Can anyone tell me what is the largest freewheel cog that I could fit to my Brompton H6?

My Brompton H6L has the BWR Hub and two speed dérailleur.

So gearing is 50T front and 16/13 rear which with 16" Schwalbe gives:

32.5/40/50.9/62.7/79.8/98.2 inches

I need the range to be lower and higher

A 53T front with the same rear would give me 35.1 to 106 inches but not low enough

A 53T front with a 20/13 rear would give me 27.6 and 104.1 inches

This would suit me fine but I guess that 20/13 is an impossible dérailleur change.

So looks like a Schlumpf Mountain Drive with the standard 52T/16/13 is the solution?

13.6 to 103.7 inches

Ian

9 spline is like a Shimano pattern, try a cassette cog.
the end of the chainstay tube hitting the sprocket teeth is the limit, there.
as you can see and measure..

SA 5 speed Sturmey Archer is also the same

28 hole hubshell makes it useful as a new 5by2 10 speed rear .

(I have a MD on my M3L 54:15) note : their speed drive with a 34t, kicks into a 54t overdrive .

check with Glasgow dealer for alternate frame parts to do a Rohloff Disc brake Build of Bromptons
https://www.kinetics-online.co.uk/fol...rear-triangle/
or the SA 8 speed IGH.

seems legit:


E.3.5.1. high-speed-drive for Brompton folding bike

" A very popular combination is the Brompton folder combined with high-speed-drive. It needs a +6.5mm cone ring to allow folding (the rear chainstay folds where normally the gear housing is located) and a wider nut on the left side to make up for the additional width.[/I]
A good set-up is the standard high-speed-drive with its 27t. chainring and integrated trouser guard. With such a chainring, you have much lower gears for climbing (27 instead of 50t.) but also much higher gears for speed (67 instead of 50t.)."

3 products..

FWIW, Speed Drive= 1.6x ,high speed drive= 2.5x MD is the inverse a 2.5 reduction.. ala 50/20 [54/21.6]

I had the speed drive on mine for a while. 1.65 over-drive. I also had the 2-speed rear, and later had a 5-speed wheel. 20 speeds, huge range of gears. Certainly possible to have almost anything.

Don't know if they're still available,but there was a 12/18t cog for Bromptons.

16/12 would be quite wide without having to do/spend anything crazy. i made a chart.

fietsbob,

Looking good for the speeddrive. I'll talk to Ben at Kinetics

Ian

Smallwheeler,

Thanks for your reply but I don't see here a wider range than my existing 32.5 to 98.2?

Ian

your 16/13 gives a 302% range. 16/12 will give you 327%. it is, however, all in the top end which, i know, doesn't meet your requested requirements. i was thinking of how to get most of the way there without spending a lot of cash.

anyway, i like charts. so i made a chart.

another option would be a 3 speed cassette. 19/15/12 would give you 28 - 108, a 389% range. whether you choose this kind of option or go with the schlumpf, i guess the thing to watch out for in the quest for a lower+higher range is the likelihood of gear redundancies across the spread.

What do they use for shifting?

same pulley pushing fork derailleur, I'd expect .. Just have to feel out the middle one..

Smallwheeler,

The 3 cog solution is very attractive to me. Being long in the tooth I'm quite familiar with non indexed rear shifting and I once owned a bike with a manual, i.e. rod operated front shifter.

I'll look around for as much info on the 3 speed that I can find.

thanks,

Ian