Wheel Circumference Help Please

neilvx
neilvx Posts: 137
edited November 2016 in MTB general
I have fitted a slick to the girlfriend MTB so it can be used on the turbo trainer but I can't figure out the wheel circumference in mm for the Wahoo sensor.

The tire size is 27.5 x 1.35

I thought I got but after 25 minutes she has covered 3000 miles lol :lol:

Thanks in advance.

Neil.
Cube Reaction GTC Pro 27.5 2017 Grey / Yellow Flash
Ribble R872 Ultegra
Skyway BMX

Comments

  • surrey_commuter
    surrey_commuter Posts: 18,867
    Multiply the diameter by pi
  • cooldad
    cooldad Posts: 32,599
    Or just measure it.
    I don't do smileys.

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  • neilvx
    neilvx Posts: 137
    Multiply what by what ? And I don't have a tape measure long enough :-(.
    Cube Reaction GTC Pro 27.5 2017 Grey / Yellow Flash
    Ribble R872 Ultegra
    Skyway BMX
  • cooldad
    cooldad Posts: 32,599
    Seriously?

    Really seriously?

    Go to your browser (that's a thingy on your computer)

    Google 'Google'

    Then Google 'circumference', 'diameter' and 'pi'.

    Or just get a bit of string, measure the circumference. (Google 'circumference')

    And measure the bit of string.
    I don't do smileys.

    There is no secret ingredient - Kung Fu Panda

    London Calling on Facebook

    Parktools
  • The Rookie
    The Rookie Posts: 27,812
    You on,y need a 12" rule, yo just move it by 12" as you measure each section until you get the whole circumference.

    Clearly you must be out by a factor of about 100, so maybe M instead of cm!
    Currently riding a Whyte T130C, X0 drivetrain, Magura Trail brakes converted to mixed wheel size (homebuilt wheels) with 140mm Fox 34 Rhythm and RP23 suspension. 12.2Kg.
  • rockmonkeysc
    rockmonkeysc Posts: 14,774
    This is primary school maths.
    Pi x diameter = circumference
    Transition Patrol - viewtopic.php?f=10017&t=13070235
  • cooldad
    cooldad Posts: 32,599
    More correctly 2(pi)r. R being used to calculate area and volume as well.

    But that might have been high school. I'm sure I remember chiseling it onto my bit of slate.
    I don't do smileys.

    There is no secret ingredient - Kung Fu Panda

    London Calling on Facebook

    Parktools
  • neilvx
    neilvx Posts: 137
    Hey I can't being this stupid, will have to try the string method.
    Cube Reaction GTC Pro 27.5 2017 Grey / Yellow Flash
    Ribble R872 Ultegra
    Skyway BMX
  • Harry182
    Harry182 Posts: 1,170
    After a quick google of "whats the circumference of a 27.5 x 1.35 tire"...

    http://www.bikecalc.com/wheel_size_math

    HTH
  • JBA
    JBA Posts: 2,852
    Place bike on floor with valve of rear wheel at bottom to act as a reference point. Mark the floor where the tyre touches it. Roll the bike forward until the rear wheel makes one revolution. Mark floor. Measure distance between marks.
    “Life has been unfaithful
    And it all promised so so much”

    Giant Trance 2 27.5 2016 ¦ Sonder Broken Road 2021¦ Giant Revolt Advanced 2 2019 ¦ Giant Toughtroad SLR 1 2019 ¦ Giant Anthem 3 2015 ¦ Specialized Myka Comp FSR 2009
  • cooldad
    cooldad Posts: 32,599
    Google 'revolution'. Then 'Che Guevara'.

    Then wait for the secret police to give you an early wake up call.
    I don't do smileys.

    There is no secret ingredient - Kung Fu Panda

    London Calling on Facebook

    Parktools
  • neilvx
    neilvx Posts: 137
    Harry182 wrote:
    After a quick google of "whats the circumference of a 27.5 x 1.35 tire"...

    http://www.bikecalc.com/wheel_size_math

    HTH

    That's what I used to start with, I did search google for the answer before I got to this stage.
    Cube Reaction GTC Pro 27.5 2017 Grey / Yellow Flash
    Ribble R872 Ultegra
    Skyway BMX
  • The Rookie
    The Rookie Posts: 27,812
    Well as you are out by a factor of about 100, maybe it's just a miss entry of where the decimal point should be?
    Currently riding a Whyte T130C, X0 drivetrain, Magura Trail brakes converted to mixed wheel size (homebuilt wheels) with 140mm Fox 34 Rhythm and RP23 suspension. 12.2Kg.
  • cycleclinic
    cycleclinic Posts: 6,865
    Roll the bike 1 revolution and measure the distance covered. It's pretty simple.
    http://www.thecycleclinic.co.uk -wheel building and other stuff.
  • LimitedGarry
    LimitedGarry Posts: 400
    edited November 2016
    Dude! This thread.

    Once, we needed to calibrate a computer out in terrain, so I marked the distance on the ground and then, much to the amusement of everyone involved, laid myself down into the dirt to mark 185cm and eyeballed the remaining distance. Ended up undershooting by 2cm.
  • cougie
    cougie Posts: 22,512
    Sod it. Just go with what you have now. There's no such thing as distance travelled on the turbo anyway.
  • kajjal
    kajjal Posts: 3,380
    Mark the road, roll bike foward on full turn of the wheel and mark again.

    Next get in your car line it up with the first line, reset mileage to zero and drive to second line. Check speedo for correct distance. You may have to do this a few times in the car to be sure and you can't do it in reverse unfortunately.

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