Pairing a Garmin 500 W/ SRM

[bearsdidit]

I recently purchased a DA SRM and had a couple of questions pairing it up with my 500. Will I still need the Garmin speed and cadence sensor? I've read a couple of different sources regarding zeroing the unit and can't seem to get a straight answer, can someone go over that for me? Sorry about redundant questions and thanks for your help!

[got2ride]

The SRM comes with its own magnet. This magnet must be installed as it activates the SRM. Generally the SRM magnet is installed under the BB getting the magnet close enough to the backside of the SRM so that it will activate the SRM. Once you have the magnet installed correctly, the SRM is activated by spinning the cranks. To pair to the 500, you go into the Menu, Settings, Bike Settings, and find Ant+ Power, click on ANT+ Power, be sure it is set to YES and click on Rescan (be sure you have spun the cranks to activate the SRM first). The 500 should start picking up the data. I use GPS for speed (so no need for Garmin speed magnet) and the SRM calculates cadence (so no need for Gramin Cadence unit). You don't have to calibrate the SRM for it to work. SRM does recommend that you calibrate at some point but it is not required.

[bearsdidit]

Great, thank you so much. While doing research between the Quarq and SRM, I learned that it was necessary to re-zero the quarq before every ride. Is the same thing necessary with a SRM? If so, what is the process?

Thanks again

[ms6073]

Generally the SRM magnet is installed under the BB getting the magnet close enough to the backside of the SRM so that it will activate the SRM.

Alternately, since some of the newer framesets with internal cable runs no longer use cable guides screwed into the bottom bracket shell, you can glue/tape a small rare earth magnet to the chainstay adjacent to bottom bracket shell.

You don't have to calibrate the SRM for it to work.

Depending on which powermeter is being used (PowerTap, Quarq, SRM, Vector, Power2Max), the 'Calibrate' selection actually has different meanings. For SRM users, yes 'Calibrate' can be used for performing a calibration of the SRM's slope but in this case, it is also how Garmin users manually set zero-offset. On a related note, I thought I had read somewhere that Garmin's firmware is coded such that when measured power output drops to zero for a period of 5-seconds, the Edge automatic runs/sets the zero-offset but I have not actually checked this during a training ride to see if that is implemented with the Edge 500/800.

[got2ride]

I am a little fuzzy on the Calibrate issue but can tell you that I have not re calibrated my 500/SRM in over a year and it works fine. ms6073 is correct, there are two Calibrate issues, one for the SRM and one for the 500. You should not have to worry about the SRM Calibrate. I believe that the 500 picks up the SRM slope when it pairs up and you should not have to change or re calibrate for the slope. If I remember correctly, you can click on calbrate and see the slope value in the 500 and that should match the slope value of your SRM. The Gramin Calibrate issue I believe Garmin suggests to do it once a month or if you travel somewhere. I think that you just click on Calibrate on let the 500 do its thing. I think that I read somewhere that this is just really fine tuning to a very small margin any changes for elevation, atmospheric pressure, etc. and any fine tuning done by re calibrating is probably not even noticiable. So no, you do not have to re calibrate before evry ride (again, I have not done it in over a year)

[ms6073]

If I remember correctly, you can click on calbrate and see the slope value in the 500 and that should match the slope value of your SRM.

In the case of an SRM, from the ANT+ Power view/screen, scrolling to/highlighting 'Sensor Details' and pressing the ENTER button on the side of the computer takes you to a screen that displays the powermeter serial # and the slope. Going back from that screen and highlighting the 'Calibrate' menu item and pressing the enter button takes you to a screen that displays the current and saved values for zero-offset. In this state, if you do not apply a load to the pedals, after ~5-seconds the Garmin automatically records/saves the new offset value and I think you then highlight 'Save' and press enter which takes you back to the previous page.

[LarsEjaas]

Depending on which powermeter is being used (PowerTap, Quarq, SRM, Vector, Power2Max), the 'Calibrate' selection actually has different meanings. For SRM users, yes 'Calibrate' can be used for performing a calibration of the SRM's slope but in this case, it is also how Garmin users manually set zero-offset. On a related note, I thought I had read somewhere that Garmin's firmware is coded such that when measured power output drops to zero for a period of 5-seconds, the Edge automatic runs/sets the zero-offset but I have not actually checked this during a training ride to see if that is implemented with the Edge 500/800.

I am almost 100% sure this is true - that some sort of auto zero is being used on the Garmin edge 500. The reason I am almost sure is, that the accepted zero offset some time changes during a ride.

[bearsdidit]

great stuff, thanks again guys.

[Geoff]

There is a big difference between calibrating the SRM and the zero-offset. The calibration really only needs to be done periodically or if you change the battery or certain components on the SRM (e.g., the cranks). The zero-offset needs to be done at least every ride.

[bearsdidit]

From my reading, the SRM gets calibrated at the factory and the zero-offset is:

For zeroing the crank, put the crankarms at 9 and 3, then go into your Garmin and press the calibrate button. I only have the 705, but it seems to auto zero my SRM while riding, I still zero it before intervals and at the start of a ride though.

Mas o menos?

[Geoff]

As opposed to the slope, which is the actual frequency at which the PowerMeter transmits, the zero-offset is an internal test of the 'base' condition in which the strain gauges are at prior to your ride. The strain gauges are affected by certain environmental conditions, like temperature, pressure etc. and the zero-offset adjusts for these daily factors in the calcualtion of power.

I am not sure on the science behind why the PowerMeter slope fluxuates over time, Uli (or Leslie) can probably help explain that better than I, all I know is that it does. Depending on the time between battery replacements, you may need to recalibrate several times before replacing the battery. It is a fairly simple process and you can do it in less than 30 minutes.

[bearsdidit]

As usual, thanks for your help.

[ghisallo2003]

Slightly OT, but:

I am having a slightly strange problem. My SRM pairs fine with my Garmin 500 and shows all values.

When I transfer to Garmin Training Centre, though, it does not have cadence data (although it fails to show a graph, rather than saying 'no data' which it would if there was no power meter attached).

When I export the file to Golden Cheetah the cadence data IS there.

Any thoughts?

[ms6073]

I download from our SRMs direct to Peaksware WKO but still have to use Garmin Training Centre for my Garmin 910XT but never paid attention to cadence after a download. This sounds like a bug with Training Centre, but Garmin discontinued support for that application more than 2-years ago, so really not much to be done.