# Speed/Cadence sensor vs just GPS



## dss8653 (Feb 2, 2013)

I'm trying to decide if its worth it to use a speed/cadence sensor on my Garmin or just rely on the GPS, which seems pretty accurate. This time of year, the trails around here are pretty muddy. Won't that interfere with the sensors?
I get the speed part, but is cadence really that crucial in mountain biking?
So who uses it and why?
BTW, I'm currently using a forerunner 305.


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## Cerberus044 (Jul 17, 2012)

Cadence is really a roadie thing more than a mtb thing. Unless youre riding mostly fire roads or lots of flat super slick xc I wouldn't worry about getting a cadence sensor. As far as mud effecting wheel magnet sensors I can't say I've ever had that happen. The rotation of the wheel keeps it off the magnet and the sensor on the fork is in a spot that doesn't see much splash. I've compared my garmin 500's speed/dist calc to my wheel magnet cateye enduro's measurements and I'd say 5-9% accuracy lost on the garmin just because of update frequency losses. Personally I use my gps for ride logging more than strava or anything else so I'm interested in altitude speed and distance and if I'm out on training rides heart rate and it's accurate enough for my purposes.


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## Noclutch (Jun 20, 2010)

I've been using the GSC10 with my forerunner 305 for the last 6 months or so. I like to use is as one rough gauge as to how I'm performing on the trail on any particular day, aside from time/avg speed/Strava data LOL. But if my avg cadence is down 5-10 rpm on flat XC trails I know that I've been slacking and pick it up mid ride. On very techy trail days it doesn't tell me much at all, though my cadence avg has been consistent and much lower (low 70's vs high 80's). I just got finished pairing the gsc10 to my 510 and looking forward to comparing the distances recorded by my cell's GPS vs both Garmins. I have no experience with mud FWIW :thumbsup:


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## ghettocruiser (Jun 21, 2008)

Ignoring for a minute the issue of whether you think cadence is useful knowledge:

If your device can do 1-second recording, the GSC-10 will only benefit a data junkie or people who frequently ride in areas with obstructed skyview (canyons, high buildings, etc).

If your device only does smart recording, distance accuracy will improve with the wheel magnet on trails that are twisty regardless of skyview.


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## willtsmith_nwi (Jan 1, 1970)

GPS is inaccurate when you are not travelling in straight lines. The method they use for distance calculation is to check position at regular intervals and then they just use the good old Pythagorean theorem. And yes in obstructed viewpoints the actual GPS positioning accuracy goes to hell.

The wheel sensor will fix the inaccuracies in the GPS. Then the GPS is just for showing where you've been (which is cool).

Yes, cadence is a roadie thing as MTBer's cadence tend to vary widely depending on what's coming up. However, A road/pathway biker will get very accurate results from an unaided GPS as roads tend to go in straight lines ;-)

The Garmin Speed/Cadence sensor is about $30.


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## Bailey44 (Dec 30, 2010)

I run the speed/cadence sensor on my road bike but couldn't care less about it on my MTB.

I couldn't imagine trying to look at cadence off road plus it's pretty easy to keep a nice cadence once you are used to knowing what it feels like from road riding.

I am certain that the speed/mileage would be more accurate if I used it on my MTB but I just don't care about all that on the trails. MTB is my fun time.


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## Harold (Dec 23, 2003)

willtsmith_nwi said:


> GPS is inaccurate when you are not travelling in straight lines. The method they use for distance calculation is to check position at regular intervals and then they just use the good old Pythagorean theorem. And yes in obstructed viewpoints the actual GPS positioning accuracy goes to hell.
> 
> The wheel sensor will fix the inaccuracies in the GPS. Then the GPS is just for showing where you've been (which is cool).
> 
> ...


It's not that bad. Yes, GPS alone has a little inaccuracy. But it's not absolute crap.


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## dss8653 (Feb 2, 2013)

Good points, thanks for the replies. I picked up a sensor and will put it on. I like trying to best previous times, so accuracy is important to me.


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## dss8653 (Feb 2, 2013)

Good points, thanks for the replies. I picked up a sensor and will put it on. I like trying to best previous times, so accuracy is important to me.


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## rsilvers (Aug 23, 2015)

I don't care about cadence on my MTB, but my power meter supplies it, and I do like having a power meter.

If you trail ride, I would get a speed sensor. I can ride with a friend side by side for 20 miles, and our GPS distances may be off by a mile. Who wants a 19.0 mph Strava speed if you went 20.0 mph. The speed sensor fixes that. Also it fixes auto-pause because it knows when you are really moving or not.


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