Fluid Trainers and Resistance

I recently purchased a Kurt Kinetic trainer. I am wondering if the resistance of the unit experiences any sort of breakdown over time. I am using a bike computer to monitor “power”. While realizing this isn’t the most accurate way of measuring power, my hope is that it is precise. In other words, my hope is that the power I produce at 20 mph today is the same that I produced at 20 mph 3 months ago and even 12 months ago so that I can draw comparisons. What are your experiences? Thanks for the input!

To answer your specific question, I've never heard reports of fluid viscosity breakdown over time in a fluid trainer. I've personally used my Kinetic ~4-5 times per week without issue for 5 months.

However, there are variables in the amount of pedal power required to drive the wheel at a certain speed, which will affect your plan to use wheel speed as a proxy for power. These include: 1) temperature of the fluid in the resistance unit, which for the Kinetic seems to stabilize within 10 minutes or so, 2) the amount of tension between the resistance unit and the tire (including tire pressure), and 3) wheel slippage. The first isn't a big deal, since it typically goes away by the time my warmup is complete. The second can present issues between one ride and the next, which means you'll want to try to create some kind of consistency here. Keeping the tire inflated to a set value, and performing a timed coastdown test from a set speed at the beginning of each ride could help with this. Avoid the third altogether.

Great info. Especially like the coast down idea; hadn't thought of that one. Thanks!