Maps show different distance than computer

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2012-10-02 7:47 PM

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Subject: Maps show different distance than computer
This has been bugging me for a little while now. Every time I come home I put my cycling (and running) workouts into an online mapping program (tried many of them, same result) and the distance that the program comes up with is different than what my computer says. The distance on the bike computer is usually about 15% longer. I'm pretty sure it isn't my computer.

Here's my thought:
I live in mid-missouri, and it is pretty hilly here. Every mile has an average of 40-50 feet of climbing. I'm wondering if the distances calculated by the map programs don't account for elevation, and if they don't, could it really make that much of difference?

for example, on a 20 mile ride with about 850 ft of climbing, the mapping program says it is only says 17.5 miles.

Anyone else have this problem?

2012-10-02 8:09 PM
in reply to: #4437890

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Subject: RE: Maps show different distance than computer

Have you properly set the wheel size in your computer?  If you're using 650 wheels, but your computer is set to 700, then your computer is going to think that every rotation of your wheel is going farther than you actually are.

There could be some differences in distance due to elevation, but not 15%...unless you're constantly climbing huge mountains.

ETA: I think the difference between 650 wheels and 700 is only about 8%...so there could be other things going on.



Edited by tri808 2012-10-02 8:12 PM
2012-10-02 8:13 PM
in reply to: #4437918

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Subject: RE: Maps show different distance than computer
yeah i measured the circumference of the wheel by making a mark on the wheel and rolling it across the floor with the wall as a guide to keep the wheel straight and measured the distance of the travel.

Edited by nolken 2012-10-02 8:14 PM
2012-10-02 8:23 PM
in reply to: #4437890

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Missouri
Subject: RE: Maps show different distance than computer
maybe it is the computer, cause i just did some quick math and even with an 8% incline the entire way the difference should only be about 0.16 miles on a 20 mile ride.
2012-10-02 10:05 PM
in reply to: #4437890

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Subject: RE: Maps show different distance than computer
Drive it? Compare the car odometer, GPS and mapping software with your cyclometer. FWI-GPS (Android) sometimes gives me some very questionable distances.
2012-10-02 10:40 PM
in reply to: #4437890

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Subject: RE: Maps show different distance than computer
I have mapped a couple of routes and they are pretty accurate to my bike computer

2012-10-03 3:22 AM
in reply to: #4437890

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Subject: RE: Maps show different distance than computer
This is quite normal, though not to the extent of 2.5m per 20m. What you have to realize is that your wheelbased distance measures everry foot of rotation from your bike. You probably dont ride in a perfect straight line but you will wobble a bit , which you correct by steering. GPS is not sooo accurate in that it smoothes this out. Same goes for taking corners a bit wide or tight etc. I always focus on map/gps speeds because in a race that is going to matter.

In a running race I bet you also run a little bit more than the actual distance
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