# Quick help with Trek "DuoTrap" / Garmin Edge 500 install



## Porschefan (Nov 12, 2011)

Maybe this should go somewhere else--but I'm not sure where. My new Trek Domane 4.0 is on the bike stand on the back porch and I'm trying to install the Trek DuoTrap speed/cadence sensor on it in time for tomorrow's ride. 

So far no real difficulty, BUT I just realized since the Edge 500 is a GPS-based computer, why would I want to measure the speed via a magnet attached to a spoke on the rear wheel? And would it even work? Could you set up the Garmin 500 to work either way?

I'm hoping I might catch someone here with info. Otherwise I'll just have to stop before I remove the DuoTrap from it's packaging.

I have the Garmin cadence sensor, but I thought I would hook that up to my mountain bike and just move the Edge 500 from bike to bike.

TIA for any help.

STP


----------



## kookieCANADA (Jan 20, 2011)

I use the 500 with the DuoTrap on my Madone. The garmin should detect the sensor and use that instead of the GPS. I think the sensor is more accurate. If the garmin can't detect the sensor it will use the GPS. Don't forget about using the cadence magnet too.

It looks cleaner too having the DuoTrap tucked inside the chainstay.


----------



## Porschefan (Nov 12, 2011)

Thanks! I was assuming that GPS would be more accurate, but not so? 

It sure does look nicer than zip ties. Thought I would treat myself but I didn't think it through! 


STP


----------



## Porschefan (Nov 12, 2011)

If I just left off the wheel magnet, would the Garmin default to the GPS? 

STP


----------



## redondoaveb (Jan 16, 2011)

Porschefan said:


> Thanks! I was assuming that GPS would be more accurate, but not so?
> 
> It sure does look nicer than zip ties. Thought I would treat myself but I didn't think it through!
> 
> ...


I use gps on my Garmin 800 for speed and it's extremely accurate.


----------



## redondoaveb (Jan 16, 2011)

Porschefan said:


> If I just left off the wheel magnet, would the Garmin default to the GPS?
> 
> STP


I can't remember for sure but I think you need to go to "system", "GPS" and make sure "GPS mode" is turned on.


----------



## Porschefan (Nov 12, 2011)

Here's some data I found at the "DC Rainmaker" site :

_*Question:

I've been running my DuoTrap without the spoke magnet and simply getting my speed readings from my Edge 500. Is this an acceptable setup or would you recommend using the spoke magnet? If so, how does the Edge know whether it should use the GPS or the spoke magnet for speed?

Reply:

Rainmaker replied
June 9, 2013 at 7:48 pm #73

The Edge will use the wheel spoke for display of speed assuming the speed is greater than zero, but actual recorded speed will always come from GPS unless GPS is off.*_

STP


----------



## Porschefan (Nov 12, 2011)

UPDATE:

I installed the DuoTrap today--no real difficulties. According to instructions the two (speed and cadence) magnets are supposed to trigger the green and red LED's for testing the proper location, but I had some problems seeing whether they were working correctly or not--instrux say they only activate on the first 10 revolutions, so that may have been the problem.

I mounted my Edge 500 (Craigslist or eBay find from a couple years ago, never used until now) and went for a ride. Everything seemed to work great--I had speed, cadence and heart rate all showing up! I can't say with certainty where the speed reading is coming from, but I'm assuming its the rear wheel magnet. When the Edge 500 fires up it just says "Speed/Cadence sensor detected and Heart Rate Monitor detected.) Anyway I'm very happy to have this on the bike so I can stay in my cadence/heart rate "box" while training.

STP


----------

