garmin 500 and speed sensor

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gubber12345
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garmin 500 and speed sensor

Postby gubber12345 » Tue Aug 20, 2013 19:54 pm

hi

for those of you who have the garmin 500 and using the cadence/speed sensor do you use the auto function to find the size of your wheel using the gps or do you measure the wheel and enter it manually?

which is more accurate do you think?
cannondale supersix

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simona75
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Re: garmin 500 and speed sensor

Postby simona75 » Tue Aug 20, 2013 20:01 pm

I just used the auto function when I first got mine. Don't know if its more or less accurate than manually setting though (hopefully less and I'm actually riding 5 mph faster than it says I am :) )

Dav1d1
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Re: garmin 500 and speed sensor

Postby Dav1d1 » Tue Aug 20, 2013 23:24 pm

simona75 wrote:I just used the auto function when I first got mine. Don't know if its more or less accurate than manually setting though (hopefully less and I'm actually riding 5 mph faster than it says I am :) )


Same

wongataa
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Re: garmin 500 and speed sensor

Postby wongataa » Wed Aug 21, 2013 07:17 am

I have an edge 800 and manually set my wheel size when I got a speed/cadence sensor. That is more accurate as GPS drift can easily make the auto setting under or oversize your wheel and your wheel size will likely change every time it auto sets the size.

Marcusww
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Re: garmin 500 and speed sensor

Postby Marcusww » Wed Aug 21, 2013 11:23 am

GOt the 500 and use the manual option due to slight GPS inaccuracy.

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TheFD
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Re: garmin 500 and speed sensor

Postby TheFD » Wed Aug 21, 2013 11:51 am

I manually enter it.

700 x 19C is 2080
700 x 20C is 2086
700 x 23C is 2096
700 x 25C is 2105
700 x 28C is 2136
700 x 30C is 2170
700 x 32C is 2155

IMHO much more accurate!
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gubber12345
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Re: garmin 500 and speed sensor

Postby gubber12345 » Wed Aug 21, 2013 19:46 pm

yeah think I'll go the manual route also seems to me it would be a lot more accurate when you think about it.

thanks for the wheel measurements FD. :wink:
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SmoggySteve
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Re: garmin 500 and speed sensor

Postby SmoggySteve » Wed Aug 21, 2013 20:05 pm

TheFD wrote:I manually enter it.

700 x 19C is 2080
700 x 20C is 2086
700 x 23C is 2096
700 x 25C is 2105
700 x 28C is 2136
700 x 30C is 2170
700 x 32C is 2155

IMHO much more accurate!


Problem with this is, 2 tyres of different makes both saying they are 700 x 23C may be different. One could actually be more like a 20 or a 25 depending on the way they measure. Also, Tubs and clinchers can be very different on the "same size" so which do you believe? They cannot all be correct if there are discrepancies between manufacturers.

wongataa
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Re: garmin 500 and speed sensor

Postby wongataa » Wed Aug 21, 2013 20:54 pm

But you can always measure your own wheel for ultimate accuracy.

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TheFD
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Re: garmin 500 and speed sensor

Postby TheFD » Wed Aug 21, 2013 21:36 pm

SmoggySteve wrote:
TheFD wrote:I manually enter it.

700 x 19C is 2080
700 x 20C is 2086
700 x 23C is 2096
700 x 25C is 2105
700 x 28C is 2136
700 x 30C is 2170
700 x 32C is 2155

IMHO much more accurate!


Problem with this is, 2 tyres of different makes both saying they are 700 x 23C may be different. One could actually be more like a 20 or a 25 depending on the way they measure. Also, Tubs and clinchers can be very different on the "same size" so which do you believe? They cannot all be correct if there are discrepancies between manufacturers.

But it will be more accurate than your bike 'guessing' wrongly the size. You could say what about when the tyre is part worn it won't be the same size as when new. I think you need to try to get it as accurate as possible without being OT about it.
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SmoggySteve
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Re: garmin 500 and speed sensor

Postby SmoggySteve » Wed Aug 21, 2013 21:47 pm

TheFD wrote:
SmoggySteve wrote:
TheFD wrote:I manually enter it.

700 x 19C is 2080
700 x 20C is 2086
700 x 23C is 2096
700 x 25C is 2105
700 x 28C is 2136
700 x 30C is 2170
700 x 32C is 2155

IMHO much more accurate!


Problem with this is, 2 tyres of different makes both saying they are 700 x 23C may be different. One could actually be more like a 20 or a 25 depending on the way they measure. Also, Tubs and clinchers can be very different on the "same size" so which do you believe? They cannot all be correct if there are discrepancies between manufacturers.

But it will be more accurate than your bike 'guessing' wrongly the size. You could say what about when the tyre is part worn it won't be the same size as when new. I think you need to try to get it as accurate as possible without being OT about it.


End of the day, it does not matter what size wheel it thinks it is measuring. When using a GPS, it will take its accuracy from the GPS track, which is more accurate anyway. It only matters if you lose your signal to give you a speedo. Do you need to know that accurate your speed at the time? I would not think a 700x20 or 700x23 would be that different anyway. The circumference is still 700. in a straight line width should not effect the measurement. This would only matter when you look at the readout anyway. When you upload the track, the GPS information will dictate how fast you actually went regardless what the screen says while travelling

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TheFD
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Re: garmin 500 and speed sensor

Postby TheFD » Wed Aug 21, 2013 22:03 pm

SmoggySteve wrote:
TheFD wrote:
SmoggySteve wrote:
TheFD wrote:I manually enter it.

700 x 19C is 2080
700 x 20C is 2086
700 x 23C is 2096
700 x 25C is 2105
700 x 28C is 2136
700 x 30C is 2170
700 x 32C is 2155

IMHO much more accurate!


Problem with this is, 2 tyres of different makes both saying they are 700 x 23C may be different. One could actually be more like a 20 or a 25 depending on the way they measure. Also, Tubs and clinchers can be very different on the "same size" so which do you believe? They cannot all be correct if there are discrepancies between manufacturers.

But it will be more accurate than your bike 'guessing' wrongly the size. You could say what about when the tyre is part worn it won't be the same size as when new. I think you need to try to get it as accurate as possible without being OT about it.


End of the day, it does not matter what size wheel it thinks it is measuring. When using a GPS, it will take its accuracy from the GPS track, which is more accurate anyway. It only matters if you lose your signal to give you a speedo. Do you need to know that accurate your speed at the time? I would not think a 700x20 or 700x23 would be that different anyway. The circumference is still 700. in a straight line width should not effect the measurement. This would only matter when you look at the readout anyway. When you upload the track, the GPS information will dictate how fast you actually went regardless what the screen says while travelling

Have a look at how many Garmins have bad gps data. Look at the rides - so many of them are way off course. IMHO it is far more accurate using the manual wheel size than bad GPS data, not just for speeds but also for distance. You can always tell by looking at the ride if they have need using manual wheel size or the GPS data by the top speed. 70mph plus is very common on GPS alone - yet very unlikely!
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SmoggySteve
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Re: garmin 500 and speed sensor

Postby SmoggySteve » Wed Aug 21, 2013 22:13 pm

If I set off from point A and arrive at point B five minutes later. It matters not one bit how much I had a signal or what the gps measured on wheel revolutions. So long as I had a signal at the start and finish, the middle date is irrelevant when it tells me how fast I was between them two points.

GPS take time stamps every second or how ever often you set it up to take a measurement. If you get an anomaly like 70mph it still can be corrected when you upload it. If it sees you were at point A 5 minutes before you were recorded at point B the program ie Strava or Garmin connect will correct it. Same way it can correct height. The Wheel measurement can only act as a checker to tell the GPS at the time that you were doing an estimated speed. The GPS anomaly will not be fixed by this.

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TheFD
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Re: garmin 500 and speed sensor

Postby TheFD » Wed Aug 21, 2013 22:33 pm

SmoggySteve wrote:If I set off from point A and arrive at point B five minutes later. It matters not one bit how much I had a signal or what the gps measured on wheel revolutions. So long as I had a signal at the start and finish, the middle date is irrelevant when it tells me how fast I was between them two points.

I don't follow your logic on this. What if it said you had gone to Australia on your way to point B, so your average speed was 10000mph. This data is next to useless. It has the distance incorrect and the speed - the only thing correct is you left point A and arrived at point B, but has no idea where and how far you went in between.
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SmoggySteve
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Re: garmin 500 and speed sensor

Postby SmoggySteve » Thu Aug 22, 2013 06:40 am

And neither does your wheel. Even though your gps uses this info in real time, if it has a signal, good or bad it will ignore it unless you tell it specifically no gps data.

ScreaminWargasm
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Re: garmin 500 and speed sensor

Postby ScreaminWargasm » Sun Aug 25, 2013 22:04 pm

When I first got my edge 500 I just used the auto detect method. When I looked into the size it had selected, it was 2096 which is spot on for a 23mm tyre.
Therefore its fairly accurate in my experience so I wouldn't worry about it too much.

Mick


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