Conversion kit to match Carrera Vulcan

[tpw]

I started a thread the other day about finding a suitable kit to help me get up a particular hill in my town. Someone in that thread suggested getting a test ride from Halfords so I could see how it dealt with this specific hill.

I did that today and it felt like exactly the level of assistance I was looking for, so I would like to buy a kit of the same power so I know it will definitely be good enough. The bike was a Carerra Vulcan with a Suntour HESC rear hub, which according to their website kicks out 50nm of torque.

From my research the XF07 that I was looking at is more like 30nm which, along with my bike having slightly larger wheels than the Carerra, leaves me thinking it won't be enough.

Does anyone have any advice on any other hub kits (or mid drives, but they'd have to be below £550 inc battery) that have that kind of torque? Or is torque actually the spec I should be focussing on?

 

[Woosh]

I would recommend the XF08C. A rear hub gives better traction on wet roads.

http://wooshbikes.co.uk/?hubkits#xf08ckit

This is a converted Carrera Bantu to give you an idea what it looks like after the conversion:

 

[tpw]

Thanks for the reply, I was going to phone you guys tomorrow anyway

Do you have the torque rating for that motor or any of the others on your website though? Or is torque a good way of finding something as powerful as the Vulcan I test rode today?

 

[Woosh]

the maximum torque for the XF08C is 40-45NM, I asked Mxus to modify their 300W motor to make it legal 250W.

 

[tpw]

So given that that would be 10-20% less torque than the one I rode today (plus my bikes larger wheels), should I expect that to give 10-20% less assistance up the hill? If so I'm not sure that would be powerful enough..

Or are there other statistics that I should be considering?

 

[Woosh]

So given that that would be 10-20% less torque than the one I rode today (plus my bikes larger wheels), should I expect that to give 10-20% less assistance up the hill? If so I'm not sure that would be powerful enough..

the XF08C is torquier than the Suntour HESC. The XF08C is also a little larger and heavier. The HESC system runs at 15A max, the XF08C at 17A.

 

[tpw]

So what specifications did you look at to arrive at that conclusion, considering on paper the Suntour HESC has a higher torque rating than the XF08C?

Like what should I be taking into consideration when making these comparisons? Are you saying that the current changes the rated torque?

I understand if that question requires too complex an answer! Happy to just be given a link or a search term

 

[Woosh]

So what specifications did you look at to arrive at that conclusion, considering on paper the Suntour HESC has a higher torque rating than the XF08C?

manufacturers do not give the RPM at which they measure their motor's torque. The torque is higher at lower RPM, and is very high at near stalling speed which is meaningless in practice because you cannot ride the bike at too low speed. The chart below describes the approximate behaviour of the XF08C:

The figure 40-45NM I gave is the torque at around 6mph (80 RPM), a practical speed that you need to climb a steep hill.


There are better indicators of performance of a motor like diameter and weight, maximum power rating. They are easier to tabulate for comparison but they are only indicators, not the real thing which is the motor performance test chart that the manufacturer has done on the actual motor.
This one is for a direct motor but similar to those we use to select
motors:

For a quick comparison, the key points are:

- voltage
- maximum current
- motor diameter
- magnet weight
- internal reduction ratio
- maximum output power
- noload speed

 

[Benjahmin]

Hi tpw, as woosh has said torque is a slippery one to get hold of, depends where in the drive train the measurement is taken, at what revs etc. One thing you can be sure of is that the quoted figure will present the best picture from the manufacturers point of view.
I have two conversions. One an Ezee, the other a Panda. The Ezee is a large diameter motor (similar to Bafang bpm) develops lots of hill climbing torque. The panda (not sure who's motor it actually is) is a smaller diameter. It's lighter and faster but not so good on the hills.
The winding code of the motor is a factor here. This determines the no load rpm of the motor, a high rpm motor in a big wheel will give more speed but less torque. Put it in a small wheel and it will climb a wall - slowly.
The maximum current rating of the controller gives the maximum power output to the motor. So a 20A controller on a motor will develop more power than a 10A contoller, on the same motor.
Then, the battery has to have the ability to deliver that maximum current without voltage sag, which would have you feeling a diminishment of power as you climb a hill.
And there's more ! So, yes, lots of variables.

How to zoom in?
First what's the wheel size of your bike? How handy are you with the spanners? Sounds like you want a hub drive with cadence sense, would that be right? How far do you want to be able to go? Do you have a budget? Just for starters.

My Ezee is a front hub on a Carrera crossfire. Origionally 24 gears but granny ring was removed to fit pas disc, so now 16. 48/36 on the front gives me the combination of hill climbing and speed I want. It gets me up some daft hills around here.
The Panda is a front hub on an old Silver Fox hybrid with blade forks and is lighter than the Carrera. It has the original 21 gear in place. The rear gear cluster has a mega range first gear, so this with the granny ring is near a 1:1 ratio. Even so I cannot get up some of the hills on this bike that I do on the Carrera. The motor just doesn't have the guts. However it's great on the flat easily reaching it's cutout of about 17-18mph.
Sorry, bit of a ramble, but you've asked a complex question.

 

[Laser Man]

That graph is informative but a bit disappointing - it shows that we can only get the best power and efficiency by de-restricting and going illegal!
Best power/efficiency at roughly 25/26 mph for a 26" wheel and 28/30 mph for a 700C.

It would be interesting to see the torque curve for the "high torque" 48V 250W SWX02 motor.

That said, the XF08C is more than adequate for my needs. I've never ridden any other e-bike so I have nothing to compare it with, but it has exceeded my expectations by a long way.

 

[Woosh]

That graph is informative but a bit disappointing - it shows that we can only get the best power and efficiency by de-restricting and going illegal!
Best power/efficiency at roughly 25/26 mph for a 26" wheel and 28/30 mph for a 700C.

that graph was of a H4540, a direct drive motor.
I picked it for the shapes of the plots. I could not find the same for the XF08C. Where you see 390 (noload RPM), you should substitute 230, that's the noload RPM for the XF08C.
The peak power of the XF08C is 170-180 RPM whereas on the graph, it's around 300 RPM for the H4540.

 

[Laser Man]

Ah! Hadn't realised that the graph was just an example of the curve shapes.
So peak power at around 14/16 mph depending on wheel size - just right for UK/Europe.