Note:

Whether a bike computer is accurate or not has nothing to do with whether it is wired or wireless. Each tire & wheel combination is a little bit different, so no matter what kind of computer you use, you will have to adjust it if you want it to be highly accurate. Also, the weight of the rider makes a difference. Light riders depress the tires less than heavier riders and will have a slightly larger effective tire diameter. So, to get the best accuracy, you have to RIDE a course of known length and adjust you computer so that it reads identically with the known measurement.