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Dropouts of various sensors with 935 not seen on edge 1000

Former Member over 7 years ago

So I just got a new Forerunner 935 from an authorized dealer and paired it with my heartrate monitor, cadence sensor, speed sensor, power meter, DI2 and VIRB radar. I performed my first ride on Sunday while wearing it on my wrist. I also used my trusty Garmin Edge 1000 at the same time to capture and compare the data later. The 935 suffered several dropouts of the power meter and cadence while loosing the heart rate meter as well. The 1000 performed much better and didn't experience such dropouts so the averaged data between the two is quite a bit different.

See the attached images where I compare the recorded power between the two devices. The 935 has 0 watts for a much longer time indicating the time it was disconnected from my P1 power meter pedals. The average power between the two is 30W. I've also attached images of the same segment captured by the 935 and edge 1000. The 935 drops the power and cadence several times and even drops the heartrate monitor.

Any suggestions? Should I contact Garmin for an RMA? I've read some people experience dropouts with the 935 but it can be device specific so I may have just gotten a bad unit. My goal is to use the watch to capture all the data and use the edge 1000 only as a display screen while I ride (since Firstbeat Training info isn't shared between devices I must use the watch for running and biking, not just the edge alone while biking)

0 timgrose over 7 years ago

I have similar problems with my Rotor PM (an older model not their current one). It does however work fine if it is nearer the power meter source. So given I also use an Edge as my main unit on the bike, I sometimes just put the 935 in my top tube saddle bag and it works fine there. On my wrists and out on the aerobars and being very tall (1.95m) it largely drops out altogether. Other sensors like HRM-Tri, Garmin speed sensor, cadence sensor (if not using bike with a PM) are fine for me however.

TBH I think the problem is with some PMs not emitting a strong enough signal. All the Garmin watches I have had (910, 920, 735) have has the same problem with my PM. In fact the others were worse. Stages is another one where lots of people find issues. That said not heard of many issues in this regard with the P1 pedals.

It does tend to work a bit better if the watch is on the right wrist as better line of sight so you could try that.

It's possible one 935 may work better than another but I doubt it will make a huge difference.

0 Former Member over 7 years ago

I've also read that having DI2 enabled on the watch can cause dropouts. Has anyone experienced this?

I may place the 935 on my handlebar but that will make things crowded since I already have the 1000 there. It absolutely makes sense that the wrist is hurting the receive sensitivity of the 935. I like the 1000 for biking because of the enormous screen.

0 timgrose over 7 years ago

In one TT on my P3, I wrapped the 935 around the top tube just with the regular strap. Given I sometimes still see dropouts when on the drops then the handlebars might still cause issues although clearly would be better than say out on your aerobars.

0 Former Member over 7 years ago

I understand occasional dropouts but over my ride it was disconnected at least 13 minutes. There were many times when I looked at the 935 and it would say nothing for the wattage. When I'm in the hoods, it's at most 3 feet away line of sight to my pedals. I've never seen this much dropout over the years with my Garmin 1000, 820, 810 and my old Forerunner 305.

Either I have a bad unit, the firmware is buggy or maybe this isn't the solution I thought it would be. Does one really have to take the watch off and place it on the bike during the bike stage of a triathlon?

0 timgrose over 7 years ago

Clearly not the general idea. It does seem that your power meter is as much to blame. Suggest also contacting Powertap to see what they say. I did start a thread here on this general subject of drop outs with power meters and did get a huge number of adverse findings although I wonder how many 935 users actually use a power meter. It is rather annoying but given works fine with all the Edge devices have got and as they are my primary device when cycling, I am perhaps not so bothered. Then again when I next look to buy a power meter one that does not seem to cause these issues will be top of my list of points to look for.

0 Former Member over 7 years ago

Clearly not the general idea. It does seem that your power meter is as much to blame. Suggest also contacting Powertap to see what they say. I did start a thread here on this general subject of drop outs with power meters and did get a huge number of adverse findings although I wonder how many 935 users actually use a power meter. It is rather annoying but given works fine with all the Edge devices have got and as they are my primary device when cycling, I am perhaps not so bothered. Then again when I next look to buy a power meter one that does not seem to cause these issues will be top of my list of points to look for.

Please see the attached images from my first post. The image labeled "935_segment_many_dropouts" shows cadence readings dropping to zero 12 times during this couple minute segment, as recorded by the 935. It also shows my heartrate going to zero 3 times.

Now look at the image labeled "edge_1000_segment_no_dropouts". This is the same activity recorded at the same time by the Garmin Edge 1000. The cadence goes low a few times indicating I slowed down but it doesn't go to zero. The heart rate doesn't drop at all. The cadence sensor and heartrate monitor are both Garmin.

The power meter is not to blame. There are dropouts across the various sensors at the same time. If it were the power meter you'd see dropouts on both the 935 and the edge 1000 but this is not the case. I've also used this same power meter with an indoor trainer to relay power to my laptop using a garmin ANT+ dongle. Even in a WIFi noisy environment, I experience little to no dropouts and the laptop is 8 feet away.

Do I have a bad 935 or is this just what I must accept? Do I have too many devices connected to the 935? (I just looked at my heartrate data recorded by the 935 during a 1 hour treadmill run and there's no dropouts.)

0 Dr Phil over 7 years ago

Edge 1000 likely has a larger aerial than the 935. As Tim has noted what you are seeing has been reported with other power meters connecting to watches rather than to Edge cycling devices. The power meter might not have a strong enough signal for the watch's smaller aerial. Again this has already been said.

Talk to Garmin Support and your power meter support.

0 timgrose over 7 years ago

What I meant with the power meter is that the Edge largely records it all but the 935 is more flaky. This is clearly a range issue as when I move the 935 nearer the power meter source, the drop outs on the 935 stop.

If HR is dropping out then that is not something I am generally experiencing. How fresh is the battery in your HRM? If that is OK then it may well point to something defective with your 935. I do recall the odd report here where a replacement 935 "solved" this issue.

What is the actual source of cadence? If a power meter also does cadence (as mine does) then that tends precedence over a separate cadence sensor.

0 Former Member over 7 years ago

The cadence meter is Garmin GSC 10 and I believe the heartrate monitor is Garmin 010-10997-00. The battery on the heartrate monitor is a month or two old but the cadence meter's battery is over 6 months old.

I've also read that a replacement 935 solved someone's issue but I didn't want to replace this one just to find out it's a problem with the new device as well. If I can just turn off the DI2 and radar receiving on the 935 to fix it, I'd be glad to go that route. I haven't had the time yet to experiment but I came on here to see if anyone else has found a common fix that I could try.

I should note, other than this dropped sensor issue, everything else is working flawlessly. The optical heartrate works great, the tracking seems spot on and I haven't had any syncing issues with my phone.

0 timgrose over 7 years ago

Is this an indoor or outdoor ride? If indoors then recall some people have found issues with their WiFi interfering so that might be worth looking into.

Otherwise there is no obvious reason for drop outs with standard Garmin sensors unless your watch is somehow faulty.