If you want a cyclometer on your folding bike, you are likely to be constrained by the funny geometry of small-wheeled folding bikes, in that the maximum working distance between the sensor and the computer module is likely to be exceeded due to the small wheels and correspondingly longer distance to the handlebars, where the computer module is usually mounted. Going with a wired cyclometer presents its own difficulties, in that the stem is designed to fold, which means that the wire going up to the computer, on the handlebars, from the sensor on the fork, will similarly be subjected to constant folding and unfolding, which can't be good for those wires.
I found an obvious potential solution to this sensor-computer distance problem and thought some might find it useful. Warning! This will not change your life! Same dog who pees in the house, and same annoying spouse Or did I get that backwards?
The "test" bike in this case is a Dahon Curve D3, and the test wireless cyclometer is the ultracheap Chinese SunDING SD-548C model widely available on ebay from Chinese and US-based sellers. I bought two of them for $19 including the shipping from a US based seller; you can buy this item from a Chinese-based seller for less than $6 each including shipping. I am not recommending this particular item, have no idea how long it will last, and dislike the fact that the sensor uses an expensive (in the USA) 12v battery, whose longevity is uncertain. I am just using it as a test case.
I first tried to mount it with the computer module on the handlebars, in several different locations, and the instruction manual was correct in stating that the maximum distance had been exceeded between the sensor and the computer. I then "dry-labbed" a couple of potential locations and the one that worked out the best in terms of readability and ease of installation was to remove the front reflector on the bike and use its mounting hardware to hold the computer module. In this particular case I partially disassembled the computer mounting bracket, removing the piece that is intended to form fit around a round-shaped handlebar, then used a sheet metal screw and nut to secure it to the reflector mounting hardware. I'm sure there are very many other possible ways to mount the computer module to the reflector mount depending on which bike and wireless computer you have. The reflector mount hardware, at least on the test bike, can be angled in various directions and given reasonably good corrected vision, the display, at least for the speed and odometer functions, is quite legible. Granted, you will need to steal glimpses of the computer display, because what you should be doing most of the time is looking where you are going as the bike is rolling . . . . . I did find this to be a very usable "poor mans" system, if you have to have a cyclometer on a folder where the distances for a wireless cyclometer are exceeded by mounting the computer module on the handlebars.
Other potential "solutions" for this situation include such things as buying a handlebar mounted GPS system, such as what normally would be called a "handheld" GPS like a Garmin Dakota or any number of other models. I do have such a GPS system and intend to use it in addition on some folding bikes.
Please don't tell me that your municipality would deem removal of the front reflector as a violation of their nanny-state laws. I am sure that there are many places like that around the world. I do not ride at night generally, and to the extent that I will ever do so, I'll use a temporarily mounted set of LED front and back lights, which I think would be much more likely to protect the bike rider than would a simple reflector.