AeroPod, PowerPod and Newton

So we have all bought into PowerPod but we are outliers to an extent as we are not using strain gauges to measure our power. We are relying on Velocomps boffins witchcraft to calculate how hard we cycle. A common thread here is "please check my calibration" and unless you have a DFPM to do a comparison (and even then is the DFPM accurate) we probably never know if it is actually correct.

I know I always wondered if my PowerPod was accurate.

I came across this GCN video (https://www.youtube.com/watch?v=sqb-WhzCAgw&t=250s) which gives you a method to work out if your PowerPod is accurate. You will see from the video their DFPM is within 3 to 6 watts of the calculation.

The test comes from this site (http://www.wolfgang-menn.de). You pick a short climb which you ride 3 times, put your time, rider/bike weight and elevation climbed into the web page and it gives you your average power. You can also amend the aero and Crr figures. It obviously does not allow for wind (which your Powerpod can tell you!).

I chose a 1.5km steady climb just outside my village. It has a elevation gain of 54m. I rode it 3 times no warm up just rode from the house down the hill and started ride no 1. Here are the results

RIDE PP POWER CALC POWER DIFF HR
1 306 293 13 138
2 281 273 8 141
3 280 274 8 141

So pretty close! I adjusted my aero on the webpage to match what PowerPod is set at and my Crr was the same. You can see from the attached IBR ride file wind was minimal.

Pretty happy with those figures and it looks like a good wee test to double check your calibration rides. Obviously it is important to put in the correct values for tyres, tyre pressure, ride and bike/kit weight etc to get best out of PowerPod.

Regards

This is a nice test and the principles behind your reference website are sound.

I often use this website to check PowerPod measurements:

http://www.aerocoach.com.au/power-from-speed/

I like this site because it also incorporates the effects of headwind/tailwind wind speed and CdA.

Just for fun I took your first hill climb and plugged your measured numbers into the website I use.

PowerPod: 318.9W

AeroCoach: 319.1W

That is VERY close!!

One thing to be aware of when using these sites: the sites assume that your riding conditions are not changing. This means constant slope, wind speed, and bike speed. I picked only a section of your ride, where slope was nearly constant. You did a very nice job of holding bike speed constant, which improved the accuracy of the site's calculations.

Thanks for that link John good to have another site to test things on.

Will be interesting to run the same test on my other two bikes in due course to see how the calibrations match across three profiles.

Regards

So did the same procedure for my CX bike and using the same hill etc the power figures were pretty accurate again.

Ride 1 Actual AvPower -282 - Website AvPower - 280
Ride 2 Actual AvPower - 276 - Website AvPower - 273
Ride 3 Actual AvPower - 283 - Website AvPower - 278

The ride file is saved below. I would note after the third calibration climb all of the ride is off road on gravel, mud and grass.

A couple of questions re power outputs on different surfaces. My cx bike has 33mm Schwalbe X One tubeless tyres which I run at 25psi and 30psi front and back. This is calculated at a CRR of 0.0063 by Issac. So from my figures above the PowerPod looks well calibrated. This climb was on a tarmac.

However, I notice sometimes, when I am grinding at a slow speed in mud or on grass often the power figures are very low. For instance I rode up a grassy field today and the power on grass was below 200 watts but my heartrate and RPE felt more like 300 watts. So how well does PowerPod cope with differing surfaces?

Second question, what would the difference be in CRR between a 33mm CX tyre and 38mm Gravel tyre if they are run at the same pressures? Just weighing up if it worthwhile buying another speed sensor as I run two sets of wheels on my CX with those different tyres. Will the gravel tyres be out by much in terms of average power?

Regards

PP assumes that Crr is not changing. If you are riding in grass or mud, PP will likely be low, because Crr is much higher (mud and grass presents more frictional resistance).

I don't have an answer to your second question...you might want to look on a bicycle site that has Crr for various tires.

John,

So should you change anything on the initial setup of the bike will ride predominately off road?

Regards

Bump.

John as above should you change initial during your initial setup if you ride mainly off road?

Bump.

John as above should you change initial during your initial setup if you ride mainly off road?

Sorry, I missed your question!

If you are riding on grass/mud) you might want to set up a new profile, with a higher Crr, perhaps as high as .015

A little late to this thread, Yes, spangelsaregreat, I saw that GCN video and went to that wolfgang site, too. My calculations fell 1-3% of the PP data. Pretty impressive. I'm going to dig out those numbers and run them through the site John linked us to.KB.