Lightweight rear hub kit

[sjpt]

A few years old, but look at https://www.pedelecs.co.uk/forum/threads/pro’s-and-cons-of-buying-cytronex.32165/
The system was clearly not right for us, but could well be right for your wife. The shop is quite close to us; we've been in a few times, considering their system and for other general bike issues and they've always been very helpful.

It is a proprietary system which has its downsides when it comes to spares and repairs. I can't remember the details but I have a memory of people with their earliest system having lots of issues getting replacement batteries. That was some time ago though, and it may be a distorted memory.

 

[Nealh]

My small G370 hub is simply fitted in to nice Surly chromoly steel forks, all that resists rotation is the tight fit and one anti rotation washer and the nuts nicely tightened in the dimples. The motor cable exits the hub in a way that doesn't allow a torque washer on that side, unlike most hubs the thread uses std SA or alfine threaded nuts on 10mm axle. The axle shaft is 10mm in dia and the only part that has opposing flat sides is the tiny bit that sits in the drop outs, this motor is low power but quite pokey for a lightweight install. It isn't designed for high power usage and must be fitted in to a steel drop out rather the soft aluminium.

 

[Nealh]

All I will say is the cytronex kit is bepsoke and quite expensive, for spares one is tied to cytronex.

 

[Hummerst1]

All I will say is the cytronex kit is bepsoke and quite expensive, for spares one is tied to cytronex.

Up to now I have not been considering front hub kits, and the Cytronex stood out as having had a great deal of thought going in to it, not least the control software - I might look again at putting something together myself, but it does seem that there are pitfalls... Woosh is also an option I might revisit - previously dismissed due to the weight of their rear hub kits - MH

 

[Nealh]

Any hub kit to get the best out of them is one with high internal gear ratios as this allows for more unassisted riding without the treacle affect often associated with hubs. The larger hubs 129mm or greater tend to be mostly 4:4:1 geared down where as the smaller lighter hubs are much higher geared, the larger hubs being heavier means all the weight is centrally located so one has to over come the inertia of that central mass when unpowered. It will feel like motor resistance but it isn't internal resistance as they freewheel but the gearing internal gearing does make a big difference.

The direct drive hubs are massively heavy at over 5kg and nearly 20kg for the 8kw monsters, these have no freewheeling or are geared inside and are near impossible to ride without power.

So for any geared hub one needs to know the internal gearing if wishing to ride with less power or no power.

 

[Hummerst1]

Any hub kit to get the best out of them is one with high internal gear ratios as this allows for more unassisted riding without the treacle affect often associated with hubs. The larger hubs 129mm or greater tend to be mostly 4:4:1 geared down where as the smaller lighter hubs are much higher geared, the larger hubs being heavier means all the weight is centrally located so one has to over come the inertia of that central mass when unpowered. It will feel like motor resistance but it isn't internal resistance as they freewheel but the gearing internal gearing does make a big difference.

The direct drive hubs are massively heavy at over 5kg and nearly 20kg for the 8kw monsters, these have no freewheeling or are geared inside and are near impossible to ride without power.

So for any geared hub one needs to know the internal gearing if wishing to ride with less power or no power.

Thanks again - this latter point is critical - feedback seems to suggest that the Cytronex kit doesn't offer much resistence when switched off - are any of the motors brushless? Presumably that would help as well as a high internal ratio

 

[Nealh]

All modern day hubs are brushless.

 

[Malcolm]

@Hummer: It sounds like we're chasing similar solutions, though I'm limited to rear wheel motors as my wife's bike has carbon forks. I'm also very tempted by the Cytronex kit for my own bike, but as mentioned it's on the pricey side.
I got a reply from Woosh about the 85SX kit. Unfortunately the lightweight 85SX is unavailable at the moment and they will only sell a kit with battery. Andy at Woosh did suggest an XF08 instead, but the added weight of this and a large battery would be too much for my wife.

I would build a rear wheel myself if I could find a lightweight rear motor, but they seem very thin on the ground. Not sure if that's just general supply issues or simply lack of demand. Not so keen on buying from China, mainly because it's difficult choosing the right combination of components. Will keep on looking...

 

[Malcolm]

Neal: I just noticed your guide to selecting components from Topbikekit. Much appreciated! I'll take a closer look.

 

[Nealh]

Buying form China is the option and source for most hubs when one wants a more bespoke motor, the KT component stuff is quite easy to put together as all is compatible. All one has to do is decide on waterproof or block connector style and how they wish a controller to be integrated.

Once one makes up their mind one posts the list of items selected to get a second/third opinion on suitability.

With the KT dual controller one can decide on the battery to use 36 or 48v but must decide on this at the time of buying the motor as one ideally is better to buy a motor rated for the voltage for better efficiency.

 

[Nealh]

With the lighter weight motors don't expect them to have the grunt of the larger heavier motors, though tbh my one feels good. It has carried my 84kg + 30kg of cat litter in the panniers and on the rack, also it has towed my trailer and 40kg of hand tool etc with no problems.
The acceleration isn't as fast as larger hubs (though it doesn't mean they are slouches) but all the same they are easier to pedal unassisted, for a light motor I think a front motor is better then a rear motor as the bulk of the rider and bike weight isn't affecting the motor so much.
With them being a little lighter and less powerful any tendency to wheel spin is unlikely, I have't yet spun the wheel on mine but did so often with the heavy 4.4kg front BPM hub.
For the lighter motor opt for the 201rpm version for max torque .

 

[Hummerst1]

@Hummer: It sounds like we're chasing similar solutions, though I'm limited to rear wheel motors as my wife's bike has carbon forks. I'm also very tempted by the Cytronex kit for my own bike, but as mentioned it's on the pricey side.
I got a reply from Woosh about the 85SX kit. Unfortunately the lightweight 85SX is unavailable at the moment and they will only sell a kit with battery. Andy at Woosh did suggest an XF08 instead, but the added weight of this and a large battery would be too much for my wife.

I would build a rear wheel myself if I could find a lightweight rear motor, but they seem very thin on the ground. Not sure if that's just general supply issues or simply lack of demand. Not so keen on buying from China, mainly because it's difficult choosing the right combination of components. Will keep on looking...

Just FYI, I have been chasing the 85SX motor kit at Woosh for the last 6 months - not sure why they are advertising them beyond trying to sell you a different product that you don't want... (this has been their response every time) - if you look at the AKM motors (AKM-100CST@2kg) on Topbikekit.com, that is the closest equivalent that I could find to the 85SX - beyond that, I defer to the very knowledgeable/helpful chaps on this forum

 

[Nealh]

The Woosh listing must be wrong for the 85sx as they list it as 100mm but then say it is a rear motor which it isn't.

Topbikekit sold out of the 85sx quite a while ago the only lightweight sub 2kg hub is the G370 at 1.7kg for 100mm drop outs, the 75sx is available but is ultra light at 1.4kg . I think one would also need to very light as well to use one.

BMSBattery sell the akm85 and GBK sell the Bafang G311 front hub at 2.3kg 11:1 gearing ratio.

 

[Woosh]

Thank you for pointing that out.
the 100mm is the diameter of the 85SX motor shell casing.
the dropout is 135mm.
The data table on the web page is confusing.
I'll fix it tomorrow.

 

[Nealh]

Ok thanks Tony, for pointing that out.
In that case then yes, Woosh are or were the only sellers I know of who sold the 85sx as a rear motor/kit.

 

[Nealh]

Another 100mm front motor is the Xiongda ytw-06 at 1.35kg .

 

[Malcolm]

Just ordered an AKM100CST hub with T-06S controller, PAS and KT LCD4 from Top Bike Kit – thanks for the guidance Neal.

It took some time working out which sensor would fit the bike, but eventually went with the BZ-10C. Would have liked a higher magnet count, but I can always upgrade later.

I tried ordering a pre-built 27.5 wheel and 10s2p 10Ah battery, but the shipping would have almost doubled the price, so I'll be building my own wheel and have bought a 7Ah bottle battery built with Samsung cells from UPP Battery on eBay instead. I'll use the spoke calculator at ebikes.ca to work out what length spokes I need. Any other tips for a novice wheel builder?

Total added weight should be around 4 kg.

Even buying this way the combined cost will not be all that far off what Woosh charge for their smallest kit, so all credit to them. The upside for me is getting a lightweight solution that will hopefully suit the bike well, and learning a new skill.

 

[Nealh]

10 poles is more then enough, if you fitted a 12 pole one I doubt you would tell much difference on the motor pick up.

 

[Nealh]

If you have no truing stand or don't make one, true the wheel up in the drop outs.
Use a cable tie around the stay and cut the tail end to use as a marker against the rim wall on one side. For spokes one should be able to use one length for both side even though the drive side will be a mm or two shorter as one will need to dish the rim once the wheel is built.

 

[Nealh]

Buy a decent spoke wrench/key, I prefer to use spokey single size type to suit the nipple size I'm using but there are also 6 way spoke keys.

A couple of wheel lacing utube vids I quite like.

lacing a 3x bike rim - Search Videos

www.bing.com