How Accurate is trainer mode?

[Foothills Rider]

Definitely. But, I train with DVD's, either Spinervals, Ventura, or Carmichael. It is easier for me to tolerate a purely suffering pace on the trainer when I am following directions. It's also easier for me to do tempo riding and not break above my LT on the trainer than it is on the road. The trainer has no downhills, no coasts, just 100% spinning. I was thinking that it was pretty common to post higher numbers, maybe not so much because of technical artifact, but because it's easier for me to dig and sustain in a controlled environment. What do you think?

Bill

[jslopez93]

Well that's the thing I want to clarify
- Do I have higher watts because in general it's "easier" to generate more power on a trainer

OR

- Is the ibike trainer more over-reporting watts ( if it's a known fact that trainer mode over reports watts then shouldn't it be adjusted accordingly?)

I just want to manage my expectations (and numbers) when using the trainer.

[Site_Admin]

I just spent some time with a couple who own two iBikes, and we did a test with a power-tap and a Fluid trainer, to determine which load curve fit best. The wife's test showed that the manufacturer-supplied value was best. I'd say it was off by maybe 3%. But then, when her husband hopped on, and attempted the test, the numbers were WAYYYYY off. None of the four curves would fit.

I think this is due to a couple of things:

1) The fluid trainers are notorious for the heat on their load generators. I think that the heat will screw up the load curve.

2) I think the load curves are based on different weight riders and bikes. I think Kurt Kinetic talks about "crank Armstrong" and how accurate he is... But I don't know if that's after 10 minutes or 30.

3) Remember- these are numbers given to us - it'd be next to impossible to determine the load curves for each individual rider, on each individual trainer. I'd love to get some PT data from someone on a Magneto trainer... Less heat, so we might be able to determine just how good or bad the curve is.

And if you REALLLLY want to go with indoor training.... e-mail me off-list and we can talk about something entirely perpendicular.

[ahaile]

What Richard said. If it's useful, here's what I wrote on my web page that does the same kind of math as the ibike's trainer feature:

A note on accuracy: A trainer's power equation can vary between units of the same model, with different tires, different tire psi, drivetrain condition, wheel inertia, etc. In addition, some trainers vary their resistance as they warm up. The numbers here are likely to be good but not great. They should be fairly consistent between trainer sessions but may be a bit off from what you would see with an actual powermeter on your bike. If you have a friend with a calibrated powermeter, ask if you can borrow it for an afternoon to determine your specific trainer's power equation. From http://curveship.dyndns.org/trainerpower

The best trainer for this kind of use is (not surprisingly) the Kurt Kinetic, because they specifically designed it to have a stable power/speed curve. Other makers are playing catch up. Older Fluid2s in particular seem to be bad, though the newer ones are reputed to be much better. Rollers are a real problem.

On my trainer, a cheap Performance model manufactured by Elite, I see a difference of about 30w as the unit warms up. This is measured by my Powertap.

[MultiRider]

I have a Kurt Kinetic Road Pro with a Kurt power meter. My iBike matches the Kurt meter pretty consistently. The Kurt display jumps around a lot -- pops up and down by 20-40 watts pretty much constantly -- but tracks the iBike display. It is easier to watch the iBike than the Kurt when trying to produce consistent power. I've used them both up to around an hour and have not experienced a difference between them.

My subjective feeling is that the watts displayed is more than I'm used to for the same effort outdoors, but I'm new to power training and my seat-of-the-pants feel is probably not very accurate.

[Site_Admin]

It will be harder, since you've got about 4x the force on the tire, and you've got a lot less heat dissipation from convection and evaporation.

Indoor training sucks, but it's the most consistent workout you'll get all week, all season, all year. Thus the evil necessity of it.