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I have a cheapo offroad tandem I use with the mrs (she can't ride a bike) and it's a real good laugh, we only do cycletracks and fireroads with the odd exception if we need to reach a spot to camp for the night
Problem is it's pretty limited, I'm pretty fit but she isn't, it's a cheap heavy bike and is often loaded with our wildcamping setup and I can only pull that lot up a few steep hills before my legs start crying so I'm thinking about putting a motor on there, could be a laugh as well getting some MTB mates on there (one a time obviously)
I'm thinking of getting a conversion kit as buying the parts separate doesn't seem to save much and of course requires alot more research to make sure everything's compatible etc
Anyway I'm just starting investigating properly now and am leaning towards a rear hub motor @ around 48v 1000w with the most battery I can get, which looks to be around 17Ah. Looking at Vandervolt kits at the moment as they seem to be available
Has anyone done this before that could share some tips? Found a couple of posts on the interwebs which help but nothing too in detail, especially for hub motors
Likewise if anyone who's done a normal bike conversion and could envisage any issue with this I'd be keen for any info!
I have looked into this
firstly I wouldn't use a hub motor on a tandem - will it be strong enough a wheel? Rear wheel motor would be the simpliest
On my bike ( I have trial fitted it but not used it) I can put a tongsheng BB mount unit in the rear BB using a set of front tandem cranks from SJS ( that I had to grind the granny gear mounting lugs off to get clearance) to allow a normal crossover drive
the clearance for the motor is very tight however - the bafeng is easier but bulkier. tongsheng is torque sensing which IMO is much better £700
BB mount kits work much better when grinding up hill at low speed
the other option if you have the clearance is to put the motor on the front BB mount - this means you need a freewheeling chainring for the stoker which has advantages ( she can coast while you pedal) and disadvatages - you end up out of sync
If yo have a front eccentric for chain tension tho clearances may not allow this
I was going to offer to show you my setup but covid forbids that at the moment
I am intending to fit it all up soon - I'll post pics
Edit - what bike have you got? Photos of the two BB areas might help me work out if you have the clearance for the BB mount kits
Tqndem club has some folk who have fitted kits
The bike is a Viking cheapo Stornoway style one so eccentric front BB rules out front mid drive and I was discounting mid drive from the few forum posts I found suggesting extra complication. I should add this doesn't get used lots and is fine without a motor so this is more of an improvement and more importantly just a project to keep me busy, I finished my 4 week van conversion and now I'm bored again!
Is the only con to the rear hub motor wheel strength? That doesn't concern me much as we're not heavy(there are solo bikes carrying more weight out there) and the lesser cost is very attractive for this application!
I'm about to buy one of these to fit to a full sus. Probably a bit out of your price range but worth a look. There may be similar Chinese products?
https://www.lift-mtb.com/accueil-faq-english/compatible-english/
Is the only con to the rear hub motor wheel strength?
the other issue is at low speeds when you need a lot of power ie uphill the motor is working very hard at low revs so gets hot and is less efficient. You also do not get the torque sensing in the same way ( some hub motors do have torque sensing but it still does not work as well as mid mount)
Mind you mid mount at the rear BB which is what i am going for means no granny gears as minimum chainring is usually around 36 or so. We run hub gears so this is not an issue for us.
Perhaps a cheapish hub motor might be the best option for you? its a compromise but then what is not?
I got my kit from https://wooshbikes.co.uk who were very helpful
Thanks
Yeah, usually I'm not but I'm all about compromises here!
Losing the granny ring would be an issue as it's on 7 speed so no big cassette to bail out on. Could go up to 10 or 11 speed but then that's a new rear wheel anyway plus a load of other stuff! Rear hub setup seems to come in ~£500 whilst the mid drive is already more and if I need to add a new groupset it quickly becomes alot to invest on a £100 tandem
I'm thinking to go hub motor and if the slow uphill becomes an issue I'll upgrade to mid drive
Did look at woosh as they actually have a converted customer tandem on their site but there's a message saying out of stock until September on their site so I didn't bother investigating further
That Lift one looks awesome but that's proper Ebike money there!
Please also bear in mind that 1000 watt motor is no longer an ebike but a moped and you then need to register it, lights, plates, motorbike helmets etc. and is no longer legal on cycle paths, bridleways or forest tracks. 250 watt motor and 15 mph cut out are mandatory for UK use.
Stick a motor on both hubs!
I've done a front wheel e-bike conversion, where the motor is in the front hub and the battery sits on the handlebar (see Swytch). That was okay to fit and although there was a problem with a sensor connection, once we sorted that and got it working it's not bad.
My brother converted their road tandem to electric with a hub motor once my sister inlaws MS meant she couldn't add much to help power uphill - it was only on road but he may have some tips 🤔
Cheers for the input!
@slowol don't worry, I'll be doing all of that obviously!
Starting to think maybe a front may have some advantages, (I assume that it's) easier to fit and the tandem gives plenty of weight over the front for grip as opposed to normal bikes. Have heard it makes the steering weird though, which on a tandem is already far from ideal!
Edit: Also, my mrs CAN pedal, she just doesn't want to 😀
Edit: Also, my mrs CAN pedal, she just doesn’t want to 😀
Maybe bike riding is not for her. Get a motorbike?
Why bother with a tandem? Just get her an e bike.
Maybe bike riding is not for her. Get a motorbike?
Why bother with a tandem? Just get her an e bike.
I have a KTM 690 so that's covered. Not allowed it on cycletracks though and it's on slicks so no offroad. That loud 690cc single might give away our wild camping spots as well, along with the bright orange paint!
I would get her an ebike but it would be wasted money as she cannot ride a bike and is a few sizes smaller than me
Bike riding itself isn't really for her, however exploring areas further than we can reach on foot without an ICE is for her, hence the tandem
Plus, have you ever been offroad on a tandem? It's hilarious!
There were a couple of tandems with ebike conversions mentioned in a Facebook group. I think they had conversions done by Really Useful Bikes.
From memory it used a front wheel motor in Circe Helios tamdem with triplet conversion.
The really useful website also shows a Bafang hub motor designed for cargo bikes which should give you the extra starting torque a tandem would need. Might be worth asking for their recommendations.
Also worth double checking your axle length as tandems often have (or had) longer rear axles to accommodate a drum brake on the non-drive side. This might decide whether a rear wheel motor is useable or not.
There is a discussion on this on the tandem club facebook page right now including someone who put a rear hub motor in. they used a Bafung 8 fun rear hub - beware it has 145 mm spacing.
Please do not use an overpowered motor. apart from illegality it will put a lot more stress on the bike and eat batteries
I have converted our tandem with a Bafang BPM front hub motor. Works just fine, but not as nice as a torque sensing mid drive.
Our tandem experience was that fully laden with camping gear and big hills was possibly the slowest two wheeled thing on earth 🙂 (and that was with a stoker who raced elite xc World champs the previous year). Hub motors really aren't going to like running that slowly.....
I've done a Bafang mid-drive conversion for a colleague's wife (solo bike). Could it not be made to run on the front? Will it not still work with ebb provided most of the adjustment is set to the front? If required use a half link in the front chain to minimise the adjustment range needed.
You could skip the crossover drive and go single sided / all rhd using the big ring on the back to run to front ring on Bafang.
mickr - if you do that yo need a freewheeling crank as an e bike chain ring continues to turn a bit after you stop pedalling
I did read about the low speed issues with hub motors. Maybe I need to look into mid drive a bit more..
You could skip the crossover drive and go single sided / all rhd using the big ring on the back to run to front ring on Bafang.
That seems like something that should be possible! Excellent idea, thanks
I’ll have a look at the Facebook groups as well, see what I can find
Ah I'd forgotten that the chainring can turn separately to the cranks. That could cause some fun 🙂
Are all mid-drives the same?
The only (not very) sensible way of that working would be the rear lhs timing chain driving to the front lh crank to keep everything in synch and then Bafang on front all the way to the rear on rhs, maybe with some kind of ball raced idler thing in place of the rh rear chainrings. Sounds hideous enough that I'd try it but not recommend to others 🙂
What about a front hub motor?
Easy to do but hub motors aren't keen on grinding out max power at 3mph. Mid drive goes through the gears (so both you and motor get to twiddle in 1st gear).
Mickr - you can run a mid mount at the front, Just needs a freewheeling crank for the stoker and all chains on the RHS - using a dual chainring on the freewheeling crank
My preffered option tho is to use a mid mount on the rear BB and use standard tandem front cranks on the motor unit. I'll take photos of my setup this week
All interesting stuff. Do you not end up with random timing synch between the front and rear cranks using a rear crank freewheel and front motor?
Where does you rear mid-mount dangle - underneath the boom tube? Guess it is a little protected by the timing chain but also remember we occasionally grounded out on drop-offs and buzz sawed the edge of wooden bridges. Could be expensive with a motor down there......
Mickr - yes you end up out of sync which is why I am going for a rear bb mount motor Stoker being able to freewheel has some advantages tho - going up step the pilot can pedal while the stoker freewheels which helps prevent rock strikes
Mine will go under the boom tube but it hardly hangs down at all maybe 15 mm below the chainring. but would be very vulnerable to being hit when bridging
As I say i have not ridden it yet just done a trial fit I'll do some photos when I do a final fitup
Yes we always thought stoker freewheel would be a 50:50 advantages / disadvantages thing.
Sold the tandem in the end as just not getting the use and had some compatability issues - we had differing lead legs during techy descents, weighed the same (heavier captain is needed off road) and stoker was a very capable mtber - so might fancy alternative line choices 🙂 We did master bunnyhops but not reliably or fast enough to try and clear obstacles....
This sounds like fun, will read whole thread later. Good luck.
I bought a tandem for me and my lass to convert into a mega-e-tandem. I’d looked into registration, and had decided that dual 1000w bafangs would be possible. I had a dream that we could keep up with traffic on Sheffield parkway whilst laughing our heads off (in our motorcycle helmets of course). I should be clear, we dreamt up this plan whilst in the pub and hadn’t gone into the finest of detail.
The bike arrived, a 2005 26” Dawes mtb tandem in good nick but low spec. We rode it 100m and I swore never to get on the thing again. Never in my life have I felt flex like it - and that’s with all 130kg of our combined weight on board.
It went back on eBay immediately and I lost £50 or so. Not a terrible result in the end!
A report on fitting the tongsheng to my tandem:
Its was a real pain to get totally fitted up. Clearances for the motor unit were very tight so I had to remove the outer cover and fit the motor unit then put the outer cover back on after grinding the back of some lugs on it to get fag paper clearance, Timing side cranks despite grinding away all the lugs where a granny ring would go is still too close to the cover and indeed it flexed enough that it has put a slight gouge in the cover. I also had to grerind away a bit on the back of the taper fitting on the crank to stop it binding but leaft plenty of strength in it. I had to make up my own anti rotation bracket to anchor it
As for riding it was really good. Very intuitive to ride and very natural feeling and plenty of power - climbed arthurs seat at twice our usual speed
I need to find a better solution for the timing side crank because I fear as bearings wear in the BB it will grind the cover away too much
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The clearance is actually less than it looks in this photo
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That looks like a good setup TJ. Steep hills are definitely the achilles heel of a tandem, especially with a child on the back like I have.
If you can't change the BB spindle for a longer one (I guess it is parts of the motor system) then if it's JIS taper and you can find a crank with an iso taper (old campag is the one I can think of) then the crank should sit slightly further out. Sheldon Brown inevitably explains it better then me.
Don't know what the taper is on Thorn cranks or Spa Cycles own brand as it could be like finding hens teeth for LHS drive cranks.
https://sheldonbrown.com/bbtaper.html
Couldn’t you shim the taper to get more clearance - make a shim out out of something like .002” shim stock?
I’ve done that in the past with Middleburn cranks/SKF BB.
would shimming work? I thought is unlikely but I have only seen it used in the past for worn cranks / axles
It’ll move the crank outboard, at the expense of a similar amount of engagement lost, of course. It worked for me on my singlespeed, but I was only looking to gain maybe .060” clearance (1/16”).
That would probably be enough clearance - I have 2mm at the moment but under pressure that disappears with movement in bearings and flex
Could you shim the ring out?
its the bolts that hold the ring on where the clearance is least. The score on the cases is right on the middle of the bolts
Looked up which cranks might use the ISO taper.
Bad news is old campag seems to be stupid money (see ebay link). Strong
light is JIS taper so probably the same as you have, but I think TA may be ISO taper although I couldn't be certain I understood the French on their website a good tandem shop should know for certain. If it is it should give you an extra 4.5 mm.
Thanks
would shimming work
My mate Pete shimmed his tongsheng tandem setup. The shim failed and jammed the crankset completely, i had to go out on a rescue mission to pick them up. When it worked it was fine so maybe an issue with the materials used for the shim
I am looking at this for a long tour so need something reliable. I might modify the case a bit.