Author Topic: Childback tandem - stoker position advice, please  (Read 5281 times)

Childback tandem - stoker position advice, please
« on: 23 January, 2014, 09:00:16 pm »
I'd be grateful for some advice on improving Master Lardy's position on the back of our Thorn childback - the 'school bus'**. The position and those stoker bars have sort of worked ok up to now, but the chap's grown a bit since we first got the tandem in the summer.  He's now definitely doing his share of the pedalling (rather than being a passenger) and we both feel he now needs to lean/put his weight a bit further forward, and his hands a bit lower and further forward. I can't see how I'm going to do that with the current bars (they're a weird shape with a long drop/rise and very long) so any help would be appreciated.



http://www.youtube.com/watch?v=9P-Z-byTmPQ

I'm considering these bars (stem size fits) but haven't entirely convinced myself that they'll help either.  http://www.tandems.co.uk/m8b0s34p174/JD-TANDEMS-Stoker-Bars
** But not at this time of the year as normally 2 year-old Ms Lardy occupies a Weeride seat on the front as well.

Kim

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Re: Childback tandem - stoker position advice, please
« Reply #1 on: 23 January, 2014, 09:14:15 pm »
Flip the bars 180, bullhorn-style, and extend the (telescopic?) stem a bit?

Re: Childback tandem - stoker position advice, please
« Reply #2 on: 23 January, 2014, 09:24:49 pm »
Flip the bars 180, bullhorn-style, and extend the (telescopic?) stem a bit?
That would work if they're wide enough to clear the pilot's thighs.

Re: Childback tandem - stoker position advice, please
« Reply #3 on: 23 January, 2014, 11:37:54 pm »
My 4'10" fiance and I have this problem on our tandem. It fits her on the back, but only if she is fairly upright. Otherwise she gets to inspect my arse cleft at close quarters, rather than the view.
I like maps me

Kim

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Re: Childback tandem - stoker position advice, please
« Reply #4 on: 23 January, 2014, 11:41:00 pm »
My 4'10" fiance and I have this problem on our tandem. It fits her on the back, but only if she is fairly upright. Otherwise she gets to inspect my arse cleft at close quarters, rather than the view.

Hase Pino.  You know it makes sense.

Re: Childback tandem - stoker position advice, please
« Reply #5 on: 23 January, 2014, 11:47:11 pm »

Hase Pino.  You know it makes sense.

Don't I just! I have suggested it, only to be met with derision. She needs exposure to people who ride bents.
I like maps me

Re: Childback tandem - stoker position advice, please
« Reply #6 on: 24 January, 2014, 12:04:34 am »
My 4'10" fiance and I have this problem on our tandem. It fits her on the back, but only if she is fairly upright. Otherwise she gets to inspect my arse cleft at close quarters, rather than the view.


George Longstaff made a tandem for a couple with a similar height differential. He raised the rear bottom bracket and so moved the stoker's position up several inches.

Re: Childback tandem - stoker position advice, please
« Reply #7 on: 24 January, 2014, 03:44:23 am »
Flip the bars 180, bullhorn-style, and extend the (telescopic?) stem a bit?
That would work if they're wide enough to clear the pilot's thighs.

Looks to me like that should work (and Lardy is far from lardy, so it seems even more reasonable).

Is it just me, or is the stoker's top tube length fairly short? It seems to me that once Master Lardy has grown another few inches and started leaning forward to any degree1, his face is going to be not far at all from the small of the pilot's back.




1: Yes, you saw what I did there

CrinklyLion

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Re: Childback tandem - stoker position advice, please
« Reply #8 on: 24 January, 2014, 07:19:29 am »
I need at some point to get someone who actually know something about bike fit to sort out the stoker position on the Helios for my small boy if we're going to start upping the miles.  *watches thread with interest*

Re: Childback tandem - stoker position advice, please
« Reply #9 on: 24 January, 2014, 08:58:18 am »
The existing bars are that size & shape so that a range of arm lengths can reach them. Are they 'grippable' in a different place? It's not like Master Lardy is at the end of them at present. Is he the only person who sits in that seat?

Your suggested bars are not dissimilar to mine and I'm a lot bigger than Master Lardy. Mine point away from me, but in order to get that 'lean' you think you want, my saddle is further back WRT the BB. And if we're proper hammering it my head has to be turned aside to get my nose out of the pilot's back.

I'm not sure he needs to be leaning forward much at all. A lot of the reason we have that position on solo bikes is aerodynamics rather than power transfer. For short journeys it wont matter much either way but for longer distances he'll be more comfortable more upright, as long as his weight is evenly distributed, and that's as much height differential saddle-pedals-bars as a more 'forward' position.

In summary- if that was No2Daughter (the only one who's ever been much more than a passenger) I wouldn't change it. Yet.

Re: Childback tandem - stoker position advice, please
« Reply #10 on: 24 January, 2014, 10:01:52 am »
A lot of the reason we have [a more forward] position on solo bikes is aerodynamics rather than power transfer. For short journeys it wont matter much either way but for longer distances he'll be more comfortable more upright, as long as his weight is evenly distributed, and that's as much height differential saddle-pedals-bars as a more 'forward' position.

Is that right? I'd always understood that putting in the power was easier if there was a sharper angle at the hips, and similarly that a more even split of weight between hands and sit-bones was only really going to happen with a forward lean. Certainly I find that on bikes where I'm sitting upright, I put in a lot less power than if I'm leaning forward (this might, of course, have to do with only really sitting upright on Barclays bikes).

Mind you, I've only really cycled as an adult, so kids' MMV.

Re: Childback tandem - stoker position advice, please
« Reply #11 on: 24 January, 2014, 10:42:04 am »
I appreciate all the comments and suggestions.

Yes, Master L is the only one on the back for now and I'd be happy to get some bits (stem & bars) to make it fit with a view to all bits being recycled in some way when it comes to Ms Lardy's turn in a couple of years. I should explain that the bike's a bit small for me (which I'm happy to live with) so my saddle's a bit far back. In fact, I've just bought a slightly longer front stem so that I can take my saddle a couple of cms forward and make space for the stoker. From the comments, I think I've realised that its the rear top tube that's short which, along with the short arms of the young chap, limits the amount he can lean. So I dont think flipping the bars would work. I take your point, fboab, about whether he needs to lean at all - perhaps I'm misleading myself when I see how he sits on his own bike - although he's the one who piped-up and said that he's not comfortable. The cow-horn bits of the bars are bent such that they have three hand positions, something like:

  __/
/

and I've tried to imagine any combination of bar angles and stem extension (stoker stem is fully extended, I think) and I just can see it. I shall experiment thios weekend and report back.

Is it just me, or is the stoker's top tube length fairly short? It seems to me that once Master Lardy has grown another few inches and started leaning forward to any degree1, his face is going to be not far at all from the small of the pilot's back.

Seems to me to be the beginnings of a business case for a grown-up tandem in due course...

(It has taken me nearly an hour to write this whilst looking after my 2 year-old - clearly I'm no good at multi-tasking).

Re: Childback tandem - stoker position advice, please
« Reply #12 on: 24 January, 2014, 11:38:54 am »
I'm looking for SCIENCE (via google, so not real SCIENCE) to back me up but as it's all about solo bikes you can't really find anything about the angle of the torso. Bike fit just talks about a) not minimising the hip angle too much as it restricts lung capacity and b) the difference between a 'comfort' angle and a 'racing' angle.

perhaps I'm misleading myself when I see how he sits on his own bike - although he's the one who piped-up and said that he's not comfortable.
It's a mistake to try match your solo bike position with your stoker position too much. You're never going to get toe overlap, you don't ever have to tuck down on the drops, you never have to steer. You're restricted in the angles you can get by the presence of someone else, and by a wish not to have a bike 8 feet long.
If he's not comfortable that's a different thing. Where isn't he comfortable? Arms, neck, backside?


Re: Childback tandem - stoker position advice, please
« Reply #13 on: 24 January, 2014, 11:45:10 am »

It's a mistake to try match your solo bike position with your stoker position too much. You're never going to get toe overlap, you don't ever have to tuck down on the drops, you never have to steer. You're restricted in the angles you can get by the presence of someone else, and by a wish not to have a bike 8 feet long.
If he's not comfortable that's a different thing. Where isn't he comfortable? Arms, neck, backside?

Yup.

Re: Childback tandem - stoker position advice, please
« Reply #14 on: 25 January, 2014, 11:10:48 am »
It's a mistake to try match your solo bike position with your stoker position too much.
OK, noted.
If he's not comfortable that's a different thing. Where isn't he comfortable? Arms, neck, backside?
Two things really: feels he wants to lean forward a little and put some weight on his arms (so I guess 'just a little' will do), and doesn't have a comfortable hand position on the bars (due to the three angles available, none of which give him the right 'feel').

I'll take your comments into account and try and 'tweak' the position slightly today (rather than the radical change I had envisaged) and see how I get on.



Re: Childback tandem - stoker position advice, please
« Reply #15 on: 31 January, 2014, 04:57:20 pm »
I think that flipping over the bars would work or put some straighter bars on.  As long as he is comfortable riding it and not bashing his head on you then that is the most important thing.

Oh yeh and when Ms Lardy grows out of it consider selling/donating it to Charlotte's Tandems.  CharlottesTandems.co.uk

Alex Reeves
Charlotte's Tandems
Registered Charity 1148053
CharlottesTandems.co.uk

Re: Childback tandem - stoker position advice, please
« Reply #16 on: 31 January, 2014, 05:14:38 pm »
I think that flipping over the bars would work or put some straighter bars on.
Yep. Tried flipping the bars and ended up with the stoker stem at max height and flexing the seat post lots. The position was ok-ish but eventually decided, funnily enough, to go for straighter bars. Fitted but not yet tested & tweaked but we'll have a go this weekend when the sun comes out. Hopefully not an unnecessary expense (he'll appreciate the new bar tape at any rate).

rr

Re: Childback tandem - stoker position advice, please
« Reply #17 on: 16 February, 2014, 07:24:48 pm »
What length are the cranks? if they are too long for his legs that will mean too much movement of his hips which will produce discomfort.

Re: Childback tandem - stoker position advice, please
« Reply #18 on: 17 February, 2014, 02:57:35 pm »
Just to wrap up this one, I should say that I've fitted these bars:

The little chap says its better but I'm not sure I've achieved much at all really (hey, ho) - also, the bars are a bit narrower than the originals which I think suits him better, and the 'longitudinal' bits are shorter which is more convenient for getting on and off (not so much in the way).

What length are the cranks? if they are too long for his legs that will mean too much movement of his hips which will produce discomfort.
Cranks are short (140mm) which is the same as his own bike. They're also drilled at 115mm.

Re: Childback tandem - stoker position advice, please
« Reply #19 on: 18 February, 2014, 08:30:39 am »
If he feels better on it then it is better.

(It's quite possible he just likes the look of the new bars better. We're all more comfortable on bikes we like more)

Re: Childback tandem - stoker position advice, please
« Reply #20 on: 18 February, 2014, 03:26:57 pm »
The good point is that now you can fit an adult stoker by merely flipping the bar. I would guess the captain's hips are not too wide for the narrower bar  ;)