Two riders, different average

Quoted post said:

Originally posted by Chaim
How can two riders that start at the same time and finish together have different ride speed average? If I do simple math, distance/time I should always get same answer.

It sounds like a joke... but it is a real question that comes up at almost every club ride I do when people compare averages.

…and yes I am assuming that the cycle computers are accurate…

How much is the variance? Is it only very tiny differences? If people don't round the corners on exactly the same path, they will have different distances. If the distance measurements are accurate, this will be displayed on the computer as differences in distance on the same ride, and it won't be a computer error. Another way to get a variance is if some riders keep circling at traffic lights while others put their feet down and stop.

But I am guessing that the biggest differences will be for the following. Some computers have a function which allows you to eliminate the effects of having to stop. You can choose on these GPS computers how quickly it will stop the timer when you have interrupted cycling, like for example at traffic lights. If you choose 5 seconds, the computer senses that the GPS readings are not advancing, and after 5 seconds momentarily shuts off the timer. Then you wait as long as it takes. When you begin riding again, the computer senses the GPS readings advancing again, and the timer starts back up where it left off. It doesn't have to be a 5 second sensitivity. You can set it to whatever you want, I think.

Those that do not have this timer shutoff function will record slower average speeds on the club ride even though they went the same distance and maybe even finished before the others who recorded faster average speeds. This is because their timers never stopped running, but the others did every once in a while when they stopped.

Quoted post said:

Originally posted by gntlmn
How much is the variance? Is it only very tiny differences? If people don't round the corners on exactly the same path, they will have different distances. If the distance measurements are accurate, this will be displayed on the computer as differences in distance on the same ride, and it won't be a computer error. Another way to get a variance is if some riders keep circling at traffic lights while others put their feet down and stop.

But I am guessing that the biggest differences will be for the following. Some computers have a function which allows you to eliminate the effects of having to stop. You can choose on these GPS computers how quickly it will stop the timer when you have interrupted cycling, like for example at traffic lights. If you choose 5 seconds, the computer senses that the GPS readings are not advancing, and after 5 seconds momentarily shuts off the timer. Then you wait as long as it takes. When you begin riding again, the computer senses the GPS readings advancing again, and the timer starts back up where it left off. It doesn't have to be a 5 second sensitivity. You can set it to whatever you want, I think.

Those that do not have this timer shutoff function will record slower average speeds on the club ride even though they went the same distance and maybe even finished before the others who recorded faster average speeds. This is because their timers never stopped running, but the others did every once in a while when they stopped.

Very good points!

I am talking about small differences.

Now you made me think: On a hilly ride, one can climb fast and wait at the top (computer on)...stopping the computer prior to circling the parking lot...slowing down before traffic light / intersection / food stop…

Thanks.