Fluid trainer with power data

netscriber said:

1. Are there any good ones in the market within 500$?
2. Are the power readings accurate on them?

Answer for 2: My guess is that the trainers in your desired price range do not have accurate power.

Here is a thread with a few posts on your topic (hopefully that link works properly and jumps you down to the relevant posts):
cyclingforums.comt287311.htmlOpen ↗

I looked at the Elite brand briefly when I was buying a new trainer. That particular one seems odd. If I remember correctly, the reviews were pretty positive. I ended up with a simple trainer since I was thinking about a Power Tap.

Flatscan said:

Answer for 2: My guess is that the trainers in your desired price range do not have accurate power.

Here is a thread with a few posts on your topic (hopefully that link works properly and jumps you down to the relevant posts):
cyclingforums.comt287311.htmlOpen ↗

I looked at the Elite brand briefly when I was buying a new trainer. That particular one seems odd. If I remember correctly, the reviews were pretty positive. I ended up with a simple trainer since I was thinking about a Power Tap.

Thanks man. Good read.
Yes, the elite I am looking at is a little odd.
I already have a mag trainer I am satisfied with. I am struggling so much because I want to join the power bandwagon but do not have 1000$ for a powertap which is what I would buy if I buy a real powermeter.

Flatscan said:

Answer for 2: My guess is that the trainers in your desired price range do not have accurate power.

Do you know about maybe percentage of inaccuracy and where? Meaning is it in the short 5 second range? in the 1 min, 5 min, 20 min range? And by 1% 5% or outrageous?

Try the Kurt Kinetic road machine turbo trainer and computer. The trainer is a fluid unit that is calibrated to give power Vs speed and is reputedly accurate.

In the UK the trainer costs around £150 including the computer.

netscriber said:

I already have a mag trainer I am satisfied with. I am struggling so much because I want to join the power bandwagon but do not have 1000$ for a powertap which is what I would buy if I buy a real powermeter.

In your situation, I would save up for a Power Tap Pro, which has an MSRP of $1000, but can be bought for less. For example, Performance Bike sometimes has sales and coupons that can be combined, or Analytic Cycling has a bundle with CyclingPeaks software.

Here is my reasoning on why cheaper trainers with power are probably not worth extra money over "dumb" trainers.

1. Trainers that definitely have accurate or near-accurate power like the Computrainer or Velodyne, and maybe the Tacx iMagic and Fortius, are very expensive. I think they all use active resistance systems that are somehow calibrated in the factory. On-bike strain-gauge-based power systems (PT, Ergomo, SRM) are also expensive. It's possible that a trainer could be made to use strain gauges more cheaply since it would not be limited by weight or size. However, it's much easier and cheaper to test some units in the factory and assume their resistance curve holds for all units and can be used to calculate power. The Kurt Kinetic computer is an example of this - it mounts on the bike like a conventional cyclocomputer and reads speed from the rear wheel.
   
2. When trainers (I think they were Cycleops Fluid2s) were informally tested with a PT, there was a wide variance in resistance curves among all the samples, including ones from the same model year. The test was done a while back, so current trainers may be more consistent, but I doubt it. Without consistency, assuming a resistance curve and deriving power from speed is invalid. Fluid trainers also have fade (decreasing resistance) as their fluid heats up.
   
3. Friction between the tire and trainer drum determined by tire pressure and trainer tightness would affect power readings also. Variance can be introduced here when unmounting and remounting the bike.
   

You will note that I assume that trainer under $500 implies "fake" power. If you find a counterexample, please post back here.

You can pretty cheaply estimate your power on your current trainer. Mag trainers tend to have very linear resistance curves (or constant, I can't remember), which makes it easy to convert from speed to power estimate. If you can find the resistance curve for your trainer online, you can do the calculations and make a printout to consult (e.g. 200W = x mph) while you're riding.