can you trust cycle computers?

[gavroche]

went for a ride this afternoon and I noticed that the computer was going mad, showing silly speeds totally different from the true speed. For example, going downhill showed 8mph when actually more like 30.
So my question is: would that reflect in the actual distance covered?
I am not bothered about the speed but I do like to know how far I have travelled.
When I got back, it showed that I had covered 15 miles when in fact I am quite certain it was more like 20.
Tomorrow, I will do the same circuit again, in the car, and compare the two readings. At least the car reading will be true.
But if I am correct, what would cause the computer to go beserk? Dirt on magnet?

 

[enitharmon]

Computers have been my bread and butter for 35 years and I can assure you I wouldn't trust one further than I could spit!

 

[HLaB]

It sounds like something was interfering with it so it was only recording every 3-4 revolutions of the wheel. It won't be 100% correct on the distance, the extent to the under measurement depends upon the magnitude of the interference. I've found my cheaper raleigh echo wireless computer can get interfered with my my LED's, Car LED's or ignition systems or electrical boxes at the side of the road particularly when the batteries are near flat.

 

[david k]

mine are fine

 

[Muddyfox]

I use a Garmin Edge which seems to be extremely accurate

Simon

 

[slowmotion]

It could possibly be that the magnet is slightly too far away from the pick-up on the forks.....close enough to trip the Hall Effect sensor (or reed switch) on some revolutions, but not all. This will cause it to under-read. It's worth checking.

My two pennies.

Edit: Sorry, cross post with the post above.

 

[PedAntics]

Check the alignment of the detector. I knocked mine slightly out of alignment, taking the bike of a car rack, causing spurious readings. Also check your battery. Are you certain it was 20 miles you'd done?

 

[snorri]

If your computer display unit is demountable, it might be worth buffing up the contacts and checking the spring tension on the back of the display unit and on the handlebar mount. (but be gentle with the buffing, no sandpaper)

 

[gavroche]

You could calibrate your distance on THIS site. You could also calibrate your cars odometer from this site as cars speedometers are not all that accurate.

Is your cycle computer wireless or wired ?

Wireless ones can suffer from interference but this usually results in higher speeds and distances.

Dirt on the magnet or sensor will not make any difference but sometimes if the magnet is too far from the sensor it can miss beats and give lower readings

It is wired but never had problems before.

 

[Norm]

Check the magnet is passing the right part of the sensor. Check there are no breaks in the cable.

And don't believe that "the car reading will be true".

 

[PK99]

wireless orr wired

went for a ride this afternoon and I noticed that the computer was going mad, showing silly speeds totally different from the true speed. For example, going downhill showed 8mph when actually more like 30.
So my question is: would that reflect in the actual distance covered?
I am not bothered about the speed but I do like to know how far I have travelled.
When I got back, it showed that I had covered 15 miles when in fact I am quite certain it was more like 20.
Tomorrow, I will do the same circuit again, in the car, and compare the two readings. At least the car reading will be true.
But if I am correct, what would cause the computer to go beserk? Dirt on magnet?

wired or wireless ? - my cat eye sigma wireless did not like overhead power lines

 

[albion]

semi-deleted duplicate

"An Error Occurred
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[albion]

Considering it is wired it sounds like the magnet has moved slightly.My wired one matches up with Endomondo so I know it is currently set fine.I choose my cheap wired with cadence for the increased reliability.

 

[HLaB]

Wireless ones can suffer from interference but this usually results in higher speeds and distances.

I thought that but every time I've had interference its been the exact opposite something blocks the signal and it only picks up every 3 or 4 revolutions, I can be cycling fast down hill and the computer is only registering 3-4mph

 

[Fnaar]

The one on my roadie (wired) cuts out in heavy rain, which can be a bit annoying.