Brompton mods - 2x3 gearing to 3x3

[Bugsbunny]

My 2016 S6R has had a 38T chain ring in place of the original 50T. I've now done a bit of climbing and flat lander touring on it and its pretty darn good for my needs. In brief, I'm focused on ensuring I have sufficient gearing catered to climbing. With this current gearing, on the flats/downhills it can also do about 30km or so before cadence gets overly high. This is fine as my Brompton is for cruising/commuting/touring.

What I want now is to explore gearing with a greater *range*. A tad more for easier climbing and a bit more for flats/downhill gearing.

I've done a bit of research on gearing and AFAIK the Sturmey Archer hub 5 speed has exactly the same range as the 3 speed hub. So that doesn't fit my needs.

The Schlumpf crank gear is completely new to me. I wouldn't rule it out but its a bit "out there" in my thinking for now.

I've seen and read that some folks stick with the same 3 speed BWR hub but somehow add a 3 speed shifter cassette. This seems to fit my needs and AFAIK not gonna break the bank. Reliability I believe would also be pretty good. I'm not 100% sure, but does the frame need some hacking to fit the 3 cogs?

Appreciate any suggestions.

Bugs

[Brucey]

I've done a bit of research on gearing and AFAIK the Sturmey Archer hub 5 speed has exactly the same range as the 3 speed hub. So that doesn't fit my needs.
s

http://www.gear-calculator.com/?GR=SAX5&KB=52&RZ=13,19&UF=1330&TF=90&SL=2.6&UN=KMH&DV=teeth

[armadillo]

I have heard of the modification you mention. As far as I recall, it involves squeezing another cog on the back, but I think it just gives more choice of gears within the existing range.

A simple way to get climbing gears is to have two front chain rings. It does mean stopping for a few seconds to manually swop the chain across (I carry an old tent peg for this to avoid dirty hands) but you end up with a much bigger range. Just remember to pop the chain back onto the big ring for folding.

[Brucey]

just to be clear, the BWR hub has a wider range than a standard 3s hub, but in the standard arrangement of 2x3 the gears are half-stepped. The way you set up a 5s hub to give a wider range is to one and a half step the gears instead. Your extant setup compared with a 5s x 2 system compared here

http://www.gear-calculator.com/?GR=SAX5&KB=38&RZ=13,19&UF=1330&TF=90&SL=2.6&UN=MPH&DV=gearInches&GR2=BBWR&KB2=38&RZ2=16,13&UF2=1330

as is, you get lower gears and just a small increase. WIth a larger chainwheel the gears can be higher too.

cheers

[djnotts]

I also need lower gearing a Brompton 6 speed. Manual change front double seems the easiest and cheapest way to go. Some useful discussion here

https://www.cyclechat.net/threads/doubl ... 003/page-3

[hoogerbooger]

Me and my missus have a Schlumpf speed drive on our 6-speed brommies. Missus has a 28t chainring and I have a 30T. Speed drive adds an extra 6 gears by a ratio of 1.65. We live in Wales and the original 50t chainring was of no use !

We both had these on the SRAM hub and the spacings worked well (15t & 13t cogs I think) We've done a bit of touring and the gear range was reasonable but not as wide as on our normal touring bikes. When we selected the chainrings we prioritised the lower gears and lost a little at the high end. But the spacings are reasonable.

The BWR gears spacing was too large to sensibly use with the Schlumpf

Schlumpf drives are supposed to be reliable. I've had mine for 5 years without problems.

I more recently I fitted a SA SRF5w on my brommie. ( not sure if you can get a wheel in UK ?? I had to import with right driver and build it into a wheel.This gives me 20 gears and a wider range than the SRAM did. But it's bonkers locating the gears !!... but at least I have an option to find the right one should I be doing a long alpine climb!!! not that I have yet !..)

The hub seems to be known to be fiddly to set up. Whilst after a couple of attempts I got it to work fine..... I've since had intermittent problems with 3rd gear slipping to 4th ( or is it the other way round ?) . 3 & 4 are the tricky ones. Not sure if anyone else has got one working ok on a brommie...but at the moment I'm wondering if the folding/unfolding doesn't work well with the fine tuning needed/close cable distances between gears.

I'm guessing Brompton don't use it as its too fussy.

I have seen the 3 cog conversion and considered a super bonkers set of 30 gears !!!.......but with any more gears to search for I wouldn't have time to see the views

By the way on my first tour on the brommie in Ireland before I started changing the gearing I had to get off and walk up some hills....but the views were lovely !!

I used this site for working out gear ranges/best options: http://xldev.co.uk/bgc.html

[Tigerbiten]

I've used a Schlumpf HSD on my ICE Sprint recumbent trike for around 7 years/35,000 mile without any bother.
They are expensive but I think they are a fantastic bit of kit if you're after a very wide gear range.
It gives me an extra 7 gears on my Rohloff.

Add a HSD to a brommie and I reckon you should be able to get 12 evenly spaced gears from ~20" to ~100".
The only downside is most of your flatland cycling will be done in overdrive mode where there is a little extra drag due to spinning an extra set of planetary gears.

Luck ..........

[Bugsbunny]

Thanks guys. A ton of info here for me to explore. Its a rather foreign thing for me as I'm used to road bike gearing - which in contrast seems so much more simple. I think I've also not yet understood all the options before jumping to the conclusion 3x3 is the best solution.

I'm trying to keep the fold as simple as possible. So the front 2-by front chain ring is complicated by needing to move it to the outer ring for each fold. Where I ride, I can see myself using the inner chain ring (currently 38T) the most.

I can totally get that too many gears can make it even more complicated to ride. I would imagine going from 2x3 to 2x5 would be a nice compromise. I'm also thinking about removing the left gear and having a single sided gearing mechanism, but then I heard the Sturmey Archer 8 speed is much heavier. Darn!

3x3 seems (now at least) too extreme a mod (frame filing to fit?) and I'm not even sure if/how it increases the range or if it merely adds closer ratios? Mental maths wasn't my forte! And how does it all work in practice - as I'm thinking it gets rather finicky.

I've had a look on the Sturmey Archer catalogue and I got a headache from the zillion options and model numbers!

Reliability and simplicity is also key here. And I'm wondering if I'm asking for too much. My current 3x2 (BWR) with a 38T chain ring is almost perfect. A bit difficult in the urban jungle of Hong Kong (where I live) as I'm trying to make sure I'm in the right gear to make quick accelerations to avoid cars/trucks.

I think I'm gonna go find a dedicated Brompton mechanic and have chat with them to see what he's recommendations are.

Bugs

[Brucey]

the 5s hub goes into the bike with minimal modifications; you just need to buy one with the BWR driver already fitted (they sell them like this on ebay BTW) or to put the driver from your BWR hub into an X-RF5(W). Also needed is a washer that prevents the RH cone from rotating (not fitted as standard on current SA hubs but available as a spare part).

The end result is a bike that looks and works like a standard Brompton, apart from the RH shifter. Issues are that

a) if you don't get on with the 1-1/2 step gearing you can run it as 1/2 step most of the time (different large sprocket to a BWR one BTW) and only fit the larger 19T sprocket when you are going touring.

b) the SA 5s thumbshifter that matches the X-RF5(W) hub is usually faulty, in that it has ever-increasing backlash, and overshoots/sticks between gears on downshifts. If you don't pull the lever back to the detent after each downshift, the hub can break.

cheers

[andyh2]

May have been all in my mind, but I felt the 5sp SA was more draggy than the 3.

Probably be worth contacting Ben at Kinetics in Glasgow www.kinetics-online.co.uk as he’s done several Brompton gearing upgrades including Shimano Alfines and Rolhofs.

[Brucey]

May have been all in my mind, but I felt the 5sp SA was more draggy than the 3.

I'd agree with that; the X-RF5(W) has (unlike older SA 5s hubs) pinion bushings that are not particularly well designed. Better lube can help and I'm not sure how it compares with with the ( often spongy feeling) shimano hubs etc in the real world. But obviously if you set the gearing so that you use gear 3 in the 5s hub, which is direct drive, most of the time, it is not inefficient over the whole duty cycle.

So for example this setup

http://www.gear-calculator.com/?GR=SAX5&KB=48&RZ=13,19&UF=1330&TF=90&SL=2.6&UN=MPH&DV=gearInches

using a 48T chainring and 13,19T sprockets gives a gear range of 26" to 98" and has a nice efficent 62" gear for 'tapping along'. I'd also find myself using the (equally efficient) 42" gear when climbing quite a lot too.

The big advantage of the 2x5 conversion is that it uses mostly standard Brompton parts, virtually no weight increase, and is (esp if you buy a new wheel) completely and quickly reversible, leaving you with a conversion kit and a standard Brompton to sell. Very many of the other options leave you with a bike that isn't really a brompton any more and can't be converted back again or maintained as easily.

BTW I have a carrier bike fitted with an X-RD5(W) which is basically the same internal as the X-RF5(W) and this (once fitted with a decent shifter and with decent lube in the hub) has proven to be both reasonably reliable and pleasant to use. It is geared so that it has a ~55" 'tapping along gear' in gear 3. Something like this

http://www.gear-calculator.com/?GR=SAX5&KB=48&RZ=13,19&UF=1330&TF=90&SL=2.6&UN=MPH&DV=gearInches

I very rarely use 5th gear and fortunately the hills where I am don't require a lower gear than first (~34"). If gear 4 was the tapping along gear I think that overall efficiency would suffer.

cheers

[andyh2]

That makes sense Brucey. Mind you on my Brompton I chose to change from 3 speed to singlespeed, which was fine at the time for the routes I was using it on.

[hoogerbooger]

RE: a SRF5(w):

a) what would be a more reliable compatible shifter than the SA one ? ( I have the supplied SA SL-S50)

b) what would be the right washer for the RH side ? Is there a part number/link I can follow up with as sounds like I won't have it fitted.

[Brucey]

three choices of shifter

1) thumbshifter SL-S50, but modified
2) SA twist shifter TSS56 HP (query whether this is for (W) or non (W) hub; can't be both....)
3) SA trigger shifter DLS52 (HSJ958)
.
washer is HMW147. It is also a good idea to fit a slimmer locknut on the RHS.
You will need to have a BWR driver fitted to the SRF5(W) hub.

FWIW the shortest axle will (just)work in a bormpton but a longer one would be better.

If you want the SL-S50 shifter modified I can do it but it probably doesn't make sense to post such a thing half-way around the world.

cheers

[hoogerbooger]

What modification is needed to the SA thumbshifter SL-S50 ?

Is there a link I can follow up ? or is this a Brucey special mod ? If so is it something you can outline ?