greenlight149

I know that trainer road virtual power isn't necessarily accurate, but it's consistent and reliable, and this error can arise from the amount of pressure the tire exerts on the trainer as well as temperature changes as both the tire and the resistance unit heats up. What I have failed to find on the internet is how accurate virtual power is on rollers without resistance, since the pressure of the bike on the rollers is less variable than turbo trainers, and temperature changes are less dramatic due to the lack of resistance, should trainer road give a more accurate estimation of power?

As far as I understand, the power curve on rollers without resistance units is somewhat linear, wouldn't this make it easier to compute virtual power than turbo trainers?

can anyone who have a power meter and rollers test this out?

trevorderuise

You make a lot of good points. What we typically find with rollers with no resistance unit is that the power curves can still be pretty accurate, they just usually do not go as high as many athletes would like, since again, there's no resistance. It's discussed breifly in this blog post: Training Smart Indoors - TrainerRoad

If you FTP tested on your current set of rollers and have done some higher intensity workouts (v02 or anaerobic) and can still hit all of your power targets without spinning out, then you're good to go!

-Trevor from TrainerRoad

greenlight149

Thanks for the response Trevor, I thought I wasn't going to get any replies.

I guess my question is how close can trainerroad be to a power meter when using rollers? I have seen tests on the internet with turbo trainers that are constantly off by 30 watts, so how close is it for rollers?

Thanks

mlamb01

Its all relative... If you want to track progress, all you really need to see is your speed on the rollers. When you do the same workout twice, and the last time you averaged +1 mph faster and your average heart rate stayed the same or dropped, that's progress. Just make sure when on rollers that you always use the same tire pressure for each session. Room temp should ideally be about the same too.

greenlight149

I understand the concept of consistency, and that's all I need to track progress. I was just wondering how many actual watts I'm producing, just for my own information.

Kopsis

The problem is calibration. On resistance trainers the amount of resistance is (or at least can be) a design parameter. Rolling resistance is a significant variable, but within the bounds of the designer's assumptions, resistance curves can be very consistent from unit to unit and bike specific variables (like drivetrain losses) are a small enough percentage to be negligible. Consistency between rollers (even of the same model) isn't as easy to control and bike-to-bike variation becomes a much bigger factor. Without a way to perform the initial calibration of your specific setup, there's simply no way to assess the accuracy of the vpower numbers. They might be dead-on, but there's nothing inherent in using rollers that allows you to make that assumption.

greenlight149

Makes sense