Discrepancies between PowerMeter and SmartTrainer

Equipment
1

Hello everyone,

New to TR and smart trainer so if the answer if obvious I apologise now.

Background:
I paired my trainer to TR and my PM to a head-unit to compare to two numbers, just to check for any discrepancies. Reason for this is that only one bike has a PM (TT) and the other doesn’t (road). When using the TT bike I can use PowerMatch… no problem. Problem occurs when I use the other bike.
I performed a test using ERG mode where I increased the watts by 25 every couple of minutes (created using the Workout Creator). This provided a decent time period for things to settle in and capture a reasonable power average. As expected… the trainer reported exactly what I had set it to but the head-unit (PM) was out. At lower watts, less than 150, they matched well, 1-2 watts difference. However, above that the gap grew quite drastically. When the trainer in ERG said 200 the PM reported 221 (average for a couple of mins). This gap remained constant through to 300w (reported ERG mode). I terminated the test there as i know have 9 intervals to compare.

After a 15 minute warm up the PM was Zero Offset and the trainer had a Spin-down Calibration.

Question:
What is my best course of action when using the bike without a PM? Is there any way of calibrating my trainer to match my PM? Is there anyway of offsetting the trainer? Or do I just get on with it; whenever I use the road bike on there I just change my FTP by the required amount?

Any tips or tricks welcome.

Ben

2

Can you tell us what trainer you are using and what PM you are using?

3

Quarq D-Zero. 16 months old. Calibrated 2 months ago.

Tacx Flux. Brand spanking new.

4

This is pretty common–I always expect my power meter to read slightly higher than my trainer (Kickr Snap).

While I would recommend trying to always use the bike with the power meter, you could just do two Ramp Tests—one with the PM, one with the trainer power. Then when you do workouts on your bike without the PM, you can simply adjust your FTP for that test since you’ll know both numbers.

5

Now I feel like an idiot. That is a very obvious thing to do.

Thank you.

6

See also discussion at PowerMatch Experiences.