Tacx vs Wahoo wattage and ftp differences

I took delivery of a shiny Wahoo Kickr Core yesturday and decided to try it out with a sweetspot workout. Instantly I could feel it was more difficult than a similar workout had been on my Tacx Flow smart t2240. Admittedly I was on tired legs and so gave up and am planning a ramp test on the new machine this evening.

I will update this post after the ramp and for reference my ftp score on the Tacx was 280. I always consistently calibrated the machine and checked tyre pressure etc.

For me as an ironman athlete the accuracy of my turbo training is important for race day relevant to power meter percentage riding.

Just thought this might be insightful for triathlete or cyclists alike looking to rely on power numbers from a wheel on trainer.

You can’t compare power from one trainer to another, even if it were the same brand and setup. As long as it’s consistent that’s all that matters. If you want your indoor power to match your outdoor power you’ll need a power meter to verify the numbers or at least know your offset (unless using powermatch).

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I agree with you. But actually consistency isn’t all that matters when you are relying on ftp as a benchmark to workout intensities for an ironman ride.

The kickr is supposedly within 2% and to my knowledge has an inbuilt power meter so for me that is reliable enough. Dcrainmakers review demonstrated the accuracy.

I’ve got a Kickr and a Tacx Neo along with power meters on all my bikes. My Kickr reads 25 - 30 watts higher than my Quarq power meters. Both the PM and the Kickr are calibrated. I use Power Match, so not a big deal.

My Neo is much closer in power to my Quarqs, usually within 1 - 2 watts.

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Ah that’s not so reassuring, I guess for accuracy closer to an event powermatching or outdoor ftp testing is the way forward…

Yup. It would be nice to “trust” that the manufacturers were always right, but that is not the case.

You are best to verify and drive power from your actual meter, for the needs you described.

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Wheel-on trainers are much less reliable in measuring power than direct drive ones, as the power estimation is calculated from roller speed and resistance level, but the actual load depends strongly on tire pressure and roller position. Spin-down calibration tests attempt to reduce this dependency, but they on the other hand depend themselves on wheel inertia - yet another factor thrown into the mix. So a wheel-on trainer can be consistent, if you keep the same bike with same wheel and same tire at same pressure; but consistent does not mean right.

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Interesting. I have a Kickr '17 and a Neo 2. Based on ramp testing with the Neo a day after the Kickr, I only saw a 1.5% difference in FTP (4 W).

I realize it’s not as direct a comparison as yours, but I don’t have another power meter.

I think there is a fair bit of variability with the between trainers. I have a First Gen Kickr and use it as my “backup” trainer with the Neo as my primary.

I worked with Wahoo support a couple years ago because I had determine that there was a discrepancy between the power readings on the Kickr vs my power meters on my bikes. The first gen Kickr used a different method to calculate power via a strain gauge. Wahoo removed the strain gauge in subsequent Kickr and used the brake to calculate power which was thought to be more accurate. They came out with an update for the first gen Kickr that essentially disabled the strain gauge and turned it into a second gen device by using the brake to calculate the power. Wahoo support recommended I try this since I was having issues.

https://forum.cruzbike.com/threads/kickr-v1-users-upgrade-to-kickr-2-accuracy-for-free.11609/

I did this but the accuracy did not improve and perhaps even got a little worse. However power match worked great with TR, so at least with TR workouts it was not an issue as long as I used a bike with a PM on it. I was doing some Sufferfest workouts at the time though and these were a pain since power match didn’t work with Sufferfest.

Wahoo support said there really wasn’t anything else that could be done regarding the high power readings and that some of the Kickr’s do read differently than the PM’s on bikes.

Lately I’ve been using my Kickr again while waiting for a new free hub for my Neo. For fun I sync’d up my Garmin with the Kickr during last night’s workout. It was SSB between 235 - 250 watts (again I was using power match so that was what my Quarq was reading). However my Garmin was reading 265 - 280 (getting data from Kickr).

The only other weird thing the first gen Kickr does is every workout or two it suddenly raises the resistance super high for a half second or so. It shows up as a big spike in my workout. Googling this issue shows this happened with some first gen Kickrs but I don’t think is a problem with newer ones. The Neo does not do this. Its a pain when it happens but happens infrequently enough that it isn’t a huge deal. On the plus side I had none of the mechanical issues that the 2018 Kickr’s are plagued with.

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I’ve got a 3rd gen Kickr (Kickr 2017), and it uses an optical power meter. I was having super high resistance issues, although usually lasting 5 to 10 seconds. Called Wahoo and after some conversation they said light and/or shadows can interfere with the optical sensor. Recommended putting a black mat under the bike - its in a garage with smooth cement floors. And to turn off any lights directly overhead, so shadows from my body wouldn’t cause interference. Sure enough that worked. Wahoo CEO mentions light interference issue at 9:10 into this video https://www.youtube.com/watch?v=6MgromwkTOs

After my original post I have just completed a ramp test. Scored 285 so up 5 points after final 3 weeks of sus power build.
Perhaps I made a fuss over nothing :see_no_evil: sorry folks!

I think it feels a little harder In a way as there is no tyre slippage or letting off and the power delivery is smoother. Difficult to explain but the 285 has left me with a smile that will last all night :slight_smile:

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My Kickr Core and P1 pedals are very close…the Core on average is around 3 watts higher over 20 mins.

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Interesting - I’ll have to watch for that and see if there are any lighting changes that occur with the spikes.

Here is the spike that occurred during third set yesterday. Again, very brief but really high increase in intensity. When I feel this I immediately let off the pedals and it lets up, but then it takes power match a little bit to adjust.

Hmm, the easiest one to find is from ramp test June 2018. And its the opposite, resistance dropped low:

37%20PM

Here are my notes:

Bad test, assuming optical interference when Kickr dropped power on step 14. KICKR trainer in erg mode, paired to iPhone over BT with power match (Stages left only). KICKR “gave up” and dropped power below 200W at beginning of 306W / step 14 interval. Maybe 20-30 seconds in the KICKR went back to actual target power. Ruined test.

My Kickr 2018 has exactly the same difference between that and my P1 pedals. Good enough for me.

OMG! That is brutal.