Retro fitting to tandem?

Electrically assisted bikes, trikes, etc.
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Si
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Retro fitting to tandem?

Postby Si » 27 Sep 2017, 8:13am

Retro fitting a standard e-motor and battery to a tandem.....would it be able to take the extra weight or would you need a tandem specific unit?

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[XAP]Bob
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Re: Retro fitting to tandem?

Postby [XAP]Bob » 27 Sep 2017, 9:31am

When you say motor...?

If it's a BB unit then I'd suggest it went with the stoker
If it's a rear wheel then it might need a bit of extra beef (spoke count/strength) - but you would likely be fine with a decent hub hand built into a decent rim by someone who knows what they are doing...
If it's a front wheel then you'll likely be OK - but again, making sure the wheel is stress relieved would be good.
A shortcut has to be a challenge, otherwise it would just be the way. No situation is so dire that panic cannot make it worse.
There are two kinds of people in this world: those can extrapolate from incomplete data.

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Si
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Re: Retro fitting to tandem?

Postby Si » 27 Sep 2017, 10:43am

I'm having difficultly visualising a BB unit for the stoker what with the straight through bottom tube, the eccentric BB and chain rings on both sides, but then I know nothing about E bike fitments. Do they make them that would work in this situation?

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Re: Retro fitting to tandem?

Postby [XAP]Bob » 27 Sep 2017, 10:57am

Si wrote:I'm having difficultly visualising a BB unit for the stoker what with the straight through bottom tube, the eccentric BB and chain rings on both sides, but then I know nothing about E bike fitments. Do they make them that would work in this situation?


The eccentric might be an issue - but I *think* there are some that will fit an eccenctric. Personally I'd have though an EBB for the captain would make more sense than one for the stoker, but hey - what do I know.
The bottom tube shouldn't be an issue, although I can see why it might be - the motor might end up canted further 'back' than normal, but that's OK if it can avoid the chain stays...

wrt wheels though - unless you are going seriously loaded then a 'normal' 36 spoke wheel, if built well, should cope with the rigours of doubling the weight...
A shortcut has to be a challenge, otherwise it would just be the way. No situation is so dire that panic cannot make it worse.
There are two kinds of people in this world: those can extrapolate from incomplete data.

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meic
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Re: Retro fitting to tandem?

Postby meic » 27 Sep 2017, 11:01am

I can understand why you would want to fit a not tandem-specific motor, after looking at the prices of conversions at JD tandems.

However by the time you include the weight of the motor and battery, with an adult as the "other" then you are at the same weight as a small solo motorbike, not just moped but motorbike.
At least a hub motor takes some weight from the frame's load but not from the spoke or hub much.

Normally I am all for "give it a go" but tandems are often pushing the limits beyond what fittings on a solo bike can take and that is before you introduce the power of a motor and the weight of a motor and battery. Would you be planning on loading it up with luggage on top of that?
At least with the wider axle a wheel built on a solo's hub could be entirely dishless which would help a bit (except for the poor axle having all that length unsupported on the left side).
Yma o Hyd

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Si
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Re: Retro fitting to tandem?

Postby Si » 27 Sep 2017, 11:16am

Would you be planning on loading it up with luggage on top of that?


Probably not. I was just idly speculating as I now have problems on the tandem up hills due to the knee injury. My wife is not a regular rider and so isn't really ride-fit, thus I have to do more than usual on the climbs.

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Re: Retro fitting to tandem?

Postby meic » 27 Sep 2017, 11:20am

As it is a specific pair of riders on a specific bike, I would factor your relative weights into the equation.
If I was to mount a motor on my tandem, then comparing my 90Kg to my daughters 30Kg then a solo's rear electric hub would be the best answer at least for a few years time.
Yma o Hyd

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Si
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Re: Retro fitting to tandem?

Postby Si » 27 Sep 2017, 11:31am

I think we are looking at well over 20 stone

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[XAP]Bob
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Re: Retro fitting to tandem?

Postby [XAP]Bob » 27 Sep 2017, 3:39pm

I would suggest that a wheel builder would be able to advise on the strength of a new front wheel - tandems do load them more heavily, but the tension spoke wheel can be seriously strong...
A shortcut has to be a challenge, otherwise it would just be the way. No situation is so dire that panic cannot make it worse.
There are two kinds of people in this world: those can extrapolate from incomplete data.

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Re: Retro fitting to tandem?

Postby Si » 27 Sep 2017, 3:57pm

I notice i seem to be talking rubbish about eccentric bbs. Its been a hard week.

reohn2
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Re: Retro fitting to tandem?

Postby reohn2 » 27 Sep 2017, 8:01pm

Si wrote:Retro fitting a standard e-motor and battery to a tandem.....would it be able to take the extra weight or would you need a tandem specific unit?

We're about to find out in a few days time when I fit one to our Circe tandem.
I'm assured by Electric Bike Conversions:- http://www.electric-bike-conversions.co.uk/ we won't have any problems and they've fitted a few tandems out with their kits.
Weve gone for the biggest battery they have available @ 17ah,I'll post some reports on fitting and riding when its up and running
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Re: Retro fitting to tandem?

Postby rjb » 27 Sep 2017, 8:15pm

Not tandem related but may be of interest. Bumped into a guy riding a Brompton couple of days ago who was trialling Bosch batteries meant for power tools. They were rated at about 4 Amphour, and he was carrying a spare in his rack bag. May be of interest as the batteries were readily available unlike some battery packs meant for bikes. And if you were only doing a shorter ride you may be ok with one smaller one.

Link here. http://www.nanoelectricbikes.co.uk/

I have no connection with the company. :lol:
At the last count:- Focus Variado, Peugeot 531 pro, Dawes Discovery Tandem, 2 Dawes Kingpins, Falcon K2 MTB dropped bar tourer, On One Pompino, Longstaff trike conversion on a Falcon corsa. :D

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SimonCelsa
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Re: Retro fitting to tandem?

Postby SimonCelsa » 17 Jul 2018, 9:00pm

Any updates from Si or Reohn2 regarding tandem conversion??

I am considering doing the same on our tandem, a 700c wheeled basic Viking Tarantino getting on nearly 10 yr old. The wife has been in hospital for a while and lost a fair bit of leg strength so with a nipper in a child seat on the rear some hills can be a bit of a struggle. I am still a bit ignorant to the pros & cons of the different set ups, however I have been in touch with 'whoosh' and am leaning towards their XF07 front hub kit with 15ah battery for around £520. I would like to retain the possibility of towing a Bob Yak trailer which requires maintaining the rear quick release (hence the recommended rear hub motor is not really feasible).

I still prefer to pedal myself but I have plenty of other bikes for that. This idea is purely for a little help when out with the wife. Anyone have any experience of similar tandem conversions??

Cheers, Simon

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Re: Retro fitting to tandem?

Postby reohn2 » 18 Jul 2018, 11:01am

We haven't used ours a great deal only short 10 to15 mile trundles due to Mrs R2's health issues,but its very good and the 17ah battery returns approx 30+miles per charge.
It has 5 power settings which on the flat 1 or 2 setting is enough increasing the number upto 5 for steeper 10% climbs where it really is surprisingly powerful.
We made enquiries with the supplier about it's use on tandems before buying and was given assurances that it was more than adequate for the job.
Ours is a front wheel hub motor built into a 20in wheel with thick plain gauge spokes that needed a little prestressing and tensioning before use as can be expected from a machine built wheel,but once sorted runs great.
I felt a front hub motor to be better for a tandem with a 50/50 or even front heavy weight distribution,and as the quite heavy battery is mounted in the purpose built rear rack,a rear wheel motor would've put all the weight at the rear of the bike,it's worked out really well.
With the system switched off there's no drag on the motor with the wheel spinning as freely as an ordinary standard front wheel and other than the weight penalty rides like an ordinary bike.
We're very happy with ours :)

EDIT:- we bought ours from here, http://www.electric-bike-conversions.co ... -kits.html
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Re: Retro fitting to tandem?

Postby SimonCelsa » 18 Jul 2018, 8:15pm

Thanks for that Reohn2, I'll do a little more research before pulling the trigger but think the front wheel hub motor is the way to go for the tandem. Still feels a bit expensive but don't think you'll get much for less than £500.