Yesterday i assembled my zwift ride frame, and replaced the cassette on my Kickr v6 with the zwift Cog. After a couple of testing sessions the issue i am running into is my power is way way off. Like 150-200w off. I feel like messed something up with the cog install because my numbers are lower than last year at this time when i was using my bike on the kickr and had way worse fitness than i do now.
Should i take the Cog off and re-install on the freehub? Also i have the COG in position 1.
Hi @Will_Simonds welcome to Zwift forums.
Shuji at Zwift HQ here.
Can you provide a little more context for when you notice this discrepancy? In the middle of a structured workout? During a free ride? Did you do a fresh FTP test? In the end-of-ride summary screen? Comparing peak power to your outdoor rides?
Swapping out your cassette to a Zwift Cog has no bearing on this discrepancy. There are no electronics in the Zwift Cog. It’s just a 14 tooth cog, no different than any of the individual cogs on your multi-speed cassette.
Something did change on your KICKR, though - the firmware upgrade that makes the KICKR v6 capable of virtual shifting. It went from v 5.0.14 on December 20 2023 to v
5.3.5 on September 17 2024. (Welcome back to Zwift season!)
It may be worthwhile to read Wahoo’s support article on auto-spindown calibration and make sure you’ve given the KICKR a chance to save the calibration settings to its internal memory.
Let’s start with that. Do let us know about where you’re seeing the discrepancy?
Hey @shooj ,
I noticed it right away on free ride, end of ride summary, on screen HUD strava analysis. Compared to my outdoor rides.
Basically i noticed it from the first second i started riding with the new setup.
My zone 2 for outdoor ride (230w) felt like a zone 4 effort on Zwift.
I updated my kickr V6 to the latest firmware prior to setting up the Zwift Ride frame and adding the zwift Cog.
I have not done the calibration spindown, do you think that will resolve or help?
When i first set it up and started pedaling i had the Thru Axel over tightened and after about 90 seconds of pedaling, the cranks physically could not turn over. I quickly loosened the Thru-Axle and it was pedaling fine after that but the power was still off. I was concerned that this may have damaged the COG and maybe that was the reason why the power out put was so far off, that or the thought that maybe i over tightened the cog on the free hub body, i followed the instructions of only tightening the a quarter turn. This logic might be flawed because that probably wont affect power.
For reference last year when i was using zwift my ftp was 187, after this season of riding outdoors, with structured training, and racing, my FTP is 264. The power numbers im producing on the zwift ride are less than last year when my ftp was 187 and fitness wasnt half of what it is today so i know something is wrong.
It couldn’t hurt. 
Are you doing structured workouts in ERG mode on Zwift? After you do the auto-spindown calibration, it may be worthwhile to do an FTP test in Zwift. Since last December, we rolled out a new FTP test in the Watopia expansion called The Grade. If you ride the Elevation Evaluation route and maintain a full effort until you reach the top - it will tell you if your FTP has increased.
What are you using to measure your power outdoors? Is it a crank or pedal based power meter reading to a GPS head unit, and if so, which make / model?
There will always be a discrepancy comparing to power read at the pedals vs at the rear axle. This is due to power losses in the chain - typically up to ~5% loss. That said - if your pedal power meter says 230w, a 5% loss means ~218 watts indoors, and that doesn’t seem enough to account for your discrepancy.
There are other places where inaccuracies are introduced.
If they’re pedal-based power meters, you should also verify that you’re compensating for the crank length on your bike. Power meters transmit a torque value that’s read by the head unit / pedal manufacturer’s mobile app. The head unit / mobile app should have a way to input your crankarm length, which then does the conversion to power. Please check the manufacturer sites for both your pedals and your head unit.
While you’re looking at the pedal manufacturer’s site - please read their installation instructions carefully. Not to pick on Garmin, but their early generation Vector-series pedals were very sensitive to how tight the pedal axles were installed into the cranks, and specified a torque that you needed a 15 mm crow’s foot socket installed on your torque wrench to measure with precision.
Other brands of pedal-based power meter may also have specific installation instructions. Crank-based power meters should be factory-adjusted for the crank arm length, but worth verifying with the manufacturer.
I also have a kickr v6 and I think I know whats up: the cog v2 is rubbing against the ZWIFT frame creating massive restistance if you do not install the drive side spin cap.
try if you can spin the cog freely when the frame is mounted. If not make sure to check if the drive side spin cap from the kickr is installed. The zwift video manuals get this wrong and show only to use the lock nut but forget to mention you nee the lock nut PLUS the drive side spin cap.
Dude you are SPOT ON. Put the drive side spin cap on and it is so much better now.
Small miss by Zwift with a big impact.
Cheers man!