Page last changed August 9, 2002

Bicycle computers, mirrors...

• Quick repairs on the roadside - Mini pump

Bicycle computers on a Brompton

• Nico J. de Boer, Nov 1998:
  I use a Cat Eye type "velo 2", on which I could enter the 130cm (...inches?) of the tyre circumference. BUT: I had to solder a new piece of cable between the computer and the sensor. I've strapped it to the set of cables that's running from the handlebars to the rear triangle anyway, and mounted the sensor on the horizontal part of the rear triangle, inside when folded. It has been running without problem for 1458.0 kilometers since then. Be careful to mount it "tilting forward" on the handlebars, because if you don't, the button to change functions on the computer (used for zeroing your trip total) will be the most outside point of the folded package, causing the computer to zero at unwanted times (eg. between chairs in trains). I hope you don't consider this "jerrymandering"? Apart from the soldering, mounting was no problem at all.
• Richard Lighton, Nov 1998:
  I fitted an Avocet 15 to Arnold with only the minor problem of having to change the position of the detector attached to the fork because the first attempt interfered with the folding. It was just another of those things that led me to curse, then admire the ingenuity of the folding design. The battery powered light has so far defeated me. That has to come off before folding. (Another 10 seconds)
• Peter Holden, Nov 1998:
  I have an Avocet 15. Works great. No problem. Just took time and care to route the cable off the front tire, giving care where it bends. The 16" wheel: well, I've got mine set for 1285 (for miles); but you can set yours simply bymeasuring the rolling circumference--roll the wheel a few times with a load on it, then divide inches into miles or whatever the calculation is. (its late, can't think) there are instructions in the packet. the Avocet 15 is simple and gives me distance and speed on the same screen (not all do)
• Bob Goldstein, Jan 2000:
  I have mounted the Cateye Enduro 2 such that the folding and neatness of cables is just fine on my Bromptons (mine and my wife's). Can't say that it's the best computer, because it's the only one I've ever had and it has a maddening user interface. But that may be true of all of them. It does time of day, speed, distance, average speed over a trip, whether you're going over or under your average speed, etc etc etc.
  I had to replace one signal sending cable because I bent it too sharply and tightened the plastic tie-down too much.

Bicycle computer technology

• Stein Somers, Jul 1999:
  Yes, there the (linear, not angular) velocity of the magnet is smallest, so the sensor has more time to notice it passing by. The sensor is not a coil measuring a magnetic pulse. At least the sensors I've openened were Reed relays, small vaccum glass containers containing two tiny metal plates that attract eachother while in the magnet's field, thus establishing an electric contact monitored by the main unit.
• John Blackburn, Jul 1999:
  Reed relays can suffer from "contact bounce", which may lead to a double pulse, giving twice the correct reading. But this is rare and could only happen if the magnet is weak, or too far away, or the various fixing screws haven't been tightened up properly.
  A cycle computer is usually a 4-bit microcontroller with built-in LCD (liquid crystal display) driver, running from 3 volts (2 watch cells or 1 lithium) or 1.5 volts (1 cell, with voltage doulber for the LCD).
  One of its input pins is connected to the supply rail (eg +3 volts line) via a high resistor (typically 3.3 megohms). The reed relay is connected from this input pin to ground; when the relay closes the voltage on the pin falls from +3 volts to zero. This change is detected, "debounced" (rejecting multiple contact closures), and used by the built-in software to calculate speed etc.
  A reed relay is used because it removes the need for an on-off switch. The computer is always running (using a tiny current), and thus can always detect if the reed contact closes, but the LCD is switched off after a few minutes of inactivity to conserve the battery.
  If you leave the bike in such a position that the reed-relay is next to the magnet, there is an extra battery drain because a small current flows through the 3.3 megohm resistor.
  Example (measurement made by me, on a real cycle computer using a Lithium battery): Bike parked with reed-relay not near magnet: battery life estimated as 5 years. Bike parked with reed-relay next to magnet: battery life estimated as 3 years.
  In other words, it isn't very important, on this particular computer at least.
• Frank Abbing, Jul 1999:
  I once installed a magnet without my glasses on, that is at a 90 degree angle from what it should be. This gave me a very stable double reading....

Wireless bicycle computer on a Brompton

• Leonard Rubin, Aug 97:
  I have had good luck with the Sigma Sport BC 700. There are others as well, and often, although the literature (table or chart) that comes with a unit may only show figures down to 20", you find that you can, in fact, type in a smaller rollout number yourself.
• Norman Tulloch, Aug 1997:
  The Cateye Cordless 2 works fine, though the transmitter unit isn't altogether an ideal fit onto the Brompton's small front fork and I did have some initial difficulty with getting it properly mounted.
  • Willi Mindak, Oct 97:
    [Cateye Cordless 2] does not work properly on the Brompton. In the instructions that came with the unit a max. distance of 45 cm between sensor and main unit is given. Because of the Brompton's small wheels and long stem the closest you can get is about 55 to 60 cm (with the main unit mounted on the handlebar). For the cateye this distance is too long, and at best it works intermittently.
    If the main unit is held a couple of inches closer to the transmitter, everything works fine, but I feel that the only sensible location for the main unit is on the handlebar in direct view of the rider.
  • Norman Tulloch, Oct 1997:
    Initially, I fitted the sensor unit on the front fork where its shape seemed to fit the curve of the front fork best - that is, below the mudguard stay. The computer didn't work consistently and gave unreliable readings.
    However, I then tried fitting it above the mudguard stay and (somewhat to my surprise) it worked just fine and has continued to do so. The sensor isn't the neatest fit in the world onto the front fork in this position, and I used some black insulating tape (which doesn't look too horrible on my black Brompton) to make it more secure. Though I wasn't too confident about this arrangement, it has given me no problems over 425 miles, including quite a few rough roads.
    I should perhaps also have said that I have the computer itself mounted on the lowest part of the handlebars, beside where they clamp onto the stem
    [...] on the Brompton the distance between front fork and the lowest part of the handlebars is much greater than on conventional bikes. The Cateye instruction manual states, "The distance between the sensor and the main unit must be kept within 45cm." However, on the Brompton the best I can manage is about 55cms.
  • Nov 1997:
    [..] curiously enough it is now giving inconsistent readings or none at all. I tried replacing the batteries but this made no difference.
    I strongly suspect that the problem is caused by the colder weather which has now arrived. Temperatures here in south-west Scotland are now around 45 degrees Fahrenheit during the day and it may be that this sort of temperature is low enough to prevent the lithium batteries from working at full efficiency. Since it is not possible to obtain ideal positions for mounting computer and transmitter units on the Brompton (because of the distance between the front fork and handlebars), I guess that the units need to be working at their best, and it may be that in winter temperatures this does not occur.
    I have tried removing the computer from its mounting bracket on the handlebars and holding it a few inches closer to the transmitter unit on the front fork. This seemed to cure the problem. I think I shall have to adopt Channell Wasson's solution of mounting the computer on the Brompton's frame instead of on the handlebars -- at least until the warmer weather returns!
    • John Blackburn, Nov 1997:
      LITH.LST 11 November 1997

      Lithium cells operate over a wide temperature range. Data sheets from the main manufacturers (Sanyo, Saft, Varta and others) show that even at -20 °C, cells still have more than 60% of their room-temperature capacity. Cell voltage is nominally 3 volts per cell, falling to 2.5 volts below -20 °C. Capacity loss is as low as 1% per year in most cells. At low temperatures, it is even better.

      The very high cell voltage (at least 3 volts, and 3.6 volts in some types) means that only one cell is needed in order to construct a calculator (or bicycle computer) with LCD display. If a cycle computer contains 2 cells, they are more likely to be silver-oxide cells, as used in watches.

      I doubt if any cell or battery has a poor performance at 45 °F as claimed.
    [...] The attraction of the wireless computer, as far as I was concerned, was that I felt the wire of a wired one might get in the way when the bike was being folded, or that it would become snagged or broken. The wireless computer also looks just a bit neater, too. However, it may well be that the wireless computer is more bother than it's worth.
  • Willi Mindak, Oct 97:
    I've tried to mount the sensor unit as close to the main unit as possible, that is above the mudguard stay on the right forkleg, and I also tried the left forkleg (with the unit 'reversed' (in front of the fork. The receiver was mounted as low as possible, next to the habdlebar clamp. I got it working 'in the lab', but when out on the road I noticed that the little blinking indicator was not pulsing at the same frequency when at constant speed, so this arrangement did not work very well.
    If it works for you I'm going to try a new battery on the sensor (even though the unit is brand new the battery may have suffered from long storage.
• Norman Tulloch, Aug 1997:
  [...] The Sigma range (which has an optional wireless transmitter unit) also works on 16" wheels. However, cable ties are used for mounting both the computer (to the handlebars) and the transmitter (to the front fork). I feel this is a fairly crude method of fixing which makes it difficult to get the units securely attached. The Sigma also looks a bit cheap, whereas the Cateye is generally of better quality.
• David Cox, Nov 1997:
  Sigma wireless computers work up to 70cms.
• Frank Abbing, Jun 1998:
  ... the [Sigma 300 cycle computer's] cable IS long enough. I installed the pickup device on the left leg of the front fork, taped the cable to the front lamp cable up to the point where it does a V-turn. From there I taped the computer cable to the rear brake cable. I could pass the cable through the factory installed cable guides by disassembling the slider contacts (undo two extremely small screws). After the installation there is almost no slack cable left, the bike folds and unfolds as it used to do. The Sigma 300 is rather simple, with large figures. Good, because it is farther away than usual, on the lower part of the handlebar. The computer protrudes about a centimeter from the folded bike. Because it is mounted by a simple rubber ring it just moves to a safe position if you hit something when carrying the bike.
• Willi Mindak, May 99:
  I returned three different computers, until I happened to stumble across the Sigma. The range of the Sigma's wireless unit is about 90 cm, so you can fit it almost anywhere on the handlebar. You can use any computer from the Sigma range, because they sell the transmitter/ receiver for wireless operating seperately. You can use the normal 'wired' sensor on your second bike.
• David Cox, May 1999:
  I've used wired computers on my Brompton with no particular problems although I am now on my 3rd. Ist was old when fitted but second one only lasted about 2 years.
  On a Bike Friday I have a wireless Sigma which is fine except when I pass the big BBC Transmitter at Wychbold near Bromsgrove in Worcestershire (Archer country for those who follow that radio soap !) The effect was to momentarily halve the indicated speed and then cut out the reading. I did some fiddling with the connections and magnet to no avail then less than a mile later it reverted back to normal.
• Mike Hessey, May 1999:
  Computers in general are discussed on the Bike Friday User Group UK web page and Birdy page, accessible from the Folding Society web pages at http://www.whooper.demon.co.uk/foldsoc
  I found the Sigma the only wireless one which I tried that was satisfactory with small wheelers. Problem is that I have to take it off when boarding local electric trains, as it starts reading vast distances while the bike is on the train.
• Channell Wasson, Jul 1999:
  I use a cordless Cateye with sender mounted on right side near fork crown and receiving/dispay unit mounted on main frame just behind main frame hinge. Seems to work flawlessly. Receiver mounted on handlebar was giving intermittant readings, especially over 18mph.
• Bob Gelman, Jul 1999:
  I've been using a Wireless Heart Rate Monitor on rides for a while now. I note quite a bit of interference from electric wires strung on poles. I've heard lots of stories of electrical interference of various sorts regarding speedometers too. I think this may be the main consideration.
• Marv Gozum, Jul 1999:
  After playing with [a TREK Wireless cycling Computer] for almost 5 hours, I got the same thing interference issues. Its not highly reliable, the cheapo reed switch versions are better, despite wire routing.

Wireless bicycle computer installation

• Norman Tulloch, Aug 1997:
  Don't ask me about the physics of the matter, but in my experience a loaded front pannier makes no difference to a wireless computer.
• Leonard Rubin, Aug 97:
  If the elements used infared transmission to communicate (they don't) then line-of-sight would be crucial; as I infer that they use RF (radio frequency) communications, the only issue would be signal strength, which must be, admittedly, very weak, given the minute size, batteries and price! Ergo, I can offer an educated guess (as I no longer (very temporarily) have a Brompton to experiment with).
  My guess is that it should still work under most imaginable circumstances, as most of the mass of the bag/cargo is in front of the line-of-sight, where the signal would be most reliable. I believe I recall using both bag & computer on a few trips and having it work fine, but I may be inventing again! ;-)
• Channell Wasson, Oct 1997:
  Yes the handlebars are too far away for the wireless speedometers to bick up a signal from the transmitter on the front fork. I have tried several diferent speedos and found this always to be the case. My solution has been to mount the speedometer on the main frame just behind the folding hinge. The unit I like best is the Cat-Eye. I modified the mounting bracket and made two holes to accept a plastic zip tie to attach the speedo mounting clip to the frame. Problem of transmission thus eliminated.

Bottle cage

• Graham Patterson:
  Try the 4 or 5 o'clock position (looking down from the riding position). That's where I have my Blackburn mini-pump.
• Steven M. Scharf, Apr 1998:
  I found that the Ibis Hot Unit bracket mounts nicely on the handlebar and doesn't get in the way of folding (when you remove the bottle).
  The Hot Unit is a 'silver bullet' stainless steel vacuum bottle with a die cut steel bracket that holds the vacuum bottle (or a standard water bottle) into place with a bungee like cord.
  I attached it with 5 cable ties, but as it has holes for a water bottle mounting holes, I'm wondering about the wisdom of drilling and tapping two holes in the post.
  http://www.ibisbicycles.com (though the link wasn't working this morning).
  • Doug Faunt, Apr 1998:
    Unfortunately, Steve's setup would conflict with the front pannier while steering, if you have one mounted.
• Tom Vogt, Apr 1998:
  A company called Twofish Unlimited in Berkeley California manufactures a strap-on cage (http://www.lickbike.com/i3251050.htm) that works very nicely! A soft rubber block and velco straps keep it securely in place (US$8.95). I attached it to the top of the frame tube and it does not impede folding.
• Velovot, Feb 2000:
  I found a Twofish Technology in Alameda, California (39 Ross Road). You can reach them at 510-865-2330. I'm not sure it's the same company.
• Bob Gelman, Feb 2000:
  Both coloradocyclist.com and bikenashbar.com sell them mailorder ($12), which includes a bottle. I've got mine on the front of my steering post on my Birdy, facing forward, where it doesn't interfere with folding and is easy to reach. I have seen them on the top tube (horizontal) on Bromptons and am told they don't leak in that position. They really go just about anywhere (the velcro fastener is very strong). A cheaper solution (at least for the Birdy) is an automotive "hose clamp" on the steering post to hold a conventional cage.
• Jim McLaughlin, Feb 2000:
  Mine is on the handle bar stem closest to me. Folds without removal. I left it on when I converted to recumbent too. I put the adhesive backed sandpaper that Two Fish supplies on the stem under the rubber cage mount and it does reduce movement. But I placed it so that the stud that clips the stem to the fork when folded also prevents the bottle cage from sliding down.
• David Cox, Apr 1998:
  I usually keep a water bottle in the neat little bag that came with the Brompton soft bag. For longer rides in Italy I fitted a bottle carrier behind the saddle (Selle Turbo saddle and carrier from St Johns Street Cycles in Bridgewater Somerset UK) They do a single and double carrier in high quality plastic which fits the rails with allen key fixing. Chris Boardman uses something similar for time trials for aerodynamic reasons ! Doesnt affect casual folding but sticks out.

Horns

• David Cox, Dec 1997:
  I've seen people use aerosol powered airhorns fitted in bottle cages. They are from chandlers shops and used for fog warning in small boats. Behind the saddle would fit.
  I use a bell for pedestrians and a very loud Oi for anything else. If you've got time to press/squeeze something its not a real emergency
• Custfold, Dec 1997:
  A marine fog horn - operated by compressed gas, is similar in volume & note to that used on large trucks (around lower A or B flat). I believe a version with pump up reservoir is available.
  Alternatively get a Xenon light (Vistalite) with a clear lens and touch fire switch for that critical 2 flash burst - Guaranteed to make a motorist slow right down to at least the legal speed limit.
  Further alternative is to use a sounder unit which produces a distinctive 2-tone sequence - which our legal eagles can let us know whether its use on a BIKE is in same classification as its use on a car (which is illegal). A drivers hearing is improved by this even at low volumes, just as their sight is improved drastically by introduction of a bright daglo stripe on your vehicle - especially if you fit a white fairing :-))
• Bob Gelman, Nov 1999:
  Thirty-five years ago, give or take, I used an aerosol boat horn to take a somewhat aggressive stand in the jolly streets of New York City. This was a thing that looked like a shaving cream aerosol can (same size too) with a horn on top (you replaced the canister when it was empty). Quite effective for dogs, trucks, cabbies, etc. It fit in a bottle cage. It was probably louder than the Zounds.
  I frequently found that getting off the bike and putting it between you and the dog was effective (you kind of move the bike around as if you had a cape and were a Matador).
  My most interesting animal confrontation was in the Canadian Rockies, near Jasper, on the fantastic Banff-Jasper run; it was with a bear. I removed a sandwich from my handlebar bag and threw it some distance opposite to where I intended to head. When the bear "attacked" the sandwich I hauled tail pronto!
• Derek. J Baker, Jun 2000:
  I am using a simple cheap (under £5 u.k. pounds) personal attack alarm as a bike alarm on my brompton. the alarm is black and about the size of a cigarette packet with laynyard and pin. since it is intended for it to be worn on the body it comes complete with belt clip. with the brompton in the parking mode that is with the rear wheel tucked under it is quite simple and quick to attach the lanyard to the wheel and the alarm below the saddle. try moving the bike by lefting the saddle and out comes the pin followed by quite an ear shattering alarm. all this for under a fiver. anyone out there thinking of alarming their bike should try this device.

Air Zound 2

• Zach Kaplan, Dec 1997:
  How about an Air Zound 2 pneumatic horn. These are about as loud as a car horn, have a volume control, are lightweight, and the plastic bottle is easily recharged with a bicycle pump.
• Leonard Rubin, Dec 97:
  I've found just the item: Air Zound 2 by Samui Corp. in Canada (tel: 1-416-425-2583). It is ridiculously loud, absurdly light, and very cleverly designed! It can be installed/removed in a few seconds, uses a "pressure vessel" (common soda bottle) that can be quickly and easily recharged with any bike pump capable of 100psi (frequency of recharge depends, of course, on usage). It even has a volume adjustment knob, for when you merely want to politely signal a pedestrian of your approach, (as oposed to causing them a heart attack!)
• Mark West, Dec 1997:
  I remember when I was a lad, about 30 years ago, we had a craze for collecting bike bells, horns etc. I expect it was something to do with our big brothers all having fancy mirror encrusted motor scooters. Anyway, I recall a friend of mine, wealthier than I, bought and fitted a starters' AIR HORN into a bar mounted bottle cage. It was LETHAL, Even better, it was DIRECTIONAL and just about at car window height. I well remember him sounding off at left turning road hogs and making them swerve across the road. Trouble was they were all self righteous "responsible" motorists entitled by divine right to drive over schoolboys in the nearside lane and would usually stop to tell us off for our reckless behaviour (trying to save our own lives was considered reckless in the extreme) Eventually one of our own teachers confiscated it following a complaint from the old biddy next to the school who would regularly drive out into the flow of children without pausing to look.
  Point is it worked. The trouble we got into was because it worked. They couldn't ignore us so they persecuted us so beware of reprisals if you try it.
• Tom Vogt, Dec 1997:
  Ah, now here's a suggestion for a LOUD horn. AirZound 2 is a rechargable air horn. It has a variable volume and, at its loudest, can be heard within any vehicle. I'm not sure how it will be distributed in the U.K. Drop an e-mail to Andrew at BICYCLENUT@AOL.COM. He should be able to direct you to the right place. I've been using an AirZound 2 for a few months and LOVE it!
• Jfreewheel, Dec 1997:
  Try the airzound 2. Its an airhorn system. You pump compressed air in a water bottle sized plastic canister using your pump. Good for about 50 blasts. Will wake up your soul when you here it. Volume is adjustable too. I use one for commuting and you sound bigger than actually is.
  I think we still have a picture under the Closeouts section of the site.

  J Gaerlan - Gaerlan Custom Cycles "framebuilding supplies for the homebuilder" (415)362-3866: (415)677-8943 fax JFreewheel@aol.com http://members.aol.com/Buildhpv/bike.html

• Stein Somers, Aug 2000:
  The air vessel of my AirZound 2 is fixed on top of the main tube, in front of the saddle when folded, so not in the way. The horn is obviously on the handlebars and doesn't project from the folded package, although the air switch does form a local peak. This results in the slight problem of blasting awake other passengers when the air switch touches its environment in unforeseen ways.
  They are definitely loud and keeap pressure like tires do. I'm not too happy with the air switch, it's not optimized to be blown in an emergency situation, but I managed to fit it so that I can fire away while applying the brakes. More precisely, the plastic gizmo that you fix to the handlebars, where the AirZound clicks into, broke, together with the volume control. So I hooked the AirZound directly around the end of the bracing bar and tied it up with a few loop of metal wire. The volume is hard to adjust, so it's always at its hardest. I've only used in a few times; on one occasion the offending motorists didn't seem to notice. Its main use is to make the rider feel confident and to impress the crowd gathered around the folder.
  
• Velovot, Oct 1998:
  Gotta put my nose in on this one....
  YES! THE AIR ZOUND WORKS LIKE THIS TEXT READS--LOUD!!
  The beauty is that by using the control valve one can dial in an almost pleasant toot. But, if you need to be heard this thing can damage ear drums. People think it's a truck. I think I've induced two or three heart attacks in the S.F. Bay Area.
• a2bmagazine, Oct 98:
  They are very good indeed. We fitted one to a Brompton - just - without impeding folding, but I think we'll transfer the whole outfit to a front pannier.
• Bob Gelman, Oct 1998:
  "Freon" Boat horns are louder than AirZounds. They look like a shaving cream can with a horn on top. Fit right in water bottle cage. I used one in manhattan in the 50s. You don't use it very often. Has the added advantage that you can take it out of holder and stick it right in the window of the offending car that has almost killed you. More effective than kicking doors or hoods (bonnets). Still, any of these activities may, these days of road rage, lead to bicyclecide. I personally like to just smile at offenders; totally disarming.
• Clive Page, Oct 1998:
  Picture and details on this useful bicycle web site: http://www.edinburgh-bicycle.co.uk/catalogue/detail.cfm?ID=1329
  (Disclaimer - I have not (yet) used their services.)
• PHolden960, Nov 1999:
  Mounted one a few months ago, and recently made it permeant. The horn itself is on my left-hand-side of the handlebar; the "bottle" is mounted on the frame, on the left side, behind the joint. I've just let the line run free from here to there. It is not a problem with folding; although I do have to be careful carrying, as its possible to knock into the "bottle" with my leg. ( maybe I should jsut swap out that folding pedal, then everything would be OK).

Dog deterrents

• Jim McLaughlin, Nov 1999:
  I usually carry an ultrasonic "Dazer" which will keep most dogs a good distance away if you aim it well. I've seen some dogs jump and turn 180 degrees and others ignore it. My other device is a can of serious pepper spray, not the weak stuff they sell in most bike shops in the US, although the same handle bar mount works. The spray is OK at close distances if the wind is in your favor, but be careful. I prefer the kind with an Ultra Violet dye which shows up under "black light". Dogs usually leave you alone the second time if you get it in their eyes but they are angrier, so who is to say what is best? The ultrasonic "Dazer" is better in wind and cold but rain will wreck it for weeks. If it is cold, keep the spray in a pocket to warm it or it loses pressure.
  Actually the air horn (meant for cars) works somewhat on dogs and usually alerts their Humans, at least in the country. I haven't figured out how to mount a "Zound" brand air horn on Brompton. They have trouble in the cold too unless you keep the pressure down.
  The best results I have had on regular routes is to call the animal control office, and they give me the phone number of the dogs owners after they issue a citation. Then if I still have trouble, I call the owners before I ride by the next time. Actually my female riding buddy called them on the cell phone last time and I haven't seen the dogs loose since. Hate to see a pretty girl get bitten I guess.

Mirrors

• Frank Tompson, Jan 1998:
  I recommend the Zefal bar end mirror. Just bought and fitted one. Easy to fit and folds in on itself when folding the bike. Can be purchased from (larger?) Halfords in UK.
• Stein Somers, Feb 1998:
  Better late than never: I also bought one, mainly - I admit - because it was so cheap. I soon realised it was cheap because it was a right side model, less usefull on the continent. Turned out left side wouldn't have been usefull either because it would scrape the ground on a folded B.
• Daniel Meyerowitz, Nov 1998:
  Having tried several, I found the best mirror for the Brompton to be the Rhode Gear Multi Mirror (made by the ubiquitous Bell Sports). It has two hinge points, so it can fold completely out of the way when the bike is collapsed (it tucks between the two bicycle wheels when the Brompton is folded). It is much more durable than other folding mirrors, and has a larger, oval-shaped viewing area. It's a natural, flat glass mirror and doesn't distort the objects reflected in it. The mirror is vibration resistent, adjustable to almost any viewing angle, and reasonably lightweight. I've had absolutely no trouble with mine after a year of daily riding, touring, taking the Brompton on planes and trains, etc.
  Cycling in the States, where a mirror is placed on the left side of the handlebars, I made one small adjustment to my mirror. The mirror plugs into the left end of the handlebar, and is tightened in place with a bar-end knob. That knob can scrape against the ground when the bike is folded, so it's best just to remove it altogether and replace it with a 5mm nut. The bolt that the nut threads onto can be replaced with a shorter one, or the original can be sawed off to a shorter length. In either case, this is all accomplished in a few minutes.
  Once the mirror is attached, the tightening knob is unneccessary, since the mirror stays on the handlebars all the time. And if for some reason you need to remove the mirror, you simply unscrew the 5 mm nut.
  I think a mirror (360 vision, anticipating approaching vehicles, seeing a dog bounding towards you) is as essential to safe riding as a helmet. In my experience, the Multi Mirror is an elegant, inexpensive, and practical solution for the Brompton.

The Brompton Folding Bicycle FAQ