Does the Brompton use a special crank, or can I find a suitable replacement at any decent LBS?
Robert Renger, Oct 97:
Basically any crankset will fit a Brompton, although you might have to
change the bottom bracket spindle to have the chainring at the
appropriate offset to maintain chainline (actually quite forgiving in my
expereience). I did it easily myself and any LBS will be able to manage.
Standard narrow chainrings work fine with the wider chain.
Custfold, Oct 1997:
Most decent manufacturers will have track rings, and some specialists
will carry Bicycle Polo rings made for non derallieur chain.
Alternatively a quality ring from Middleburn - often pays off in less meat
in the wrong place and tougher meat in the places it's needed.
My bikes have Sakae (170) & Shimano (175), and the b/b units are often
tweakable by up to 5mm on locking in to the housing.
Leonard Rubin, Oct 97:
I don't know about elsewhere, but in the US, most professional bike
shops offer a selection of replacement lightweight bottom brackets, which
range in spindle length from 103mm to 125mm, accomodating the wide range of
cranksets (single-, double-, triple-chainrings, low-profile to not-so-low
profile, etc.).
Many have adjustable chainline, which enables much fine-tuning and even
some overlap between lengths. In addition to gaining usable gears, much
weight can be saved by choosing among the CAD/CAM-produced, featherweight
components which abound in pro shops and mail-order catalogues these days.
Careful gear calculation and selection of chainrings will eliminate the
duplication problem mentioned earlier.
Custfold, Jan 1998:
Lots of peeps have fitted doubles & some even triples, with large and very
small rings it's possible to tigthen up the rear pivot
without taking off the cranks.
Largest ring (est) around 65 teeth, before front forks hit chain, a small
(c.36) would probably fit inside pivot.
Pierre-Philippe Coupard, July 2003:
The left crank has to have a "head" (where the folding pedal is bolted
on) with a low profile, to leave clearance for the folding pedal's
plastic lockplate to pass over it when folding. Other than that, it's a
standard crank.
Is the chainring integral to the crank, or can I replace just the crank arms?
Pierre-Philippe Coupard, July 2003:
The Brompton chainring is a Stronglight crank+ring combo. If the either
is broken, you need a new chainring/crank set from Brompton (I paid mine
EUR 60), or you can change to a standard crank with a spider and a 50T
ring. If you do the latter and you don't want to change the bottom
bracket to get the ring to end up where it should be, you'll have to
test differend cranks at your LBS. I've found that an Efmega crank drops
the chainring just where it should be, about 4mm fron the right rear
hinge pivot.
What special tool or tools do I need?
Pierre-Philippe Coupard, July 2003:
To get the pedals out of the crank, long and solid 15mm open wrench.
To get the crank off the BB spindle, a standard crank extractor does the
job. The crank bolt is 14mm.
Robert Payne, July 2003:
You need two tools to get the cranks on and off. Crank
wrench and crank puller. These are the Park tool
numbers
CCW-14R Cotterless Crank Wrench
CCP-2 Cotterless Crank Puller
Is there also any routine servicing I should do while I have the crank arms removed?
Pierre-Philippe Coupard, July 2003:
The BB is sealed, it shouldn't require any servicing (Spotlight on the bottom bracket - Is maintenance required?).
However, if you've done 2000-2500Km with the same chain, chances are
you'll need to reverse or change the sprocket (Spotlight on the rear sprocket - Replacement rear sprockets) to use the new chain
without skipping, as the old chain has probably stretched and damaged it.
At least that's the mileage I get out of my sprocket in the same conditions.
Multiple front chainrings
Channell Wasson:
I have added a second chain ring to my Brompton.
I use a 53t and a 39t with a Shimano crank and derailleur.
It's easy to instal the chain rings [...]
I have also managed to instal a braze on derailler that works
flawlessly with these chain rings,
after a bit of bending to accomodate the natural folding features.
In lieu of a
derailleur one can change the front gears by hand for occasional use.
Sometimes the chain line needs some adjustment when setting things up.
The use of the wider chain with the Brompton helps give wider allowances
with the chain line.
I elimated the chain guard.
I use pant clips, so I haven't missed it.
Graham Patterson:
I thought I'd try a double chainring on my T5 to see how practical it
was. I 'borrowed' the 48/39 setup from my tourer, and found that it
fitted, though the frame clearance on the ring securing bolts is
*really* tight when folded.
John Blackburn, Oct 1997:
WHAT I DID:
The Stronglight chainwheel as fitted to a standard Brompton seems to be
of good quality, so I bought a 38-tooth Stronglight chainring and bolted
it to the 50-tooth standard wheel. There were a couple of problems, but
nothing difficult. This gives me a 32-inch bottom gear (compared with
the standard 41-inch gear) and a 70-inch top gear (compared with the
standard 92-inch).
This has transformed the Brompton, for me anyway. My "Standard Hill
Test" is the gradient from the National Maritime Museum to the Royal
Observatory, in Greenwich Park. Before fitting the 38-tooth ring, this
was sheer misery. It is now quite pleasurable. A slightly lower gear
than 38-tooth might be better, but I find that the range of 32 inches to
70 inches is quite reasonable for local cycling, and I don't use the
higher range much. In fact, any Brompton user with a hill problem should
seriously consider the easy solution and go for the "18% reduction"
option.
Changing from one chainring to the other is done electronically, by a
servo-motor. After many years in the electronics industry, I find it
easier to do things the electronic way. It also avoids fitting yet
another carefully routed cable.
It's still a rather crude setup but it will be quite elegant eventually.
There will one tiny button on the handlebar. One press for "Up", another
press for "Down".
Custfold, Jan 1998:
Alternatively for weight and hassle
saving, don't bother with a changer - knock down with welt of shoe, and pick
up with finger. Works perfectly as most significant is changing down when
hill looms, you can leave changing up until convenient. This method comes
thoroughly recommended by the Crane Brothers who are minimalist cyclists,
notable for riding Kilimanjaro, and to point in China furthest in world from
sea - regularly riding with no front changers.
Len Rubin, Nov 1998:
[...] no, you can't
just try clamping a front derailleur to a Brompton -- even if the correct
diameter clamp were available, the derailleur would be pretty useless, in
terms of decent shifting in the resultant location. It would be way off in
all three axes!
Phil Gough, Nov 1998:
I adopted the solution of manual change between chainwheels for my old Moulton AM7,
a machine that has similar features of fat tubing and unorthodox geometry to the Brompton,
although of course it doesn't fold but separates.
I found a little plastic chain-holding hook, marketed I think by Park, which had a clip
formed at one end which meant it could be stored fitted around the handlebar stem.
With a little practice one could reach down and hoick the chain down to the smaller ring
when a really long gradient loomed.
Usually had to stop though to pull the chain back up to the big ring, but the arrangement
was acceptable for infrequent trips laden with camping equipment.
richard lighton, Aug 1999:
My complaint about all the gear ranges is the gaps between 2nd/3rd/4th.
The shift from 4th to top and 1st to 2nd is a manageable 18.4%, but
the other two changes are 26.7%. For me, there's too many slopes or
wind conditions where I would like something in between. Channell Wasson's
arrangement (53/39) allows 16-18% changes over the whole range with
a slightly strange shift pattern (H5/H4/L5/L4 high range, H2/H1/L2/L1
low range) or at least 16-18% at the top end with a more conventional
H5/H4/L5/L4/L3/L2/L1 pattern.
I've also looked at the possibility of using a 54/48 double combined
with Schlumpf Mountaindrive [Spotlight on the bottom bracket - Geared bottom bracket - the Schlumpf Mountain Drive]. This gives a half step gear pattern
with 12.5% changes between gears (apart from a couple of 5.4% oddities)
all the way from 100 gear inches down to 16. This seems to be
theoretically possible, and I would very much like to try it, but the
cost of upgrading my bike would almost reach the price of a new one!
Channell Wasson designed and sells a front derailleur kit for the Brompton.
Tom Vogt, Sep 1997:
The damned [front deraileure and shifter] thing works!
I had previously mounted a double road-type crank to
my Brompton. However, to use it required that I shift with my shoe.
I'd kick the chain down to the lower gear when I hit a climb.
At the hill's top, I'd dismount and, with my finger, put the chain back
on the big ring. This system worked but I tended only to use it
when a hill was REALLY nasty. Now, with the deraileur, I shift like
a madman. I was worried that using a front deraileur would hinder
the folding process--it hasn't.
Peter Amey, Jan 1998:
I currently have Mr Wasson's prototype kit on my T5 (it's the actual one
tested in A2B). It is very neat and easy to fit and has transformed the
bike for use in hilly Bath. I did find that the modification ruthlessly
exposed wear in other transmission components; I also ended up having to
un-seaze the chain tensioner and replace chain, sprocket and jockey wheels
as well.
One thing to watch out for. Many (all?) front changers have a piece at
the rear which joins the sides of the chain guides. This piece gets
trapped between the chain and the chain ring when the back of the bike is
flipped under and the pedals cannot easily be moved thereafter. On my kit
this piece is removed completely which weakens the changer. A better bet
would be to fabricate a joiner which went above the chain line in normal
use rather than below it. I think the "cycling vicar" featured in the
latest A2B may have done this if it was his bike I saw in the Avon Valley
Cyclery some time ago.
Channell Wasson, Aug 1998:
Our front derailleur uses a 53tt and a 39tt Shimano chainring
combination. With a 14tt rear sprocket, gears range from 30 inches to
91 inches in high. With 13tt rear sprocket range is 33 inches to 98
inches high. A robust and trouble free system from my many miles of
Channell Wasson, Aug 1998:
The front derailler kit is available from our company for $285 USD.
Includes Shimano chain rings (53tt and 39tt) Shimano braze on deraileur,
custom mounting clamp with cable stop for derailleur, cable and friction
type shifter.
Bruce Correll, Sep 1998:
Hello from Detroit,
I installed Channell's front derailler and it works great.
My Brompton now has a much wider range of gear selections.
I can keep up with most non-folding bicycles and climb hills
much better. It is a bit expensive, but it makes a hugh
difference in the way the Brompton performs.
Lawrence Wenner, Oct 1998:
You do need to get down to 20 gear inches to
get up San Francisco hills. However, I don't think that Channell's kit will take care
of your problem. I think he uses a 53/42 or 53/39 front double, and you
can see that the 39/14 is still not going to drop you into the 20" range.
I think you'd be better off going with a 48/34 front double and getting the
low end down.
Peter Holden, Oct 1998:
I think one really needs to get to a 26TT front ring ( = ~20").
But then, with a double derailler that means a max of 41 TT, which gives top
end ranges lower than the 18% reduction, and not a personal favorite with this
spinner.
Tom Vogt, Nov 1998:
Yes! It actually works very well. I've used Channell's derailleur mount and
set-up for a couple years now and have had no problems. I continue to use the
"track" 1/8" chain and standard rear cog--the shift isn't silky but it is
reliable and I'd enthusiastically recommend it. To an engineer, the
proposition might seem a bit iffy but the bracket is well though out, there
are no "alignment" challenges.
felix lee, Feb 1999:
I met Channell [...] and was able to see his upgrade kit and trade
notes with him on front derailler modifications. I had a local bike
store fit a front derailler onto my Brompton, but I think Channell's kit
is quite a bit more elegant and better quality. With more gear
options, you'll reduce stress on the aluminum handlebars. Before
adding the front derailler, I was pulling on the handlebars like it was
a rowing machine!
Can Channell's setup be made to accommodate TRIPLE rings?
Len Rubin, Nov 1998:
No. Channell's fixture locates the derailleur in a position where it would
hit the seat tube and bottom out before shifting onto a third (inner) ring.
The problem is not just the fixture's limitation, but that, even if the
derailleur's position were rotated a bit further counter-clockwise, it
would hit the outboard vertical member of the frame's rear triangle, as it's
in the way of the derailleur's inboard travel necessary to reach a third
chainring. This is one of the areas I immediately found I needed to redesign
when I first started the SuperBrompton project. On the very first prototype,
we cut the bottom of that tube about a half-inch from its end and relocated
(bent) it a little bit more than 1/2" toward the bike's centerline,
re-attaching it with a small piece of plate between the bit of old tube end
(still attached at its original point and the new one (now inboard). This
worked fine, and provided the necessary clearance for the front derailleur
to swing inboard to a third chainring. Our current design ("UFB") has that
clearance (and numerous other improvements large and small) engineered into
its geometry. Someone might propose moving the chainline outward instead,
but if you think about the Brompton's folded clearances for a moment you
will realize that this is a really dumb idea-not to mention the horrible
resultant "Q" factor!
"Q" factor is the name that was coined a few years back (by Grant Peterson?)
to measure the distance between the planes formed by the crank arms, on center.
It is an important factor in the
overall cycling ergonomics. When it exceeds a reasonable figure, discomfort
and injury increase. "Small is beautiful" (E.F. Schumacher) here as well!
Refer to Grant Peterson's article from several years ago (in Bicycling
magazine perhaps?) or Grant can be reached at his bike shop:
Rivendell Bicycle Works
1561-B 3rd Ave.
Walnut Creek, CA 94596
Voice: (925) 933-7304
FAX: (925) 933-7305
Channell Wasson, Nov 1998:
I use a triple ring, but chain allignment and shifts to small ring
introduce some problems.
