Originally Posted by
merlinextraligh
Incorrect. The GPS is very accurate, particularly over some distance. (i.e. immediate speed reading can fluctuate with reception, but over a number of miles its very accurate.)
The Cateye is only as accurate, as the programmed wheel circumphrence. If you really want to dial that in, you need to do a rollout, with the bike loaded with your weight, and the tires at the same pressure you are riding.
Absent such a rollout, just using the numbers off a chart will not be nearly as accurate as GPS.
I disagree.
The precision of a commercial GPS unit is not very good. You're only precise to about 10 to 15 ft at any given moment. As such, a GPS cannot tally accurately the total distance traveled unless the route is straight within these 10-15 ft intervals. For example, if you are weaving around cones all day, the GPS cannot detect that; it will only give you the linear distance between your start and end points very accurately though, but your actual sinusoidal path (i.e., distance traveled) will be considerably longer than the GPS linear path. Most of us don't weave around cones on our bike rides, but we do make many small movements that a GPS cannot detect, but can add up to a significant chunk at the end of a day.
The Cateye's precision and accuracy is all dependent on its clock (crystal oscillator) and the wheel circumference setting configured by the user. Digital clocks are very, very accurate and precise nowadays. Even cheap ones. It's actually quite hard to find one that will be off by a minute every day and most reasonable ones are off by a minute per month. Given this level of accuracy and precision, and given that the wheel circumference is programmed correctly, one shouldn't see more than a 1% error rate in the Cateye's readings. In fact, I would expect that the limiting factor will be the measurement of the wheel circumference, which measured to the nearest centimeter for a 700C wheel, should give an error of no more than 0.3%.
I don't know if further accuracy is required for my purposes.
Originally Posted by
dennisa
considering the cateye uses a 4-bit (2^4 =16) microcontroller I'm surprised it's even that accurate.
So in theory over a mile you can only resolve 330ft increments (5280/16) , which is +/- 6.25% error. This also assumes there is no errors associated with the rims and tires.
The Garmin claims an accuracy of +/- 1%
What does a 4-bit resolution got to do with the Cateye's accuracy?