My Bullhorn Kinetics Brompton
version 1/4/2020 3:01 PM
Here is a dream bike – the Bullhorn Kinetics Brompton. There are many different dream bikes. Some people want la light weight titanium bike, others special editions or paint or stylish accessories. My goal is a combination of functionality and elegance without caring too much about weight. For me, the most essential functional parts are foot retention, gearing and having a bike which fits my body. For the foot retention, I prefer clipless pedals and managed to modify the folding Brompton pedal. The gearing was provided by Kinetics in Glasgow who sell modify Bromptons with a wider rear triangle and a choice of hubs. I got the Shimano Alfine 11. Fitting my body was accomplished with a bullhorn bar and the Andros stem.
A folding bike poses some challenges for adding accessories. Many standard mounting options don’t work or interfere with the fold. This is even more challenging with the Brompton than with my Bike Friday due to the more compact fold. However, after some frustration and iterations, I found very good solutions for all accessories – there is no need to move or rotate them for folding, and they don’t interfere with the elegant look of the Brompton. There are a few exceptions: I wanted a permanently mounted bottle cage, but the best solution I found is not compatible with the T bag. When I use the T bag, I have to remove the bottle cage or turn it around, and turn it back for folding the bike. For the Garmin GPS speedometer, I found no place on the handlebar which didn’t eliminate one possible riding position. Eventually, I mount it on top of the Andros stem, and have to remove it when folding the bike.
Many of the modifications have been posted on the Facebook page “Brompton hacks”, URL https://www.facebook.com/groups/796190400521866/ There you will find additional comments by other people. Some recent updates are in this document, but not on Facebook.
Improving the fold and handling
Kinetics Alfine 11 modification Back to top
I ordered the Brompton from Ben Cooper, Kinetics in Glasgow and chose his special rear triangle with the Shimano Alfine 11 hub and the Jtek shifter. Works well! The triangle is well designed.
The only thing I don’t like about the Alfine 11 is the large step in gear ratio between the lowest and the second lowest gear.
Jockey wheels: Ben Cooper installs a modified Brompton chain tensioner. For the Alfine 11, he used the pulleys from the 2- and 6-speed Brompton. They are very noisy. I exchanged them against Tacx pulleys (Tacx Standard Ball Bearing Bicycle Jockey Wheels). They made a big difference and are much quieter. I had to make a round aluminum disk for the lower pulley similar to what Brompton provides with the 1- and 3-speed tensioner (but the disk is not available separately). It was easy to swap out the pulleys, all I needed where some 4 mm and 6 mm washers to adjust the chain line.
Jtek shifter: With a file, I added marks for gears 4 and 7
Bullhorn bar Back to top
Bullhorn handlebar with folding handlebar stem:
I have a 2018 Brompton S type and was able to fit in a bullhorn handlebar using the Tern Andros stem, around $ 60, see
Note that the S bar, compared to the M bar, has the handlebar mounting point 3 cm higher and 3 cm more forward which is helpful if in the end, you want a higher and more forward position with the bullhorn. I am 1.89 m tall. If you are shorter, you may not need the extra 3 cm, and the M bar will work for you.
This setup allows me to ride in a natural position. Also, the stability of the steering is greatly improved --- feels now almost like a regular bike. The brake levers are Tektro R720, the shifter (for Alfine 11) is Jtek. The bullhorn bar is Fyxation Rodeo Bullhorn Handle Bar, 42cm, Silver.
Folds into a compact size – still fits into the Brompton carboard box.
When I put in the Andros stem, I had to adjust the fold by moving the handlebar catch further out by a couple of turns (just rotate the plastic part with pliers) . This allows the catch to snap in before the Andros stem touches the fork.
For the folded position, the first angle of the Andros stem is adjusted for the Andros stem to be parallel to the fork, the second angle to move the bullhorn bar as much in as possible (that’s when the tip of the handlebar hits the front fender). You have to find two specific angles when folded, and two when unfolded. I clearly marked those angles, so I always get them right without fiddling.
The specs for the torque for the Andros stem vary in different manuals and instruction videos. It says 6-12, 9-12 Nm, or in the installation tips: do not exceed 8 Nm. I found this too much - it is very hard to close the lever, or to rotate the handlebar in the open position. Also, the 6 mm bolts got bent in this range of torque. I am now using around 20 inch pounds (about 2.3 Nm), and it feels right. Also, you are told not to put any grease on it. I found that the stem didn’t rotate smoothly after I while and decided to grease it with carbon fiber seatpost grease (which has some grit in it).
UPDATE: After lubricating everything (levers, clamps) with lithium grease spray, I increased the torque to 60 inch pounds (7 Nm) and it seems to work well.
The Andros stem is very nice, but in some ways marginal. You have to keep the quick release at maximum tension, when you can still rotate the handlebar in the open position, and close the levers using some force by pressing on it with the palm of your hand. When the quick release was less tight, I had occasional (once every few weeks) slipping of the stem when I drove through a pot hole while riding with my hands all the way out to the tip of the bullhorn. But the slippage was only by a few degrees, sometimes hardly noticeable. Or in other words: The length of the bullhorn and me being a tall rider puts a lot of torque on the handlebar. When this is augmented by driving over a bump or through a pot hole, this can push the Andros stem to its limit.
Andros stem - important improvement:
Even at low torque setting (20 inch lbs) the long screws got bent. I replaced them, and they got bent again, near the end where they are screwed into the clamp. This is probably ok, I have seen with seat post clamps that the screw bends due to the torque, but then it stays like this. The problem with the Andros stem is that you have to rotate the screw for adjusting the tension of the quick release to keep it tight (see above), and then the bent is rotated to a different angle. When you rotate the screw, you feel a wobble due to the bent. When rotated, the bent will try to rotate the screw back.
My solution: Combine a piece of threaded rod (cut off screw) with an allen head screw and an M6 standoff. I could now use permanent red thread locker to connect the threaded rod to the quick release clamp. I assume this rod will slightly bend in the future, but adjustments are now done with the other screw (which I expect will not bend) which can be smoothly rotated by small increments. Since the rod is permanently glued to the clamp lever, I can now generously grease this part (which improves performance) without risking that the screw will rotate under tension. Any rotation in the M6 standoff is prevented by using counter nuts. I highly recommend this modification - it has taken away a serious concern I had about long term integrity of the Andros stem.
Another improvement for the Andros stem:
By keeping sufficient tension on the quick release, the Andros stem clamps well. It is only every few weeks, when I hit a bump or pothole, that the handlebar rotates down a centimeter or so. This is so little that it has never caused any issues for steering the bike. However, I am always a little bit concerned that the handlebar could rotate more when I would hit a bigger pothole. I have now found a simple solution to make this less probably, or in other words, to make the Andros stem even safer.
The solution is a clamp (from Chain Reacton Cycles) around the vertical Brompton stem which is adjusted in such a way that it touches the Andros stem when it is in the riding position, thus limiting the range of rotation. This is also very convenient when unfolding the bike, because it provides a stop. Therefore, the Andros stem is unfolded every time to the same angle, without looking at markings or fiddling around.
The Andros stem has two axes of rotation, and the solution above provides a stop for only one, but it is the axes which experiences the higher torque due to the larger lever arm for the rider’s weight on the handlebar.
Power Grips Straps Back to top
I have cleats on all my other bikes, and was looking for a way to hold the feet on the pedals of the Brompton. I tried out the Power Grips straps and like them. For me, they are not as good as cleats, but clearly help to keep the feet well positioned on the pedals. Mounting on the Brompton pedals is straightforward, but tedious --- you have to drill holes, cut treads and find oversized washers (see photos).
Improving the adjustment hardware:
The Power Grips straps have to adjusted when you wear different shoes. Originally, this required a screwdriver or allen wrench, but I added a wingnut. The screw presses against the strap through a U shaped piece of sheet metal. The piece (on the right side in the photo) caught on the straps when you tried to shorten or lengthen them. I replaced it by a bigger piece (made from thin aluminum, shown in the middle), and now it works very well --- you just loosen the wingnut, and then the strap slides through the attachment.
Folding eggbeater pedal Back to top
I like clipless pedals. For the Brompton, I tried for a while Power Grips Pedal Straps and started liking them, but I enjoy even more riding with clipless – I have them on all my other bikes. For the Brompton, the only available option is removable SPD pedals – but I have Crank Brothers eggbeaters on all my other bikes, and several pairs of shoes with eggbeater cleats. Also, removable pedals are less convenient than folding pedals. So I was motivated to build a folding eggbeater pedal. In essence, I used an old Crank Brothers Candy pedal, a folding Brompton pedal and combined them, using a hacksaw, a grinder and files. Amazingly, it did fit! I could even use the original black plastic folding plate which keeps the pedal unfolded, by cutting off two thin sections and connecting them with a small plastic plate using glue and screws. The folding plate no longer has the spring, but stays in place through friction.
The foot on this pedal is further out relative to the crank. I first wanted to compensate for this by using a pedal extender on the right pedal, but I didn’t like the larger stance (or Q factor). So I had to bring in the folding pedal by using a vintage crank which is straight and not bent outwards as most modern cranks. Also, with some filing, I could move the eggbeater spiral closer to the crank. Now the two pedals are almost symmetric, only a few mm difference. I have used the pedal now for several weeks, also on a bike tour, and it performs (and folds) very well.
Note: I disassembled two different eggbeater candy pedals. They were different. In one of them (shown in the photos) the spiral was held by a tube with 8 mm inner diameter, the other one had 6 mm. Since I had first opened up the 8 mm, I used M8 bolts and nuts to connect the spiral to the Brompton pedal.
Smaller axle nuts Back to top
The Alfine 11 hub came with acorn nuts. They are standing out and can pierce a cardboard box when I pack the bike for air travel. I replaced them by normal nuts. They are still the widest point of the frame on the left side and can scratch furniture or damage the Brompton cardboard box when I package the bike for travelling. Therefore, as protection, I added a 15 mm rubber wheel nut cap.
Hinge clamps Back to top
Here are my 2 cents (and parts list) on how to modify hinge clamps to avoid rotation. File away 1 or 2 mm of the upper lip, add a spring and an M8 hex jam nut.
Springs: from Amazon, Compression Springs, Outside diameter: 7/16", Length: 1-1/16", Gauge: 041.:
Hex jam nut (from Bolt Depot) is adjusted to within a quarter turn for the hinge just to release, and then fixed with Thread Locker. Has been working perfectly for many months.
Note: A hex jam nut is a thinner version of a hex nut. The original M8 bolt is too short to pass through a whole lock nut with its nylon piece, so the nut may not lock (but you can always use thread locker). I prefer the thinner nut, since I want to be able to insert an inner tube into the main tube of the bike, and with the jam nut I have just enough clearance.
Saddle height limiter Back to top
Saves 5 sec every time I fold it :)
Piece of (leather) shoe lace
Rubber O ring
You can easily pull out the saddle by sliding the knot through the rubber O ring. That’s nice for packing the bike or for exchanging saddles.
Update: The leather shoe lace turned out to be somewhat elastic and can be stretched. I replaced it by a piece of webbing which is stiffer: It stops the seatpost always at exactly the same height. Also, I added a quick release buckle. It is now very easy to make small adjustments to the saddle height, and also to take off the saddle (for packing the bike) or to swap against another saddle.
I always carry the Brompton using the nose of the saddle. I bent it inwards for optimum balance, to put the nose closer to the line above the center of gravity. The Brompton saddle has a nice built-in grip. I was missing this feature on the Brooks saddle. I first tried to add some foam padding, but it was too soft, and the saddle rails were pressing through. What worked well: A piece of garden hose, reinforced by putting a round piece of wood inside, and putting black shrink tubing around it (for the nicer look).
Frame protector for fork clip Back to top
A piece of thin aluminum shim metal, cut with scissors, pre-bent, and attached with double sided tape.
I like that it doesn't cover the top of the tube.
Update: The aluminum piece got bent and came lose. I am now using a thin stainless steel shim metal glued to the tube with Gorilla glue.
Mudguard wheels Back to top
Double mudguard wheels
When folded, I usually roll the Brompton using just the two front rollers or Eazy Wheels. The mudguard wheel serves as protection to the mudguard, and for occasional rolling the bike into its storage place. However, many people said that four wheels (with the rack version) make it sometimes easier to roll the Brompton around. So I got interested in double mudguard wheels.
For this, I found a simple and inexpensive modification of the single mudguard wheel: You put an M6 bolt into the holder of the mudguard wheel and add two M6 coupling nuts ($2 each on Amazon https://amazon.com/gp/product/B07R46STQP or hardware stores). Now you can add any wheels you want (Eazy Wheels, Brompton rollers, skateboard wheels). The modular setup allows you to try out different diameter of wheels (to get the right clearance), and by adding another coupling nut or shortening the coupling nut you can adjust the width between the wheels. I first used the Brompton rollers, and they had sufficient clearance, but then I wanted to match the wheels on the other side and used Brompton Eazy Wheels. By-the-way, Nov designs has an “L type adapter” for $ 44, which is similar in function to my solution.
I like to have the option of rolling the folded bike on four wheels, without the need of lifting it. There is some flex due to the fender stays, and you can make the front wheel touch the ground (and my front wheel does not spin freely). However, when I pull the folded bike on its four wheels using the unfolded handlebar, the bike twists a little bit to the side, and the front wheel does not touch. Works very well! My only concern is whether the mudguards will be too weak and crack in the long run. In the end, I added reinforced fender stays (see below).
Rear fender stays
By improving the mudguard wheels, I realized two things: (1) Wider wheels add a lot of stability to the folded Brompton (2) When the wheels are extended with a rod, they easily bent. So I came up with the design shown here:
The wide separation between the wheels makes the Brompton super-stable when it is in the kickstand mode, or folded. It is now much easier to roll it around when folded, and you can easily pull it behind you with the handlebar, and it is also very stable in Shopping Cart mode. Big improvement! I think I have now the performance of Eazy wheels mounted to a rack, plus an Eazy Wheel extender – but in a more minimalistic version.
An extended width between the Eazy Wheels is very useful. However, extending the width between the front wheels is limited by heel strike, and telescoping extenders may have their own problems. The ideal way to extend the width between wheels is on the rear, where the extra width (on the right side) does not interfere with the fold and can be realized with a very stable rear stay without any moving parts.
Why is none of the Brompton accessories companies offering such a solution? Wouldn't many people who buy the rack buy this instead? There are several commercial versions for mudguard stiffeners, but it much more effective to have stiffer fender stays which connect directly to the rolling wheels.
Parts list: M6 threaded rod, stainless steel tubing (OD
8 mm, ID 6 mm), M6 locknuts
Aluminum Rectangular Bar, 3/16" Thickness, 1/2" Width, https://amazon.com/gp/product/B003U6HT82
The fender is connected to the tubing with a modified mudguard holder: I enlarged the hole to 8 mm and then used a set-screw arrangement. A simpler (but less elegant) solution could use hose clamps or cable ties.
Note added: The setup is very stable and rigid. However, the fender is necessary to prevent the whole setup to rotate. When you put weight on the rear Eazy wheels, there is a pulling force on the fender. I think the fender is very strong and doesn’t need reinforcement. However, the small angle bracket (a piece of bent sheet metal) which connects the fender to the rear brake bolt is thin, and it once got bent and stretched out (when I took the Brompton on a flight using the original Brompton cardboard box). I could bend it back and ride the bike, but afterwards, I replaced it by a thicker aluminum bracket (around 3 mm thickness) – see photo.
Note added: With four wheels, some alignment is needed to make sure that all four touch the ground. I can adjust the fender stays after enlarging the mounting holes to slots with a file. I align tem by placing a flat board on top of the wheels and checking that all wheels touch the board.
Note: Here is an earlier version of the rear fender stays. The new version is wider, and more stable.
Front mudguards Back to top
Reinforcing front fender:
My front fender had cracked due to some incidence. To stabilize the crack, I replaced the mounting hardware: Cut a piece of aluminum (1/16”), connect with screws and glue.
Front lamp Back to top
I have various front lights on my other bikes, and want to use them on the Brompton. So I build a holder for the lamps --- I used the reflector clip, bent it into shape and connected it to a piece of tube from a white seatpost, and used handlebar plugs (which I could color match to the bike). I placed the lamp holder as much as possible forward and down for enough clearance with the front carrier block and Brompton bags. I think the commercial lamp holders are less versatile.
Battery pack Back to top
The best place for the lithium battery pack turned out to be the front carrier block. I built a small holder and secured the battery with a velcro strap.
For the cabling: I avoided cable loops by permanently installing an extension cable along the front brake cable. The battery plugs in on one side, the lamp on the other.
Works well with smaller and larger battery packs.
Rear lamp Back to top
I wanted to use a third party lamp which blinks and is removable. I was able to make a mount for a Planet Bike light. It fits well, but has only mm size clearances to the seatpost, the brakes and the ground when folded (using the original Brompton wheels. With the larger Eazy Wheels, there is more clearance). Well, with the Brompton, everything is a tight fit!
Pump Back to top
I like to store the pump in the seatpost. However, when I drove through a pothole, the plastic bung and the pump fell out. Here is my solution:
A rubber plug with a wing nut which can be fully inserted into the seatpost and tightened. This solves another issue with the original bung: It prevented the seatpost from being fully pushed in and therefore added to the height of the folded bike. I got the parts from pool supplies. I bought plugs of various sizes and combined a larger plug with the wing nut.
PS: I don't need the bung as a brake for the folded bike. When I fold the handlebar, the caliper brakes are pulled tight and prevent the front wheel from turning.
Tool kit Back to top
As many others, I store my tools and inner tube inside the frame. Here are pics of my solution. The inner tube is attached with velcro to a sheet of flexible plastic. In addition to the 15 mm ring wrench (a bigger wrench cut with a Dremel tool), the bits and the two tire levers I use an 8/10 mm wrench (Park tools) which is kept with the folded inner tube. The tools are wrapped in a rag and secured with a rubber plug.
Wired speedometer Back to top
I have permanently installed a wired speedometer, Cateye Strada Cadence. I like those, since they are small and the battery lasts a whole year. I use a GPS device (Garmin) only when I am going on a bike tour. The Cateye has speed and cadence. The speed sensor is on the rear wheel. I had to extend the wires by cutting the wires and connecting them by soldering extra pieces of wire between them. Make sure you use highly flexible wire, on my other bikes I had wires broken by frequent bending.
Garmin Back to top
Mounting a Garmin on the Andros stem
I mount a Garmin GPS on the Andros stem using a quick release mounting kit for Forerunner 201 or 301. With the front light under the carrier block and the bell between the two clamps of the Andros stem, this creates a very clean cockpit.
Of course, when I fold the bike, I have to remove the Garmin. But I use it only for occasional touring, since I have a small wired speedometer permanently installed.
Bell Back to top
I like the small bell made by Spur Cycle (or cheaper copies). It can be mounted on the bullhorn bar between the two parts of the Andros stem.
Update: The cheap copy of the Spur Cycle died (the hammer fell out). Replaced it by Crane E-ne Bicycle Bell.
Bottle cage Back to top
On all my bikes, I like to have a rigidly mounted bottle cage. However, this is difficult on the Brompton due to the fold. In my view, the only suitable place is to the left side of the stem. The bottle cage is not interfering with the fold, you can even leave a water bottle, accessory bag or a rolled up DIMPA bag and fold the bike.
(1) My favorite solution is to use a simple clamp (Chain Reacton Cycles) and mount a Planet Bike metal bottle cage directly --- very minimalistic, very small gap to the stem (modifications done: drill central hole in bottle cage, replace allen screw by screw with wingnut, enlarge the screw hole with a file, protect paint by gluing a piece of a plastic milk container to the clamp). Since the bottle cage is held by only one screw, I use thread locker. I can highly recommend this solution.
I leave the cage permanently mounted. It doesn't interfere with the fold for my S type stem), and also works with a Brompton shoulder bag. For a larger bag (e.g. T bag), the mount has to be removed or rotated (but then stands out when the bike is folded).
(2) The Minoura quick release clamp is also quite nice. I bought the bottle cage mount, but removed the ugly hardware to attach the bottle cage and used only the quick release clamp (modifications done: drill central hole in bottle cage, protect paint by gluing a piece of a plastic milk container to the clamp). Since the bottle cage is held by only one screw, I use thread locker. I use this if I need a second water bottle cage (but have to take it off before folding the bike).
(3) Lixada bottle cage holder
https://www.amazon.com/Lixada-Multifunctional-Bicycle-Anodised-Handlebar/dp/B072ZLQKG1 and replaced the allen screw with a screw with a wingnut. Similar to solution (1), but more bulky.
(4) A plastic quick release bottle cage mount also works:
Amazon, $ 8.99
I exchanged the knurled knob by a seatpost quick release, and eliminated the two different orientations by gluing (more sturdy). Not a bad solution, but less sturdy and uglier (in my view) than the other options.
(5) TOPEAK quick release bottle cage mount ($ 7), mounted with simple clamps from Chain Reaction Cycles. I like that you can use a bottle cage and bottle of your choice, and that the mounting is very sturdy (compared to other systems, e.g. monkii cage, two-fish). I saw that Trek/Bontrager have a quick disconnect mount for water bottles, but it is expensive.
As a bottle cage, I use a Cateye, black plastic bike bottle cage (often used on Bike Fridays). It is sturdy, bends without braking and doesn't scratch paint.
I like the TOPEAK quick release bottle cage for its functionality. However, on the Brompton handlebar stem, it doesn’t look elegant when the cage is removed. I use it on my Bike Friday where it is less prominently visible.
Warning flag Back to top
On all my bikes, I have those warning flags to make passing cars keep a minimum distance. These were very popular in Germany a while ago. This is how I mounted it on the Bronpton, fully compatible with the fold.
For the Brooks saddle, I modified a Minoura saddle-mount bottle cage bracket.
Tool case Back to top
I tried to find small bags which can be left on the Brompton without interfering with the fold or increasing the size of the folded bike. One is a sunglass case strapped to the seat tube, from Amazon, $ 10,
This case carries a spare battery and some extra tools, and I leave it on the bike all the time. I had to cut down the rear triangle release lever by one cm. Another option is to turn the release lever around so that is points upward.
Bottle cage case Back to top
I tried to find small bags which can be left on the Brompton without interfering with the fold or increasing the size of the folded bike. One option is a case held in a bottle cage (which is permanently attached to my bike).
Dimpa bag Back to top
The Dimpa bag (from Ikea, nice to carry the bike or cover is when you take is into a restaurant or hotel) can be left on the bike, even when folded, using a bottle cage.
Small clip-on bag Back to top
I tried to find small bags which can be left on the Brompton
without interfering with the fold or substantially increasing the size of the
folded bike. One option is a mall handlebar bag with a carrier block adapter.
As long as the bag is shorter than 10 inches and has a diameter of less than 5
inches, it will not substantially increase the size of the fold. There are
many small handlebar bags of similar size, and I modified one from Amazon, $11,
with a carrier block adapter.
Brompton bags Back to top
I have the T bag and the waxed canvas rolltop shoulder bag, and like both of them. They are well-designed bags!
Front pannier Back to top
I have used the Brompton carrier block adapter to mount non-Brompton bike bags. There is a big difference between available adapters. I first got adapters via ebay from lamkevin123, Australia. They are 3D printed. When I mounted them, they cracked easily along the print direction (but I could glue the crack). The adapter has a lot of play on the Brompton carrier block, which is acceptable for small bags, but not for a bigger bag. The adapter from AGEKUSL is much more stable and made of thicker material (I assume it is injection molded), and it has no play --- it fits as well as original Brompton bags. It makes a big difference in stability for larger bags like this front pannier.
I received an improved 3D printed adapter from lamkevin123. This one is much better than the previous version. I like the larger holes (M5) and the wider spacing. The crisscross pattern should avoid cracks (but I didn't do any tests ...). The new adapter has no play and should hold bags well. I don’t like the embedded M5 nuts – they can be pulled out. Therefore, I would use longer screws and add a washer and a nut or acorn nut. In conclusion, the new version has all the functionality of the molded AGEKUSL adapter. Aesthetically, I like the smoother finish of the molded adapter.
Modified luggage frame Back to top
I wanted to use some older bags from other bikes on the Brompton. They were attached with hooks to the front or rear rack. I got a Brompton luggage frame (the "Tote bag" version, which is as tall as the T or C bag version, but narrower and without handle). I needed extra height, so I added an aluminum rod on the top. For securing the bags, I added a piece of threaded rod and covered it with shrink tubing. Now I can mount various bags - I am showing a big Blackburn shopping basket and a front pannier.
Handlebar bags Back to top
For day touring, I wanted a light bag, about 10 l. From Amazon, I got the Schwinn Expanded Bicycle Handlebar Bag for $ 13. It has some stiffener inside. I mounted a Brompton carrier block adapter, which worked pretty well. However, the bag sagged down too much (which may not be a problem if you don't have front lights mounted above the front brake). A piece of alumnimum sheet metal (1/16 " think) solved the problem. An inexpensive nice light bag, medium size!
Here is another bag which is smaller. The original stiffener was sufficient.
Seatpost bag Back to top
A nice pouch, attached to the seatpost with velcro. It is very light, and can carry rain gear or warm clothes. The pouch used to be a removable side pocket for a backpack.
Seatpost mount for Brompton carrier block Back to top
The Brompton carrier block system is very nice, bags can simply be clicked in and out. You may want to have the same convenience for a bag at the rear of the bike. So I built a seatpost mount for the Brompton carrier block.
A good starting point is a quick release clamp on rack – available for USD 10-20. I used some older ones and don’t remember where I got them from. With a hacksaw and by drilling a few holes, you can attach the carrier block. I have two versions: a short one for mounting smaller bags close to the saddle, and a longer one for bigger bags which should be mounted low, but then they need heel clearance. It is good if the rack has a rectangular profile which can be easily bolted to the carrier block.
Rear rack Back to top
I used this clamp-on rack on older bikes, but it fits well on the Brompton. I modified the clamp using a seatpost clamp.
Double chainring Back to top
For bike touring in the Alps I want even lower gears than the Alfine 11 provides. A simple way to extend the gearing on the Brompton is to use a double chainring.
For a double chainring, there is always the question about bottom bracket compatibility and chain line. Here is my experience: I have a 2018 Brompton (Alfine 11), and swapped out the original crank with a 50 teeth chainring against:
Crankset Stronglight Impact Compact Argent 170mm - 50x36, Square JIS Bottom Bracket. The ratio of smallest to largest gear is 409 % for the Alfine 11. With the double chainring, it is now 568 %.
Note added: I replaced the 36 teeth chainring with a 33 teeth: total gear range is now 621 %, highest gear 7.59 m, lowest gear 1.23 m. The small chainring effectively gives me three extra gears. I added 1 mm spacers between the two chainwheels. This was not absolutely necessary, but when the chain is on the small chainwheel, it touched the big one, and the extra spacer gives more room to the chain.
The new crank is a perfect fit. After swapping the small and big chainrings, the 50 tooth ring is exactly in the same place as the original 50 tooth ring, and no adjustment of the chainline was necessary. Since I use the small chainring only occasionally, I wanted to keep the best alignment for the large chainring.
I expected that the front fender stays would need some bending to allow folding, but for the compact Stronglight crankset, no bending was needed.
With the small chainwheel, the chain has lower tension. Sometimes, when I pedaled backward, the chain came off. This is solved by increasing the tension of the chain tensioner. For this, you carefully loosen the central screw until you can wind up the spring by one full turn by rotating the tensioner arm over the molding, and then retightening the screw.
Since I want to kick the chain up with my heel, I installed a big washer to avoid the chain from "over-climbing", using a a Zefal GIZMO UNIVERSAL clamp. Works OK. Without a lot of practice, the chain is dropped 5 or 10 % of the times I shift up. The washer could be replaced with a bigger plate (see below).
Foot derailleur Back to top
For switching between the two front chainrings, I added a “foot derailleur”.
I will use the smaller chainring only infrequently (when I go on a tour in the mountains) and therefore prefer the lighter and more minmal solution without extra cable and shifter for a regular front derailleur. I regard my solution as in between the "greasy finger" and the "front derailleur" solutions.
Shifting the chain up works better after increasing the tension of the chain (see above).
Exchanging the chainwheels made it easier to design the foot derailleur, since you need some guide to prevent the chain from climbing past the largest chainwheel.
The aluminium piece moving the chain was initially flexible enough, but after some use it got bent. I would say that its elastic range (before it got bent) was marginal. So I decided to replace it by stainless steel which is more “springy”. I found an ideal part: a 6” metal ruler, about 1 mm thick. It even has the mounting hole in the right place, I just cut it off by an inch and slightly bent it for the right distance to the chain. Works much better!
Disc brakes Back to top
I bought the Kinetics Alfine 11 Brompton without disc brakes, but then decided to add them since I want to take the bike to the mountains. I decided to leave both Brompton caliper brakes. So I have now three brakes --- this will give me extra peace of mind on long descents.
PS: I am very happy with the performance of the TRP Spyre disc brakes.
Carrying Bags for the Brompton Back to top
The IKEA Dimpa bag is very inexpensive and fits the Brompton perfectly. It is light and thin. When it is rolled up, it fits into a bottle cage or a bike shirt pocket. I use it when I travel and want to keep the Brompton in a hotel room.
Bike Travel Carry Bag
The DIMPA bag is light and thin, and has to be handled carefully to make it last. Also, it has only carrying handles and no shoulder strap. That’s why I use a more sturdy bag when the extra weight does not matter, e;g. when I transport the Brompton in a car and want to protect the bike and the car.
There are many inexpensive big carrying bags for folding bikes, but most of them are “one size fits all” for bikes from 14 to 20 inches. This means they are too large for the Brompton. Special “Brompton Carrying Bags” tend to be much more expensive, e.g. Radical Design Brompton Transport Bag from Perennial Cycle ($ 100), BW bag ($ 60-70, bikebag.com), Carradice bag ($ 100, Perennial Cycle).
I found a reasonable bag for $ 20. It comes in a 14 inch version and is sturdy:
However, the shoulder strap is too weak, and also the D ring attachment. I replaced both. The D ring was replaced by an M5 Delta Quick Link, https://amazon.com/gp/product/B07QDD96DX/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1
Here is a comparison between this bag and the DIMPA bag, when rolled up:
Packing the Brompton Back to top
Using the retail cardboard box:
For air travel, many people use a soft bag and reinforce it with cardboard or a plastic frame. My solution is to use the original Brompton box and put it into a large backpack. Very light, very sturdy, very inexpensive! I also want to share how I can very quickly pack the Brompton into the box.
Since some people have reported bent Eazy Wheels, I glued three pieces of wood to the bottom of the box which supports the bike at the seatpost, the front tire and between the rear Eazy Wheels. I also reinforce the box with some extra pieces of cardboard and plastic sheet (the plastic sheets protect the box from being pierced by the axle or the brake levers).
Preparation of the bike: protect protruding axle nuts.
Update: I now use plastic caps (wheel nut covers) for protection. They stay on the bike all the time.
Put velcro straps on two brake lever (to reduce the width of the folded bike).
I don’t remove the hinge clamps, but screw them in all the way. This protects them from being bent. For the stem hinge, I want the lever to be parallel to the clamp for secure packing. Since the lever didn’t stop in this position, I put a piece of thin plastic or metal (of just the right thickness) between the clamp and the frame.
Add PVC crush protector (from Bike Friday).
Put bike into the box, add saddle, helmet and water bottle (in cloth bags), add foam and cardboard on the top.
In the end, I was lucky: My bike is still fits into the Brompton cardboard box, but there is no room left. Note that I have a wider rear triangle (wider by 20 mm, for the Alfine 11 hub) and the bullhorn handlebar with the Andros stem. It needs the full 12” width of the box and would not fit into a smaller suitcase.
Carrying the Brompton cardboard box Back to top
I found two solutions how to carry the box:
Put the bike it into a backpack. I use the one from www.radel-max.de(40 Euro). possibly the Dahon backpack will also work (USD 169). You have to check that the bag is high enough (the Brompton box is 25 inch (63.5 cm) high). My backpack was too large. I used a few laces to make it tighter, and also added some cinch straps. With the backpack, you could put the empty box into the backpack, bike to the airport, and then pack the bike.
My second solution was based on a lucky find: I found a bicycle carrying bag which has the perfect size for the Brompton cardboard box:
Here with the Brompton box inside:
(Ideally, the bag should be 1 or 2 cm higher, and 1 or 2 cm narrower, and the handles could be a little big longer – but as you can see, the fit is almost perfect)
The bag looks quite sturdy. However, the shoulder strap is too weak, and also the D ring attachment. I replaced both. The D ring was replaced by an M5 Delta Quick Link, https://amazon.com/gp/product/B07QDD96DX/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1
To turn it into a rolling “suitcase”, I added 4 one-inch casters:
They were attached to the bag with a piece of plywood put inside at the bottom of the bag.
The cardboard box with the bag and the casters are equivalent to an expensive rolling hardshell suitaces, and they cost less than $ 40. This has even additional advantages (such as lower weight, easy ways for repair, or replacement of the cardboard box). Let’s see how it holds up in the longer run!