Advertise on Bikeforums.net



User Tag List

Page 1 of 2 12 LastLast
Results 1 to 25 of 26
  1. #1
    Newbie
    Join Date
    Apr 2004
    Posts
    4
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)

    How Accurate is your Computer?

    How accurate is your cycle computer? I just put on a Sigma BC1200. I road a mile and marked exactly on the road where it came up a mile. I then jumped in my truck and drove the same route. It probably came out to be about 1/15 of a mile off.

    My truck could be off or the computer could be off; I am not sure. Is it impossible to get them to read perfectly accurate?

    Thanks,

    Person

  2. #2
    We drive on the left. Dutchy's Avatar
    Join Date
    Sep 2001
    Location
    Adelaide, South Australia
    Posts
    1,096
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    This is from one of my posts last year.

    An easy way to do a roll out measurement it this:
    1) Pump tyres up to pressure
    2) Find a line to follow, gutter, concrete groove in driveway etc.
    3) Place valve at bottom of tyre
    4) Sit on bike and roll out 5 complete rotations. Measure the distance.
    5) Repeat 2 more times.
    6) Add the 3 measurements together and divide by 15. This should give a very accurate measurement.

    Even with an accurate measurement it can still only get to within +/- 1% as when we ride we rarely ride in a perfect straight line and we take different lines through corners than other cyclist's.

    CHEERS.

    Mark
    I'd rather be riding.

  3. #3
    Senior Member mindbogger's Avatar
    Join Date
    Jul 2003
    Posts
    933
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by Person
    How accurate is your cycle computer? I just put on a Sigma BC1200. I road a mile and marked exactly on the road where it came up a mile. I then jumped in my truck and drove the same route. It probably came out to be about 1/15 of a mile off.

    My truck could be off or the computer could be off; I am not sure. Is it impossible to get them to read perfectly accurate?

    Thanks,

    Person
    Is your computer calbriated to your wheel size? If so, it shouldn't be that inaccurate.
    00' Cannondale R1000
    01' Devinci Chilipepper

    When sh*t hits the fan, everything I'm not, made me everything I am.

  4. #4
    Senior Member
    Join Date
    Feb 2004
    Location
    Cleveland, OH
    My Bikes
    2004 Trek 4600, 1980's Univega Supra Sport, 2006 Lemond Reno
    Posts
    2,287
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    I was wondering that too. Theoretically, the faster moving part of the wheel is higher up, but then again, no matter where on the wheel you put the sensor, it still is going to pass the sensor the same amount of times...Anyway, my CatEye enduro seems to be pretty right on. It once registered that I was traveling at 37 mph in a 20 mph zone on m mountain bike(steep downhill in a park), and my favorite local trail, which is 2.5 miles one way, came up as 2.3 miles on the computer, but I carried over a muddy area.

  5. #5
    Guest
    Guest
    I believe mine to be pretty accurate, since it's based on a satellite signal I get in real time that tracks me as I'm moving.

    Koffee

  6. #6
    Senior Member
    Join Date
    Feb 2004
    Location
    Cleveland, OH
    My Bikes
    2004 Trek 4600, 1980's Univega Supra Sport, 2006 Lemond Reno
    Posts
    2,287
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by Koffee Brown
    I believe mine to be pretty accurate, since it's based on a satellite signal I get in real time that tracks me as I'm moving.

    Koffee
    Oh my!!!

  7. #7
    Adios, Mofo J-McKech's Avatar
    Join Date
    Oct 2003
    Location
    SXSW central
    My Bikes
    Bianchi Brava, Surly Instigator FR
    Posts
    1,651
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    How much did THAT cost koffee
    I am Signature-less

  8. #8
    Senior Member mindbogger's Avatar
    Join Date
    Jul 2003
    Posts
    933
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by Koffee Brown
    I believe mine to be pretty accurate, since it's based on a satellite signal I get in real time that tracks me as I'm moving.

    Koffee
    heehe do you have to pay a monthly service charge
    00' Cannondale R1000
    01' Devinci Chilipepper

    When sh*t hits the fan, everything I'm not, made me everything I am.

  9. #9
    DEADBEEF khuon's Avatar
    Join Date
    Aug 2002
    Location
    Catching his breath alongside a road near Seattle, WA USA
    My Bikes
    1999 K2 OzM, 2001 Aegis Aro Svelte
    Posts
    12,155
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by Koffee Brown
    I believe mine to be pretty accurate, since it's based on a satellite signal I get in real time that tracks me as I'm moving.
    GPS isn't always super-accurate either. CEP can be as low as 12ft. but can be as high as 300ft. or more... especially if SA is in effect. Now of course you may be able to get to the 1ft. accuracy scale using dGPS or WAAS but that's also subject to SA. So the problem is that while GPS may be (most of the time) more accurate than a standard wheel-sensor based recording device, it is not reliably accurate. The amount of jitter can be considerable. The best system is a hybrid one. That is to say that like those found in aviation units where an INS uses GPS with WAAS/dGPS to checkpoint itself.
    1999 K2 OzM 2001 Aegis Aro Svelte OCP Club Member
    "Be liberal in what you accept, and conservative in what you send." -- Jon Postel, RFC1122

  10. #10
    ÖöÖöÖöÖöÖö Dannihilator's Avatar
    Join Date
    Oct 2002
    Location
    Annandale, NJ.
    My Bikes
    2014 Surly Steamroller, 1977 Puch Pathfinder
    Posts
    18,789
    Mentioned
    20 Post(s)
    Tagged
    1 Thread(s)
    Very Accurate.

    Don't use one.
    Strike like an eagle and sacrifice the dove.
    Words and Stuff.

  11. #11
    Keepin' it real since '84
    Join Date
    Jan 2004
    Location
    Oklahoma
    My Bikes
    Jamis Komodo
    Posts
    348
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by Koffee Brown
    I believe mine to be pretty accurate, since it's based on a satellite signal I get in real time that tracks me as I'm moving.

    Koffee
    mine has a rocket launcher on it to remove obstacles or chubby hikers.

  12. #12
    DEADBEEF khuon's Avatar
    Join Date
    Aug 2002
    Location
    Catching his breath alongside a road near Seattle, WA USA
    My Bikes
    1999 K2 OzM, 2001 Aegis Aro Svelte
    Posts
    12,155
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Assuming the organisers of the ride did accurate measurements themselves, I'd say my bike computer isn't entirely all that accurate... well... at least not on the second day.

    First day was supposed to cover 100 miles....



    Second day, 106 miles..



    Also keep in mind that stray EM can sometimes screw with the readings too. Here's a maximum recorded speed on one descent that ended with me standing on top of a traffic sensor. The EM pulses that the sensor (essentially a metal detector) uses to induce an EM response field in order to detect the metal of cars can play havoc with your wheel pickup and create anomalies.
    Last edited by khuon; 05-03-04 at 11:14 PM.
    1999 K2 OzM 2001 Aegis Aro Svelte OCP Club Member
    "Be liberal in what you accept, and conservative in what you send." -- Jon Postel, RFC1122

  13. #13
    Senior Member mindbogger's Avatar
    Join Date
    Jul 2003
    Posts
    933
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    146.1 miles/hour...hmmm...New York to Chicago in.....

    As for the first pic, COMEON! for a 206mile ride your bound to be a bit off! For that distance I would give or take 10 miles
    00' Cannondale R1000
    01' Devinci Chilipepper

    When sh*t hits the fan, everything I'm not, made me everything I am.

  14. #14
    DEADBEEF khuon's Avatar
    Join Date
    Aug 2002
    Location
    Catching his breath alongside a road near Seattle, WA USA
    My Bikes
    1999 K2 OzM, 2001 Aegis Aro Svelte
    Posts
    12,155
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by mindbogger
    146.1 miles/hour...hmmm...New York to Chicago in.....

    As for the first pic, COMEON! for a 206mile ride your bound to be a bit off! For that distance I would give or take 10 miles
    Actually, that's what another rider at the finish line said to me when I pointed out the mileage on my computer. He showed me his and it was off by about 8 miles (reading high). I guess what I should have said was that it wasn't entirely unexpected to see a discreption but that there is one.
    1999 K2 OzM 2001 Aegis Aro Svelte OCP Club Member
    "Be liberal in what you accept, and conservative in what you send." -- Jon Postel, RFC1122

  15. #15
    1.64x10^6 posts Grendel's Avatar
    Join Date
    Aug 2002
    Location
    Spring, TX
    Posts
    501
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    I calibrated both of mine (roadie and MTB) by measuring the rollout while on the bike and found that there's about a 2-3% difference from what is given in the wheel sizing charts. Not a big difference, but enough to notice on longer rides like khuon mentioned.

  16. #16
    DEADBEEF khuon's Avatar
    Join Date
    Aug 2002
    Location
    Catching his breath alongside a road near Seattle, WA USA
    My Bikes
    1999 K2 OzM, 2001 Aegis Aro Svelte
    Posts
    12,155
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by Grendel
    I calibrated both of mine (roadie and MTB) by measuring the rollout while on the bike and found that there's about a 2-3% difference from what is given in the wheel sizing charts. Not a big difference, but enough to notice on longer rides like khuon mentioned.
    Well, I calibrated with the rollout method too using an average of several back-to-back rollouts. Also note that several factours will effect tyre dimensions slightly across the course of a ride. In addition, the computer itself may not have as fine a precision when setting the dimensions. My Shimano FlightDeck has 5mm granularity for tyre circumference.
    1999 K2 OzM 2001 Aegis Aro Svelte OCP Club Member
    "Be liberal in what you accept, and conservative in what you send." -- Jon Postel, RFC1122

  17. #17
    droppin a deuce
    Join Date
    Apr 2006
    Location
    Regina
    My Bikes
    1996 Raleigh Tarantula - haha!!
    Posts
    13
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Any recommendations as to where to mount the Cateye Micro Wireless sensor (distance from hub) to attain a fairly accurate measurement. The manual says at the top of the fork, but this seemed a little unclear...any tips?

  18. #18
    Senior Member
    Join Date
    May 2004
    Posts
    1,398
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)

    Suggestion ...

    Quote Originally Posted by deuce_nuts
    Any recommendations as to where to mount the Cateye Micro Wireless sensor (distance from hub) to attain a fairly accurate measurement. The manual says at the top of the fork, but this seemed a little unclear...any tips?
    It doesn't matter. One trip around is a single rotation, it doesn't matter at what distance from the hub it is measured.

    My hunch for making a unit more accurate is to get an extra sensor and put the second one on the exact opposite spoke. Than you input a circumference half as much as you roll out. This will keep the speedometer from jumping around and making large jumps.

  19. #19
    Senior Member
    Join Date
    Jan 2006
    Posts
    307
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Shouldn't it be better to get the magnet as close to the sensor as possible?

  20. #20
    droppin a deuce
    Join Date
    Apr 2006
    Location
    Regina
    My Bikes
    1996 Raleigh Tarantula - haha!!
    Posts
    13
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    ... oh yeah, thanks! Sometimes my fingers type before I think...

    Happy trails!

  21. #21
    Senior Member
    Join Date
    Sep 2005
    Location
    Monterey, CA
    My Bikes
    Stumpjumper FSR 30th Anniversary
    Posts
    247
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by deuce_nuts
    Any recommendations as to where to mount the Cateye Micro Wireless sensor (distance from hub) to attain a fairly accurate measurement. The manual says at the top of the fork, but this seemed a little unclear...any tips?
    The distance from the hub doesn't matter - what does matter is the distance of the sensor from the computer. Cateye says keep it within 70mm to not compromise reception and get crappy readings, hence the top of the fork.

    I have mine mounted about 8-10" above the axle to and it's well within the 70mm specified. Remember, the sensor mount doesn't have to sit square on the fork - the sensor swivels in the mount so you can get it close to the magnet and still have the face of the sensor square to the magnet. If you like, I'll take some pics later on tonight to illustrate what I mean.

    Edit: BTW - the manual says to have the magnet within 5mm of the sensor as it goes by...

  22. #22
    Senior Member ken cummings's Avatar
    Join Date
    Dec 2005
    Location
    northern California
    My Bikes
    Bruce Gordon BLT, Cannondale parts bike, Ecodyne recumbent trike, Counterpoint Opus 2, miyata 1000
    Posts
    5,605
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by Person
    How accurate is your cycle computer? I just put on a Sigma BC1200. I road a mile and marked exactly on the road where it came up a mile. I then jumped in my truck and drove the same route. It probably came out to be about 1/15 of a mile off.

    My truck could be off or the computer could be off; I am not sure. Is it impossible to get them to read perfectly accurate?

    Thanks,

    Person
    Perfectly accurate? "No" Werner Heisenberg. Close enough? "Yes" any engineer. A local agency put 1/2 and 1 mile marks on a local flat, straight MUP. My bike was 0.4% low. I went back the other way dodging and weaving like there were a lot of other path users. Now it read 2% high. Close enough.
    This space open

  23. #23
    Senior Member
    Join Date
    Sep 2005
    Location
    Monterey, CA
    My Bikes
    Stumpjumper FSR 30th Anniversary
    Posts
    247
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    there's also a lot of discussion in this thread from the mechanics forum:

    Circumference Question

  24. #24
    Senior Member iamthetas's Avatar
    Join Date
    Aug 2003
    Location
    colonial heights Va
    My Bikes
    Devinci Guzzler, 04 Canadian version
    Posts
    1,200
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    my 1200 was dead accurate after doing the wheel measure thing. I started at the valve stem down and marked a spot then rolled the wheel until it was down again and made another mark then measured. different tires use different settings, even ones with the same width.
    I have done the same thing with my 1600 and its just as acurrate
    for the creation was subjected to futility,not willingly , but because of Him who subjected it in hope...that he might be the firstborn among many brethren. Romans 8:20-29
    the truth may not always be popular but its always true
    http://mysite.verizon.net/vzer3fnu/p...pcomingevents/

  25. #25
    Senior Member
    Join Date
    Apr 2006
    Location
    Polo, IL
    Posts
    201
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    I just got the same computer today as the poster did. After calibrating with the instructions, I found that mine was about 6/100 of a mile off (under). That's good enough for me. I might recalibrate based on what I've been reading here, but i don't think i'll get or need much better.

Page 1 of 2 12 LastLast

Posting Permissions

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