# average speed

Discussion in 'Cycling Equipment' started by Mr_Tee, Apr 6, 2010.

1. ### Mr_Tee New Member

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If I ride 30 miles in 2 hours with no rest stops, is my average 15mph as the simple math would seem to indicate or 16.5mph as my cyclometer says? Can someone explain the discrepancy?

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2. ### NoRacer New Member

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It's 15 mph...

...and you need to fix the wheel size in your computer...

...or do a "roll-out" to find out how many millimeters one revolution of the wheel gets you with you on the bike at a particular amount of pressure in the tires and set the cyclo-computer for that value.

3. ### 64Paramount Active Member

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+1, you probably need to correct the tire size in the computer.

4. ### rschleicher New Member

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Agreed with the above suggestion, but if it is your cyclocomputer that is also telling you that you've ridden 30 miles, then there is something else going on. (Since the wheel-size assumption would be used by the computer to compute both speed and distance traveled.)

Some cyclocomputers don't count stop-time, even if it is just for a minute at a red light. It depends on what brand it is, and their algorithm. So it may be the case that you are averaging 16.5 mph "while in motion", but that due to a number of short stops you only cover 30 miles in the two hour ride.

You might also see if the computer's view of ride time is any different than the total elapsed time of your ride.

5. ### 64Paramount Active Member

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Good point, both of my computers have the "auto start - auto stop" function. I'm sure that's not 100% percent accurate, but it certainly helps, and if his computer doesn't have it at all then that would also account for the large discrepency between time and miles ridden.

6. ### genedan New Member

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Is your computer wireless? Sometimes electronic interference (power lines, car radios) will up your speed while you're riding.

But yeah, we need more info. Did the actual computer say 30 miles in 2 hours at 16.5mph or is one of the variables of your own calculation? I.E., it shouldn't be the case that the computer displays 30 miles AND 2 hours AND 16.5 mph...

7. ### Mr_Tee New Member

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I have the CatEye Micro Wireless. I'm 99% sure the wheel size is correct: (1)I double checked it when I set up the computer, (2)the total distance at the end of the ride agrees with what the route says according to mapmyride.com, (3) and my speed always seems to match what is on the guy's next to me when I have a opportunity to glance over. There are a handful of intersections, but in theory, if the computer was including my stops in its calculations, wouldn't this make the computer's avg speed be lower if anything? Maybe it excludes idle time and that is why it is higher. I have it set on auto and that must have something to do with it. I guess I can dig out that cursed instruction booklet again if I must (sigh).

8. ### jhuskey Moderator

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My advise is to not fret over it but if you want to consider average speed, consider your progress each time you ride the same route. Although head winds, traffic will always be a variable factor.

9. ### Mr_Tee New Member

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OK, aside from the computer aspect, when other riders speak of average speed how do they typically figure it? Does the term have a universal definition? It's nice to compare apples to apples. 2mph can make a big difference. If I'm considering joining a ride or group that claims to maintain a particular pace how can I know if I will be able to keep up or not?

10. ### jhuskey Moderator

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2 miles an hour is a lot and it all varies according to the terrain, how many in the group, weather etc. The only way to know if you can hang with a particular group on a specific route is to ride with them. In most groups there those that like to hammer down up fron and those that lay back and you can usually find your place.

11. ### 64Paramount Active Member

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You should be able to take the elapsed time of your ride from the computer and the total miles you rode, and divide it out on a calculator to get the correct average mph.

For example, my last ride was 48.7 miles, 3 hrs 9 min elapsed time (I don't remember how many seconds), with an average speed of 15.4 mph according to my Cateye Cordless 7 computer.

If I do it on my calculator:

3 hrs 9 min = 3.15 hours

48.7 divided by 3.15 = 15.460317

I've got mine set on auto start/auto stop. So, if you can't get the computer to agree with the calculator, then something's not right with that computer your using, either in the set up or maybe it's just defective.

I've also got a Nashbar Temp Wireless on my other bike and the only difference I've noticed is at certain point on one of my riding routes my Cateye measures as 10 miles, and the Tempo measures it as 10.1 miles.

I should have mentioned that stopped many times on the ride I used for an example: Several times for stoplights/traffic, or to gawk at the high river water, or to blow my runny nose......

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13. ### Jangust New Member

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[lang=no][Lang = no] Jeg vet Ikke Helt jeg, Det ER Vell Sant Det.
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