Hi out there,
I recently purchased a Sigma Rox 5.0 (bike/run HRM computer that also measures cadence). I was excited to find it at REI for a fraction of the price of the garmin equivalent (~$200) and thought this was likely due to the fact that the Sigma Rox 5.0 does not have GPS (a feature I did not think necessary).
Anyway, my cadence sensor is spotty at best. Really frustrating. The only time it reads is if I'm under 50 rpm and it's still inconsistent.
Has anyone out there had experience with this? It could be me but I've played with it quite a bit and tried to be patient - just dont know at what point to stop. I'm typically not great with technology - but my $20 performance bike computer never gave me a issue.
REI does have a pretty generous return policy...
I won a Sigma Rox bike computer a few years ago, but I never used it because of the lack of GPS. I think GPS is a very important feature for a bike or run computer. Mostly so that the gadget takes care of the numbers and I can just enjoy riding. I load the data to my computer later on because I like to have some idea of what my training is like from week to week and month to month.
But during the ride, I don't want to focus on all those numbers. I go for a set time or certain intervals at certain effort levels, and I let the bike computer keep track of all the data.
I wouldn't think that a non-GPS computer is going to track distance or speed that accurately. That would make it a glorified watch, I think.
So my recommendation would be to return the Sigma and get a Garmin or other GPS bike computer. It will be more expensive than the Sigma. But you could look for an older Garmin model online. The unit would still be new, but just not the latest and greatest model. DC Rainmaker has good reviews of various tri-related gadgets and recommendations based on how you are likely to use them.
No experience with a Sigma - but I do know that a Garmin 910 paired with a Garmin speed/cadence sensor will default to the speed sensor over GPS (sensor tracks rotations of wheel) to track speed/distance. This is also how simple Cateye and the like bike computers work to calculate speed/distance. So as long as everything is set up correctly I'm not sure GPS is actually 'better' than a speed sensory. Most forums and articles say the speed sensory should be more accurate.
I know cadence sensor's can be finicky and after traveling with your bike or even just going out for a ride you made need to readjust the magnets to ensure everything is working properly. It looks like Garmin actually recently came out with a new magnetless cadence sensor. http://www.dcrainmaker.com/2014/05/garmins-spd-cad-magnetless-sensors.html.
I have a simple (and cheap) CatEye Strada Double Wireless that measures speed and cadence. It works just fine and has all the data that I need to train. The sensor measures the back wheel so it also works on the indoor trainer too.
As Holli stated, you may want to check the distance between the sensor and magnet to verify it is within the right distance. If they are not correctly aligned, the measurement may be off or not work at all.