Garmin speed sensor

bugsrabbit
bugsrabbit Posts: 182
edited April 2014 in Road buying advice
Would i see an improvment in accuracy by using the garmin speed/cadence sensor over just the gps tracking?

Comments

  • wishitwasallflat
    wishitwasallflat Posts: 2,927
    Yes the distance travelled and hence speed and other related derived measures is more accurate with the speed sensor than gps. Also cadence is the most useful of all data IMO

    PS - If you want to try it and see for less money the Decathlon ones are often recommended and are way cheaper than Garmin GSC 10s

    http://www.decathlon.co.uk/ant-speed-ra ... 81211.html

    .
  • cattytown
    cattytown Posts: 647
    Bear in mind the job the speed/cadence sensor has to do, and you have to consider it a consumable. Get the decathlon one.
    Giant Defy 2
    Large bloke getting smaller :-)
  • ai_1
    ai_1 Posts: 3,060
    Yes, speed accuracy and update speed will be far more accurate with a speed sensor.
    cattytown wrote:
    Bear in mind the job the speed/cadence sensor has to do, and you have to consider it a consumable. Get the decathlon one.
    This makes no sense!
    In what way is it a consumable?
    Mine is 3 years old and still in perfect condition. There are no moving parts so no reason for it to wear out amd the battery is replaceable.
    Your comment couldn't be much less accurate. Barring an accident, it should last longer than nearly every other part of the bike including the bike computer.
  • wishitwasallflat
    wishitwasallflat Posts: 2,927
    Not sure about cadence but speed is measured with a reed switch which is not the most robust of things,they sit on the chain stay with no protection and click on and off thousands of times per ride. I expect the point is that take some punishment so don't expect them to last forever.
  • JackPozzi
    JackPozzi Posts: 1,191
    I've managed to kill several GSC10s, although they're fine in wet conditions they often malfunction after being washed for some bizarre reason.
  • ai_1
    ai_1 Posts: 3,060
    JackPozzi wrote:
    I've managed to kill several GSC10s, although they're fine in wet conditions they often malfunction after being washed for some bizarre reason.
    Are you spraying them with a water jet or using detergent on it? It's an electronic device. They seem to be sealed just fine for normal use, wet or dry, but washing it in degreaser, submerging it or hitting it with a jetwash is just silly and I have heard stories of a few people killing them that way. I haven't heard of one failing for any other reason. Doesn't mean it can't happen but it doesn't seem to be an "issue". You can clean them just fine with a damp cloth. I think if I'd killed several by washing them as you have, I'd figure out not to wash them! If you're planning to use a jet washer or lots of degreaser around the sensor just wrap a bit of cling film around it until you're finished and it'll be fine.

    It's perfectly reasonable to expect to get several years use out of one.
  • JackPozzi
    JackPozzi Posts: 1,191
    edited April 2014
    Just wash my bikes with car shampoo and rinse with a hose on the gentle setting, I figured out to stop using gsc10s on the bikes that get cleaned regularly! Happily I use a powertap wheel which handles cadence adequately on my nice bikes so not an issue, and gsc10s on winter steeds that get cleaned so rarely it's not too much hassle to remove the sensor for washing
  • DiscoBoy
    DiscoBoy Posts: 905
    Taping a sandwich bag/ some cling film over your sensor stops issues with water when you're washing your bike :)
    Red bikes are the fastest.
  • cattytown
    cattytown Posts: 647
    Ai_1 wrote:
    Yes, speed accuracy and update speed will be far more accurate with a speed sensor.
    cattytown wrote:
    Bear in mind the job the speed/cadence sensor has to do, and you have to consider it a consumable. Get the decathlon one.
    This makes no sense!
    In what way is it a consumable?
    Mine is 3 years old and still in perfect condition. There are no moving parts so no reason for it to wear out amd the battery is replaceable.
    Your comment couldn't be much less accurate. Barring an accident, it should last longer than nearly every other part of the bike including the bike computer.

    In the crappy spray from the wheel, easily caught when changing a wheel and knocked out of alignment. If hung below the chainstay it will just get hit by spokes and the magnet until it is out of the way. If mounted above the chainstay and knocked, the contact with the first spoke may not be that safe. A slightly hamfisted battery change and the seal doesn't anymore.

    Happy with that explanation, or are your maintenance skills so perfect that your sensor never gets moved out of position?
    Giant Defy 2
    Large bloke getting smaller :-)
  • Sprool
    Sprool Posts: 1,022
    oh, seem to have strayed off topic as is the custom here. ;)
    Speed sensor is only as accurate as what you set up the wheel size to be. The Garmin units auto-calibrate using gps data to verify distance along with the wheel revolutions. A mm or two out on circumference will make a big error in distance over a long ride whereas gps data will tend to get more accurate as distances increase. Take your pick. But do put a bag over it before you take it into the car wash.
  • ai_1
    ai_1 Posts: 3,060
    cattytown wrote:
    ....Happy with that explanation, or are your maintenance skills so perfect that your sensor never gets moved out of position?
    Nothing to do with maintenance skills. I simply think you're making a big deal over nothing. If I knew nothing about the things and read your comments and JackPozzi's I'd leave thinking these were temperamental, unreliable and shortlived devices. That's simply nonsense!
    I've treated mine as nearly fit and forget. I've never had to do anything with it since I fitted it 3 years ago. Haven't even had to change the battery yet. I check the magnet isn't coming loose every so often or if I change wheels I transfer the magnet over and check to make sure the clearance doesn't need to be adjusted. The end. So maybe 1 or 2 minutes of consideration a year.
  • cattytown
    cattytown Posts: 647
    Treat them with care and they will last - fair enough, but they ARE in a vulnerable position, so there's little benefit in spending a lot of money on one when you can get the decathlon.
    Giant Defy 2
    Large bloke getting smaller :-)
  • porker33
    porker33 Posts: 636
    Definite more accuracy with the speed sensor and cadence.....I used my Garmin 500 with just GPS tracking for a while and the speed would dance between 19.80 to 20.2 to 20.4 etc....without any noticeable change....the data from the speed sensor was less erratic.....although momentary speed is not that important as the avg speed for the ride seemed to make sense on Strava...

    I have both Gsc10 & Decathlon sensors.....The Decathlon one just fits so much better on the stays of my Madone than the Garmin....it may come down to your bike design.
  • slowbike
    slowbike Posts: 8,498
    Ai_1 wrote:
    Yes, speed accuracy and update speed will be far more accurate with a speed sensor.
    cattytown wrote:
    Bear in mind the job the speed/cadence sensor has to do, and you have to consider it a consumable. Get the decathlon one.
    This makes no sense!
    In what way is it a consumable?
    Mine is 3 years old and still in perfect condition. There are no moving parts so no reason for it to wear out amd the battery is replaceable.
    Your comment couldn't be much less accurate. Barring an accident, it should last longer than nearly every other part of the bike including the bike computer.

    Actually - there are moving parts - but they're inside ... the magnet triggers a relay ... in theory that could wear out, but in practice you'll probably bust the unit by kicking it into the wheel first ... ;)
  • ai_1
    ai_1 Posts: 3,060
    Slowbike wrote:
    Ai_1 wrote:
    Yes, speed accuracy and update speed will be far more accurate with a speed sensor.
    cattytown wrote:
    Bear in mind the job the speed/cadence sensor has to do, and you have to consider it a consumable. Get the decathlon one.
    This makes no sense!
    In what way is it a consumable?
    Mine is 3 years old and still in perfect condition. There are no moving parts so no reason for it to wear out amd the battery is replaceable.
    Your comment couldn't be much less accurate. Barring an accident, it should last longer than nearly every other part of the bike including the bike computer.

    Actually - there are moving parts - but they're inside ... the magnet triggers a relay ... in theory that could wear out, but in practice you'll probably bust the unit by kicking it into the wheel first ... ;)
    Yes, mea culpa, I had missed the fact that the switch is a moving part. Nevertheless, these seem to have good lifespans and the comment that they should be considered a "consumable" is nonsense.
  • ai_1
    ai_1 Posts: 3,060
    porker33 wrote:
    Definite more accuracy with the speed sensor and cadence.....I used my Garmin 500 with just GPS tracking for a while and the speed would dance between 19.80 to 20.2 to 20.4 etc....without any noticeable change....the data from the speed sensor was less erratic.....although momentary speed is not that important as the avg speed for the ride seemed to make sense on Strava...
    The location accuracy on Garmin GPS sports devices is not that fantastic. There can be an error of several metres or more which can vary continuously. This is reflected in the accuracy of speed calculations, especially at low speeds, as the calculated distance travelled in a given period of time is inaccurate for short periods of time. GPS works very well for distance and average speed over long periods of time (as long as you don't have lots of sharp turns and high buildings/dense trees) but for dynamic measurements it's poor. The wheel magnet based sensors are much better for instantaneous speed data as you get an accurate time measurement for every rotation of the wheel.
    I believe the uploaded speed data from your Garmin are based on GPS data as it doesn't always match exactly with what you've seen on the screen during the ride - not certain about this though.
  • wongataa
    wongataa Posts: 1,001
    Ai_1 wrote:
    The location accuracy on Garmin GPS sports devices is not that fantastic.
    The location accuracy of consumer GPS devices is not the most it coud be because it doesn't need to be. The possibility of being 5-10m out is fine for consumer GPS uses.
    Ai_1 wrote:
    I believe the uploaded speed data from your Garmin are based on GPS data as it doesn't always match exactly with what you've seen on the screen during the ride - not certain about this though.
    The overview speed data on Garmin Connect will match what was on your screen during your ride. Other sites can only use the GPS logs to calculate the various speeds. Any graphs on any site will be generated from GPS data.
  • ai_1
    ai_1 Posts: 3,060
    wongataa wrote:
    Ai_1 wrote:
    The location accuracy on Garmin GPS sports devices is not that fantastic.
    The location accuracy of consumer GPS devices is not the most it coud be because it doesn't need to be. The possibility of being 5-10m out is fine for consumer GPS uses.
    Agreed, it's sufficient for most endurance sport activities. Wouldn't be much good for tracking 100m sprints but then with 1s intervals for recording that wouldn't be much use anyway.
    Top level GPS accuracy is superb by comparison (errors measured in millimeters not meters, even in the vertical plane) but completely unnecessary for most purposes.

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