Questions about my FTP test

Triathlon Forum
1

I did the 20 minute FTP test on TrainerRoad last night and have a few questions. Going in, my FTP was set to 203. My setup is as follows:

Tablet (bt):
Running TrainerRoadKickr v2Powertap P1 pedals
Garmin 820 (ant+):
Garmin HRMPowertap P1 pedalsGarmin cadence
I have never been able to get my pedals and trainer to really “match” power over the course of a session to my liking. One of the reasons I have a kickr is I thought something was wrong with my first trainer, a TacX Vortex smart. All firmware is up-to-date and I did a spindown/calibration before I started; both through TR. The tablet is using the default “powermatch” setting. I’ve tried powermatch on/off/+/- and it doesn’t really seem to matter when it comes to comparison with the P1 pedals.

After the 20 minute test, TR said my average power was 214 and my new FTP was 203. The Garmin, with only the P1 pedals, said my average power was 224, which would equate to an FTP of 212.

On my previous FTP test, I used the same pedals and my TacX, but don’t think I thought to separate the pedals out that time.

Questions:

Do I trust the kickr, the pedals, or split the difference with respect to FTP?My average HR during the 20 minute session was 160. Can I use that as my LTHR for my run zones? If so, straight up 160 or 160*0.95?
As always, thanks for any insight or advice.

2

It won’t matter on the trainer as long as you always use the same power measurement device.

However, outside (races) you will only have the pedals, so race target power has to based on their test results.

3

Obviously the higher one is correct.

4

If you are using power match… there really shouldn’t be a 10 watt difference. TR should report what the P1’s are doing.

The Garmin might be 1 or 2 watts different… but not more.

I don’t see why you have that big of a discrepancy. I use an SRM + PM and I am never more than 1 watt off between what my Garmin reports and what TR says. The only reason I even use the Garmin is for live info about “lap” info.

5

You’re running HR is likely a good chunk higher than you’re biking HR. You’re better off doing a running test and knowing for sure.

6

The reading differences you are seeing is 4.5%.

Most power meters are accurate to 1-2%, so that could be some of the difference. I think it would be a stretch to say that your P1s were running 2% high and your kicker was running 2% low to make a 4% difference, but a straight 1.5 to 2% difference would be plausible.

Now factor in that your reading power in two different places that are at opposite ends of the drive train. That could be another 1-3% depending on how smoothly your drive train is running. So it could be explained.

You mentioned that you did a spin down on the trainer, but didn’t mention if you calibrated the P1 pedals. I don’t own them, so I’m not even sure if it’s necessary.

In any case, unless you plan to execute and FTP based pacing plan only on the trainer and never outdoors, I would go with the FTP from the pedals, assuming they were properly calibrated.

7

How are you transmitting to trainer road? Bluetooth? TR only takes the left leg and doubles it if using bluetooth, and I believe with a dongle it will give an accurate split.

I ran into similar confusion a year ago with P1s and TR reading about 10 watts higher than my edge. Went through multiple tickets with Garmin, powertap, and TR before stumbling onto that answer somewhere else (really don’t remember where). Try it out though, do single leg work with the right leg and TR will give a reading of 0 power, but if you do left leg only the power will stay the same as if both legs were pedaling.