crank vs hub power

Electrically assisted bikes, trikes, etc.
Red Kite
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Joined: 10 Sep 2012, 5:20pm
Location: Hertfordshire, UK

Re: crank vs hub power

Post by Red Kite »

I've a crank-drive torque-sensing Bosch-powered hybrid, and a converted Brompton with front hub drive and only cadence sensing.

They are obviously very different to ride although that is more to do with differences in the bikes than the drive. I like and use both. As far as the drive difference is concerned, I think that is more to do with the sensing than the motor position.

The Bosch is far more natural (as distinct from better or worse) - no sense of a 'motor bike' feel, more like having stronger legs and more breath to spare. The trick to keeping rider effort low is to use the gears when gradient and headwind increase as well as upping the assistance level. The reason is simply that the motor is torque-limited and whilst it might nominally add 300% to rider-applied torque, there is a point where it can't. It's very easy when getting used to the bike just to turn up the assistance as a first response but to give more power the motor needs to spin faster when the torque is maxed out.

The cadence-only bike feels unnatural (not necessarily worse) by comparison because the power levels are much closer to being literally that - if one reduces pedalling effort to stop accelerating, the motor power continues unabated. One soon learns to stop pedalling to cut the motor and I no longer notice the 'push' effect. Again, using gears as well as higher power if one has fragile knees is the way to keep effort low.

I have no real sense, when riding, of where the motor is or its type.

It's clear that a crank drive can increase transmission wear, whereas a hub drive should in theory reduce it. On the other hand, a hub drive will stress wheel it is fitted to. I haven't had either bike long enough to experience either problem but I keep an eye on spoke tightness and chain lubrication.

The hub drive on the Brompton is geared and gives a fair amount of shove, especially considering the weedy 5.2Ah battery.

With the right technique and low enough gears perhaps either kind can be kind to bad knees, but it is obviously worth trying out the type you are contemplating before you buy if you can.
Cube Touring Hybrid One e-bike, Brompton P6R with Swytch conversion
swscotland bentrider
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Re: crank vs hub power

Post by swscotland bentrider »

"Notwithstanding the success of the aforesaid conversion I'm considering an off-the-shelf ebike and had been looking at the Ribble range / maybe the CGR E and would be interested in any further more detailed comments regarding your experience with this bike, in particular: sizing, range, pulling away, changing power assistance, gear ratios, drops v straights, will it take mudgards, can the batteery be removed easily for charging, suitability for touring etc.? One thing I like about my converted bike is that the power control has x5 settings and can be operated without moving your hands off the bars and can therefore easily finesse my needs and requirements, it seems the downtube button could be more awkward by comparison?"

My apologies for not responding sooner - I was away from home and hadn't got my log in details.

As I said the Ribble CGR E has been a success for me.
Sizing. I am on the cusp between medium and large. I bought a large because I wanted my bars level with my saddle. I went fro 165 cranks. The result was a perfect fit. Yes it can take mudguards and a carrier. All fittings are present. Gearing is a 34/50 compact, 11-34 cassette. (gearing does not need to be as low on an E bike) I live in Scotland, not flat but have never used bottom gear.

Battery cannot be removed except under workshop conditions so re charging on a trip needs to be thought about. The supplementary battery on the seat tube could be removed and charged.

Drop bars are shallow and the tops are angled back. The cabling and taping has produced a fllattish shape to the top. They are remarkably comfortable. STI with hydraulic brakes. Again very good ergonomics.

I worried about cadence sensing rather than the torque sensing I had used before. In practices it is a non issue. Pick up and shut down occur within a split second of commencing / ceasing pedalling.

The control button is on the top tube. Longest ride so far 100 kms in hilly country, light load. Used 70% of charge.

The ultimate review came from my wife. A non cyclist who had asked be to build a flat bar bike for her to start proper cycling. She took out my bike with the seat right down and far too large for her. She had never ridden a drop handlebar bike. Came back with a grin on her face and said "get me one" She now has a GT E Gravel bike.

Hope this is useful.

Monkey boy
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Joined: 14 Sep 2021, 10:19pm

Re: crank vs hub power

Post by Monkey boy »

Hi all

Sorry I’ve been quiet since asking my initial question.

Thank you all so much for the advice and experiences, it is much appreciated.

I went to a dedicated electric bike shop on Friday and tried a couple of their offerings.
I finally plumped for this ... nche-28-3/
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Joined: 6 Jun 2018, 10:24am

Re: crank vs hub power

Post by stodd »

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Joined: 22 Mar 2014, 7:34pm

Re: crank vs hub power

Post by ChrisF »

[XAP]Bob wrote: 15 Sep 2021, 3:24pm I have to say that I think the cadence/torque sensing differences are huge, particularly when starting from a standstill (i.e. when you most benefit from the motor).
Torque is just leagues better.
I think the sensing differences between cadence and torque will diminish with time (due to software). I had a basic cadence sensor system (hub upgrade kit) and indeed it was pretty bad in some situations: particularity starting pedaling while maneuvering, the bike would suddenly lurch me forward into traffic or while I was trying to turn a tight radius.
But now I have a cadence sensor based ebikemotion bike (also with hub motor) and it's miles better: the system knows your speed and acceleration as well as pedal rotation, and makes very good sense of it all. There's absolutely no sudden changes of power, everything is very smooth.
Chris F, Cornwall
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Re: crank vs hub power

Post by hjd10 »

Monkey boy wrote: 26 Sep 2021, 10:12pm Hi all

Sorry I’ve been quiet since asking my initial question.

Thank you all so much for the advice and experiences, it is much appreciated.

I went to a dedicated electric bike shop on Friday and tried a couple of their offerings.
I finally plumped for this ... nche-28-3/
Enjoy the bike...
A few thoughts from my foray into Ebiking. For those with a mid-drive set up do be careful when cleaning the bike, as mid-drives don't like water! Obviously more of an issue on mountain bikes with people cleaning them with power washers, don't use one!
I have a Voodoo Zobop Ebike and a Touring Bike rear hub home build. They both work really well and are suited to their different expected operating environments! I really like the simplicity of the rear hub motor setup as it is cheap and likely easy to repair and keep going in the future.
With the E mountain bike (emtb), however, it isn't a matter of if, it's a matter of when will it go wrong. The Shimano motor isn't really repairable and as such and will probably result in a warranty claim (Just read any emtb forum for this topic).
My passion for biking is primarily mountain biking and emtb has transformed my riding and has introduced more fun into my rides.
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Re: crank vs hub power

Post by simonineaston »

Just an extra thought, before I turn in. My local cycle / road routes are quickly filling up, compared with how they've been over the past two or three decades. Lots of folks on 'leccy bikes - myself amongst them - and now the very popular Voi scooters and their less-legal alternatives. So, in summary, more single-track vehicles using the same spaces.
If it keeps down the no. of internal combustion engines and contributes to our over-all fitness levels, both in body & mind, I rejoice! I'll doubly rejoice if all users make liberal use of their bells (or plain just shout!) when they're heading my way, especially from behind, just before they whizz past, or at junctions. :D Nighty night - pleasant dreams...
(rides: Brompton nano & ever-changing Moultons)
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Re: crank vs hub power

Post by TonyN »

I am an unapologetic user of front hub motors and conversion kits for one's own familiar bike. One main point seemingly ignored by most commentators is the cost comparison, a kit using a bottom bracket motor is more expensive and generally needs more expensive maintenance beyond that of a DIY home mechanic. Other points are :-
1. Most batteries fit onto the downtube and with a hub motor there is little stability difference than with a slightly lower bottom bracket motor.
2. A front hub motor distributes weight along the bike, has two tyres driving the bike and chain wear is less than on the original bike.
3. Commercial big name Ebikes start in price at about £2000, at this level weigh over 22kg and require expert expensive maintenance.
4. My ex cyclo-cross bike conversion cost £450 for kit and battery, weighs 16.5 kg and has a 70 mile range on a charge. The bottle battery as the name indicates looks like a large water bottle and the aesthetics are, I think, better than a big fat downtube.
5. Even if the local bike shop has to fit your kit any maintenace replacements are cheaply available and easy to fit by them or yourself.
6. I read a contribution a few weeks ago by a keen cyclist, used to travelling at 18 mph with his club bunch, very dissatisfied because his commercial Ebike cut out at 15mph with no resetting method available. So he was pushing a heavier bike by his own efforts to keep up with his mates. I have installed a number of kits over the last few years and every kit was capable of setting the cut-off speed between 10 to 25mph along with the supply of a hand throttle. Note that an Ebike can only be legally used on public roads with the cut-off speed set at a max of 15mph and without a throttle fitted.
7. Power settings on Ebikes have generally been by push button with a range of up to 5 settings. My kits provided roughly 50 watts on the lowest, 100 watts next, 200 watts next and so on. This power is constantly provided at these settings irrespective of rider effort.
Just to put this into context I seem to remember that Bradley Wiggins averaged 440 watts when he broke the hour record.
On my latest kit automation has taken over and the power setting now seems to represent a maximum. In normal riding the power provided is sufficient for progress but it automatically increases dramatically if pedal effort for a slope is encountered. This means two things, no power is wasted when it is not needed, thus more range for a charge. And changing gears to cope with a hill now does not need a combined juggle between gears and power buttons, the power is increased by the controller. In addition to this the first turn of the pedals gives an automatic powered surge, very handy for setting off and crossing roads.
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Re: crank vs hub power

Post by groberts »

Thanks for your reply John on the Ribble CGR E which is very helpful - I'm toying between this or a Cytronex conversion of my Dawes Audax.

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Re: crank vs hub power

Post by bikes4two »

  • I've forgotten how many times in this thread that it has been said that mid drives wear the chain/transmission more than hub motors
  • Well, I can see that that is likely the case but how much is that additional wear? For instance, if on an unpowered bike you needed to change your chain every X miles, with a mid drive system would the chain change be at 1/2 X miles? - something more than that or less so?
  • And what price a chain - £20? So hardly an issue is it? (and no bottom brackets to change either).
  • If you're into a Bosch or Yamaha or Steps mid drive, then I guess you're tied into that particular system and the top-loaded pricing, but the kit motors from Bafang and Tongsheng are easily maintained by even those with modest 'spanner' skills.
  • My recently purchased TSDZ2 with 10Ahr batery cost £352 all in which if my web searches are anything to go by, is a comparable price to a hub kit.
  • And wait until the puncture fairy visits and you're faffing with the electric cables and large nuts on a hub motor to change the inner tube.
  • and if you have a mind for such things, the motor characteristics of the Bafang and Tongsheng can be fine tuned via a laptop to your heart's content.
But as has been said, all motors have there plus and minus points, but I've raised this post to bring another perspective into the mix.
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Re: crank vs hub power

Post by hemo »

Both have their virtues and both work.
I have hubs and can't fault them where as my BBS mid drive has not been great.
I Tongsheng my be a future buy and a 48v 250w model would be my preferred choice esp on a longtail.
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