingly without any bias. What are the short-comings of your present bike that you want to overcome?
Not too sure on the technical difference as far as hill climbing etc but I have just order a KTM with central Bosch Drive.
My reason: my current throttle driven bike has a large rear hub with large battery hidden inside of rear pannier. Power is not an issue but **** end weight is. Makes the rear very heavy and a such, not suitable if one wants to throw the bike around.
The KTM has the motor and battery weight central. Having ridden the bike, it can be thrown around and feels balanced like a regular bike. It is however a pedelec and it remains to be seen if this system will suit me. We'll see.
I am sure there are others that will give you the technical merits of each system but I am more interested in the balance and handling. I also wish to be able to swap tyres without the added hassle of motor wiring.
My reason: my current throttle driven bike has a large rear hub with large battery hidden inside of rear pannier. Power is not an issue but **** end weight is. Makes the rear very heavy and a such, not suitable if one wants to throw the bike around.
The KTM has the motor and battery weight central. Having ridden the bike, it can be thrown around and feels balanced like a regular bike. It is however a pedelec and it remains to be seen if this system will suit me. We'll see.
I am sure there are others that will give you the technical merits of each system but I am more interested in the balance and handling. I also wish to be able to swap tyres without the added hassle of motor wiring.
The main difference is that, for a given power, a hub drive motor can only work at maximum efficiency over a fairly narrow range of bike speeds, whereas a bottom bracket drive can be very efficient over the full range of bike speeds, because it drives through the gears.
The main difference, in practical terms, is that a bottom bracket drive will tend to perform better when climbing hills at low speeds, where hub motor efficiency drops off quite markedly.
The main difference, in practical terms, is that a bottom bracket drive will tend to perform better when climbing hills at low speeds, where hub motor efficiency drops off quite markedly.
if you need assistance climbing hills a centre drive driving through the gears...very quiet, and a natural bionic feel. On the flat maybe a hub drive faster..I have both and dont really know what I prefer to be honest, its hard as both lovely bikes....but for hill climbing its a no brainer and thats the main reason most of us have e bikes.
D
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You can't generalise. A code 17 BPM hub-motor can climb better and probably more efficiently than just about all the normal crank drives. It'll blitz any Bosch or Panasonic. There's other hub-motors that can do the same. Wait til you try the new Kudos bikes before saying that crank drives climb better. The biggest advantage of a crank drive is its ability to produce its maximum power over a range of speeds, but the 15mph limit takes away half of that advantage.
Of course you can generalise. The physics and engineering limits are simple and straightforward.
A single speed gear system (a.k.a. a hub motor) simply cannot ever be equally efficient over the normal range of bike speeds. You can optimise a hub motor for good low speed efficiency, or good high speed efficiency, but not both. On the other hand, a bottom bracket drive can be designed to maintain near-equal efficiency over the full range of normal bike speeds.
FWIW, the code number only makes a small difference to motor torque for the BPM range. The max torque for the code 17 is only around 10% greater than that for a code 8. They both have roughly the same amount of copper in the windings, so both have pretty much the same maximum continuous torque. That's one of the engineering equations that govern permanent magnet motor performance.
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As others have said if you have steep hills the crank will be better compared to a legal hub motor, with a hub you need to try and keep the speed above the point where they become inefficient and the power output drops on steep hills, no such issue with a crank drive.
In hills the crank drive should give better range as well.
In hills the crank drive should give better range as well.
Hub motors are certainly a better option, IMHO, than a crank drive for an ebike conversion, or for an ebike that's likely to be ridden on the level much of the time. There are lots of advantages to having the motor in a hub, including the one of not being tied to proprietary parts if you ever need to replace something. Crank drives are either highly proprietary and so tie you in to only a single source for spares, or, in the case of the one or two aftermarket crank drives that are available, not that neatly engineered in terms of a nicely finished package. Often a small hub motor will look more discreet too, which may be a useful consideration.
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Deleted member 4366
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That would only work if your talking about the same motor driving the crank or hub, but a BPM or MAC isn't the same as a Panasonic or Bosch. Some of them are designed specifically for clinbing with high torque and efficiency.
you're correct about the torque difference between code 8 and code 17, but there's a massive difference in efficiency when climbing slowly, which is what the code 17 is designed for. I chose code 17 for its ability to climb very steep hills at 40 amps without over-heating. No normal crank drive can run at 40 amps, in fact you'd be hard pressed to get them half as much current, so there will be a huge power difference, and it's power that you need to climb hills unless you want to go very slowly. I'm talking about bikes with normal gearing and going up normal hills that you'd encounter on the road. I tried a code 15 BPM at 40 amps, and it went up any hill I have here round the rather steep Ironbridge gorge without pedalling. I've tried just about all the normal crank-drive bikes on the market, and none would be able to do that even if they had throttles.
I'm sure that you've seen that MAC go up that 30% hill in San Francisco, where he said he hardly had to pedal on 29" wheels. Is there a normal crank-drive that can match that? None that I've been on, in fact I had to pedal with a fair bit of effort to get the Bosch (Haibike) up the Presteigne test slope that was 15% at most. Here it is to remind you.
MAC motor hill climbing test - YouTube
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Ok Zebb you may not climb many hills but for offroad starting, stopp[ing and accelerating the crank drive comes into its own. Slow speed trail riding- or mountain biking is the best fun you will get on an e-bike and crank drives are the best for just that.
That's difficult to answer Zebb and although Jeremy points out, rightly, that crank-driven machines do have an advantage, (although it's not always manifested clearly in practice) Eddie's point reflects my own experience. To avoid muddying the waters, I'll restrict both hub-drive and crank-drive to bikes limited to 15mph +/- a tad and equipped with 250 watt motors or less.
Up until about a year ago Zebb, I would have backed crank-drive every time over hub but my experience was limited to a very low-power Panasonic system on a heavy Dutch bike which meant beautiful and very comfortable ride over all surfaces but any steepish hills had to be taken slowly. The hub bikes I'd ridden at various, low-rent "dealers" were all budget-priced machines, every one of which was eminently forgettable although they still performed the function.
Hub-drive is pretty basic and a good crank-drive with torque sensoring seems quite sophisticated by comparison, in my view. At least, that was my thought up until I tried some of the more modern hub-driven machines which resemble my Dutch bike. Some of those have torque sensoring, the equal of my crank-drive, providing seamless power over most terrain although ultimately losing out on the everest slopes against crank-drive.
That said, not all hub-drives are equal; some have internal gears and they can be very powerful though noisy, from memory. Bikes I disliked riding included Powerbike, Powacycle, (may need to spellcheck those!) Infineum, Wisper and something from Halfraud's, the name of which escapes me right now. More enjoyable were Sparta, (various models) Koga E-special, (delightful) and Haibike. The Haibike's power was slightly underwhelming after the way it had been hyped but the full-susser is a great bike and even if it didn't have Bosch power, it would still be a very creditable MTB.
My Cytronex-powered Cannondale is a great ride if you like fast road bikes but it's not a great touring bike. It makes me seem like a quick rider but I'm more at home on old-fashioned, sit-up-and-beg Dutch bikes with their "built for comfort; not for speed" demeanour.
For my next bike, I have made up my mind then changed it so often, you wouldn't believe it. Bosch-power is king at the moment in legal bikes but Panasonic is still nice. Prices of what we, 6 months ago, deemed high-end stuff are now "affordable" but Kudos bikes may have hit on something with their new line-up so it's wait and see over the next few months as I suspect others will hit the shops with good spec and nice price tags.
A good kit fitted to one of my bikes in Spain is my current plan but if Kudos bikes are now as good as the spec suggests, I might just pick up one of those. On the other hand, Costco are knocking out a diamondback machine right now for £150 which weighs in at 12 Kgs. Methinks that has the makings of a nice ebike!
When you come to a decision for yourself Zebb, I'll be interested to hear which way you've opted.
Indalo
Ok thanks Indalo, it's good to hear the OAP view on the current state of affairs. £150 for a 12kg bike is something to see though. I thought that the whole point of a £1500 bike was it weighed only 12kg? Do people really spend that much money because it is 'triple butted' or 'hydroformed' or has it's very own human machine interface. But I'm with you old boy, those shady dealers are all on the make, you wont meet many ebike salesmen in heaven eh?
Thank you again for the replys, it makes enjoyable reading.I think it would be best for me to ride a crank drive on one of my rides too see just what difference they have compared to my hub drive.I dont think I would buy kudos ever again so would look else where. Its good that there is quite a lot of choice out there.
In your humble opinion. Personally I find my NEO's fine for these activities (although I dont do any real extreme stuff just trail riding)
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Deleted member 4366
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Unless you have something against Kudos, you should try their new bikes: The Arriba, Tornado have big hub-motors that should change minds about hub-motor climbing ability, and the new Ibex has a crank-drive.
I'm not against crank-drives. The Bosch, 36v Panasonic and Kalkhoff Impulse all climb a lot better than your average 250w Bafang SWX motors; however, the Bafang BPMs and CSTs in the Emotion Neos and those new Kudos bikes are extremely capable as anyone that tries them soon finds out.
D
Deleted member 4366
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As most ebikes are illegal anyway, it makes little difference. The main point is not to make it too obvious: A 250w label helps; always pedal; make sure your bike looks like a bike; hide it behind a large disc brake and one of those plastic shrouds that goes behind your cassette/free-wheel; try not to annoy anybody except the lycra brigade as you cruise past them up hills; don't go too fast.
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