Computer accuracy

[Benthedoon]

I've just bought a Cateye Strada to replace the cheap and cheerful computer that my kids didn't like, I assume they didn't like it as one of them threw it in the bin, anyway my question to those who know is - how accurate are cycle computers? Should I take speed and distance as gospel or use the information more as a rough guide?
It's all been fitted and set up in line with relevant measurements and instruction, yes I'm a man and I read the instructions. (1st time for everything)

 

[PaulSecteur]

I used Google maps to measure half a mile on a local straight and flat road and my cateye micro was bang on. I think over 30 miles is gained a mile, so reasonable accurate.

 

[Peter91]

The only part of a bike computer where it could go inaccurate is if you enter the wrong wheel diameter.

 

[APK]

I went out this morning and both my bikehut 11 and endomondo on HTC desire came back with 17.03miles, very impressed! the only thing that differed was maximum speed, as the gps will measure horizontal speed, the bike computer the actual distance travelled which could be more depending on hills (so on that basis, the gps should read a bit less than the bike computer?

 

[soulful dog]

The only part of a bike computer where it could go inaccurate is if you enter the wrong wheel diameter.

Could the position of the sensor on the wheel have any effect on inaccuracies?

 

[screenman]

Only if it was not picking up the signal. The pickup counts how many times it goes past, it makes no difference where on the spoke it is mounted. I do know where your thinking is coming from but it does not apply here.

 

[Benthedoon]

So information displayed can be trusted, that's nice to know. At least if it says 20 miles I can believe I've done about 20 miles.
I'm loving having the info right in front of me avg. speed and distance etc. the only problem is I seem to spend more time looking at/ checking the bloody thing than concentrating on riding!!

 

[jig-sore]

the computer measures one pass of the censor per wheel revolution, regardless of where it is positioned.

a point on the rim of a wheel will travel further per revolution than a point near the hub BUT its still only once per revolution... think about it.

the tyre size that you type in is simply the distance traveled per revolution, usually in cm or mm. dont rely on the figure in the instructions. measure it yourself. sit on your bike and mark the tyre with chalk at the point it touches the ground and mark the ground. then roll forward one revolution and mark the ground again. measure between the two marks and use this as your setting.

if you find this is still out over a fixed known distance then simply adjust the figure using some basic calculations.

using this method i have all of my 3 bikes calibrated to read the same

 

[zacklaws]

Could the position of the sensor on the wheel have any effect on inaccuracies?

There is a school of thought that says the magnet on the spokes should be mounted as far away from the hub as possible, the reasoning being, it sweeps past the sensor far quicker than it would closer to the hub so therefore the pulses are far more instantaneous and positive than a longer drawn out affair as it slowly passes. This way the reed switch opens and closes far quicker so the computer can make calculations more accuratley.

I do not know if it makes a difference where the magnet is mounted, but regarding accuracy between a cycle computer and a GPS, I only get a very slight difference between the two which measures in 100ths of a mile even over 100 mile rides, maybe only 5 or 6 100ths on a good day. But I did spend a lot of time setting it all up.

 

[ray.m]

I measure the circumference of my tyre and key it into the computer. Sometimes this varies slightly with the measurement given in the tables supplied. I've always found the results very accurate.

 

[coffeejo]

I've got a Strada but am looking suspiciously at it. Apparently, my top speed yesterday was 61.6mph

 

[Alessandro Petacchi]

I always measure my wheel and also test it on a set mile.