Calibrating a computrainer and rolling resistance

kevpam

 Hello,

I have had my computrainer for a little over a year and have been on it about 6 times. I am frustrated with it because I calibrate it each time to 2.0 after being sure my tire is inflated. I set up the course, and do the course. However, my effort is RPE 8-9 and my speed is really low, about 11-15 mph. The watt range is equally low about 85-110. I can ride  outside with averages 18-20, with Quark avr. 125 over 5 hours. On the computrainer, it feels like I have a brake stuck on, so I am thinking it is the rolling resistance pressure. Where does the standard calibration of 2.0 come from, and could it be a lower number should be used for a rider weighing 115 lbs.? It seems to me that the rolling resistance would be a number based on surface tension from road riding, based on a heavier person. Please if someone could help me with this, I would appreciate your help. Thanks, 

Pam

darren.wrigley

Hi Pam, I am no expert, however one thing to check might be your rider weight setting. most documentation i have seen is the weight should be you + your bike, so about 135 in your case.

Tom Glynn

Calibrating to 2.0 every time seems unusual. My calibration number bounces around a lot, typically in the 2.3-2.7 range. How long are you warming up for? The tire really needs to be warmed up and takes 10-15 minutes to get there. I'll usually calibrate a couple of times, 5 minutes, 10 minutes and somewhere around 15. I'll often see a change in the calibration number from 5 to 10 minutes, but not much from 10-15 minutes.

They use the 2.0 number as a starting point so that if you don't calibrate, that's what you get. Most people don't calibrate from what I can figure out because it's just not intuitive. The new software has/is going to have self calibration built in - the only good thing about the new software

David Ambrose

I read somewhere, sometime ago, that a calibration number of at least 2.5 is preferable. Like Tom stated, it is critical to warm up that tire for 10-15 minutes. If my initial calibration is lower than 2.5, then I tighten the roller-to-wheel a little, warm up for a few more minutes, then calibrate again, and then again until the calibration figures between successive calibrations does not vary by more than 0.1 to 0.2; at that point I push the Start button and begin the sweat-fest.

kevpam

Thank you for your responses, yes, I wait until my tire and unit are both warm to calibrate, at least 10- 15 minutes. I will check my rider weight and see if that helps. I guess I am reading that I should increase the rolling resistance, but that confuses me. I am really struggling with the resistance as it is now, set at 2.0. What exactly is the 2.0 or 2.5 represent?I will give your suggestions a shot! Thank you.

Peter Greagg

While not exactly on your question, I would have thought that once the calibration is stable (ie doesn't change with more warm up), that you are good to go regardless of what the resistance number is.
Isn't that the point of the rolldown test?
I usually have a number around 1.8.
When I test I use my powertap as well as the CT and the results are always within a few watts — which suggests to me that the rolldown calibration is fine with my 1.8ish number.
BTW, I recall the instructions suggest that if you are using a Conti trainer tyre, that you should aim fior a number like 1.5.
Of course I could be very wrong about the 1.8 number I use?

harrast

Pam, I have a quarq and a computrainer and have encountered some of the same issues. For example, my quarq registers about 7% more power than my computrainer. So, when I set my workout for the quarq, I have to use adjusted number(adjusted up about 7%) to get the same workout resistance I would feel on my computrainer. My FTP on the computrainer is 230 and on the quarq it is about 240. I have done some casual reading and assume that some of this difference is due to drive train loss, but it really doesn't matter what the cause is as long as the numbers are consistent.

On the subject of calibration, it shouldn't matter what you calibrate to just so long as the trainer is calibrated. As mentioned, the system defaults to 2.0, and any difference between actual and calibrated pressure produces a difference of 1 watt per .02 pounds of pressure (being off by a pound creates an error of 50 watts in the reported watts). It sounds like you have this under control, but a warm up is required before calibration--usually about 15 minuted at around 150 watts (this is a number I have seen batted around, but I can't back it up). Personally, I ignore the speed on the computrainer; I have never exceed 20 MPH to my knowledge on the computrainer, and I have never averaged less than 20 MPH on any bike course. The computrainer is consistently too low on speed.

kevpam

Thank you, I really appreciate your guys help. It really is about trends right? But hard to get excited about riding that CT if it beats me up and spits me out with numbers that are so low, but what really matters is the results, right? Good to know that I am not alone.

Peter Greagg

Pam it is absolutely all about the trend — if your CT watts are growing then you must be improving.