Hub or crank?

[David Summers]

I'm still trying to decide whether I should convert my Specialised Globe city. I'm quite tall and heavy (110kg) and and there are plenty of hills around where I live, so I'm keen to avoid disappointment! There's so much info about motor winding / voltage / amps I'm doubting I understand what I need.

I'm worried that a front hub motor won't be up to the job to haul my mass uphill - I have a nexus rear hub, but also the front forks are carbon fibre which some have said can't take a hub motor. That leaves a crank drive conversion but these look more difficult. I'm capable of basic bike mechanics but I haven't tried this before. Or should I just sell the bike and buy one made by someone who knows what they're doing?!

 

[Nealh]

It depends on your cycling style and where you cycle/ride.
For a leisurely riding style with hills the a hub will be fine if you are a sportier rider then a crank drive.
Carbon forks and hub gears only leaves one option a Cadence or a TS crank drive. For hub bike look for a 201rpm motor which will provide good torque if you were lighter you could get away with up to 270 rpm.
If you aren't sure of converting then it is always better to buy premade.

 

[Deleted member 4366]

I'm still trying to decide whether I should convert my Specialised Globe city. I'm quite tall and heavy (110kg) and and there are plenty of hills around where I live, so I'm keen to avoid disappointment! There's so much info about motor winding / voltage / amps I'm doubting I understand what I need.

I'm worried that a front hub motor won't be up to the job to haul my mass uphill - I have a nexus rear hub, but also the front forks are carbon fibre which some have said can't take a hub motor. That leaves a crank drive conversion but these look more difficult. I'm capable of basic bike mechanics but I haven't tried this before. Or should I just sell the bike and buy one made by someone who knows what they're doing?!

Basically, your thinking is flawed. Instead of converting that bike, get a conventional one with derailleur gears and suspension forks. You can get a good used one for about £100, which is insignificant compared with the cost of the electrical stuff and less than the difference between a crank and hub system.

For advice on which bits you need, you need to tell us the performance characteristics that you're seeking, like speed, range, power, pedal effort, etc.

 

[David Summers]

Basically, your thinking is flawed. .

Often been said! In my defence, the bike has been a good commuter, and I like the low maintenance nexus hub, high quality saddle/brakes etc... If I *could* put a front hub motor on that would seem simplest, but I am unclear why it's considered a bad idea on a carbon fork.

As far as effort goes, I want it for commuting and so need to get to work non-sweaty which means reasonable assist over the 6 miles there I guess. Going home I'd turn down the assist and get my exercise. Probably. Some moderate hills both ways. Speed not critical and range doesn't need to be more than 30 miles or so I suppose- more is always good.

 

[Deleted member 4366]

Derailleur gears are low maintenance. I didn't touch mine in 4000 miles. The saddle can be moved to the new bike. You can get better brakes on the new bike. They don't cost much - £40 for a pair of branded hydraulic disc brakes is all I pay.

Are your forks disc brake forks and do you have disc brakes?

 

[spanos]

If I *could* put a front hub motor on that would seem simplest, but I am unclear why it's considered a bad idea on a carbon fork.

They are likely to break from the torque /weight basically. You might get away with very low power motor but I wouldn't risk it

Either ditch the forks and go front hub. Or crank and rear nexus.

I have done both with an alfine 8 hub system.

Crank systems are easy to fit. Not harder than hub anyway imho . Hardest bit is removing the crank and bb from the donor bike !

 

[David Summers]

Are your forks disc brake forks and do you have disc brakes?

No, rim - which may mean the fork is not designed for the loads I suppose - good point.

 

[spanos]

Ahh, also those forks look too narrow to take most front hubs. You need mtb / 100mm at dropouts . Plus not narrowing too quickly.

I had to swap them forks on my Hybrid

 

[David Summers]

They are likely to break from the torque /weight basically. You might get away with very low power motor but I wouldn't risk it

Either ditch the forks and go front hub. Or crank and rear nexus.

I have done both with an alfine 8 hub system.

Crank systems are easy to fit. Not harder than hub anyway imho . Hardest bit is removing the crank and bb from the donor bike !

Thanks - I think it's either crank motor or a new donor bike. Changing forks seems complicated. Any particular downside to a Bafang crank kit , other than cost?

 

[spanos]

Thanks - I think it's either crank motor or a new donor bike. Changing forks seems complicated. Any particular downside to a Bafang crank kit , other than cost?

Tend to agree but I love my alfine and wouldn't be without it !

Bafang? Nope, tried. and tested. Very available, plenty of spares, loads of info on interweb

Price aside , nothing not to like as an aftermarket crank drive

 

[Deleted member 4366]

Leave the bike as it is. it's a very good non-electric bike. there's no point in converting it into a bad electric bike. Start with an ideal donor bike and fit a nice kit to get a nice electric bike. All the things that's needed to make a non-electric bike good are not necessary for an electric one.

 

[David Summers]

Why would adding a crank motor make it a bad electric bike? I'm new to this so I'm not sure what characteristics are best-suited to a conversion - I appreciate the hub gears and carbon forks make my choices limited, but is a crank motor a bad idea?

 

[Woosh]

I appreciate the hub gears and carbon forks make my choices limited, but is a crank motor a bad idea?

It is much less work installing a CD kit compared to a rear hub kit but more work compared to a front hub kit. Your case is exceptional because you have a carbon fork. If you swap it for a steel fork, installing a £499 front SWX or a BPM hub kit is very straightforward.
This said, CD kits have advantages like you can use the bike's gearing to adapt the assistance for speed or climbing. The reverse is equally true, you can damage your CD kit and/or drive train, your IGH much more easily through using the wrong gear. On a CD bike, the stress and strain is inversely proportional to your cadence. You choose the right gear, you can climb 15% gradient with ease, spinning the cranks at 60-80 rpm. If you choose the wrong gear on the same hill, your cadence may drop down to 30-40 rpm, then half the battery power will be converted to heat and the motor's gearbox and the motor itself take a beating.
For heavy riders, I recommend the Bafang BPM kit. It's a good compromise, a large and powerful front hub motor.
http://wooshbikes.co.uk/?hubkits

This is a front BPM kit installed on a tandem. It can pull two people up a 10% hill,

 

[David Summers]

I appreciate all the advice. Will try to decide on the best way to proceed - and investigate whether I can find a reasonably priced front suspension fork and how to change it...

 

[Trevormonty]

Www.ebiketips.co.uk have article on fitting middrive kit, straight forward if you have some mechanical skills. See buying advice section.

If you do get a kit and don't like bike after woulds, you can transfer it to cheap MTB or hybrid. Ideally something with mudguards and front suspension if commuting.

 

[Trevormonty]

Just been looking at Pinion range of bikes (crank gear box), these would be perfect for rear hub motor conversion.
Get best of both worlds, rear hub with belt drive. A quick change of rear wheel and it is back to normal bike.

 

[Woosh]

I appreciate all the advice. Will try to decide on the best way to proceed - and investigate whether I can find a reasonably priced front suspension fork and how to change it...

where do you live?
if you are not too far from Southend, you could make an appointment to bring your bike to us and collect it after 4 hours. We'll supply and fit the fork and the kit for you. Total cost with front BPM kit and 15AH battery is £699. £50 extra if you need 17AH battery. Contact support if you want to go ahead with this.

 

[John_S]

Isn't the Woosh BPM kit rated at 350w? The OP might wish to stick with a legal 250w setup.

I agree that crank drives have their fair share of disadvantages. I owned a crank drive bike (a Woosh Krieger) before, and its motor kept breaking and needing to be replaced before I eventually switched to my current BPM hub-driven bike with which I've never had any problems. It does seem that crank-drives are susceptible to motor damage if you are not skilled enough to use the gears correctly according to your cadence. I've heard that unlike the Chinese crank drives, however, the German crank drives have heat sensing software installed which protects the motor from overheating when under stress.

 

[David Summers]

Thanks again for the advice. Unfortunately Southend too far - but I think the front fork option is still a possibility, unless I find a half decent 2nd hand donor bike instead - I will update the panel with my progress!