# Electronics, Lighting, & Gadgets - bike computer

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View Full Version : bike computer

vsopking
08-20-08, 02:50 PM
Hi there! I have a simple bike computer which measures speed, total ride(s) distance (adds up) and average speed, oh and it serves as a watch. Question: On my daily ride I do about 40 km. A few times I do stop at traffic lights. I have the idea that it starts over again to indicate the average speed after each stop. Is that right, or not? :twitchy:

Pig_Chaser
08-20-08, 04:02 PM
i've never heard of them 'starting over', maybe your model does... does it have trip distance and trip time? because typically they ignore the stop time. ie if your speed is 0 they don't add add that into your average speed.

assume instantaneous acceleration and deceleration for the following example otherwise the math is more involved:
eg, if you do 10kph for 10 minutes, then stop for 10 mintutes and then do 20kph for 10 minutes your computer should show an average speed of 15kph even though in reality your average speed is 10kph.

does that example help or confuse things entirely :twitchy: check your trip time when stopped, it should be stopped as well.

daven1986
08-20-08, 04:05 PM
average speed is calculated from the distance travelled and the time taken - at least that is what it says on my instruction manual!!

late
08-20-08, 04:48 PM
Your puter is giving you your average speed. You want it to ignore the stops.
I never looked for one that would. I do know I get a different one most years cause
I don't like the one I have.

I like the looks of the Specialized puters, that's what I'll try next year.

vsopking
08-21-08, 10:08 AM
Darn! It really is not that big of an issue; I just wondered - I'll check it out Pig Chaser... in the weekend. Now I am about to ride the usual daily route, and hey, the sun is shining after a week of clouded, rainy days

somedood
08-21-08, 10:19 PM
If the magnet doesn't pass over the sensor for a few seconds (it will be different for each computer) it assumes you've stopped and doesn't keep adding time to the total trip time. To find the average speed it divides the trip distance divided by the total trip time. The computer has no idea if you're moving .0001 miles per hour, stopped at a stop light, or parked your bike for the next few hours so it has to just stop collecting data after there is no movement for a particular amount of time. Otherwise you could reset the data, take a quick ride, stop and watch your average speed keep dropping down and down until the computer decides it's not in use and turns off, which makes a very easy test to verify if you computer is using speeds of 0mph as part of the trip data.