Polar S710i interference problems


New Member
Apr 30, 2003
I note with interest that a few other people have had problems with Polar S710i units not working in a car. I too have found this and while it sounds like a silly issue, it really is not. It simply shows how extremely sensitive these things are to ANY external interference.

And just to show that these concerns are not merely academic - have a look at this ride I did last weekend. It was actually an 80.22km ride. This is what my other two computers told me, plus my Garmin GPS. The S720i tells me it is actually 118km. Plus I also did the distance with a totally acceptable average of 126kph. If this was actually true, I would not be sitting here working as a computer programmer - I would be out there with Lance...
Maybe some of the extra interference is caused by having the GPS etc. in close proximity to the HRM?

The power cords of high intensity rechargable lights have been known to cause some problems.. also remember the antennae in the unit for the speed and cadence sensors are somewhat directional.

BTW although the heart rate wireless signal is encoded, the speed and cadence sensors aren't -- that's why they're more susceptible to interference. Not exactly sure why you'd have such a serious problem though, since you have a wired power sensor .. :confused:
Originally posted by rek
Maybe some of the extra interference is caused by having the GPS etc. in close proximity to the HRM?

Normally you would be correct. I have to mount my GPS at least 6 inches from the S720i, and I have mounts that do this for me. I have been using this combination for quite a few rides now, and it seems to work as well as can be expected. I have done quite a few rides where things actually worked just fine - this ride was something different though.

But there are even more puzzling things about this ride -

I use the Power Output option - this hardwires in the speed and cadence sensors, so interference is not normally an issue with those readings. The only thing I usually get interference with is the HR readings. Since that is the sole reason I bought the Power Output option in the first place, that has been ok.

The other problem is the altitude is totally wrong. This shows an almost comletely flat ride - it was not that at all. While not an alpine climb, it had a lot more hills than shown here.
Very odd indeed. All I can say that whilst there is a liitle bit of inteference on mine, my mileage is usually within 1-2 % of my bicycle computer and after editing the10 odd spikes on the speed reading (which takes 1-2 minutes) the readings are identical.

Usually the HR is perfect, no problem whatsoever.

I have found that if I wear the watch on my arm, the altitude is less accurate. I suspect that the body heat affects it.

I cant work out those interferance problems you are having. That would annoy the **** out of me. The heart rate info seems fine, is it? I cant tell what normal and interference data you have in the speed curve. I dont have any problems with cadence or speed sensors while riding (except once, a friends s720i was turning mine off during a ride if we were next to each other in the bunch. I had my s710i on my wrist so figgured it may hav been closer to him than i at points). In the car there are all kinds of interference problems. Do you ride around alot of traffic?
Originally posted by Kristian
I cant work out those interferance problems you are having. That would annoy the **** out of me.
Yes- it is extremely annoying to me as well. The thing is I can spend 10 minutes after each ride trying to "fix" the data. The problem is that the error correction screen only allows you to correct 10 or so readings at once - and usually up to a hundred get corrupted at once. Eventually, you do not believe the data at all, as you have manually entered in any old reading yourself - almost at random. What is the point if you have to enter your own random values?

Do you ride around alot of traffic?
Well, I generally ride around Brisbane, which is a fairly large town (1 or 2 million people, I think). I also do a fair bit of riding in the surrounding countryside on the longer rides - mainly dairy and light agriculture sort of countryside. A lot of the place is totally empty - no people at all.

The only point where I KNOW there is a huge problem is near electric train lines. Since all of our club rides leave from a railway station car park, I see this sort of interference all the time. So at the start of a ride, my HR readings are almost always 220 for 5 to 10 minutes (until we leave the carpark).

During the ride it a different matter. I have had interferece miles from nowhere out in rural countryside - nothing except the power poles on rickety wooden poles at the side of the road. No reason whatsoever.

I know that taxis can be a real problem - so driving past a taxi rank is a no-no.

I have now used a S710, two S720i and now a S710i. All have had exactly the same problem. So it was not simply the case of one faulty unit.

With the S710 I used the standard wireless sensors for speed and cadence. These were so unreliable I decided that I could not possibly use them at all - so I upgraded to a new S720i and the Power Output option - simply so I did not have to use the wireless sensors.

And in general this ploy has worked - the cadence and speed readings are generally ok. I have had a couple of rides (like the one depicted above) where the speed readings are totally wrong, but generally it is ok. Cadence has never played up - as far as I know. HR is always a problem as it is always wireless.

I had two S720i units as I hoped the metal case on these units would act as a better shield - it doesn't. The other big problem with the S720i units is that their LCD screen is VERY prone to rainbow artefact. In fact, it was so bad I could barely read them in the bright Queensland sunlight - so I eventually swapped my second S720i for a S710i. This is a lot better than the S720i in that respect.

The last couple of short rides I have done have been perfect - no problems at all (well, except for the HR readings which always have interference).

The thing is - I have used a Polar M24 unit on the bike for over a year - riding all these same areas - and never one little bit of interference. It even works in a car an inside electric trains. Why does the M24 work perfectly, and the Polar S series do not? Surely they would use the same technology?

I am seriously thinking of getting a HAC4 just to get around this problem....apparently these do not suffer from this problem.
I had a ride yesterday and for about 10-20 seconds my cadence went to round 190 and hr upto 220ish. I thought of you straight away and quickly looked around for taxis or somthing. All that was around was residential housing and powerlines, but nothing out of the ordernary. Quite unusual, but most of my rides are surrounded by cow paddocks. Made my max cadence look good:)
I have had occasional problems but have noticed recenty that everytime I ride along the street under some new big power lines they just put in, my cadence jumps to 180 or so. Easy to fix, but we shouldn't have to!
Guess I'll have to take a longer route to avoid them, ah darn, more time on the bike :)