Trainer Road vs Power meter

Check out DC Rainmaker and his reviews of powermeters. He's ridden with 4 or 5 on the bike and the read outs were very consistent - even Stages.

You'd expect different brands of power meter to be within 5 or 10% of each other surely?

Trainerroad virtual power is consistent enough to be a useful training tool for mere mortals. Ditto any type of power meter. Keep tyre pressures the same, just as you would out on the road. There are so many other variables and life choices to make before worrying that your power meter might not be accurate or that there's a small percentage variability in virtual power over an hour's session.

I won't care what power I'm putting out when it comes to that first race of the year. I'll care that I can keep with the bunch, not get dropped or some other target that I can experience - not just a number.

If you don't race, why not just trounce your riding pals on the sprint for the town border sign rather than worrying that your max power is 50Watts down on your mates

Power meters are still pretty expensive - it's pretty poor if there's no consistency.

If I regularly measured my power I'd want it to be consistent across devices, not only for referring back to an FTP as a baseline figure, but also in calculating power to weight ratio etc. If there's no consistency then there's no ability to compare stats with peers...

So when they say 'Bradley Wiggins puts out 400W over a 1hr TT' or whatever - is that just meaningless because it's inaccurate? can that really be the case?

Surely car manufacturers have a consistent way to measure power, to enable consumer choice - so why can't the makers of expensive bike gear?

Trainer road estimates the power from the typical resistance profile of the turbo trainer you use. It's better than nothing but I can't see it being as accurate or consistent as a 'proper' power meter. My, quite good, turbo varies in resistance over time and tyre pressure can make a big difference. My turbo has it's own power reading but it's very dependent on tyre pressure and I rely on my Vectors instead.

AS long as they're installed properly, I'd trust the Vectors. You can use them with trainer road, I believe.

I recently got a stages and trainer road was about 70w too low for me. As others have said it doesn't really matter, although I found short efforts above ftp really difficult before. Obviously pm responds much more quickly than the lag in winding the speed up.

To the original poster - if you've got a Vector power meter, why would you need TrainerRoad's virtual power figure? The Vectors *ought* to be "right". But as @giobox says, accuracy doesn't really exist in power meters for normal folk like us. I have Vectors and a Kickr trainer - which has a power meter - and they seem to randomly move around between rides. For ages the Kickr was higher by 10-15W than the Vectors, then some rides they are effectively identical, then sometimes more recently the Vectors are higher. I think it's to do with temperature, and/or how well I install them after swapping between bikes (always using a torque wrench to get to 34Nm though...). I always calibrate both (although haven't been bothered to do the real hardcore calibration, hanging weights off etc).

You basically just go until it hurts so much you don't want to go on anyway, so it's all good...!!

I find that trainerroad gives me about 50 watts less than my Stages power meter.

As per previous post, doesn't matter if its accurate, just that it's repeatable for each system. Yes you will need to have different zones for different systems. Shouldn't need another ramp test, just compare the readings for both systems on the same work out and adjust accordingly.

If you're asking is it accurate you're asking the wrong question. There is no way to know if any power meter is 'accurate' (at least for normal people...), no matter how fancy it is. The important thing for any power meter is are its numbers consistent? If its consistent you can train on it.

In this regard TrainerRoad is as pretty much as accurate as any other power meter, so long as you keep tire pressure and wheel pressure against the flywheel the same.

It doesn't even matter if it says you output 100 Bananas, so long as the effort needed to generate 100 Bananas is always the same.

There's a good explanation here.