Hi David: I have just found Intervals.icu and I think it is an excellent tool. My next stop has to be a donation.
The problem I am wrestling with is that I have been training with a Tacx Vortex wheel on trainer using TrainerRoad (TR) and the TR plans. I have done the ramp tests and have seen a good increase in estimated FTP over a period of about 8 months. My FTP value has risen from 190 in November 2019 to 274 tested in June 2020. All looks good and I can clearly see a good progression. I have been riding TR sessions and exporting the data to Strava and using the same FTP so I assume it and other tools were calculating the training load (TSS) based on what I said the FTP from my indoor riding was.
I have now got a pair of Assioma power pedals and, keeping the way I gear and ride the trainer the same, the pedal power output is significantly lower and could be up to 35w lower at certain speeds and powers. This means when I go out on the road with the power pedals I have to ride taking that difference into account, using heart rate and RPE. I have checked by running the pedals and the trainer together and using the DC Rainmaker analyser to see the difference.
I really suspect the Assioma pedals are providing a more accurate power reading than the turbo and want to make sure that power based TSS recorded from my road rides mirrors the loads from my indoor rides.
I have seen how you can have an indoor FTP in Intervals.icu so I can set the indoor FTP to 274 and the FTP to what I think the more accurate FTP is when using the pedals eg 250w. That is fine but I do not understand how Interval.icu handles the training load calculations? I assume it takes that into account and makes sure my loads from trainer rides use Indoor FTP and those from Outdoor rides use FTP? which should be all good.
My question is around eFTP and how that is calculated. I have read it is based on max efforts over a minimum set time period but does it differentiate between indoor and outdoor rides? or in my case just be based on the indoor rides as they are the ones that are more likely to have higher power readings. And I also assume eFTP has no impact on training load calculations?
Yes Intervals.icu will use your indoor FTP to calculate intensity and from that training load for indoor rides and the reverse for outdoor rides. As you suggest eFTP just uses your max efforts (indoor or outdoor) and has no impact on training load or any other stats.
Bit of a bummer that the PMs are so different. You can filter for indoor vs outdoor when looking at the power curves on the /power page at least.
Absolutely. A wheel on trainer is just too dependent on a couple of factors to be as accurate. Having said that, your pedals have a % accuracy margin, which at an FTP of ~255/~260 - taking the average here - could account for 5-10 Watts.
I compared mine with my Neo and they are consistently reporting ~5 Watts lower, so I adjusted for that in the Favero app, to match them with my Neo when riding outdoors. I know the Neo isnāt necessarily 100% accurate either, but I decided to take that as a base line.
However, other than the (big) difference you are experiencing based on PM comparison, it is not uncommon that someoneās indoor FTP is different than his/hers outdoor FTP. Often it is lower, due to cooling and hydration problems, but for some it is actually higher, because they can better keep pushing the required watts, because the trainer forces you to push them. If in ERG mode that is.
I would try to calibrate your Vortex, by tightening the tyre more to the roller, even if your Tacx (calibrating) tools tells you itās too tight. Plus, the Vortex has a 5% accuracy margin, which also could be well over 10 Watts.
I have got the Tacx tightened down to the tight end of the Tacx utility and donāt get much slip. I calibrate using the Tacx utility as well. I tried to use the new Power Match capability in Trainer Road but I dont like its response too much. Maybe its because the pedals and turbo are so far apart? On turbo efforts I ride in a high gear with fast flywheel speed which I think makes the inaccuracies greater, but I like the feel of the momentum in the flywheel and can sustain higher RPMs (100-110) in this gear for longer. It just feels smoother and better to me. So I donāt want to change that and ride in a lower gear with a slower flywheel which feels like cycling up a hill.
Not sure about different FTPs indoor and out but I think I am able to Ramp test pretty well to a high FTP. I then do struggle with the workouts when starting with a new FTP and have to dial back intensity or a threshold session becomes a crippling long VO2 Max session which kills me for days!
Not sure I have concluded a constant offset but the difference is quite constant at typical powers around FTP. Adjusting in the Favero app could be an option to consider and use the Tacx power as a common baseline out on the road Does that work well for you? It would mean the eFTP might actually mean something to me on the road.
Iāve just seen I can apply a manual offset in TrainerRoad to turbo power so I could use either the trainer power or the pedals power as the baseline?
Do you think there is a preferable way to do this? Maybe If I think the pedals are more accurate leave them alone and use the TrainerRoad offset?
In your case, the pedals are (al)most certainly more accurate, so I would use those as a baseline. You could offset the pedals by +1.5% each (like I did to match my Neo), which makes the gap smaller and then offset TR to match.
And yes, if you train at 100+ RPM, the flywheel momentum will definitely skew your (real) power. Low cadence drills are a must
In- versus outdoor FTP difference is a real thing, but obviously, there are people who āsufferā from it less. Iāve done all sorts of tests in- and outdoors (I have endless pancake flat straights in my cycling backyard), so I can compare them well.
I actually score slightly better indoors, but Iāve set my indoor FTP lower, because it keeps me from blowing myself up. Itās okay for an all out test every now and then, but I have a hard time staying hydrated - cooling as such is fine, as the room is air-conditioned and I have 3 big ass fans, blowing like hurricanes, but I still sweat like a pig.
As I see it, you have some different questions and things going on.
1.) Difference between the watts reading of your smart trainer and your power meter pedals. I have a similar setup: an Elite Direto and Powertap P1 Pedals. Like Cyclopaat also hints at, I treat my P1 pedals as the ātrueā power. Depending on the calibration of my direto the Direto reads between 1 to 4 % higher.
2.) Power match in Trainerroad. Would be a nice thing if it worked. It would mean that the Trainerroad files which gets uploaded to Trainerroad and Strava (and therefor also Intervals.icu etc.) show the ārealā watts and the watts which are on (in my case) my Wahoo (I record in parallel and later load my Wahoo file into Golden Cheetah - my true efforts). Trainerroad reportedly improved (or are in the process of improving) their Power match. For me it just added another feedback loop onto the feedback loop of the smarttrainer itself. Resulting in even more fluctuations and a worsened trainer experience. So I donāt bother at all with Power match in Trainerroad. There is this dead simple Percentage toggle in the lower right corner of the TR app. Your Assiomas show you 200 watts but the TACX and Traineroad reads 210? I.E. you are riding 10 watts to easy? Just klick on that and toggle 105 %. Or 102, or 110 - whatever you like.
The results of the ramp test and your capability to complete the following workouts. As long as you donāt touch your TACX this has absolutely nothing to do with the power readout of the TACX vs your pedals nor with outdoor vs indoor ftp (since you test indoors on your trainer und do indoor workouts). That maybe the issue of either: you are not used to indoor workouts and their for most people way higher RPE compared to outdoor efforts or you may not be used to high intensity workouts all together? Or - itās just so that the Ramp test with itās inherent assumptions lets you generate a FTP-Value which doesnāt really coincide with the FTP you would get from another way of deriving the FTP as a benchmark for deriving the training zones for the ubiquitous high sweetspot and VO2 work of most TR training plans:
Yes - differences in outdoor and indoor FTP are real for a great many of people. For some the differences diminish with high cooling and frequent indoor training. For others, not so.
eFTPā¦ David will be able to clarify better. But as far as I understand it, itās not that far away from a simple: Find a high 20 minute duration effort and multiply it with .95 as a factor. Yes - this totally ignores emptying the tank to really have those 20 minutes represent mostly aerobic contribution. And yes, itās totally impartial whether you did this effort in a separate test activity or just hitting it after a 3 hour ride because you went for a Strava segment. (In reality itās a bit more complex - the eFTP is derived from a CP model but what I understand and saw in one of my activities, it just boils down to that 15 to 20 minute effort). For me that just means - it would get a good number would I ride an appropriate and repeatable test protocol outside. Which I havenāt for a good while.
And that leads me to 6:
If you only test inside (say, with the Trainerroad Ramp Test) and have a significant difference between outdoor and indoor Intervals.icu will never be able to tell you a correct eFTP for outdoors. Because the Ramp test doesnāt lend itself into a recognisable intervall for eFTP estimation purposes and if it would - it would be too low of a target for your outdoor training. In other words: If you donāt yet have a good feel how certain efforts should hurt and how big of a difference your capabilities indoor vs outdoors are you will have to test separately. Indoors and outdoors.
Hopefully (if itās the FFT data model) its not a fixed 95% but a curve fit based on an initial sample of 2000 who have best power at a range of times up to an including 60min.
āThe continuous eFTP estimation is done by using single max efforts that are long enough to place you on a predefined power curve derived from empirical data (the FFT curves). So there is a PDC curve for FTP of 300, 301, 302 etc. (with matching Wā) and your FTP is the highest curve your max-effort reaches. It is basically a generalisation of the 95% of 20m power rule to any duration (so 75% of 5m power or whatever it is). People with good Wā need to use a longer minimum duration to avoid over estimates (āEst. FTP Min Durationā in /settings).ā
I only used the first 20 minutes of the FFT curves and generated Mortonās 3P models from those to get full duration. There is a big drop off at 20 mins so clearly the data after that isnāt great.
I found my Tacx Vortex was quite inaccurate compared to my Assiomas. I now have a Tacx Flux S & that is much closer to the Assiomas. I always use the Assiomas indoors & outdoors.
Reading above I was going to suggest exactly this (using Assiomas indoors too).
I have Assioma Duo and now I use it indoor and outdoor to keep consistency.
I donāt see an important difference in my FTP regarding indoor or outdoor riding.
Previously I had a Wahoo Kickr Core trainer, after the trainer spindown and pedals zeroing the difference used to be below 2% and then I didnāt use the pedals for indoor power measurements.
Just to make sure everybody is aware of the Power discrepancies with Wheel-On trainers:
Wheel-on trainers are very dependent on tire pressure!
Tire pressure changes with heat.
The spin-down calibration does nothing more then shift up/down the speed/power curve
For best consistency:
Always check and adjust your tire pressure before starting a workout
Adjust roller tension (trainer roller to tire) for minimal slippage
Ride your trainer for about 10 minutes to warm-up everything and do a spindown calibration. For Tacx, just have it somewhere on the high green zone.
Now again ride about 10 minutes high Z2/Low Z3 and check both Power from your trainer and Power Meter. If the Power Meter reports lower then the trainer, increase roller tension and vice-versa. Do this a couple of times untill they match up pretty well.
Donāt EVER do a spindown calibration anymore because that will offset them again.
Just keep Tire Pressure and roller tension the same from now on. Apart from the first 10 minutes, you will be pretty close
When doing hard intervals you will see a power that is to high at the beginning of an interval and then fades towards a lower stable number. In rest intervals, you will see the opposite. First a lower power that creeps up to a stable higher number. That is the influence of the changing temperature of the tire and air in the tire. After a couple of minutes at stable intensity, temp becomes constant.
With a wheel-on trainer, it is best to use a controlling app that has PowerMatch. If you did the above, the offset will be low enough to get a very good experience. If PowerMatch function has to correct a big offset, things can become strangeā¦
Does that work well for you? It would mean the eFTP might actually mean something to me on the road.
