It seems I cannot complete a ride without having my Cateye or my Garmin (or both) go crazy and compromise my max speed data. Mileage, average speed, elapsed time, all seem to be OK, but, at various times, one or the other (Cateye or Garmin Etrex CS something or other) make an erroneous max speed reading - 184 mph, 78 mph, whatever.

Once in a while, it happens to both at the same time, more often, though, each will, during the course of a ride (say 60 miles) just go haywire.

Very often, it happens on a steep decline where I am really interested to see what speed I (well, the bike) achieved. I never see this occur, since none of this is so important that I would risk an accident to observe either gizmo while in the process of descending a hill.

There seems to be no pattern in terms of where this occurs. Any thoughts welcome.

Caruso

I stopped using my E trex Legend C. The last time I used the GPS odometer, it showed my max speed at 199MPH and average of 55MPH. I don't even get 100MPH when I use it on the car. Total distance covered was only 50 miles vs Topeak computer's 66 miles and 14.7MPH. Part of the problem could be that the trail I ride run parallel with power lines and sometimes I go under the power lines. The GPS signal is possibly affected by the electro magnetic produced by the high voltage power lines. I only use the GPS for mapping now when riding to avoid busy roads when I ride and depend on data from my wired computer.

I'm convinced the more "options" a cyclocomputer contains, the greater the likelihood of peculiar behavior. I had an ancient wired CatEye that worked like a charm for more than a decade and all it did was current speed, average speed, maximum speed, ride time, mileage, and overall odometer. That was also back in the day when CatEye had intelligent methods by which to attach computers to handlebars.