Difference Between DFPM and PP

[ianc]

Hi John,

I'm curious what you think about this. Just got a DFPM on my road bike, and it seems to confirm what I've been feeling for a while, which is that the PP tends to overreport power during periods of high-intensity. Most of the time the PP and the DFPM are in harmony. But when they diverge, it's usually the PP suddenly jumping up by up to 20%.

Around 1:22:50 the two track but there's a 100W difference for around 1.5-2 minutes.

flat-012300-012729.png (129.73 KiB) Viewed 2987 times

Another example, if you look at 01:51:40, the PP is reading significantly higher on a flat road for about 3 minutes.

flat-015130-020632.png (132.5 KiB) Viewed 2987 times

One more:

climb-014130-014600.png (135.01 KiB) Viewed 2987 times

[ianc]

By way of comparison, here's the PP and DFPM tracking pretty closely:

tracking-003737-005237.png (113.03 KiB) Viewed 2983 times

Attaching the ibr and tcx files I'm using to generate the Power Meter Comparison report...

[Velocomp]

I am traveling now Eurobike.

It is going to be difficult to respond quickly to postings.

However, please post photos of your PP and mount on your bike.

What kind of DFPM do you have?

[ianc]

I am traveling now Eurobike.

It is going to be difficult to respond quickly to postings.

However, please post photos of your PP and mount on your bike.

What kind of DFPM do you have?

Hi John,

The DFPM is a power2max S crank based system. I added a couple of photos--basically using the k-edge aluminum combo mount so the PP is a good 3-4" outboard of the stem. I've got about 3/4" clearance between the back of the PP and any cables, etc...

[Velocomp]

If you look at the beginning of your ride, you'll notice that PP watts are crazy-high. This is because the PP was in a different angular position from its calibration.

I looked at your underlying data, and the amount of correction PP had to make to "fix" the angle problem is really large. So, I'm worried that some of the subsequent data differences may simply be because PP is working "overtime" to correct the angle problem.

Make sure you properly attach PP to your mount. Then, I'd do a new calibration. Please post a ride file afterwards.