Polar inaccurate Speed and Distance

[Trek Ferreira]

My Polar S725X is inaccuarte in both speed and distance. I have set up the correct wheel size (700 x 23) but it is under reading by about 5 or 6 %. Any ideas or thoughts would be apreciated.

[Joe Low]

I guess you can either:

 

adjust the wheel size setting til it gives u the right readouts or

 

return it.

 

5-6% is a lot.

 

[splat]

Measure the diameter of your wheel:

Inflate your tyre to your correct pressure.

Make a mark on the floor and the tyre and line them up.

Sit on the bike and move forward for 1 wheel revolution till the mark on the tyre touches the floor. Mark that.

Measure distance between marks on the floor and enter that into your computer.

 

Get someone to help you.

Accuracy is the key here.

The accuracy of the readings are only as accurate as the settings and input you provide.

splat2009-08-17 01:18:23

[Trubie]

My Polar 725x does the same. But how do you know its wrong.

I use a Topeak together with my Polar, on comparison the Topeak - which I believe to be correct - but don't know it for a fact, gives a slightly diff reading.

Ie I rode in SBR on Sat, the Topeak gave me 58.17 vs the Polar that read 57.3. About 1.5% diff.

Agree with JL that 5-6% is a bit steep to swallow, so maybe you have a battery problem. Take it in to IHF in Midrand to check it out for you.

 

 

[Minion]

The speed is based on the distance, so the distance would be the one that is inaccurate.

 

Is the actual distance that you are comparing the Polar to correct? How are you measuring it?

I have found that most car odometers and published race distances are around 5% too far compared to GPS and distances measured off a map.

 

If the actual distance is accurate, how did you determine the correct wheel size?

The value of 2096mm in the Polar manual is a typical value for 700c wheels, but may not be accurate for your wheel. You can get a more accurate wheel size by marking a point on the wheel and then rolling forward one complete revolution. You then measure the distance that you covered. It's best to do this while you're sitting on the bike, so you might need an assistant.

Otherwise, if the actual distances are correct, you can apply a correction factor to your current wheel size to get a new, more accurate, wheel size:

 

New wheel size = old size x actual distance / Polar distance

 

[Nialls101]

I agree with splat, you can also use a piece of string and run it in the centre of the tyre.

[DRIVETRAIN]

Mine did the same - I completely erased all the data - re-set the wheel measurements and I've got it accurate now -

I also have a Cateye mounted (mostly for Indoor training) also set - up correctly but give a slightly different reading on the raod -

I was told you will never get them to read exactly the same - there are variances.

"DT"

 

DRIVETRAIN2009-08-17 00:47:02

[Cassie]

Ever considered that the magnetic pick-up on your fork might be positioned incorrectly? (or slightly incorrectly)?

Or maybe slight interference from other magnetic devices e.g. your other device?

I'm jsut speculating here...

 

My Polar CS300 is also out with reference to my "other" cycling computer...

~2km over 50km distance

[GTRacing]

On the 725x you can choose between bike one and bike two. If you set up one, but ride under the other this hapens.

[Yang]

Absolutely right GT- especially if you got the Polar already set up from someone else, eg bike 1 for a road bike and bike 2 for a MTB. Sometimes I forget to change between the two and get different readings on my 33,6km route.  Yang2009-08-20 13:49:31