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Polar HRM Circumference Settings(12 posts)

Polar HRM Circumference Settingsllbr22
May 13, 2002 11:20 AM
I can't seem to get my Polar S510 wheel circumference settings right for the speedometer. Does anyone with the Polas S series of monitors w/ bike mount have any suggestions on the circumference settings of the HRM for a road bike (700C w/ 23mm tire) wheel? (btw I weigh about 158lbs).

Good Question!grzy
May 13, 2002 11:24 AM
I too have been messing around with mine (S710) and can't get it to reconcile with my Flight Deck. I used the same value for circumfrence, but get a noticable difference on longer rides. I haven't played around with it enough to get it sorted out yet. There is a procedure for measruing the circumfrence from the bike detailed in the manual. Have you tried this yet? I'm going to get to it one of these days.
Good Question!llbr22
May 13, 2002 12:12 PM
I tried the procedure, but still didn't get it right. I'm thinking I did it wrong though...
re: Polar HRM Circumference SettingsBikewithadam
May 13, 2002 12:50 PM
Are you asking about how to determine wheel circumference, or how to enter it into the computer?
Wheel size setting - a surveyllbr22
May 13, 2002 1:32 PM
Actually, I'm asking for specifically what wheel size setting in mm's works best for a road wheel. I've entered what I thought as the right circumfernce (so I thought) and it doesn't seem to show the right speed.

So I'm wondering what ##'s others are using for there Polar?

Wheel size setting - a surveyavitar
May 13, 2002 2:59 PM
In the manual it says it defaults for a Road bike 700 x 23 which I think they say had a rollout of 210. Are you thinking that they are inacurate with their default measurement?
The Wheel Dealgrzy
May 13, 2002 3:49 PM
No, the problem is that if you put in the "correct" value for the wheel you don't get the right milage reading. I'm thinking that there is an error in the software on the order of 5% to 10% on the low side.

With a little math we could determine the exact error then apply this "correction factor" to the wheel value and get better results. This assumes that the error is in the way the wheel circumfrence value is being used, not some algorithym further on down the line. One of my concerns is that the speed reading is failry close while the milage is not. However, this could simply be in line with a small but presistent error. You tend not to notice a 5% error (at 20 mph this is 1 mph), but after 100 miles it's a difference of 5 miles.

Anyone else notice this problem?
The Wheel DealLen J
May 13, 2002 4:32 PM
I have both a S-710 & a flightdeck, and they both are set up for the 700X23 automatic rollout value. They both consistantly give the same milage.

The Wheel Dealllbr22
May 14, 2002 11:11 AM
cool. What ## did you use? 2155?

The Wheel Dealllbr22
May 14, 2002 11:16 AM
you know my problem mainly was w/ speed, so I would change the setting as I rode to match it up to another speedometer that I thought was more accurate.

So my first guess was thinking that Polar's default #'s were wrong. I didn't feel I was getting acurate enough w/ the speed to get to the mileage probs...
You can determine wheel circumference from this:Frank
May 13, 2002 8:52 PM
The ISO (i.e. 28-622 in this example) numbers can be found on the sidewall of the tire.

Looks like you could program the bike computer to any setting using this formula that I think came from Sheldon Brown's site:


Deriving tire diameter from ISO/ETRTO numbers

The I.S.O. tire size consists of a tire width and a bead seat diameter. Both of these numbers are in millimeters. For example, a 28-622 (700 x 28C) tire has a nominal width of 28mm on a rim with a bead seat diameter of 622 mm.

To get an approximate diameter (in mm) add the bead seat diameter to twice the tire width (since the tire comes into the diameter twice: 622 + (28 X 2)= 678.

Multiply this by pi (3.142) to get the circumference in mm (F) 2130.

Appropriate calculations will yield calibration numbers for computers in other groups.
No disrespect to you or Sheldon...spdplayr
May 30, 2002 3:34 AM
but this calculation is way off. I just computed my circumference for a 700x23 tire using your equation and got 2098. I then did the rolling tire test where I actually measure and got 2114. big diff.