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Help me calibrate my PM trip distance.

 I'm running a SRM wired unit, one of the few in da Haus. Here's my issue: my trip distance is 1% optimistic. Not really an issue until I started doing these loony brevets; I need to navigate, lots, often with cues coming fast and furious. My mental acuity is shaky enough after 150 miles without having to constantly make rolling adjustments. 

I THINK the right thing to do is change the tire circumference via computer interface, but which way? Up or down? I know this will be a simple answer for the math whizzes among us; I'm not one of 'em. 

Thanks!

Comments

  • OK- I don't have an SRM so I'm not sure how you set the circumference. But the most accurate way to set your circumference is to do a roll out test and measure it. There is some difference in circ on different tires, so while the charts you see in manuals and such are good starting points, they aren't exact.



    Chalk the tire & the ground at the same spot, roll the bike forward until the chalk line on the tire comes all the way around and then chalk the ground again. Measure the distance between the two lines. That's the number you should use.



    Now, that said. Lets see. This is one of those "if a train left Chicago going 30 mph and Timmy ate tunafish for lunch, what color was the conductors hat" kinda questions!!



    When you say "optomistic" I'm assuming you mean that if an accurate measure of the road traveled says you went 100 miles, your SRM is telling you that you went 101? And if that's the case then I would think you need to adjust the circumference in the computer down. But then again, I was always pretty horrible at those word problems! Blue? no Green! Ahhhhhhhhhh!

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