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Odometer inaccuracy vs. speed(8 posts)

Odometer inaccuracy vs. speedfbg111
Feb 9, 2003 11:33 AM
I'm using a basic Cateye wired odometer and just noticed a discrepancy in its measurement. I went for a short ride this morning, straight out to a turnaround point and back. At the turnaround point my odo was 12.6 miles. I followed the exact same route back home, and the odo ended at 20.5 miles. 12.6 miles out and 7.9 miles back on the same course? Don't think so.

The only difference going out was a nice tailwind, and I averaged about 22mph on the straightaways, 20mph overall with stops. On the way back into the headwind, I averaged about 16mph.

Has anyone had problems like this before, and do you have any suggestions for resolving it? Thanks!
Feb 9, 2003 12:54 PM
Doesn't make sense. Was the speedo working the whole time? That is, check for auto start/stop, or sensor not detecting magnet all the time.

... that's my guess...Akirasho
Feb 9, 2003 1:07 PM
... no matter how hard you try to duplicate your return route... there's a degree of error... but that's excessive unless the 'pooter was not sensing the magnet (unless your eyes are glued to said 100%, you might not see it, or it might be indicated when you see large jumps in indicated speeds (going from 20 to 6 back to 20 in a second).

Check both the magnet position and the contacts on the head/mount interface as well as your wireing harness (and sensor positions on wireless units). Oxides can build up (it doesn't take much) making for sporadic contact.

Also consider changing batteries... finally, the unit could be headed for the crapper.

Good Luck.

Be the bike.
I agree...Dave Hickey
Feb 9, 2003 2:17 PM
If the magnet wasn't set up correctly, my speedo will zero out. I'd look down and I was going zero. Five seconds later I was going 20mph. I also had maximum speed spikes. I had a maximum speed of 45mph even though I never went over 30.
Feb 9, 2003 6:22 PM
I checked out the sensor and magnet, and they are aligned and snugly attached, and the magnet passes within a few millimeters of the sensor. The metal leads where the computer attaches to the mount are clean and oxidation free. It's only 6 months old, and still looks it. I've never looked down and seen 0mph on my speedometer while moving, or big jumps in speed, but of course I probably spend less than 5% of the time looking at it. This is very strange, and is only the first time I've noticed this. I guess I'll start paying closer attention on subsequent rides. With luck, it'll turn into an unsolvable problem, and therefore a great excuse to pick up a new Flightdeck wireless model. ;)
re: Odometer inaccuracy vs. speedJimP
Feb 10, 2003 9:21 AM
As Dave & others have mentioned, the sensor pickup may not be picking up all of the pulses from the magnet. The sensor is actually a magnetic reed switch. There is a voltage sent from the Cateye to the sensor. When the magnet passes, the reed switch closes for a fraction of a second and the Cateye counts the pulse. Several things can cause malfunctions with this setup: The contacts between the Cateye and the mount can have some corrosion. The sensor wire may have a short or break in it. The sensor may be too far from the magnet. The sensor may be twisted in its mount.
I have used Cateye computers for many years and have had enough problems with them that I have taken apart some of the pieces and replaced parts out of curiosity. I have noticed that some of the sensors work better when offset from the magnet - the reed switch wasn't under the little mark on the outside of the housing. Another sensor was rotated in the housing causing problems. I have noticed that the faster the wheel is spinning, the more likely the problem of missed pulse will be - the magnet is going that much faster past the switch and didn't pull the switch closed.
Even though I have had many problems with Cateye over the years, I still prefer the Astral with the cadence pickup over the other brands.

Can't believe they use reed switches...MrDan
Feb 10, 2003 10:18 AM
Don't get me wrong, I believe you, but it makes no sense this day in age to use something so ... primitive, but then again they probably have more experience than me ... seems they could use something like hall-effect or capacitive. No movement, no wear, solid-state.
Solid state wears out all the time.the other Tim
Feb 10, 2003 10:38 AM
Hall effect sensors require consant current: shorter battery life. Capacitive: how would you make that work?