CompuTrainer In Game Calibration

There are a zillion CompuTrainer (CT) riders. Why hasn’t this feature been added yet. It seems like a simple task for a programmer. Zwift knows you are on a CT. There should be some way for Zwift to have a code that keeps Zwift ‘connected’ to a phantom CT while a rider takes 30 seconds to calibrate. Actual calibration probably takes 10 seconds. Instead we have to end Zwift, calibrate, log in, reconnect CT, etc. and a 10 second task turns into a 2 to 3 minutes exercise in patience.

Hi Paul,

When on Zwift and on the pairing screen, just Unpair the CT, calibrate, then pair again. Takes 5 seconds and you don’t need to exit Zwift to do so (we do this in our office).

So if I am understanding you correctly I would ride a warm up for 5 to 10 minutes. Press “A” to go to the pairing screen, click “UNPAIR”, do my calibration, then click “SEARCH”, select CT and I should reconnect to CT without issues? Does that sound right?

Well, I don’t do the warm-up (though perhaps I should), but the process is similar, yes.

How we handle it currently (and adding in-game calibration for each trainer that uses it is a discussion that we are having):

  1. Hook up bike the CT
  2. Start Zwift and log in
  3. At pairing screen, unpair CT (as it tends to automatically pair since it’s plugged in) but stay there
  4. Run the CT calibration tool (very simple to do)
  5. Pair the CT again
  6. Ride and/or do a work out


This doesn’t work for me. After calibrating the CT, repairing (step 5 above) finds nothing. The USB has to be removed and then re-inserted for pairing to come back with the CT. 

This is on Windows10 with ANT+ for HR and cadence.

same here. I had to unplug USB twice to finally get Zwift to see CT again.

Same for me but unplugging USB did not work.  I needed to quit out of Zwift and restart before Zwift reconnected to my CT.

I have been experimenting with calibration. This is my latest results. I already have Zwift started, BUT I have not plugged in the USB dongle yet. I turn the tension knob 1 1/2 turns. I hop on the bike and immediately do a calibration spin up. This sets the initial load so the resistance, watts, etc are enough for my next phase. I ride for 3 minutes at level 5 on the CT display. Then I calibrate once more. I always see about 2.25 to 2.28 calibration numbers. Next I plug in the USB and tell Zwift to ‘Search’. Zwift finds CT and I am good to go. 

This method works since the tension is not too high. I found that if I turn the knob 2 to 2 1/2 turns I have to ride CT for 10 minutes or more to have satisfactory results with watts on bike and watts on Zwift matching. With y 1 1/2 turns and short warm up/calibration the watts on my Garmin (reading from my Quarq) and CT/Zwift watts are nearly identical.

@ Eric C - In-game calibration would really be an excellent addition. I have a Kickr Snap and have a similar problem - I cannot calibrate that during a Zwift Workout.

I’ll try the suggestion above for unpairing/calibrating/pairing-again but a 30 second calibration block built into each workout would simplify the process greatly.

@ Eric C. - Additionally, in game calibration for CycleOps PowerBeam would be a plus.

In-game calibration is well done In Erg Video (Paul Smeulders) and there should be a simple programming solution to allow for it similarly in Zwift.

We seriously need a way to recalibrate a Computrainer in-game. I like to do at least 3 calibrations - one before I start, one 6 minutes in, and one before I start intervals. At present I have to unplug the USB connection to do so, which creates power spikes in my ride file (I have to manually remove those to prevent skewing my power curve), and I have to GET OFF THE BIKE to plug the USB back in. This is crazy! I’ve been doing this since Zwift was Beta, please add a feature to allow in-game calibration. As noted above, others have been able to do this, so it is possible. 

The point of calibration on the Computrainer is to have the trainer within an acceptable range of resistance. Attempting to attain an EXACT calibration value each time out is not really doing anything for your fitness.

As the tire warms, the calibration changes dramatically. This changes the reported watts. Because I am targeting watts in my intervals, it is important that the calibration (and therefore the watts I see) be correct. Therefore, it is necessary to recalibrate after a period of warmup.

For example, my initial calibration shows 2.7. In the first 6’ minutes, it becomes much easier to push the same number of watts, say 150w goes from feeling hardish to feeling easy. Then I recalibrate and it shows 2.0. That returns the effort required to get to 150w. Typically, it is pretty stable after that, but if I’m going for precise or hard intervals, I want to recalibrate again. Often it will drift up slightly, say to 2.1.

It also makes a difference in the resulting file. If I did not recalibrate, my power numbers would be artificially elevated. This would result in an inaccurate PD curve and FTP, and I would be setting future intervals targets incorrectly. So, long story short, yes, it does affect my fitness because proper calibration allows me to accurately see what I am doing, and help me predict what intervals I need to do.

What I’m trying to explain, perhaps poorly and too lengthy, is that you need to recalibrate after the tire warms up to get precise watt measurements.

I’m with Susan on this.

Susan is 100% correct. I can ride CT without calibrating. My Garmin 810 may show 200 watts, but due to incorrect calibration Zwift will show I am only putting out 170 watts. I ride 8-10 minutes and calibrate and the numbers are nearly exact. 200 on Garmin, 200 on Zwift. 
Susan - Here is what I did. I got myself a USB extension cable. I plugged this into the PC. On the other end I plug in the USB adapter thingy that CompuTrainer provides. I have a three legged stand that mounts my CT control head. I have the cable hanging over my CT control mount. This way I can ride, hit A to enter the Zwift calibration/setting mode. I unplug the adapter (leaving it hanging on mount). I do the spin up to calibrate CT. Plug it back in. Sometimes Zwift quickly rediscovers the CT is plugged in, sometimes I have to Search and select to get it to reconnect. This process takes me about 30 seconds at most. No more having to hop on and off the bike :slight_smile:
I believe in getting a slow easy leg spin for at least 3-4 minutes before I start cranking out more than recovery watts. Then I ride another 5 minutes at tempo to get the tire warmed and my legs ready for a real warm up. This total of about 8-9 minutes is enough for me to calibrate once and have accurate readings for the rest of the ride. Then I move on the the real workout with warm up , etc without having to worry about calibrating again.
Hope this helps.

Why didn’t I think of a USB extension cable?? That’s great! I’d feel better about not yanking it out of the computer all the time, too. Do you ever see power spikes when you disconnect with this option? 

I have never noticed a spike. I was just looking at data and the last ride it took me 25 seconds to stop pedaling, unplug, spin up, calibrate, reconnect…and never got off bike. If you have ever used ERG Video you know how the calibration works. No unplugging…just one button push, spin, calibrate, done. Zwift could easily do something like this. ERG is so quick, if used on Zwift you could do it while with a group…on a downhill and never risk losing contact.

Yes, I’ve used Erg video, which is one reason this frustrates me so. I’d really like to see them address this issue. I’ve actually managed to recalibrate on a Zwift downhill, dismount and all, but it could be so much better and faster!