Brompton Folding Bicycle Upgrade

Andrew Hague

The full range of Andrew's pictures can be seen in the Photo Gallery: Folding Bicycle

Hit a cattle grid at 40 mph and nothing less than 27 x 1¼ will do. That's what you soon learn cycling in the Pennines where a long descent is punctuated by a bone jarring clatter. Then years pass by and life moves on. There is more international travel. Cars are part of the vehicle mix and big wheel bikes are difficult to carry around. Maybe a folding bike will allow the same pleasurable cycling. So I buy a Brompton and am surprised. It is not the same as the big wheel bike but it works.

Fit toe clips, move the saddle and handlebars forward, fit a Mountain Drive to extend the 5 gears to 10 and the bike can go everywhere, even into the hotel bedroom and, on one occasion, into the shower to get the mud off. The ultimate freedom and independence. Someone should write a book on routes to airports by bicycle. Did you know that, in effect, it is illegal to enter or leave Dulles airport in Washington, USA, without an engine? Zurich and Amsterdam, on the other hand, both international airports, are a delight by bike.

So I am hooked on a folding bike and am deluded in thinking there might be something better than a Brompton. The magazines mislead me and I buy a Bike Friday and am disappointed. It did have V brakes and a 14 speed Rohloff gear and that is a revelation. This is the gear for touring, mountain biking and racing, why not? It is plenty strong enough. The next experiment was a Birdy Grey also with V brakes and a Rohloff but apart from the better components is not in the same league as a Brompton for folding and riding. Although my modified first Brompton was better than the other more expensive bikes, I had time to spare and an engineering workshop so I wanted to see if I could fit the best equipment to the best frame and create something better than money could buy.

I bought a new Brompton L3, the one with the new hinges making it longer to improve the handling. The gears and brakes were discarded. Here's how I fitted a Rohloff Speedhub, V brakes and lights to create what, for me, is the ultimate folding bike. This is not a DIY job; we are going to invalidate every warranty there is. You have been warned.

We used to sing the praises of quality equipment like Campagnolo and Shimano but Rohloff is in a higher category on its own. For a full eulogy and explanation view www.thorncycles.co.uk and find the Rohloff pdf files. It's all true. Look at www.rohloff.de and there are no exaggerations. Brompton's own propaganda is surprisingly modest; the bike does a lot more than commuting. A Rohloff feels like an infinitely variable drive. You are always in the right gear and it never breaks down. It only costs more than the bike itself because the Brompton is cheap.

Start by building the Rohloff Speedhub with 32 spoke holes (only 32, no options) into a 28 holes Brompton rim. Abandon the idea of using a 36 hole Sun CR18 rim because its well is too shallow and if you manage to get a 37-349 (16 x 1⅜) tyre on, for sure you will never get it off at the road side to repair a puncture. Bernhard Rohloff forbids the spokes on the sprocketless side crossing the screw mounts of the hub casing. The answer is to drill five extra holes in the Brompton rim: one for the high pressure valve and seal off the larger hole for a Schrader valve and four nipple holes at 90° to each other.

The spoke length is 128 mm. Using a P&K Lie wheel truing jig, get the rim centred, round and true to 0·1 mm in each of the three dimensions and also do the front wheel whilst you are at it. This accuracy is impossible without such a dial gauge jig and makes a noticeable difference to the free running of the bike.

The space between the rear fork ends of the Brompton has to be opened to 135 mm exactly and the back wheel must be exactly in line with the front. Both your wheels are precisely dished and true so you have reference instruments to check that the wheels are in line. To do the job properly you need a jig and should maybe have made a new rear end for the bike but I did it the hard way and eventually got it right but it was by trial and error and I won't do it that way again. There are no short cuts in precision engineering.

Extend the left fork end to accommodate the torque boss of the Rohloff gear and at the other side double the thickness of the fork end so that the Brompton chain tensioner sits on it with the rollers in line with the 13 teeth Rohloff sprocket. Discard the ⅛ chain and fit 3/32 with quick release links. To get the chain in line, fit a spacing washer to the right bottom bracket cup. A 15 teeth sprocket will not be in line. File away that part of the fork end that catches the chain. The hub needs a quick release skewer. Make a nut in stainless steel tapped M5 with an M8 external thread on which is fastened finger tight an aluminium knurled nut to hold the chain tensioner. It looks neat, works and no spanner needed.

Make a gear control boss in polished stainless steel and mount it on the vertical section of the handlebars where it does not hit the front wheel when folded. The cable run is to the right of the seat tube and the left of the rear wheel. Follow the Rohloff instructions on cable length. The manual with the latest gear sets such a high standard that few other manufacturers of anything will ever equal its clarity and comprehensive detail.

The bosses for the rear V brakes are straightforward and the cable routing follows the gear cables. I like my back brake lever on the right. The bosses for the front brake have to be mounted in reverse position facing outwards. This means that three holes (you might get away with one) have to be drilled on the convex side of the boss to take the snub of the brake return spring. Routing the cable is straightforward until you fit the bag boss and discover that the cable collides with the boss on folding. You have to run the cable to the brakes from the other side. In stainless steel make a cable grip with an M5 socket screw and a cable channel for the other leg, then the bike folds neatly. Wet weather braking worries and finger strain on Alpine descents don't happen with V brakes. You climb the mountain with a 44 teeth chainwheel and 13 teeth sprocket giving evenly spaced gears from 15 to 80 and descend under full control.

Now lights and a tool kit. On the other Brompton I fitted a Schmidt hub dynamo as I also have it on three other bikes and it is the brightest and free running of all lights but for the Rohloff Brompton I have only fitted LEDs. At the back, the bracket is made from polished 8 mm diameter stainless steel tubing, holds the light and serves as a stop against the seat tube when the bike is folded. At the front, the lamp bracket has two fingers touching the underside of the fork crown as a precaution against rotating.

A long socket screw enters from the back of the crown and also clamps the tool bag bar. Every bike has to have its own tool kit permanently fitted to the bike. The spare inner tube for the other Brompton is in the frame tube with some tools in the shorter section of tube forward of the hinge and a small bag is mounted to the front of the rear triangle's seat stays. The frame triangle above the bottom bracket is crying out for a blow moulded drinking bottle to fit the aperture; with a few thousands of pounds of tooling this could happen. Otherwise, the water bottle travels in the rear pocket of the front bag.

I searched for a void for a wedge shaped bag I had left over from somewhere and found when the bike was folded that there is space between the saddle and front bag boss. The wedge bag's bracket was removed and the bag is now screwed direct to the aluminium bar that runs down the mudguard from the fork crown to the mudflap. An unconventional location indeed but it works and that is the basis on which this whole bike has been designed, that form follows function.

As I have got older and the handlebars higher my toolkit has got lighter. What I am not carrying on this bike are spare spokes, spoke key, chain rivet extractor, pedal, cone or headset spanners because in many miles on small wheels a spoke has never broken and the bearings and chain never needed attention. The weight saved is put on at dinner after a day's ride.

For me, this is the most satisfying bike I have ever ridden and the pressure on Brompton to increase output to meet demand shows that I am not the only cyclist impressed by this bike. The machine is more than a good bike, it is a market phenomenon; it has opened up a market where one did not previously exist and I feel deserves a chapter or more in MBA textbooks.

The Brompton also holds the answer to the problems of traffic congestion, poor health and pollution but the politicians don't yet understand any of this. One day, cars will be made without ashtrays and there will be two Bromptons in every boot so that the occupants can ride into the traffic free town from the compulsory out of town car park. They can also ride across Europe.