Computer ... wheel size

spacemonkeys
spacemonkeys Posts: 32
edited January 2009 in Workshop
If you have you computer set to 700x23, and then put a 700x25 (trying to find a gatorskin was a night mare, everybody must be getting punctures) but don't change the computer, your going (slightly) faster and farther than the computer says yes ?

Comments

  • Anonymous
    Anonymous Posts: 79,665
    Yes.
  • doobie919
    doobie919 Posts: 119
    Yep because your producing more torque per push than you were before, so farther and faster is true.

    Correct me if i'm wrong tho.
    2007 Fuji Newest 3.0.
    !!Upgrades!!!!!
    Cateye Velo 5 Computer


    2009 Mongoose Subject BMX
    !!Upgrades!!!!!
    Sky blue tires
    New seatpost and seat ( made by pivotal)
  • plug1n
    plug1n Posts: 204
    If you're using Gatorskin 25s then the magic number for the computer is 2122 (mm wheel diameter)

    Gatorskin 23s are 1969mm

    (on the side of the packaging)
  • spadey
    spadey Posts: 54
    Am I just being thick here, but once the wheel circumference is programmed in, how does the computer know how high up the fork it is? Surely if the magnet and sensor was closer to the hub, the circumference that it spins around is less resulting in the computer thinking it is going faster than if it were mounted higher up the fork.

    As I said I'm probably being extremely dim, please explain!
  • redvee
    redvee Posts: 11,922
    The computer only registers when the magent passes by regardless of how far it is from hub and calculates your current speed based on the formula within its brain for the wheel/tyre size you've inputted.
    I've added a signature to prove it is still possible.
  • doyler78
    doyler78 Posts: 1,951
    spadey wrote:
    Am I just being thick here, but once the wheel circumference is programmed in, how does the computer know how high up the fork it is? Surely if the magnet and sensor was closer to the hub, the circumference that it spins around is less resulting in the computer thinking it is going faster than if it were mounted higher up the fork.

    As I said I'm probably being extremely dim, please explain!

    The placement of the magnet is unimportant so long as it placed somewhere on the spokes because one complete revolution of the magnet at the spoke takes exactly the same time as the tyre takes to rotate therefore so long as you know the circumference of the tyre then one revolution of the magnet will tell you exactly how far the tyre has travelled.
  • spadey
    spadey Posts: 54
    thanks - makes perfect sense now!
  • Cheers, not that it makes LOADS of difference but just wanted to confirm that my previous 3 rides, my figures were on the side of pessimistic (e.g if two rides 6 months appart had the same average and the tyre is now bigger, I wasn't under performing)

    As to to positioning the magnet, the computer basically times the number of times round by the circumference of the wheel .. so the magnet is only used to count the number of times the wheel went round, placing the magnet closer to the hub will mean it will travel slower, but has less distance to travel, and the revolution count of the wheel will be the same

    Cheers people .... means I had some good rides this week :-)
  • bill57
    bill57 Posts: 454
    doobie919 wrote:
    Yep because your producing more torque per push than you were before, so farther and faster is true.

    Correct me if i'm wrong tho.
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