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Cunning Plan

E-bike conversion

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Plan junior, for his latest hairbrained idea, wants to convert his mountain bike to an electric bike. He seems convinced it isn't difficult and he can get 40mph  out of it.

Any advice?

(Apart from getting him a Kevlar bodysuit)

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Posted (edited)

Its not difficult if you've ever changed a bottom bracket/crank on a bike.

I converted mine using a 500w Bafang crank drive kit with a 37aH battery. On 5deg hills I could do 14mph, with iirc a 12t rear sprocket. I could cruise at 24mph on the flats keeping a comfortable quick cadence. I went single speed for ease of maintenance. My round trip commute it 22miles and over 2000ft of climbing, I could do it on 1 charge.

To get 40mph you'd need to keep the gears and need a bigger motor.

Legally you should stick to 250w and a max assisted speed of 15mph of course :P

It was a great bit of kit for 3000miles of all weather commute until some cunt swiped it.

Edited by Cosmic Apple

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2 minutes ago, Cunning Plan said:

Plan junior, for his latest hairbrained idea, wants to convert his mountain bike to an electric bike. He seems convinced it isn't difficult and he can get 40mph  out of it.

Any advice?

(Apart from getting him a Kevlar bodysuit)

Easily done.

I know 40mph is an exaggeration, but 15mph is the legal limit -- above this and you're effectively riding a motorcycle without MoT, insurance or a valid license -- if you're caught it'll not be a good start to getting proper driving sorted.  15mph is okay on-road, but brilliant off-road.

Anyway, cheapest way is to get a geared rear hub with wheel and hubset attached.  This won't be brilliant technology, but will be cheap.  Frankly, I'd restrict it to 250w (for the reasons above), but I would go with a twist (or thumb) throttle -- there's grandfather rights about this, and with a diy job they (the law) wouldn't be able to tell that it didn't date from the time when it was allowed.  Rear motor is better than front; you'd think that a front conversion would be easier and would give better off-road capability, but IMO the power coming from the front upsets steering balance, particularly off-piste.

The battery will be an expensive component.  For my electric bike conversions I use balance board batteries.  These are a bit weedy compared with full electric bike batteries -- 4-5ah@36v rather than 10-15ah@36v, but with the 250w limit there's no difference in actual 'putting the power down', and the only impact will be on range -- about 15 miles compared with 50.  But that's a fair whack of riding anyway, and if you find you need more it is very easy to just buy a second battery.  And they are much, much cheaper.

After all that I'd note that there will certainly be a major want of having a 500w+ motor beast of a thing.  I'd still, however, suggest that 250w is a better option for a first conversion; if more is wanted at that point it can be a point of discussion (and would be easier to dissuade as IMO they're getting into moped territory at those powers, and I'd think that training, a full helmet and some protective clothing starts to be in the 'needed' list).

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Don't bother, you want a crank drive electric bike, 40mph will require a big heavy rear drive unit on a bike with forks to take the torque (you can add reinforcement to get there sometimes),  battery and controller will not be cheap.  There's quite a few crank drive bikes knocking around now s/h, one of those with a shot battery might be a good candidate for tinkering.

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6 minutes ago, The Masked Tulip said:

Do not do it.

If he wants an electric bike buy one - about 3 to 4 K for a decent electric mountian bike. The conversion kits are rubbish.

How old is junior?

16 in two weeks. He is looking at spending £400 max

To be clear, I don't want him doing 40mph. I would rather be got a 50cc trials bike it he wants to do that.

(I am giving him full bike training lessons for his surprise birthday present)

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1 minute ago, Cunning Plan said:

16 in two weeks. He is looking at spending £400 max

To be clear, I don't want him doing 40mph. I would rather be got a 50cc trials bike it he wants to do that.

(I am giving him full bike training lessons for his surprise birthday present)

 

Get the trials bike. More fun and longevity plus a 16 yr old has no reason to be wanting an electric pedal bike unless he is a lazy fat tub of lard. Most electric pedal bikes are ridden by lazy feckers.

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1 minute ago, Cunning Plan said:

16 in two weeks. He is looking at spending £400 max

To be clear, I don't want him doing 40mph. I would rather be got a 50cc trials bike it he wants to do that.

(I am giving him full bike training lessons for his surprise birthday present)

A better bet with the trails bike and the kit tbh and I'm a big fan of electric bikes, £400 will not get the bits unless they've dropped in price a lot. 

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1 minute ago, The Masked Tulip said:

 

Get the trials bike. More fun and longevity plus a 16 yr old has no reason to be wanting an electric pedal bike unless he is a lazy fat tub of lard. Most electric pedal bikes are ridden by lazy feckers.

Just an anecdotal about one person I know who is overweight but not obese. Person figured that they needed more exercise so they splashed out on a top of the range electric pedal bike almost two years ago. Still the same weight and size! All person does on bike though is go to post office to collect mail when weather is suitable!

 

 

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Either go super cheap on conversion kit or get the motorcycle  (and proper training).  My conversions come in at about £150, so there's scope for cheapness way beyond your budget.

But I don't like 50cc.  When on road it's too fast for easy car manoeuvring around, but too slow to not be getting in everyone's way all the time.  They're a terrible compromise.  E-bike at 15mph or 125cc IMO.

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Just now, Economic Exile said:

Just an anecdotal about one person I know who is overweight but not obese. Person figured that they needed more exercise so they splashed out on a top of the range electric pedal bike almost two years ago. Still the same weight and size! All person does on bike though is go to post office to collect mail when weather is suitable!

Round here, even on the eBike, if you want to keep a reasonable pace you need to put effort in :) Still got sweaty on mine and I'm no fatty!

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1 minute ago, Economic Exile said:

Just an anecdotal about one person I know who is overweight but not obese. Person figured that they needed more exercise so they splashed out on a top of the range electric pedal bike almost two years ago. Still the same weight and size! All person does on bike though is go to post office to collect mail when weather is suitable!

The problem with bikes in the UK is everyone (pretty much) considers them to be a health thing.  So you get pelotons getting in the way every weekend, fat people and elderly buying e-bikes and everyone actually driving most of the time.  This really annoys me.  People in other countries seem to understand what bikes are for, just not the UK.  I think the phrase is 'Britain is a nation of cyclists, the Netherlands a nation of people that just ride bicycles'

Bicycles are an excellent means of transportation.  Electric bikes are even more excellent.  Getting completely focused on exercise is completely missing the point.

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Just now, Cosmic Apple said:

Round here, even on the eBike, if you want to keep a reasonable pace you need to put effort in :) Still got sweaty on mine and I'm no fatty!

The person I’m referring to lives in a very low hill area and the round trip to post office is about two miles.

I wouldn’t mind an eBike myself but I’d be thinking about using it for regular 10+ mile outings!

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2 minutes ago, Economic Exile said:

I wouldn’t mind an eBike myself but I’d be thinking about using it for regular 10+ mile outings!

They are a good gateway if used properly rather than 'abused'.

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56 minutes ago, dgul said:

Either go super cheap on conversion kit or get the motorcycle  (and proper training).  My conversions come in at about £150, so there's scope for cheapness way beyond your budget.

But I don't like 50cc.  When on road it's too fast for easy car manoeuvring around, but too slow to not be getting in everyone's way all the time.  They're a terrible compromise.  E-bike at 15mph or 125cc IMO.

Agreed. I had to do a year on a FSISE due to age and they are bloody lethal.

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1 hour ago, The Masked Tulip said:

 

Get the trials bike. More fun and longevity plus a 16 yr old has no reason to be wanting an electric pedal bike unless he is a lazy fat tub of lard. Most electric pedal bikes are ridden by lazy feckers.

I think he wants to build it for the challenge.

He isn't lazy. Early morning training most days with the schools ex para fitness instructor. 

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1 hour ago, dgul said:

Either go super cheap on conversion kit or get the motorcycle  (and proper training).  My conversions come in at about £150, so there's scope for cheapness way beyond your budget.

But I don't like 50cc.  When on road it's too fast for easy car manoeuvring around, but too slow to not be getting in everyone's way all the time.  They're a terrible compromise.  E-bike at 15mph or 125cc IMO.

I am liking the sound of the cheap conversions. I think it is more of an 'i did it' than a long term use project.

The balance board battery makes sense. Any more hints?

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Posted (edited)
21 minutes ago, Cunning Plan said:

I am liking the sound of the cheap conversions. I think it is more of an 'i did it' than a long term use project.

The balance board battery makes sense. Any more hints?

Nothing really.  Wheel kits should be less than £130* new on ebay (none on ebay at the moment but if you wait one will turn up).  Don't expect to buy them from China as the postage will be crazy.  Battery should be less than £40*.  The difficult bit will be getting a suitable box for the battery (I use triangular frame bags -- you can get 'hard' ones that work well) and sorting out the battery -- the battery will come with a nice xt90 connector (female), so the easiest thing would be to get some male xt90 connectors and heatshrink and use to make everything else compatible with the battery.  You'll need to be able to solder.  That's a bit of a faff in terms of connecting/disconnecting etc but it will be cheap (there are better connectors, but it'll be more cash.  I just put up with xt90s).  I forgot that you'll need a charger -- I've only got one and it covers all the e-bikes in the family, but clearly having no-charger won't be any good -- that'll be an extra £15-20 and you'll need to put the XT90 connector on to actually make it connect to the battery.

[I have to admit that I never quite trust li-ion batteries and am always a bit careful with charging them -- but that's true of all li-ion, bar the ones in laptops/phone/etc.  I don't trust them either, but it too disruptive to be too careful with these]

[* the best I've done is £120 for the kit and £30 for the battery, but it looks like everything is a little more expensive at the moment]

Edited by dgul

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2 hours ago, Cunning Plan said:

Plan junior, for his latest hairbrained idea, wants to convert his mountain bike to an electric bike. He seems convinced it isn't difficult and he can get 40mph  out of it.

Any advice?

(Apart from getting him a Kevlar bodysuit)

 

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Posted (edited)

There’s a site/FB group called drunkcyclist I used to follow. I stopped because their rants about e bikes were getting boring, but worth five minutes of your time to find out what many cyclist, especially mountain bikers think of e bikes.... hostility is putting it mildly. Also note you can’t actually legally use an e bike in most of the places you might want to go off road cycling.

good on the road for the old and inform though.

Edited by Melchett

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1 hour ago, Cunning Plan said:

I am liking the sound of the cheap conversions. I think it is more of an 'i did it' than a long term use project.

The balance board battery makes sense. Any more hints?

Well if it the learning experience head over to Endless Sphere,  a goldmine of information.

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Posted (edited)
14 minutes ago, Melchett said:

There’s a site/FB group called drunkcyclist I used to follow. I stopped because their rants about e bikes were getting boring, but worth five minutes of your time to find out what many cyclist, especially mountain bikers think of e bikes.... hostility is putting it mildly. Also note you can’t actually legally use an e bike in most of the places you might want to go off road cycling.

good on the road for the old and inform though.

See, I really don't get that attitude.  Why wouldn't you want to reduce the effort?  Does it always have to be about being fit?  I know loads of 'cyclists' -- they seldom cycle to work, they don't go out with the kids, it is always about Strada, about being better.  But better involves always taking the car, bar that evening pointless ride in a big circle!

The electric bike is this fantastic thing that sits somewhere between the bicycle and the moped.  It reduces effort on your commute (why would that be a bad thing?), increases your speed up hills (is that a bad thing), reduces your sweatiness when you reach your destination, increases your range for a given amount of effort.  I just don't see how any of that could be considered bad.  

I'm not at all interested in cycling for exercise or sport.  I do my 10-15k a day run with the dogs on the hills and that keeps me happy enough -- why would I want to complicate things by taking my exercise by fighting with traffic?  I am interested in cycling as a really functional means of transportation and the electric bike is only better at doing that than a normal bike.

Sure, I can see that people like to cycle for exercise and some mix that with their commute -- and if you're doing that an electric boost is a weird 'what's the point of that' -- but these people surely have to accept that not everyone is like them.

[cycling seems to be like a religion at the moment.  ebikes challenge that dogma.]

Edited by dgul

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This is what the Chinese call an e-bike and it does not require a test/licence to ride one. I am not even sure if they have a minimum age to use one, not that an age limit would be an issue with this lot:

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