Tyre size - effect on computer

Discussion in 'Beginners' started by Mortiroloboy, 9 Oct 2007.

  1. Mortiroloboy

    Mortiroloboy New Member

    I have just purchased a GIANT FCR4 as my winter bike, it came with Kenda Kontender 700x 26c tyres, My Polar CS200CAD will only allow me to set 25c tyre into its 2nd bike set up memory. What effect will this have on the accuracy of my speed/mileage readings? Will the 'puter show me going faster than I actually am, or slower?:biggrin::biggrin:
  2. fossyant

    fossyant Ride It Like You Stole It!

    South Manchester
    Should be very minor difference - not noticeable !
  3. OP

    Mortiroloboy New Member

    Yes, but in which way? Too fast, or too slow? LOL!
  4. gbb

    gbb Legendary Member

    Cant remember which way it goes Motir, but its VERY negligable.
    I worked it out a couple of years ago, i'd had the 'standard' setting entered on the computer. When i did an actual measurement and worked out the difference, it was a paltry 1/2 mile lost or gained in 45 miles.
  5. Smokin Joe

    Smokin Joe Legendary Member

    Your computer will over-read your speed and distance.
  6. Elmer Fudd

    Elmer Fudd Miserable Old Bar Steward

    Faster Slower and more less mileage but nowt to worry about.
  7. bonj2

    bonj2 Guest

    so you will be lying to yourself. Best change it so it's lower.
  8. Smokin Joe

    Smokin Joe Legendary Member

    He'll stil be lying to himself but he won't be so happy. He should go the whole hog and fit two magnets to the wheel.
  9. Elmer Fudd

    Elmer Fudd Miserable Old Bar Steward

    I've got a spare ..........
  10. Elmer Fudd

    Elmer Fudd Miserable Old Bar Steward

    If your computer says you are doing 20mph or kph you will actually be doing 20.09mph or kph.
    A discrepancy on speed and distance of 0.47%
    If you want to be really pedantic, get a calculator and multiply your mileage by 1.00469 to give your real mileage (same for speed).
  11. I'm impressed Elmer! :biggrin:
  12. Panter

    Panter Just call me Chris...

    It will actually underestimate your speed and distance.

    Just to be picky :biggrin:
  13. twowheelsgood

    twowheelsgood Senior Member

    Zurich Switzerland
    Quite right, you put a bigger tyre on then you cover more distance per revolution and the computer will under-read.

    Saying that tyre sizes are largely nominal, it's perfectly possible your 26c is in reality the same size or smaller than a 25c, you'll also lose a mm or two over the life of the tyre. It varies from manufacturer to manufacturer and even different products made by the same people.

    Anyway AFIAK, the 25/26c refers to the width of the tyre and not the profile which would be the significant factor here.
  14. Elmer Fudd

    Elmer Fudd Miserable Old Bar Steward

    :blush: :angry: :biggrin: :sad: :blush:
  15. OP

    Mortiroloboy New Member

    Thanks for all the replies, so basically I will look like I'm going slower, but I'll go further :angry: OK as stated it's so marginal as to not be a major concern, well certainly not for me at my level anyway!:blush:
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