Spinning out on a 8 min FTP test

Hi all,

I did an 8 minute FTP test yesterday and I ended up spinning out during the test intervals to a point where I was at a high cadence (for me) but felt like I had more power to give. I’m a relative newbie to TR and whilst I’ve read threads with similar issues mine differs slightly and I would really appreciate some advice.

The FTP result should be public. I ride on a Tacx Vortex. Normal riding in Erg mode means I’m on the smaller of the two front chain rings with is going straight back to mid-rear cog.

The test went something like this:

  1. I enter a test segment a shift to the larger front cog and progressively shift up in terms of moving to the smaller rear cogs. On occasion I may start shifting just before the segment starts. Not sure if this matters.

  2. I see my power increase but not reach the target power. Instead I plateau around my current FTP. At this points I’m doing 110 maybe more cadence wise.

  3. With the exception of trying to peddle faster I can’t make any significant increase in power but I feel like I’ve more to give and the trainer is not resisting as much as it could be. I sit there for 8 mins wondering what I’m doing wrong.

It’s probably worth mentioning that calibrating prior to the test has a weird result. It actually worked ok but then gave a result of “0”.

Being honest, I’ve not had much luck with FTP tests. When I started back at the start of 2020 I did the ramp test and had a similar issue but I put it down to setting my initial FTP wrong. I should mention the result was something like 230 (was 260) and whilst I wouldn’t be surprised at a slight drop, it just didn’t feel right.

Any assistance and advice gratefully received.



Check the “Resistance” setting you are using within the TrainerRoad app:



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Chances are that you are at a moderate to low percentage. Increase that setting to something like 50-75% and you should feel a real change in the gearing you need to use to hit various power targets.


I wouldn’t have ERG on for a 20min test, I’m not sure you should for an 8min test either. Did you have it on ? ERG follows a target power, if you go above it, resistance goes down and you are inclined to spin faster. Repeat and it’s the same, resistance goes down and you are inclined to go faster again. Etc, etc. I would toggle an 20 min test to Resistance mode.

I am not sure he used ERG mode for his test. It is not possible for us to know from the data provided. Only TR can see the actual mode in use in the file.

I was under the assumption that he ran the default TR 2x8 FTP test, that automatically switches to Resistance mode for the two 8m test blocks, even if you normally use ERG for other workouts. That is also true for the TR 20m test. If that is the case for his test, the Resistance percentage setting is in play, and ERG is not relevant.

Hopefully @jasonhodder will clarify exactly what he did.


Pretty sure 8 & 20 tests disable Erg for main intervals. Been a while since I did one though

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They definitely do switch to Resistance mode, but it’s also entirely possible to swap back to ERG manually. On Win/Mac it can be done in a split second with the ‘T’ key. Mobile takes a bit more work, but is still possible.

Hence the reason we need more info from the OP to know for sure what was done here.

Check out this post I just made.

My Tacx Vortex was not very accurate and it would get less accurate as it warmed up. Also, in the youtube video the guy talks about the resistance range of the vortex. You can only get certain power in certain gears with it. That was news to me and explained some of the weirdness I had with the Vortex.

I’m on a Kickr and I’m 500% happier. And I just take the power from my Stages so that inside and outside power all comes from the same device.

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Thanks all for the feedback. It looks like the resistance setting in the app has sorted it.

I do all my routines in Erg mode. However, for the 8 min FTP test my understanding is that it runs it drops out of Erg mode for the test periods and this happens automatically. This kind of explains why I plateau in terms of power output, feel like I have more to give but the trainer doesn’t compensate.

I looked this morning and tried a few things. First I did a test on the Tacx app at the highest gearing I reached during the tests. At a lower cadence (87 compared to 110) I hit around 305watts where during my botched test it was around 260. Doing the same on the TR app resulted in similar stats.

I then looked at the resistance setting in the app and that is where I think the issue was. During tests I was definitely at 100% of the resistance setting. But the app resistance setting was at 30%. Dialling this up to 50% has made a massive difference and when testing is during a 8 min FTP test this morning I rode the same conditions as a few days ago and hit 289 watt which is more realistic and I didn’t feel like I was spinning out as I was around 90rpm.

I’m still getting odd results during calibrations and I appreciate the points on the Tacx issues which I’ll read up on too.