torque torque

[dsearb]

Looking for a conversion kit for my wifes bike (trek hybrid)
She is about 12st, terrain around here is fairly hilly (Bath, UK)

A continuation on the hub vs chain drive theme:
My A level physics suggests that for getting up hills, the torque produced by a motor is more important than the power as speed (and thus cadence) will be pretty low
I have seen elsewhere on Forums that hub drive is considered superior "because power is input direct to crank and therefore gets the advantage of gears". However, generally front chainrings are larger than rear sprockets for all but the lowest gears so torque applied at the front chainring will have a similar effect that applied at a hub. Am I missing something? Are crank drive motors just built to output more torque?

Tried a crossfire hybrid in Halfords which produced good performance up hills - this had a suntour HESC system http://www.srsuntour-cycling.com/e-bike/ats-rear-motor-system/ This has a claimed torque of 50 Nm but doesnt seem to be available as a kit in the UK. Has anyone come across a hub kit that produces a similar torque? Other hub kits quote around 15 Nm

 

[DouglasXK]

I know Bath reasonably well and if it was my wife, I’d fit a Bfang crank drive. I bought herself a Bosch Motus crank drive to give her confidence. She also has a Trek and knowing what I know now i could easily have fitted a Bfang. This sort of mid-drive is easily managed.

 

[Deleted member 4366]

Any middle sized hub-motor will give the same torque as that bike you tried. If you want better torque, use 48v instead of 36v.

If you say how heavy you are, how fast you want to go and whar sort of hills you have, we can point you to exactly the system you need.

 

[Danidl]

Looking for a conversion kit for my wifes bike (trek hybrid)
She is about 12st, terrain around here is fairly hilly (Bath, UK)

A continuation on the hub vs chain drive theme:
My A level physics suggests that for getting up hills, the torque produced by a motor is more important than the power as speed (and thus cadence) will be pretty low
I have seen elsewhere on Forums that hub drive is considered superior "because power is input direct to crank and therefore gets the advantage of gears". However, generally front chainrings are larger than rear sprockets for all but the lowest gears so torque applied at the front chainring will have a similar effect that applied at a hub. Am I missing something? Are crank drive motors just built to output more torque?

Tried a crossfire hybrid in Halfords which produced good performance up hills - this had a suntour HESC system http://www.srsuntour-cycling.com/e-bike/ats-rear-motor-system/ This has a claimed torque of 50 Nm but doesnt seem to be available as a kit in the UK. Has anyone come across a hub kit that produces a similar torque? Other hub kits quote around 15 Nm

. There are some errors , I hope, in your posting. In referring to hubs and central drive motor, I suspect you have them in y wrong sequence.
Your a level physics is correct... Unless the torque produced by the motor is greater than the static forces acting on the bike wheel the bike and motor will stall. However torque is only half the power equation it must be multiplied by the revolutions if the wheel to produce work and power. A stalled motor may be generating torque, burning up energy and electrical power but it's not doing work.
A hub motor , will either be direct drive, where the rotor of the motor is actually the wheel. or indirect hub drive. In the indirect hub drive, where the rotor spins much faster and there are internal planetary gears to reduce the wheel speed and increase the torque. A direct drive will usually have a very large diameter hub while the indirect hubs are much smaller and neater.
The increase in torque can be a factor of 3 to 5 , and the speed reduction being in a similar ratio in indirect hub drive. It is easier to make lighter and higher performance electric machines when the rotor spins fast.That is why the vast majority of hub drives in Europe are of the geared type
A hub motor of either type will be designed to operate best at a single road speed and will be more and more inefficient and less torquely when the road speed is slower. At the extreme, and if the road slope and weight on the bike is too much the motor will stall. By inefficient is meant the fraction of electrical power converted into useful mechanical power

A central drive motor , likewise has a narrow range of speeds at which it is most efficient, but and this is the big difference, the gears on the back wheel allow for very different road speeds. It can operate at say 10 different optimum road speeds and 10 different optimum torques compared to the hub drive unit. The ratio in each case being set by the number of teeth on the chain wheel divided by the number of teeth on the cog on the rear wheel. A central drive motor can also stall, if the gear ratio is badly chosen, but with multiple gears this likely hood is reduced.
I would not read to much into the torque figure on its own, as the final torque experienced on the road will be determined by the diameter of the driven wheel

 

[Woosh]

Tried a crossfire hybrid in Halfords which produced good performance up hills - this had a suntour HESC system http://www.srsuntour-cycling.com/e-bike/ats-rear-motor-system/ This has a claimed torque of 50 Nm but doesnt seem to be available as a kit in the UK. Has anyone come across a hub kit that produces a similar torque? Other hub kits quote around 15 Nm

One side, you quote 50NM for the HESC, the other you quote the 15NM figure from for other hub kits, giving the impression that the HESC can be 3 times more torquey than others. This is very mistaken.
There are plenty of motors torquier than the HESC, such as the Bafang SWX02 and BPM that I use on my bikes.
For your wife (12st), I would recommend the SWX02, fitted to my Santana and Rio MTB - that is more appropriate to Bath than the HESC.

http://wooshbikes.co.uk/?santana2

The torque produced by a motor varies with its rotational speed. The torque is highest when the motor is stalled, which is no good for practical purpose, and goes to zero when the motor spins at its noload speed.
The torque profile, ie torque value versus RPM, albeit of similar shape for the three main types of motors used on e-bikes, direct drive, geared hub and crank drive (or mid drive), are sufficiently different so to enable a reasoned choice to suit individuals.
This is a Brose crank drive torque profile, typical of the crank drive type:

the torque rises from 0 to about 50-60 RPM (at the cranks), then stay flat until about 90 RPM, then decreases gradually to zero.
The left side of the plot illustrates how poor the transformation of battery power to mechanical power is. Under 30 RPM, half of your battery will turn into heat.
The picture above illustrates also the progress made in recent years in crank drive motors. Previously, the right hand downward slope was even steeper that the left hand slope, the torque used to fall off (and still do on most Chinese CD motors) rapidly after 90 RPM, same shape as those in the image below.

This is the typical profiles of driect drive and geared hub motors:
top blue line is geared hub torque, below it is the direct drive torque.

 

[Benjahmin]

What I get from all this is that a mid drive/crank drive is a more 'technical' ride than a hub drive. With a mid drive it is imperative to be in the right bike gear to allow the motor to do it's work without stalling or overheating. With a hub, like the SWX02, if you keep the road speed at or above about 7-8 mph, all will be fine. Gear selection will not matter.
So, if your wife is an accomplished cyclist, used to pre-selecting the right gear when approaching hills, then a mid drive will probably suite her. If not then there could be some horrible crunching gear changes to be heard. Whereas a hub will continue to drive while she finds the right gear.
Another aspect I would mention is that it is difficult (not impossible) to fit a front deraileur with a mid drive. So limiting the number of gears to the rear cassette. Many will say that this doesn't matter on an electric bike and that 7-8 gears is fine. In most cases I'd agree but I know Bath has some pretty severe climbs around. With a hub motor (front or rear) you can have a double chain ring.
Declaration of interest here. I ride hub conversions in very hilly West Wales. On one bike I have 16 gears, on the other 14. I use them all in the quest for comfortable cadence. The lower gears allow me to maintain the mentioned 7-8mph up almost all hills without straining my legs with too low a cadence. I must admit there are one or two brutal 1:4 hills around here that will see me at 5mph for short spells, BUT I have never had the motor overheat or stall (Ezee mk2 BPM type). The higher gears allow me a decent speed of 25-28mph without spinning out.

 

[Woosh]

So, if your wife is an accomplished cyclist, used to pre-selecting the right gear when approaching hills, then a mid drive will probably suite her. If not then there could be some horrible crunching gear changes to be heard. Whereas a hub will continue to drive while she finds the right gear.

I fit a gear sensor in the 2017 Krieger and 2018 Santana CD (arriving end of this month, October) to fix this issue.

 

[Danidl]

What I get from all this is that a mid drive/crank drive is a more 'technical' ride than a hub drive. With a mid drive it is imperative to be in the right bike gear to allow the motor to do it's work without stalling or overheating. With a hub, like the SWX02, if you keep the road speed at or above about 7-8 mph, all will be fine. Gear selection will not matter.
So, if your wife is an accomplished cyclist, used to pre-selecting the right gear when approaching hills, then a mid drive will probably suite her. If not then there could be some horrible crunching gear changes to be heard. Whereas a hub will continue to drive while she finds the right gear.
Another aspect I would mention is that it is difficult (not impossible) to fit a front deraileur with a mid drive. So limiting the number of gears to the rear cassette. Many will say that this doesn't matter on an electric bike and that 7-8 gears is fine. In most cases I'd agree but I know Bath has some pretty severe climbs around. With a hub motor (front or rear) you can have a double chain ring.
Declaration of interest here. I ride hub conversions in very hilly West Wales. On one bike I have 16 gears, on the other 14. I use them all in the quest for comfortable cadence. The lower gears allow me to maintain the mentioned 7-8mph up almost all hills without straining my legs with too low a cadence. I must admit there are one or two brutal 1:4 hills around here that will see me at 5mph for short spells, BUT I have never had the motor overheat or stall (Ezee mk2 BPM type). The higher gears allow me a decent speed of 25-28mph without spinning out.

No .. you got the wrong end of the stick. With a hub motor you just have less options, with a crank or central motor you have many many more. The mid gear say gear 5, suitable for flat road or slight downhill equates to the power assist that a typical hub would provide, but then you have 4 others below to help with steeper climbs and 4 more above for when you are going faster and or going down hill. A crank motor is no more likely or less likely to stall or overheat as a hub motor.... Slight exaggeration here as the big direct drive motors have a huge mass of copper wiring and steel in them so they are slower to heat up.
Having driven around Bath in a car once, I would much rather having the range and flexibility of a crank drive. Having had both, albeit the hub was one of the lower 200 w jobbies, I much prefer the Bosch crank motor for flexibility, and elegance.
When you are going up your Welsh hills , you are probably providing the majority of the effort and that's why you need your second chain wheel, the motor is probably, (it does depend on the actual windings used and the diameter of your back wheel) , providing 30% of your total power. When going down those hills at 20 mph it is providing nothing.!
Had you a central drive it would be providing 100% of its efficiency even at 5mph on those brutal climbs, provided you have gears which allow you a cadence of 40 to 90, optimised at about 60 at 5mph.
Now the current Bosch model does not allow for multiple chain wheels, and other central drive manufacturers do, but the newer 2018 model is expected to have a standard sized chain wheel so presumably could. But I have not found a need for more than the 10 gears supplied irrespective of the slope. Downhill and still pedelling.. furiously , in top I reached 50kmphr. In first I can go up anything, I have a mind to.
Also there is no gear chain crunching on a Bosch, the electronics sense the reduced load and remove the torque at the instant.
Motus a very good choice for road and gravel paths

 

[Deleted member 4366]

As far as I'm concerned, crank-drives are just an unnecessary complication. All you need is a hub-motor with enough torque to get you up the hills that you encounter. Thankfully, there's plenty of choice, so you can always find a hub-motor that suits you. I've dabbled in crank-drives for a while (I still have two bikes with them idling in the shed) and I've tested many. We have serious hills around here with two that go 30%. My weight has nearly always been over 100kg, and I've never had a problem getting up them with the right hub-motor. I'd challenge anybody to a race up any normal hill on the road with their Bosch, Brose or Yamaha bike, dongled or not, and I'll lay down money that I'll win with my little Q128C.

 

[Danidl]

As far as I'm concerned, crank-drives are just an unnecessary complication. All you need is a hub-motor with enough torque to get you up the hills that you encounter. Thankfully, there's plenty of choice, so you can always find a hub-motor that suits you. I've dabbled in crank-drives for a while (I still have two bikes with them idling in the shed) and I've tested many. We have serious hills around here with two that go 30%. My weight has nearly always been over 100kg, and I've never had a problem getting up them with the right hub-motor. I'd challenge anybody to a race up any normal hill on the road with their Bosch, Brose or Yamaha bike, dongled or not, and I'll lay down money that I'll win with my little Q128C.

Would that be the 500w nominal version of q128c and comparing it with the 250 w nominal version and perhaps with an augmented 20amp controller and perhaps the 48v supply ? . If so no contest.

 

[anotherkiwi]

Gears are important on a hub drive motor - use the right gears and you will get lots more range from the battery. If you are in the wrong gear it will be more forgiving.

I have stalled a GSM mid drive in 1st gear. The hill is probably over 15% (I can't rely on Google maps slope calculator because it never seems to go above 14% anywhere). That was with the standard 46 tooth chainwheel and a 34 tooth bottom gear.

 

[Trevormonty]

Gears are important on a hub drive motor - use the right gears and you will get lots more range from the battery. If you are in the wrong gear it will be more forgiving.

I have stalled a GSM mid drive in 1st gear. The hill is probably over 15% (I can't rely on Google maps slope calculator because it never seems to go above 14% anywhere). That was with the standard 46 tooth chainwheel and a 34 tooth bottom gear.

That is very tall gearing if assist cuts out at 15mph. I switched Shimano Steps from 44t to 38t, with lowered gearing can now tackle steepest hills in Wellington but have to work a bit on steepest hills. Changing rear 9spd cassette from 11-34 to 11-40t should make those steepest hills even easier.

NB at 15mph still have 2-3 more higher gears which only get used for downhill or tail winds.

 

[dsearb]

I know Bath reasonably well and if it was my wife, I’d fit a Bfang crank drive. I bought herself a Bosch Motus crank drive to give her confidence. She also has a Trek and knowing what I know now i could easily have fitted a Bfang. This sort of mid-drive is easily managed.

Thanks Doug - will look at the Bafang, tho not so keen on the way the motor sits rather exposed in front of the crank

 

[dsearb]

Any middle sized hub-motor will give the same torque as that bike you tried. If you want better torque, use 48v instead of 36v.

If you say how heavy you are, how fast you want to go and whar sort of hills you have, we can point you to exactly the system you need.

Thanks d8veh - the user is 11stone, we are looking to do rides of up to 40miles - Hills up to 500m of 1:10, probably at 5 mph - I like the look of rear hub motor (less power being transmitted through the chain). Will probably have to go for a rear rack battery as frame is small - does this make the bike tail heavy?
I like the look of buying the kit as a package (with a guarantee)

its actually a Kona dew - rather like this, without the discs:
https://www.google.co.uk/search?biw=1920&bih=949&tbm=isch&sa=1&q=kona+dew+2015&oq=kona+dew+2015&gs_l=psy-ab.3..0j0i24k1.3165.3826.0.4952.5.5.0.0.0.0.129.457.4j1.5.0.dummy_maps_web_fallback...0...1.1.64.psy-ab..0.2.160...0i13k1.0.5NSXvtRrZzw#imgrc=BpaUh8IAfCctNM:

 

[dsearb]

Thanks whoosh - so it seems to be that I will get a decent torque of 50 Nm at 30rpm with the SWX02? Prices? Nb I want pedal assist - it shows a thumb throttle on website - is this optional?

 

[Woosh]

Nb I want pedal assist - it shows a thumb throttle on website - is this optional?

yes, it is.

 

[anotherkiwi]

That is very tall gearing if assist cuts out at 15mph. I switched Shimano Steps from 44t to 38t, with lowered gearing can now tackle steepest hills in Wellington but have to work a bit on steepest hills. Changing rear 9spd cassette from 11-34 to 11-40t should make those steepest hills even easier.

NB at 15mph still have 2-3 more higher gears which only get used for downhill or tail winds.

If I kept the GSM on the upright for round town use I would have swapped the twin chainring out for a 38 with an 11-40. Wellington riding brings back warm memories, when I was a student I lived on Tasman street and later above Lyall Bay on the aptly named View Road

 

[Benjahmin]

I still maintain that a hub gives a less 'technical' ride style. You rotate the pedals, the power comes on - end of. A kit can be fitted then the gearing sorted once ride speed/style established.
A rear hub + rack battery would be tail heavy. Probably not a problem for general road riding but would affect any more agile stuff. Have you considered a triangle bag battery? If you got one you could get Jimmy at Insat to make a battery to fit.

 

[Deleted member 4366]

Thanks d8veh - the user is 11stone, we are looking to do rides of up to 40miles - Hills up to 500m of 1:10, probably at 5 mph - I like the look of rear hub motor (less power being transmitted through the chain). Will probably have to go for a rear rack battery as frame is small - does this make the bike tail heavy?
I like the look of buying the kit as a package (with a guarantee)

its actually a Kona dew - rather like this, without the discs:
https://www.google.co.uk/search?biw=1920&bih=949&tbm=isch&sa=1&q=kona+dew+2015&oq=kona+dew+2015&gs_l=psy-ab.3..0j0i24k1.3165.3826.0.4952.5.5.0.0.0.0.129.457.4j1.5.0.dummy_maps_web_fallback...0...1.1.64.psy-ab..0.2.160...0i13k1.0.5NSXvtRrZzw#imgrc=BpaUh8IAfCctNM:

There's nothing special there, so just about any kit will give you what you want. Look for one that has a control panel with at least 3 levels of assist. The ones with sine-wave controllers make the motor very smooth and quiet.

Rack batteries are OK, but you can feel the difference. If you do go for a rack one, adjust the carrier to get the battery as low and as far forward as possible. Even an inch makes a noticeable difference.