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Old 12-26-16, 08:50 PM
  #28  
FBinNY 
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Join Date: Apr 2009
Location: New Rochelle, NY
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Bikes: too many bikes from 1967 10s (5x2)Frejus to a Sumitomo Ti/Chorus aluminum 10s (10x2), plus one non-susp mtn bike I use as my commuter

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Originally Posted by tarwheel View Post

More troubling to me, however, are the inconsistencies in mileage and time. Compared to the cycle computers on my handlebars, the distances shown by Cyclemeter are almost always longer and the times shorter. For example, on my commute yesterday, my cycle computer showed 32.0 miles in 2:11 hours. Cyclemeter showed 32.7 miles in 2:08 hours.
People report the same thing on a regular basis. However it's very possible that both are accurate, though different.

You need to understand that they measure distance differently, and which is correct depends on what you want to know.

GPS systems measure "map" distance by adding the small distances you travel between way points. This is the shortest distance for a given route from A to B.

However, the real distance can and will be longer, for example if you do a small loop back to check or your riding buddy, or swing wide on turns, or slalom to climb hills, or any small maneuver of this type that has your front wheel cover a longer distance than the shortest straight line possible. In fact if you mount two identical bike computers front and rear, the front one will slowly pull away from the rear because the front wheel does in fact travel farther than the rear, though both don't actually pull apart.

I also wonder about how GPS systems account for hills. Obviously if you ride over the mountain to get from A to B, it's a longer trip that if you went through a tunnel without having to climb.

So, what distance interests you. Knowing you got from A to B which are 30 miles apart, or how far your wheel rolled along the way? (which wheel?)
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