Brompton fixed

GaryGkn

Can a Brompton be converted to a fixed gear?

I have heard of a the 2 speed.

I have seen a Merc conversion an aluminum copy from the far east?

but not an actual Brompton is there any real reason this can not be achieved?

andyp

It can be done as this fixed gear gallery posting shows. It sounds complicated though.

meagain

Ona standard Brommie frame I assume that the fold/sus means that the b/b to rear axle distance varies (hence use of a tensioner on the 3 speed etc). On the usual assumption that a tensioner cannot be employed with a fixed, then no it can't be done!

Not studied the Gallery one in detail - it says the tensioner is only there for when folded - but unless the rear has ben altered to a unified triangle i.e. b/b and rear hub always in same relationship I don't see how it works!

GaryGkn

Ok for now I am sticking with my folding project a Raleigh 20 fixed.

Was toying with moving the brake bridge to facilitate a 24" wheel set (ISO520) if i get bored of the 406 wheels.

SamWise72

It can absolutely be dolin ne. Here's where an online buddy of mine (and fellow R20 hotrodder) did it with Merc - it's the same bike as in FGG, but here with more detail. Not too hard for a reasonably competent mechanic, and no harder than sorting out the BB on a 20.

http://www.bikeforums.net/showthread.ph ... ht=mercton

andyp

Thanks Sam - I knew I'd seen a more detailed posting somewhere as my Brompton obsessed colleague had shown it to me.

He's thinking of doing the same to his.

meagain

So the chain tension IS constant when bike on the move and IS not reliant on the tensioner? I've never examined a Brommie up close and had assumed that the b/b to rear hub distance altered under load/surface irregularities, as with non-urt rear sus.

Interesting.

SamWise72

meagain wrote:

So the chain tension IS constant when bike on the move and IS not reliant on the tensioner? I've never examined a Brommie up close and had assumed that the b/b to rear hub distance altered under load/surface irregularities, as with non-urt rear sus.

Interesting.

Not significantly. The rear frame must flex by about 10 mm relative to the seatpost, but the pivot is so close to the BB that Huw has found it makes no appreciable difference to chain tension. It's only when you fold that it moves by enough to drop the change if nothing is holding the tension.

meagain

Ah! Thanks.

brompting

If you want to be sure that the chain tension is constant, why don't you fixed the suspension.

Just exchange the rubber block for some wood? In this case you can still fold the Brommie.

Cheers, Brompting

BTW for techinical info in this case of FIXED bikes try
http://www.sheldonbrown.com/