Computrainer Accuracy

I had a Computrainer that was significantly different than another computrainer. I returned and they replaced under warranty. Even gave me the special 'Lab' calibrated trainer with a 6-point check. Perhaps check your computrainer against another computrainer, if you cant find a PowerTap or Polar Power Sensor to compare to. Did anyone else respond to your posting on either forum???

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goonly said:

I had a Computrainer that was significantly different than another computrainer.

goonly, I just recieved my new Computrainer last week...(getting ready for some witner training). Without having access to another CT, how would i know if my numbers are correct. Is there a site where I can find a reference to what kind of power numbers I should be expecting? I'm 5'7, 155lbs
--Mark

last time i rode a computrainer, the wattage was about 10% higher than my powertap.
before this, i rode a different computrainer doing the wingate sprint test. power seemed a little low, but i had nothing to compare it to.

it's not easy to know if your CT is accurate, unless you have a good powermeter.

velomanct said:

it's not easy to know if your CT is accurate, unless you have a good powermeter.

In reality I am not a pro and I am only trying to increase my cycling ability, the accuracy of my CT compared to at PowerTap, SRM..etc, is not all that important.

However, what is extremely important is that I need to make sure that I setup my CT correctly, the same what every time, so that I am getting consistent results from workout to workout.

The Computrainer has VERY GOOD Reproducibility. If you calibrate it correctly before each workout (warm it up for ten minutes and then do the calibration to create the same rolling resistance workout to workout) because the press-on force of the roller on the trainer changes each time you take the bike off of the stand, the tire pressure changes, the temperature changes, etc.

Also, I would say that my CT was a fluke and that 95%+ of the computrainers are accurate to +/- 5% of the wattage listed. You should feel comfortable with your trainer as is, and not worry about the Factory Calibration. In fact, the only reason I noticed mine was off is because I am a data geek and had done a blood lactate test on another computrainer before using mine and the HR's were off slightly.

Enjoy.

madone550 said:

In reality I am not a pro and I am only trying to increase my cycling ability, the accuracy of my CT compared to at PowerTap, SRM..etc, is not all that important.

However, what is extremely important is that I need to make sure that I setup my CT correctly, the same what every time, so that I am getting consistent results from workout to workout.

it's my understanding that the CT drifts over time irrespective of the calibration procedure, and thus at some point you have to send the unit back. an external data point is therefore important

ric

goonly said:

In fact, the only reason I noticed mine was off is because I am a data geek and had done a blood lactate test on another computrainer before using mine and the HR's were off slightly.

Enjoy.

Unfortunately, it isn't possible to compare HR's like this as atmospheric conditions will change your HR along with fatigue, training status, fitness, hydration and foods you've previously eaten. You may only be able to ascertain a difference correctly if the magnitude of difference is very large.

ric

goonly said:

I had a Computrainer that was significantly different than another computrainer. I returned and they replaced under warranty. Even gave me the special 'Lab' calibrated trainer with a 6-point check. Perhaps check your computrainer against another computrainer, if you cant find a PowerTap or Polar Power Sensor to compare to. Did anyone else respond to your posting on either forum???

[email hidden]

Hi there. Well I made that post October 2003! By March, 2004 I'd decided to get a P'tap and one of the 1st things I did was to run a ramp test on my CT.

Since then I've run numerous tests between the two with the following results:
* No apparent drift over the last 6-7 months.
* The CT is very repeatable when warmed up properly & consistently
* My CT reads ~5% low or, to be precise, a regression line of my PT versus CT power tests has a slope of 1.055 and a virtually zero intercept. R was 0.999x - very high.

I've recently tested a friend's CT and his slope is 1.085 indicating his CT reads ~8% too low. Both units were purchased and shipped together in Dec. 2002 - i.e. - should have been very close on the production line.

The tests were done in ergo mode with the CT power ramped from 150W to 450W and with each step held 3-5 minutes. The CT was warmed up for fifteen minutes at 200-250W and coast-down checks were performed within the range 1.90-2.10. Each coast-down check was repeated three times to ensure repeatability. A small fan was aimed directly at the load generator after the warmup to reduce ergo 'drift' due to heating at higher power levels.
In addition, a post-test coast-down check was performed to ensure there was no discernible drift during the test. In all cases the coast-down varied by < 0.05.

My conclusion from these two samples is that the CT is precise but not accurate and should not be taken as power measurement standard. I'm scheduled to check yet another CT in the next couple of weeks and can let you know if anyone is interested.

rmur

rmur17 said:

Hi there. Well I made that post October 2003! By March, 2004 I'd decided to get a P'tap and one of the 1st things I did was to run a ramp test on my CT.

Since then I've run numerous tests between the two with the following results:
* No apparent drift over the last 6-7 months.
* The CT is very repeatable when warmed up properly & consistently
* My CT reads ~5% low or, to be precise, a regression line of my PT versus CT power tests has a slope of 1.055 and a virtually zero intercept. R was 0.999x - very high.

I've recently tested a friend's CT and his slope is 1.085 indicating his CT reads ~8% too low. Both units were purchased and shipped together in Dec. 2002 - i.e. - should have been very close on the production line.

The tests were done in ergo mode with the CT power ramped from 150W to 450W and with each step held 3-5 minutes. The CT was warmed up for fifteen minutes at 200-250W and coast-down checks were performed within the range 1.90-2.10. Each coast-down check was repeated three times to ensure repeatability. A small fan was aimed directly at the load generator after the warmup to reduce ergo 'drift' due to heating at higher power levels.
In addition, a post-test coast-down check was performed to ensure there was no discernible drift during the test. In all cases the coast-down varied by < 0.05.

My conclusion from these two samples is that the CT is precise but not accurate and should not be taken as power measurement standard. I'm scheduled to check yet another CT in the next couple of weeks and can let you know if anyone is interested.

rmur

very interesting. Please post your next test for sure. Also, could you state whether the C-Trainer you are testing is the 6-point 'Lab' model or the normal 1-point model?? (it will have a sticker on it if it is the lab model).

Thanks