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  1. #1
    Russian Troll Farmer
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    Cycling computers and tubulars

    So, my 2 computers come with a long list of diameters for different tire sizes, but gives only 1 diameter for tubulars in general. I have 3 tubular wheelsets, one running 22mm tires, one running 24mm, and one running 27's. Is there any formula for calculating tubular diameters?
    "L'enfer, c'est les autres"

  2. #2
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    (Clincher diameter x 1) - (insignificant difference between clincher and tubular x 0)

  3. #3
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    Mark the tire, mark the floor, line up the 2 marks, rotate tire one rev, mark floor and measure.

  4. #4
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    I suggest trying your best setting guess then comparing your total ride distance from your GPS.

  5. #5
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    some Garmin's will auto calibrate the speed / distance from GPS information and your wheel sensor revolutions - don't know how accurate it is though.
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  6. #6
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    Quote Originally Posted by GKSki View Post
    I suggest trying your best setting guess then comparing your total ride distance from your GPS.
    Not everyone rides with GPS. I'm one of them.

    I determine wheel circumference by measuring from the floor to the axle. I subtract 1mm to account for tire compression (which may or may not be accurate but it's better than nothing), then multiply by 2, then by pi.

    I find the numbers in the set up manuals to be markedly different than my measured and calculated numbers. For instance, the 700x23 tire on my road bike measures out to 2098mm while the manual suggests 2133mm.

    I should use the manual's number because then, I'd be faster.

  7. #7
    Russian Troll Farmer
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    Quote Originally Posted by Peter P. View Post
    Not everyone rides with GPS. I'm one of them.

    I determine wheel circumference by measuring from the floor to the axle. I subtract 1mm to account for tire compression (which may or may not be accurate but it's better than nothing), then multiply by 2, then by pi.

    I find the numbers in the set up manuals to be markedly different than my measured and calculated numbers. For instance, the 700x23 tire on my road bike measures out to 2098mm while the manual suggests 2133mm.

    I should use the manual's number because then, I'd be faster.
    Well, if you REALLY want to go faster, try putting 2 pickup magnets on your wheel.....
    "L'enfer, c'est les autres"

  8. #8
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    Quote Originally Posted by No Time Toulouse View Post
    So, my 2 computers come with a long list of diameters for different tire sizes, but gives only 1 diameter for tubulars in general. I have 3 tubular wheelsets, one running 22mm tires, one running 24mm, and one running 27's. Is there any formula for calculating tubular diameters?
    You start with the methods outlined here (measure rollout, and for a more accurate meansurement, measure rollout with a rider on the bike). And then you do the obvious calibration. One possibility is the GPS mentioned, though there are reasons for GPS to be innacurate particularly if you have a route that is very hilly & twisty. The best calibration method is to find a road or trail will mile markings. Ride as long a distance as possible (10 miles is good, 20 is much better) and compare the reading you get from your computer with the actual mileage. Correct your wheel diameter input by the ratio of actual miles to computer miles. It's by far the most accurate calibration you can do. Guessing wheel diameters is a poor third choice.

  9. #9
    Russian Troll Farmer
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    Well, I'm going to bring in the front wheel from each wheelset to work, get out the 36" verniers, clamp the jaws really tight against my tires, and have somebody read the diameter.
    "L'enfer, c'est les autres"

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