Bicycle Mechanics - False cycle computer readings

Yesterday I started getting false readings on my computer. Cadence went through the roof and speed was jumping around. The mileage was also off by about 30%.

The other time that it happened was (I think) due to the rain. I brought the computer indoors to dry and the next day it was working fine. This time it was not raining but it was damp and there was a lot of water on the road that the tires splashed up. I did not see any water on the computer itself.

I’m thinking that perhaps moisture gets between the contacts and shorts them. I’m contemplating coating the contacts with automotive silicon gel.

What do you think of the gel idea?
Has anyone had a problem similar to this?

I had this problem a couple of weeks ago when we got our first decent rain for two years. I'll be interested in hearing the solutions to it.

Originally posted by MikeR

Has anyone had a problem similar to this?

I have a Shimano FlightDeck and sometimes on really cold or wet mornings, the gear display will jump around a bit between the 17 and 19. This has the effect of screwing up my cadence readings as the FlightDeck doesn't have a seperate cadence sensor but uses the rotational speed in combination of knowing which gears you're in (from shifter position) to back calculate cadence (assuming you're keeping up at the pedals). This is most likely due to the moisture or possibly contact shrinkage (I'm not sure how close the contacts are in there) in the shifter/computer interface. It usually goes away as the morning mist burns off.

Another thing you might consider is the route you're taking. Do you pass by a lot of sensored traffic lights? I've had times where the magnetic loop detectors in the road will cause erroneous readings due to the EM pulses they emit. This seems to happen more on my wireless mount than my wired mount.

I used to have problems with my old computer that occasionally it would get confused and not register a few rotations, then suddenly put them all together giving me occasional sporadic readings of 88mph and on one occasion 280mph. Not long after this it stopped working. I've since replaced it with a more reliable sigma sport 1400 which is reliable on speed but the cadence will jump about once a revolution to 30% more.

I have also had problems with the cold, one old computer i have was reading about 60mph as I came down to unlock the bike in the morning to commute.

I can understand water or EMF problems as some computers can trigger registering speed if you just run your fingers over the contacts. The gel might work if its a moisture problem, but it might also cause problems. If it fails then if you're using wireless I would suggest switching to wired, and failing that maybe just try a different computer.

I had this problem a couple of weeks ago when we got our first decent rain for two years. I'll be interested in hearing the solutions to it.
I don't own a CatEye but I was looking over their web site (trying to decide if I should replace my Echo with a CatEye). On one of the CatEye manuals it suggests the silicone gel for bad readings in wet weather. That's why I asked about this idea in the forum.

I think that I'm going to try that before I spend more money. Cris, I'll let you know how it works - since the problem only happened 2 times this year, it may take a while to determine if it is fixed.

BTW - it is not a wireless computer and I was far from any electronic interferences.

i always rubber band a plastic baggie around my computer to prevent /minimize this event

My CatEye HB100 has never given me erroneous readings due to weather. It has been accurate in pouring rain. The only odd reading I get is my Heart Rate when I am close to power lines or Automatic Sliding Doors (like at the grocery store) I either get a pulse of Zero at these times, or it jumps up rapidly.. I was doing an ascent once near power lines and my pulse jumped to 250 for about 5 minutes. I should have been dead!! But man did it calculate a lot of calories burned!

Alternate EM fields will screw up a cyclometer fast. I had a cateye Enduro2 get scorched bu microwve emmisions. I have never had problems in wet weather with Sigma Sports. I also notice that my wireless model of a un-named brand gets screwed up when it is near phones weird but true.

i always rubber band a plastic baggie around my computer to prevent /minimize this event I might try that the next time it rains, if I haven't gotten the silicone gel by then.

If I do get around to buying the silicone, I'm going to try it on a dry day and make sure it does not adversely effect the computer.

I have the Cateye wireless and got caught in a downpour and never had any problems with it. But I don't see any reason why you could not use the silicone gel to prevent problems your having. Try first spraying the contacts with WD40 because it displaces water than wipe it out before appling the gel.

Concerning the inaccurate computer on wet or damp days:

Originally posted by MikeR
I might try that the next time it rains, if I haven't gotten the silicone gel by then.

If I do get around to buying the silicone, I'm going to try it on a dry day and make sure it does not adversely effect the computer. Well I tried the silicone gel and that did not work at all. It made the computer have false readings even in dry weather.

I next tried RiPHRaPH's idea of the plastic baggie over the computer. That worked.