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Discussion Starter · #1 ·
I am in the market for a new computer. I have always used Avocets in the past, I really like the speed to the .1 and average to the .01 feature.

I was hoping to keep those features and move to a wireless setup (Avocet is only available in wired and their magnet set up does not fit with the hub on my new wheel).

I tried the VDO wireless and for the past month have had problems maintaining a constant readout. It only works between 10 and 75% of the time (I don't have a heart rate monitor and haven't been riding with a group so not sure of the source of interference). I have experimented numerous times with placement of the sensor and magnet but none of these setups will give me a readout for a whole ride.

Does anyone know of another wireless computer that computes average to the .01? Also other comments/experiences with wireless appreciated.

Thanks,
Stelvio
 

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The problem with many digital readouts is that they can show apparent high resolution simply because they have a lot of digits, but one has to understand the absolute accuracy of the device. The wheel diameter on the bike, for example, is not constant because the tire deflects and changes the diameter as a result. When one rides a bumpy road, for example, the diameter of the wheel is constantly changing by a small amount. This variation then skews the results of the calculations of a cycle computer that only counts revolutions and has a fixed number that represents the diameter of the wheel.

Although you may have resolution down to 0.01, you only have accuracy to +/- 1% at best, so those hundredths digits are meaningless. Besides that, the number most computers allow you to enter for wheel diameter are one percent apart or so as it is, so you don't even have the ability to enter with high resolution you're actual wheel diameter as it is.

Because of the issues that many wireless computers have I much prefer a cheap wired computer for it's only adequate accuracy.

Now if you want true accuracy, you would have to hook up one of the calibrated wheels like they use to measure distances on a road. Those devices have a solid rubber tire that barely deflects and an encoder that detects minutes of rotational angle and as such do have the resolution that you think you are getting with your Avid computer.
 

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Insight driver- are you a robot? :)

If cadence isn't important to you, check out the Garmin Forerunner. I have the 201 which works pretty well in open areas (you wont find much else in central illinois) and you get elevation and speed vs. time or distance info to boot. I got mine for $80 and its nice for running too.

The Garmin Edge and the newer Forerunner 205 are really nice too, but are a bit more expensive
 

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Cycle computer accuracy can be better than you paint it to be

Insight Driver said:
The problem with many digital readouts is that they can show apparent high resolution simply because they have a lot of digits, but one has to understand the absolute accuracy of the device. The wheel diameter on the bike, for example, is not constant because the tire deflects and changes the diameter as a result. When one rides a bumpy road, for example, the diameter of the wheel is constantly changing by a small amount. This variation then skews the results of the calculations of a cycle computer that only counts revolutions and has a fixed number that represents the diameter of the wheel.

Although you may have resolution down to 0.01, you only have accuracy to +/- 1% at best, so those hundredths digits are meaningless. Besides that, the number most computers allow you to enter for wheel diameter are one percent apart or so as it is, so you don't even have the ability to enter with high resolution you're actual wheel diameter as it is.

Because of the issues that many wireless computers have I much prefer a cheap wired computer for it's only adequate accuracy.

Now if you want true accuracy, you would have to hook up one of the calibrated wheels like they use to measure distances on a road. Those devices have a solid rubber tire that barely deflects and an encoder that detects minutes of rotational angle and as such do have the resolution that you think you are getting with your Avid computer.
It is true that the extra digits of a digital read outs can give a perception of higher accuracy than they actually deliver. But the accuracy obtainable by many cycle computers can be better than what you claim.

It is true that wheel radius can vary as the tire deflects and goes over pavement irregularities. But the two factors that you haven't accounted for are: The tire casing fabric both expands and contracts, so if the tire deflects inward the casing expands circumferentially, and when it rebounds, the casing retracts again, so that the circumference of the tire does not change as much as you might expect as the diameter changes momentarily; and speed measurements are taken by averaging wheel revolutions, so momentary changes in circumference tend to be averaged out.

Most computers allow wheel circumference (not diameter!) calibration to be adjusted to a higher precision than you claim. For example, the wheel circumference for the Avocet 40/45 can be adjusted to +/- 1mm or +/0.01". A 700x23c tire has a nominal diameter of 2087mm/82.17", so you can adjust the circumference calibration by increments of 0.05% or 0.012%, depending on units of measurement.

At a nominal 20 mph, an instantaneous speed measurement to within 0.1 mph requires an accuracy of 0.5%, and there is no reason that this degree of accuracy should not be attainable with most cycle computers when properly calibrated.
 

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Discussion Starter · #5 ·
Thanks for the responses. Hi to you Mark McM (its Tom from Bedford) long time no see.

The main reason I want the average speed to read out to .01 is the extra "carrot" effect from seeing the average rise as I put forth more effort. It can take a while to change the readout when it is to the .1, I guess it has its advantages when you are going slow.

The accuracy of the readout is not all that important as long as its as close as the others.

Does anyone know of another computer besides the VDO and Avocet that read out to .01.

Stelvio
 
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