Author Topic: Brompton with belt drive  (Read 6720 times)

Beardy

  • Shedist
Brompton with belt drive
« on: 20 February, 2012, 10:46:42 pm »
Evening all.
Just general musings, but does anyone know of a belt drive conversion for a brompton? I'm sure my time could be better spent, but hey, someone has to think out of the box :)
For every complex problem in the world, there is a simple and easily understood solution that’s wrong.

LittleWheelsandBig

  • Whimsy Rider
Re: Brompton with belt drive
« Reply #1 on: 20 February, 2012, 11:07:13 pm »
Not heard of one. Good luck with making a belt tensioner that will adequately control the belt when folded and while riding.
Wheel meet again, don't know where, don't know when...

Re: Brompton with belt drive
« Reply #2 on: 21 February, 2012, 08:43:40 am »
Fixed gear bromptons have been done:

http://www.flickr.com/photos/littlepixel/2173983253/

So a belt drive conversion should be possible.
<i>Marmite slave</i>

rower40

  • Not my boat. Now sold.
Re: Brompton with belt drive
« Reply #3 on: 21 February, 2012, 09:30:10 am »
Your first snag is that the chainstay goes through the chain.  So one has to split the chain to fit it.  It would therefore require a frame (rear triangle) re-design, so that either the rear triangle has a gap in it through which the belt can be fitted, or that the rear wheel is held with an elevated chainstay.
Be Naughty; save Santa a trip

Re: Brompton with belt drive
« Reply #4 on: 21 February, 2012, 10:11:56 am »
A hacksaw and a pipe fitting would take care of that  :demon:
<i>Marmite slave</i>

Re: Brompton with belt drive
« Reply #5 on: 21 February, 2012, 10:15:28 am »
Fixed gear bromptons have been done:

http://www.flickr.com/photos/littlepixel/2173983253/

A fixed gear bike with a chain tensioner is a brave concept, for sure.

Re: Brompton with belt drive
« Reply #6 on: 21 February, 2012, 10:17:02 am »
The tensioner is just there to take up the slack when folding.

The owner of this bike managed to find a majik gear that had the correct tension on the chain.
<i>Marmite slave</i>

Re: Brompton with belt drive
« Reply #7 on: 21 February, 2012, 10:20:30 am »
Looking closely it does only have a bit of slack, in fairness, but probably enough..   The other interesting bit of physics to consider is what happens to a folding bike when leg braking with a fixed transmission.  I don't think I'd like to try it at speed!

Re: Brompton with belt drive
« Reply #8 on: 21 February, 2012, 10:58:48 am »
I don't know Brommies intimately but, looking at the photos, it strikes me that there would be several ways of redesigning that rear triangle so that you could fit a belt or chain by removing the entire triangle from the bike rather than splitting a stay - as is the case with motorbikes with single shock back-ends and one piece chains.

Euan Uzami

Re: Re: Brompton with belt drive
« Reply #9 on: 21 February, 2012, 11:47:45 am »
Not heard of one. Good luck with making a belt tensioner that will adequately control the belt when folded and while riding.

aren't belts not meant to be folded back on themselves at all?

Re: Re: Brompton with belt drive
« Reply #10 on: 21 February, 2012, 12:02:28 pm »
Not heard of one. Good luck with making a belt tensioner that will adequately control the belt when folded and while riding.

aren't belts not meant to be folded back on themselves at all?

I think it depends on the tightness of the bend. Some ride-on lawnmowers have double-sided toothed belts so there is no technical reason not to flex the belt in both directions. The question is how and by how much.

AndyK

Re: Brompton with belt drive
« Reply #11 on: 21 February, 2012, 12:40:08 pm »
Moulton simply added a screw sleeve arrangement to their rear triangle when designing the belt driven TSR 2:

http://www.flickr.com/photos/19871340@N00/3994241790/sizes/o/in/set-72157622545366532/

rogerzilla

  • When n+1 gets out of hand
Re: Brompton with belt drive
« Reply #12 on: 22 February, 2012, 06:22:21 am »
It is possible to make a fixie with a chain tensioner, but it has to be a very heavy-duty one, preferably brazed on.

I don't see a huge problem with belt drive apart from the belt separability issue.  However, Brompton designed the bike so that the mucky chain is on the inside when folded, so I'm not sure how much of an advantage it would be.
Hard work sometimes pays off in the end, but laziness ALWAYS pays off NOW.

rower40

  • Not my boat. Now sold.
Re: Brompton with belt drive
« Reply #13 on: 17 March, 2012, 08:28:28 am »
Could we perhaps have a mod split this thread into:
  • Brompton with belt drive
  • Fixed-wheel Brompton
  • Alternatively-geared Brompton
?

While the last two are interesting and all that, the OP asked about belt drive.
I for one was about to go all spendy on an 8-speed conversion until I read that it is twist-grip gear change, and (after my 2007 crash) have no strength in my right wrist.
Be Naughty; save Santa a trip

Re: Brompton with belt drive
« Reply #14 on: 17 March, 2012, 01:28:34 pm »
Shimano will introduce electronic shifting for its 8 and 11 speed hubs next year.