Never had any interference issues with my Shimano wireless setup with the exception of the L&M ARC light. Has anyone had any luck with shielding?

I prefer wireless for easier install.

It's very simple, like a wired speedo, you have a magnet, and a reed switch, the magnet trips the switch, sending a pulse. Inside the switch unit is a very small, extremely low power radio transmitter, so low in fact that from more then about 2m away, you would not be able to pick up the signal. Inside the speedo unit is a radio receiver tuned to the same frequency. Now each time the switch gives a pulse, the transmitter sends a signal, that the receiver gets, it gives a pulse to the speedo. Each pulse means you have covered the distance of one wheel rotation, from that it can track distance, given that speed is a relationship of distance over time, it can figure that out as well.

Like any other radio receiver the speedo is subject to radio frequency interference, RFI for short, there are thousands of electrical and electronic devices that generate RFI, including the speedo's internal computer. Now different speedos can be affected different ways, for example one may use amplitude modulation, where another uses frequency modulation, they can use different frequencies, even the information sent, one might use a simple tick, another might send a set of tones. One may use the minimum transmitter power possible -- to save on batteries, another might use the maximum power legal, to get a nice clear signal.

Now, RFI can do two things, it can overpower the signal from the transmitter - blocking it, meaning that some pulses are missed, or it can appear as extra pulses, either way your speedo has the wrong count, so the computed distance, and speed are now inaccurate.

If you need absolute accurate results, like with a training program, stick with the wired units, if your only looking for an approximation, then look at reviews for various units, and see if they had trouble. Realistically though, these units have been around for a while, I would expect as the technology matures, that manufacturers will be trying to deal with the issue of RFI. However the cheap $10 unit, based on a 5 year old design, is more likely to have an issue, then a $100 unit, based on last years design.

One of the biggest issues is pagers, they use powerful transmitters, and may drift frequency wise, they tend to be powerful enough that the pager will still work, even though the transmitter has drifted off a good deal. Because pagers use a short burst of signal, and it may be hours between pages, it's hard for regulators to catch them at it.

i live in san jose. the conclusion i have come to is you use a crap computer....you know they even make crap computers that are wired .

ed rader

Not a brifter fan, then, are you? No indexing = No Brifters

This is not even close to correct. Wired computers have a very simple magnetically actuated reed switch in the sensor. Every time the magnet passes the sensor, the switch is closed for that moment. There is no "pulse". It's a very straightforward open or closed circuit. It's a digital circuit in the very simplest form - on, or off. The computer simply measures the period between the "on" states (assume "on" = switch closed) and calculates the speed from the tire circumference you enter.

If you ever suspect your wired sensor, or the 2 conductor cable (i.e, the "wire"), is bad then all you need do is pass the magnet by the sensor while monitoring the two cable conductor ends (which normally terminate at two contact pads on the computer head mounting bracket) with an ohmmeter. The circuit will show "open" or "closed" as you pass the magnet by the sensor (remember, it's a reed switch).

In the case of a wireless computer, you DO have a pulse generated by the sensor. A carrier wave is established between the sensor and the computer head and the carrier is modulated (ok, if it's frequency modulated then you'll get a momentary change in the frequency rather than a pulse on the carrier wave) every time the magnet passes the sensor. The sensor contains a Hall effect device that senses changes in a magnetic field. When cycling computers go screwy at traffic intersections, it's most likely that it's the Hall effect sensor - not the carrier - that's being affected. Trip sensors at intersections are, in effect, like a very big Hall effect sensor. They set up a steady magnetic field and when a large metal object is passed over it, the field sensor detects this and says "car over trip sensor" to the traffic computer.

One of the disadvantages of wireless computers is that, when riding in a tight group, your computer can get false inputs from other riders sensors that may be on the same carrier frequency as what your computer is using. One of my wireless computers will read the sensor as long as it's within 70cm, or 27.5", so it's easy to see why you could get a false input from someone on your shoulder. This is precisely why you see a lot of pros riding with wired units. All that being said, the algorithms in the head units are averaging the inputs out so, over time, they are still very accurate even if they do get the occasional false input. If you're doing a lot of group riding and having computer problems, then a wired computer probably makes sense.

What's the best brand for Cyclometers? I'm overwhelmed with the selection.

Oh snap, only took one post for you to turn into an ass.

This is a bit like a thief complaining that someone stole from him-

I would recommend a wireless speedo. It's those wired bathing suits that can be dangerous when swimming, especially if batteries exceed 9 volts.

i had a wireless.....too much interference...no way i max out at 72 mph! hahaha
i switched to a wired cat eye.