Monday, 26 July 2010

Dunwich Dynamo done

112 and a bit miles, 125 in total for the night. Chickened out of using the Brompton in the end and took the Hewitt tourer, which turns out not to roll much better but at least doesn't pogo when I stand on the pedals (the "firm" Brompton elastomer turns out to be not very firm at all; the jubilee clips will need to go back on).

Some odd sights, including a bloke carrying his (large) dog all the way and the Dulwich Paragon train with blue and white fairy lights.

Left just after 8pm, arrived just after 5am. First half went right according to plan, with a very fast run through to the feed stop at Sible Hedingham. Second half started fastish but then my riding companion faded a bit. Then the drag from Bildeston up to the Wattisham plateau took it out of me too and although Mike recovered after a bonus feed stop (someone selling coffee, tea and bacon rolls near Gosbeck) I got slower towards the end. However, it was a respectable average speed.

Still got a slight touch of the "never agains" but I suppose I'll be there next year, as I have been for the last six.

Wednesday, 21 July 2010

It's back!

And all assembled.

It weighs 23.2lb like this (3-speed, no mudguards but hub dynamo and lights - the rear light is battery powered). Probably 22lb minimum with no mudguards and lights. When it's running as a 4-speed and has Marathon Plus tyres and lights, probably 25lb.

Saturday, 17 July 2010

Brompton update

It's been a week and the dealer still hasn't put in the new bushes. A pox on him. One day I'll buy the £200 tool and charge other people to do it.

I have assembled the front and rear ends ready for when the frame comes back, so it will just be a case of bolting on the rear triangle (I'd prefer to do this myself to ensure the bushes are really well greased and the threadlock is a bit less permanent than Brompton's), fitting the BB and cranks and then cabling it up. Oh, and I need to glue in the new seatpost bush.

I may get it back on Monday, which is cutting it a bit fine for the Dunwich Dynamo next Saturday.

Sunday, 11 July 2010

Training for the Dunwich Dynamo

One problem of having a family and children is that long bike rides are difficult to fit in without causing resentment - after all, you can't really go and ride at 18mph all day as a family activity. This poses a problem when there are two weeks to go until the 112.7 mile Dunwich Dynamo and, as usual, my distance training has been minimal. Since January:

About 80 commutes of 5.5 miles each way. No.
One night ride of 80 miles in April. OK.
One Sunday morning rumble of about 36 miles in April. Not really.
One night ride of 80 miles in June. OK.
One Sunday morning rumble of 32 miles last weekend. No.

So today we all went over to my parents' house and the family went in the car while I went by bike. Fixed gear to make it harder, and the hilly route (which includes half a mile of 1 in 10 to get over the Marlborough Downs). 60 miles in very hot conditions, on fixed, at an average of about 16mph. That'll help a bit. The Dun Run is easier because it's cooler (less of a problem with salt depletion and cramping), flatter and I'll have a freewheel.

Reassembling the Brompton

The frame and stem are resprayed so I collected them yesterday, but immediately dropped the frame off to have the rear pivot bushes fitted and reamed (a very quick job for the dealer; the worst part is getting the rear triangle off, which of course he doesn't have to do).

I've assembled the front and rear end as far as I can without the main frame, which actually has very little attached to it anyway.

Here's the stem and handlebar with the modified shifter. It hangs just in front of the bars so that the long lever can be pulled down to engage "1", only used with a 4-speed hub like the FW. For 3-speed hubs you just use 2 to 4.

Argos masked off a bit too much of the handlebar catch nipple threads (the black plastic Tic Tac sticking out from the stem) and I'll have to put red nail polish on it. This will look OK over the white primer, since it's only a bit of thread.

You'll see that I now have bottle bosses on the stem. There are also two on the main frame tube, just before the "kink". These are about the only places you can have them and still fold the bike.

Friday, 9 July 2010

Brompton crank FAIL

The standard Brompton crank is made by Stronglight and the chainring is swaged directly to the RH crank arm. This is a cheap way to make it (although a 54T crankset is still about 60 GBP to buy), but the disadvantage is that strong riders can rip the assembly apart under starting torque:

This isn't mine, thank goodness - this is the sort of failure that really leaves you stranded.

So I decided to get a proper forged crank with a bolt-on chainring. The Sugino XD is cheap, gives the correct chainline with a short 103mm bottom bracket and looks neat.

However, there is a problem. Most cranks have too narrow a Q-factor (that's the distance between the pedals). If you put a straight edge on the back of the chainring it will usually be about 15mm behind the pedal eye. The Brompton crank is much more "sticky-out" and this dimension is about 25mm. If you go too narrow, the crank hits the folded rear frame and also reduces the already-perilous heel clearance at the rear rollers.

It looks as if the Brompton crank is going to have to go back on for now. This also means reusing the nasty FAG bottom bracket with possible the worst removal tool known to Man.

Wednesday, 7 July 2010

Weight report

Under 11st 10lb this morning. That's the first time for 8 years. Done by...erm...only eating one chocolate bar a day. It's not supposed to be this easy.

Very funny picture taken by my YACF friend Jonathan last Sunday. We were going for a suggestively camp look, as if it were a Rapha advert. I've just ordered and posted 136 jerseys for YACF from the rather brilliant Owayo. I half designed this "King Of The Mountains" one.

Tuesday, 6 July 2010

Brompton wheels

I have built quite a few Brompton wheels in the last couple of years.

Front: standard Brompton hub but with the original caged bearings thrown away and replaced with loose balls. Built radially like a factory one. No, the valve isn't very straight.

Front: Schmidt SON-XS dynamo hub. Not as expensive when I bought it as they are now. I'm not especially keen on the standard SON 28 for larger wheels, which is heavy, bulky and expensive compared to the latest Shimano alternative, but the XS is very light and compact.

Rear: 1970s Sturmey-Archer AW 3-speed hub. Runs in oil, very reliable and versatile. This has been up one of the highest road passes in England. Ratios of -25%, direct and +33%. Gives gearing of 45", 60" and 80" with 52 x 14. Velox 10mm rim tape works a lot better than the blue factory stuff, which doesn't actually fit the rim, causes pinch punctures and makes tyres nigh-on impossible to fit.

Rear: 1960s Sturmey-Archer FW 4-speed hub. Not actually tried this one yet, since I rebuilt the hub and built it into a wheel while the frame was away for respray. Yes, I have a 4-speed shifter (also works for 3-speed). Uses a special two-piece indicator spindle. This hub was probably for a Moulton originally. Ratios of -33%, -25%, direct and +25%. Gives gearing of 40", 47", 60" and 75" with 52 x 14. Decided to interlace the spokes on this one; Brompton wheels aren't normally interlaced but no-one knows why.

Rear: Looks like a modern S-RF3 but it isn't. It's a homebrew mashup of a 1948 AM, some AW parts and the S-RF3 shell. Uses a special two-piece indicator spindle, although can be converted to use a cheap and easily-available AW spindle by replacing the clutch key inside the hub. Oil-lubricated and wonderful to ride as long as there aren't any mountains. Ratios of -13.6%, direct and +15.5%. Gives gearing of 52", 60" and 69" with 52 x 14.

Monday, 5 July 2010

The SuperBrompton

Tim from Argos Cycles called today to say that the Brompton frame and stem have been sprayed. I'll collect it on Saturday and then it has to go back to the dealer to have the new rear hinge bushes fitted and reamed using the special 200 GBP tool.

It's flamboyant red (candy apple red, if you like) which should look good against the Ti forks and rear triangle. Pimped out with a red Chris King headset.

There is a purpose to all this; the Brompton is a wonderful creation but has a list of design and quality faults as long as your arm. When this is finished it will be as perfect as a folding bike can be. It needs to do the Dunwich Dynamo and get me a better placing than 96th in the World Championships.

Servicing the Sturmey-Archer S3X hub

Servicing the Sturmey-Archer 3-speed fixed gear hub

Follow these instructions at your own risk - Sturmey-Archer have not published any official workshop instructions for the hub as yet. However, I have stripped and rebuilt lots of SA hubs including this one and had no problems (except when I tried to mix incompatible parts or something else stupid)

Tools required: sprocket lockring spanner (the same as a Shimano
external BB spanner), cone spanners, small circlip pliers, tyre lever,
hammer, punch, vice and (ideally) the SA ball ring spanner.

Materials required: rags, solvent, small paintbrush, detergent
(washing-up liquid), gear oil, SA internal hub grease, lithium bearing

1. For easier cleaning, remove the lockring, sprocket, spacers and
external dust shield from the hub. Make a note of their order, or your
chainline will be affected. For reference purposes, the chainline is
45mm with the sprocket outside the two spacers. I have found it is
possible to stretch this to 46mm with an additional 1mm spacer and still
give the lockring plenty of thread to bite on.

2. Remove the locknut(s), spacer(s) and cone from the LH side of the

3. Using the ball ring spanner, unscrew the internals from the shell.
They will not be super-tight and you should be able to do this without
resorting to a mallet. If you don't have the correct spanner, SA permit
the use of a hammer and punch on the two semi-circular cutouts, but this
will normally mark the finish. As soon as the mechanism starts to move,
you will find it can easily be unscrewed the rest of the way by hand.

4. Withdraw the internals from the shell and wipe away as much grease as

5. Remove the RH locknut, any spacers and the cone.

6. Lift off the driver, clutch spring cap, clutch spring, ball cage,
ball ring, gear ring and clutch.

7. Remove the circlip and withdraw the axle from the planetary gear
unit, which is riveted together and cannot be further disassembled.
Likewise, the compensating spring and axle key cannot be easily removed
from the axle.

8. To remove the ball cages from the driver and the shell without
damaging them, insert a tyre lever between the metal dust seal and the
ball cage as if you were about to prise out the seal, but don't - this
will damage it. Holding the tyre lever in place, strike it from inside
out using the hammer and punch. This should pop out the seal cleanly
after a few blows. A slight warping is OK and will disappear when
refitted, but you must avoid denting or creasing the seal. New seals
are available if necessary.

9. Clean all parts, including the inside of the shell, in solvent. The
planetary unit and axle assemblies will need to be soaked for a while
and very thoroughly cleaned with a small brush, since you can't
disassemble them properly. You may wish to replace the bearing balls,
which are 1/4" and 3/16". Treat the plastic ball ring seal/ball cage
with care, as this is a SA-specific part.

10. Wash in strong detergent to remove any traces of solvent. Rinse
with clean water and dry the metal parts in a warm oven at about 75 deg
C as quickly as possible to avoid rust. Ensure the shell and the
plastic parts are thoroughly dried - use a hair dryer to be absolutely

11. Inspect all parts for wear or damage. Typically the most wear is to
the LH dog of the axle key, which is what locks the sun gears in
position for gears "1" and "2", and to the axle slot where the key
slides. It is highly unlikely that there will be any wear to the clutch
or to the planetary unit. If possible, replace any rounded-off parts;
hopefully SA will make the axle assembly available as a spare.

12. Replace the axle ball cages, ensuring that the solid ring of the
cage is facing outwards. Grease the cages with normal lithium bearing
grease. Fit the dust seals with the open end of the "U" shaped channel
facing outwards. These will usually require tapping into place using
the hammer and a suitable flat plate - the handle of the ball ring
spanner works well. It is permissible to fill the "U" shaped channel of
the dust seal with grease to better repel dust, although this *may*
allow water to creep in by capillary action - your choice.

13. Oil the planetary unit, paying special attention to the axles on
which the planets turn. Also run oil down the middle of the axle to
ensure the compensating spring is well lubricated. The oil is necessary
because grease smeared on the outside might not penetrate for a long
time, allowing rapid wear of unlubricated surfaces. Wipe any excess oil
off the surface to avoid diluting the grease which will follow.

14. Stir the special hub grease to mix in any free oil and smear all
parts, except the outer face of the ball ring and its cage, ensuring
that the gear teeth and the slot in the axle are especially well
treated. Pay special attention to any areas which have been polished
silver by use, since these are the internal bearing surfaces.

15. Insert the axle into the planetary unit and secure it by fitting the

16. Replace the other parts in the reverse order of (6). Use normal
lithium bearing grease on the large ball ring race.

17. Screw in the RH cone by hand until it stops. back it off exactly
half a turn then, holding the LH flats of the axle in a vice so it
cannot turn, ensure that the cone does not move with a cone spanner and
do the locknut up tightly against it. This sets the internal clearances
and ensures all the internal parts can rotate freely against each other.

18. Grease the threads of the ball ring and screw the mechanism into the
shell, tightening it firmly with the ball ring spanner.

19. Refit the LH cone, spacer(s) and locknut(s) and adjust the bearings.
You should aim for a just-perceptible amount of sideways play at the rim
when the wheel is fitted in the frame. Do not eliminate the play
completely, and do not make any adjustments at the RH cone.

20. Refit the outer dust shield, spacers, sprocket and lockring then
refit the wheel to the bike (recommended 20Nm on the axle nuts), grease
and insert the indicator spindle then connect and adjust the cable as
per the instructions. Test ride.

What's inside the Sturmey-Archer S3X hub

The S3X is a three-speed fixed-gear (or fixed-wheel, if you prefer) hub. This makes it a rather unique item. You can change gear but you can't stop pedalling. Imagine driving a car fitted with a manual gearbox but no clutch pedal; when you changed gear, the engine would have to instantaneously speed up or slow down. Well, that's what your legs have to do with the S3X.

This hub fulfils no real need, addresses no real gap in the marketplace. It's a curiosity, and it's there for fun. Consider it in those terms and you won't be disappointed.

On the outside it looks much like any other current Sturmey-Archer hub. Nice alloy shell and a slightly crass name, presumably because it's supposed to be S3XY. Hmmm.

It's the spiritual successor to the 1940s/1950s ASC hub, which gave ratios of direct, -10% and -25%. This one, for reasons of re-use and economy, has considerably wider ratios of direct, -25% and -37.5%. So top gear is direct drive (and therefore almost lossless) while the gear you're going to spend most of your time using isn't. This isn't as bad as it sounds. The bottom gear is a bit noisy and you can feel that your effort is going through a bunch of cogs, but the middle gear is very good once the hub has been run in - 100 miles gets you most of the way there, and it won't really improve further after 200.

Looking inside, you might wonder why you paid nearly two hundred quid for it. It's reasonably well known that it's a hack of the current five-speed hub, using the bottom three ratios. Some parts are carried over from that hub such as the right-hand ball ring, with redundant freewheel ratchet, and the planet cage assembly.

The way the hub works is a bit complicated, but not as bad as some of the esoterica that Sturmey-Archer and its then chief designer, William Brown, were turning out in the golden years of hub gears in the 1940s.

I wrote this piece (slightly edited and improved here) for the newsgroup.

First impressions: the hub is extremely simple and easy to strip down,
with a total absence of pawls and "R" springs. The simplicity is
largely because SA have riveted the suns and the planets into the planet
cage assembly so it can't be further disassembled. Given that these
parts don't normally wear out and compound planets require careful
"timing" when being refitted, I think that's a reasonable decision. I'm
not so enamoured of the way the axle key is fixed into the axle, of
which more later. The mechanism does not get as tightly screwed into
the shell as on other SA hubs, which makes regular servicing less

Means of operation:

The S3X is a single-stage epicyclic with selectable suns and compound planets. It has a lot in common with the old FW and the five-speed hubs.

The driver (to which the sprocket is fixed) ALWAYS drives the gear ring.

In top gear neither of the suns are clutched to the axle. The main
clutch drives the planet cage via six arms and trapezoid dogs on the
face of the cage - no AW-style extended planet pinion pins here.
Because the suns are out of action the entire planet cage turns at the
speed of the clutch (and hence the sprocket) and transmits the drive
straight to the hub shell via a three-armed dog. The gear ring plays no
part at all, since the planets and suns it drives all rotate freely and have no effect on the movement of the planet cage.

In middle gear the main clutch is disengaged from the planet cage. The small sun of the pair is clutched to
the axle by means of a sliding axle key. The gear ring drives the small
ends of the compound planets, which rotate around the small sun via
their large ends. The planet cage is forced to rotate slightly slower
than the gear ring, giving a medium gear reduction (1/4).

In low gear the large sun is clutched to the axle instead. The gear ring
drives the small ends of the compound planets which rotate around the
large sun. The planet cage is forced to rotate considerably slower than
the gear ring, giving a large gear reduction (3/8).

Note that in this hub "drive side" is always the left, since the torque
is transmitted to the shell more or less where the LH flange is.
However, a large-diameter SA shell is so torsionally stiff that this
makes very little difference to left/right spoke tension, even when cranking

There is a neutral position between medium and top when the clutch does not make
contact with the planet cage and the small sun is not yet clutched to the axle. The hub is highly unlikely to
slip out of top gear when the cable is correctly adjusted because of the
proper dog arrangement on the planet cage, so this is not as serious a
fault as on the AW, with its kludgey extended planet pinion pins.

There is also a potential slip between low and normal gear when the axle
key is out of contact with either sun. Cable adjustment is critical
with this hub, and the shifter allows selection of intermediate
positions which can be dengerous. An old-fashioned flick trigger has a
lot going for it but isn't offered for the S3X cable pull. When
changing gear, always ensure that the shifter has clicked into position
before re-applying power to the pedals.

Quality and specification:

Most parts are very heavily built, especially the gear ring which is
probably overspecified. On the other hand, the sliding axle key, which
is required to move the main clutch and to lock the suns, is very small.
The dog which does the sun-locking part was very shiny on one side after
only 200 miles' use. I don't know what proportion of the total torque
has to be resisted by the sun/axle attachment (the AW gets away with a
small cotter pin) but, coupled with the loose fit and frequent reversals
of drive, it doesn't quite seem up to the task. The slot in which the
axle key slides also shows significant wear marks on its edges.

The key
is not easily removable from the axle as it is held tightly between two
halves of a long compression spring (what was called a "compensating
spring" on the old FW), and it would be best if SA made the axle, spring
and key assembly available as a spare part considering that all of these
will wear. Nothing else in the hub showed any signs of wear beyond the
normal light polishing from running-in.

The lash in the hub is mainly from the loose fit between the main clutch
and the planet cage or gear ring (depending on the gear selected) and
not from the gear teeth, as might be expected. There is a small
clearance to allow the clutch to engage and slide freely.

Personally I dislike grease lubrication as it means periodic stripdowns,
but the SA grease is an unusually brown and oily one and does flow a
little. SRAM grease is more like toothpaste and will not migrate to
coat any uncovered internal parts.


The hub is unique and therefore it's not worth comparing it to anything
else on the market. The design is neat and the ratios are well-chosen
for general riding, although low gear is quite noisy and top (direct
drive) will rarely be used except for diving downhill. Fortunately,
middle gear is almost as efficient as top, with only fractionally more
drag when the wheel is spun off the ground; I would expect the
additional losses to be about 3%. The low gear noise and inefficiency
is likely to be due to tooth shaping, which has always been sub-optimal
on SA hubs with multiple suns.

The design has two main weaknesses: the presence of "neutrals" and the
small size of the axle key, which will wear rapidly. The "neutrals" are
compounded by the choice of a shifter which does not flick positively
between gears. The lash, I believe, is unavoidable in a 3-speed fixed
hub (the simpler 1930s two-speed TF is said to have virtually none). In
some areas, such as the choice of ratios, the hub betrays its origins as
a "hack" of the current five-speed.

Next post: how to service it and put it back together so it works. Much, much easier than most SA hubs.