Advertise on Bikeforums.net



User Tag List

Results 1 to 19 of 19
  1. #1
    Senior Member
    Join Date
    Oct 2004
    Location
    Sacramento, CA USA
    My Bikes
    not worth mentioning
    Posts
    187
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)

    CycloComputer magnet/sensor placement?

    I assume that the goal is to place the magnet/sensor as close to the rim as possible so that it can correctly get your mileage (assuming one inputted the correct tire size of course) w/o it hitting the brakes?

    Am I right?
    -- Ron
    1. 2008 Giant FCR3 [hybrid; main bike]
    2. Schwinn World Sport 4130 [mixte road bike; red]
    3. year ?? Specialized RockHopper Comp (18-spd mtn bike; all Shimano Deore parts)

  2. #2
    enginerd jeff^d's Avatar
    Join Date
    Oct 2004
    Location
    Redlands, CA
    My Bikes
    Surly Steamroller, Kona Unit, Trek 520
    Posts
    265
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Doesn't really matter. One revolution is one revolution, whether at the rim or near the hub. You are correct that inputting correct tire size is important.

  3. #3
    Senior Member FlatFender's Avatar
    Join Date
    Aug 2006
    Location
    Raleigh NC
    Posts
    989
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by jeff^d View Post
    Doesn't really matter. One revolution is one revolution, whether at the rim or near the hub. You are correct that inputting correct tire size is important.
    x2

  4. #4
    Senior Member
    Join Date
    Sep 2007
    Posts
    1,151
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by ablang View Post
    Am I right?
    Wrong.

    The sensor is a dumb switch that closes a contact when the magnet passes through it, it conveys no intelligent information other than counts how many turns the wheel does in an interval.

    Then the puter says, Avr Speed = count x magic number stored by yr calibration.

  5. #5
    Senior Member
    Join Date
    Jul 2008
    Location
    Kansas City, MO
    My Bikes
    GT Transeo
    Posts
    191
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Wouldn't it make more sense to put the sensor close to the hub than on the outside? The farther away from the hub you get, the more torque the moving sensor will have, and the more out-of-balance the wheel will be.

  6. #6
    Cries on hills supton's Avatar
    Join Date
    Jun 2007
    Location
    Central NH
    My Bikes
    2007 Trek Pilot 1.2, 1995 Gary Fisher Avantage, 1985 Panasonic Sport 1000, 1969 Raleigh Sprite 5
    Posts
    873
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Perhaps. But the sensor is usually such a small weight, and one is usually not going that fast. Put it where it works best and the wires reach.
    '07 Trek Pilot 1.2
    '85 Panasonic Sport 1000 (beater, gone now)
    '69 Raleigh Sprite 5 speed (AW instead of S5, for now)

  7. #7
    Hanging On
    Join Date
    Jul 2007
    Posts
    834
    Mentioned
    1 Post(s)
    Tagged
    0 Thread(s)
    The only valid argument for placing the magnet (and sensor) closer to the hub is that the linear speed of the magnet relative to the sensor is lower so that there is less chance that a revolution will be missed (not counted). There has been one actual instance in my experience where moving the magnet and sensor closer to the hub made a difference in the reliability of a cycling computer, so I do this now routinely. The magnet is so light in comparison to, say, a valve stem, that the actual placement probably won't make a detectable difference in how the wheel rolls.

    -soma5

  8. #8
    Super Moderator
    Join Date
    Feb 2007
    Location
    Tariffville, CT
    My Bikes
    Tsunami Bikes
    Posts
    12,151
    Mentioned
    16 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by EGUNWT View Post
    Wouldn't it make more sense to put the sensor close to the hub than on the outside? The farther away from the hub you get, the more torque the moving sensor will have, and the more out-of-balance the wheel will be.
    I agree with this, depending on the size of the magnet. Some of them are pretty clunky.

    It's hard to notice it until you get on rollers - then everything is obvious. The other time you notice it is when you're descending really fast - 50+ mph.

    Having said that my magnet is smack in the middle of the spoke.

    When I was a bit more concerned about such things I used to get slim flexible magnets and tape them to the side of the aero rims (TriSpoke or Rev-X) to keep things aero and light.

    cdr

  9. #9
    Oldschool
    Join Date
    Jun 2008
    Posts
    57
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Put your magnet exactly opposite the valve stem, that would 'balance' the weight.

  10. #10
    Senior Member
    Join Date
    Feb 2005
    Location
    Oklahoma
    My Bikes
    Trek 5500, Colnago C-50
    Posts
    9,024
    Mentioned
    2 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by Sekine View Post
    Put your magnet exactly opposite the valve stem, that would 'balance' the weight.
    Not necessarily. The heavy side of most rims is where the joint is, usually directly opposite the valve stem. spin the wheel slowly and see where it stops. On my road wheels I put the magnet close to the valve stem for better balance. On my deep profile aero rims the valve stem is 60mm and is the heavy side so the magnet does go on the opposite side.

    Al

  11. #11
    Senior Member
    Join Date
    Sep 2007
    Posts
    1,151
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    My 10 years old Avocet magnet is a RING mounted on the hub, nothing unsightly. Don't tell me Avocet got this thing patented and nobody else can use it.

    Guessing some ppl would mount the thing up on top to avoid running a long wire.

  12. #12
    Senior Member Pig_Chaser's Avatar
    Join Date
    Sep 2007
    Location
    Edmonton, AB
    My Bikes
    '07 Giant OCR3
    Posts
    1,144
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    There's allot of considerations when placing a magnet/sensor on a wheel. But the short answer is: Adjust it for best performance.

  13. #13
    Senior Member Thumpic's Avatar
    Join Date
    Dec 2007
    Location
    The Sunny South
    Posts
    1,513
    Mentioned
    2 Post(s)
    Tagged
    0 Thread(s)
    if you put 2 magnets on different spokes you'll go faster and farther..........

  14. #14
    Senior Member
    Join Date
    Aug 2005
    Location
    Pittsburgh, PA
    My Bikes
    '''96 Litespeed Catalyst, '05 Litespeed Firenze, '06 Litespeed Tuscany, '12 Surly Pacer, All are 3x8,9 or 10. It is hilly around here!
    Posts
    25,268
    Mentioned
    5 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by Thumpic View Post
    if you put 2 magnets on different spokes you'll go faster and farther..........
    Joking aside, I've seen this done. I saw a reproduction "Penny-farthing" (highwheel) bike with a huge front wheel that was too large for the cyclometer's calibration numbers. The owner had put two magnets on the wheel and set the calibration number for half of the real value.

  15. #15
    Keep on climbing
    Join Date
    Apr 2004
    Location
    Marlborough, Massachusetts
    My Bikes
    2004 Calfee Tetra Pro
    Posts
    2,070
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by soma5 View Post
    The only valid argument for placing the magnet (and sensor) closer to the hub is that the linear speed of the magnet relative to the sensor is lower so that there is less chance that a revolution will be missed (not counted).
    I have seen it argued on these forums that it is better to put the magnet close to the rim in order to produce a higher "spike" on the sensor. i.e., they were claiming that with the sensor close to the hub, it could still faintly detect the magnet at 180 degrees away and thus the "low point" reading to the "high point" reading won't be as great, and thus the sensor might not count some revolutions.

    Not saying I believe that theory... Just pointing out that it has been said. Personally, I subscribe to the theory that getting the magic tire circumference number correct is far more important then magnet placement.
    "There is more to life than increasing its speed" -- Mahatma Gandhi

  16. #16
    Senior Member
    Join Date
    Sep 2007
    Posts
    1,151
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by Pig_Chaser View Post
    There's allot of considerations when placing a magnet/sensor on a wheel. But the short answer is: Adjust it for best performance.
    My verdict is, this is all much ado fer nuthing.

  17. #17
    Senior Member
    Join Date
    Sep 2007
    Location
    Gaseous Cloud around Uranus
    Posts
    3,235
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    I know I've had computers that didn't like the sensor out to far.It went by the pickup too fast and I had to move inward.
    Everything should be as simple as possible...But not more so.---Albert Einstein

  18. #18
    Senior Member
    Join Date
    Apr 2008
    Location
    A Latvian in Seattle
    Posts
    1,020
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    I suspect that the sensor is just a simple magnetic reed switch -- and thus either completely on or completely off, with no intermediate states and no worries about spike "size" as in KF's post.

  19. #19
    'Mizer Cats are INSANE Mentor58's Avatar
    Join Date
    May 2005
    Location
    Clarksville, TN
    My Bikes
    C-dale T800
    Posts
    808
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by KevinF View Post
    I have seen it argued on these forums that it is better to put the magnet close to the rim in order to produce a higher "spike" on the sensor. i.e., they were claiming that with the sensor close to the hub, it could still faintly detect the magnet at 180 degrees away and thus the "low point" reading to the "high point" reading won't be as great, and thus the sensor might not count some revolutions.

    Not saying I believe that theory... Just pointing out that it has been said. Personally, I subscribe to the theory that getting the magic tire circumference number correct is far more important then magnet placement.
    Which is proof that on this forum (like all forums) there are people who have WAY too much time to think about things, and then argue them with a passion and intensity not usually found outside of people who should be on anti-psychotic drugs.

    I just looked at all my rides, on each one I've got the sensor mounted about 5-6 inches up from the bottom of the fork. No real reason I suppose, just where I thought to put it.

    M58
    *Surly LHT ... Slow and Steady, *Motobecane Century Pro ... Better than Me
    *Bianchi Volpe ... Well, just 'cuz , Fuji Track SS / Fixie ... Mustache bars and a big grin
    Rans F5
    Easy Racers Tour Easy
    * Now that I'm 'Bent, I will probably unload all but the Fixie.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •