Old 10-22-13, 03:21 PM
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Join Date: Apr 2009
Location: New Rochelle, NY
Posts: 35,989

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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There's a difference between theoretical (map) distance and distance actually traveled. Part of the reason is that you don't ride a straight line.

To take an extreme example, imagine you climbed a steep hill by slaloming. The actual distance as measured by your front wheel would be much greater, possibly double the straight line op that hill.

Also, I'm not sure whether google's algorithm uses flat distance based on GPS coordinates, or accounts for the longer distances that going up and down hills involves.

Lastly, steering always has the front wheel taking a longer path than the rear which rolls in a straighter line as the front wheel wiggles, and takes a smaller radius on all turns. You can see this by buying two computers, calibrating them precisely, mounting one each of the front and rear wheels. The front wheel unit will always read higher.

When I used to bother with that nonsense, (no computers on any bikes any more) I used to set the computer by theory, then adjust it based on a 10 mile stretch with NY's mile markers along the road. I've found that the adjusted computer is accurate where the state has measured (3) miles.
Chain-L site

An ounce of diagnosis is worth a pound of cure.

“Never argue with an idiot. He will only bring you down to his level and beat you with experience.”, George Carlin

“One accurate measurement is worth a thousand expert opinions” - Adm Grace Murray Hopper - USN

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