Tacx Flow T2240 - Trainer Road problems / power limits

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Zarch
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Tacx Flow T2240 - Trainer Road problems / power limits

Post by Zarch » Tue Oct 31, 2017 12:11 pm

I use my Flow T2240 on Trainer Road in ERG mode.

I encounter problems when there is a high shift in power requirement, ie anaerobic intervals. (see attached picture).

My understanding is that on my ERG trainer I should be able to keep the bike in the same gear and trainer controls the resistance at all times.

Whilst this works when there is little movement in the power requirements, between sweet spot and threshold etc. When there are large swings the trainer:
a) can't go high enough
b) can't go low enough

ImageTR by Mick Wall, on Flickr

As you can see from the picture in the red circled sections I kept the bike in the same gear and the trainer was unable to go high or low enough. (The yellow trace is the power output)

But in the blue highlighted section I used my gears to bump up 3 or 4 gears and back down 3 or 4 gears and the trainer could then hit the right numbers.

But I don't see this as acceptable?

I'm on the latest Tacx firmware, Trainer Road is at the latest version and i'm connecting everything over ANT+ to a PC. I'm also connecting via ANT+ to my Edge 520 so I know everything is connecting fine.

The Flow T2240 states a maximum power of 800w, but i'm only going upto 400w on this workout, so i'm not sure what the problem is here. Especially as it can't even just sit at 80w without intervention of gear changes.

Anyone any ideas?

Any help would be very much appreciated.

Thanks.

mcorn
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Re: Tacx Flow T2240 - Trainer Road problems / power limits

Post by mcorn » Tue Oct 31, 2017 6:27 pm

The Flow, like the Imagic before it, uses an eddy-current brake with fixed and variable magnets. That design limits how much resistance can be produced at lower speeds. I can't find power curves on the Tacx website any more, but the catalog for the older Imagic/Flow shows that you need to be going 60 kmh/36 mph with all magnets energized (typically a 5% uphill) to achieve 800 watts. I see the specs for the Flow Smart show 800 watts at 40 kmh at 6%. Not sure what speeds you were doing, but as you can see, the Flow has a narrower range. I think it is a nice brake and is quite reliable, but it hasmore limitations than the others.

Richard1970
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Re: Tacx Flow T2240 - Trainer Road problems / power limits

Post by Richard1970 » Mon Jan 29, 2018 9:46 pm

Hi Zarch,
Did you ever get to the bottom of this?

I am finding exactly the same issues, but whilst using the sufferfest app.
I've found that at 40km/hr it doesn't get anywhere near 800 watt. (I reckon its around ~485 watt)
So i'm having to whiz up and down the gears to hit the target watts, as staying in one gear and letting the ERG do its thing doesn't have enough range.

tomschlong
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Re: Tacx Flow T2240 - Trainer Road problems / power limits

Post by tomschlong » Tue Jan 30, 2018 11:27 am

What you might have to do is use the small chain-ring up front for normal and rest intervals, then for sprints you shift to the big chain ring. This works for me pretty well.

mcorn
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Re: Tacx Flow T2240 - Trainer Road problems / power limits

Post by mcorn » Tue Jan 30, 2018 7:27 pm

Richard1970 wrote:
Mon Jan 29, 2018 9:46 pm
I've found that at 40km/hr it doesn't get anywhere near 800 watt. (I reckon its around ~485 watt)
As stated above, I think your speed needs to be at 60 kmh on a 5% uphill to achieve maximum wattage.

Zarch
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Joined: Tue Oct 31, 2017 11:58 am

Re: Tacx Flow T2240 - Trainer Road problems / power limits

Post by Zarch » Wed Jan 31, 2018 2:41 pm

Didn't find a 'solution' as such..... just have to accept the limitation of the trainer. So yep, I just drop down and up gears when required.

Here's some comments from TrainerRoad support that explain the flaw with the trainer, hope these help.
After taking a look at your logs and the ride you linked me to, I firmly believe the issues you're describing are due to the wattage range of your trainer.

Basically, what you're experiencing are called a wattage floor and a wattage ceiling. It takes a minimal amount of power to turn the pedals on your bike when it's on your trainer. No matter what you'll be producing a certain amount of power. That's why, occasionally, you find that you can meet the target power in resting intervals by shifting into easier gears. You're lowering the amount of power it takes to turn the pedals on your bike.

The other side of this situation is that your trainer is only capable of producing a certain amount of resistance. As a machine, it literally just has a maximum amount of resistance that it's capable of producing. There are a couple things you can do to make that amount of resistance greater. You can increase the amount of resistance applied to your rear tire, or you can shift into a more difficult gear. Doing these things basically adds on to the amount of resistance your trainer is inherently capable of providing you with.

The wattage floor/ceiling issues are the typical complaints we hear about the Tacx Flow, to answer your question. What's good is that most TrainerRoad workouts won't have you perform such drastic swings in power.

it looks like this issue is a mechanical limitation of your Tacx trainer. The Tacx Flows Erg mode seems to struggle at really high power intervals. We've had other athletes complain about this, and we've even experienced a similar drawback while testing the Flow in-house. I even took a look at the log files from your rides and it looks like your trainer is just maxing out on resistance during your Threshold intervals.

I think the best possible solution in this scenario is to use resistance mode when you do sprint intervals and threshold intervals. So if you've got another workout like Black Giant, where you're doing Threshold intervals, you're going to want to be shifting during your workouts and using resistance mode. This way you won't need to deal with Erg mode maxing out or anything like that.

On the other hand, when you do the rest of your workouts you should be able to use Erg mode regularly. Erg mode looks like it has been working perfectly during lower intensity intervals so it shouldn't be a problem to use it for the rest of your workouts.

Zarch
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Re: Tacx Flow T2240 - Trainer Road problems / power limits

Post by Zarch » Tue Mar 20, 2018 12:54 pm

More T2240 ERG mode questions and confusion.

Are all watts created equal?

I was doing this TrainerRoad Sweetspot workout with my 10 speed 105, 50/34, 11-32 set up on the small front ring and in the middle cog.

Things went ok and I stayed like this until the final interval. Out of curiosity I then jumped to the big front ring and kept everything else the same.

The final interval was WAY harder than the previous ones. So despite the target watts becoming almost exactly the same the feeling was totally different.

Image

So what gives? Why didn't 180 watts of the final interval feel the same as the 180 watts of the 2nd interval?
There was a noticeable difference. The latter was like cycling through mud in comparison.

I also did new TrainerRoad Ramp Test X..... first time when leaving it in small ring, middle cog I had to change gears towards the end due to the trainer not getting high enough power.

Second time I preempted the need to changes and gear changed earlier. But I felt this made the whole test way harder cos of similar feeling to Sweetspot problems.

I really confused as how best to use this Flow Trainer on TrainerRoad.

It seems like whenever I am forced to use my gears in ERG mode the resistance changes for the worse..... like its no longer working to a proper power curve.

Any thoughts at all?

tomschlong
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Joined: Tue Jan 30, 2018 11:23 am

Re: Tacx Flow T2240 - Trainer Road problems / power limits

Post by tomschlong » Tue Mar 20, 2018 1:57 pm

The built in "power meter" is just a virtual calculation based on "speed" and "cadence" (afaik). So to get the best consistent results you need to calibrate in the gear you plan to use for your target intervals and then it's best to just leave it in that gear and even better try to stay at the same cadence for intervals that matter. Any gear changes and cadence changes will mean different virtual speeds and that will change the calculated watts on the power curve. Since you are using ERG mode it's meant to stay in one gear and this is the best way to get consistent power readings.

I use a real power meter simultaneously with TrainerRoad and use their powermatch feature. I can then compare the Tacx power readings with my real power meter in real time, and believe me, you don't want to know how inconsistent the Tacx power reading is. :?
Firstly, there's a significant drift over the duration of a workout. Meaning as time goes on the resistance will drop and the trainer will be reading way higher watts than it was at the beginning of a work out. So I if I calibrated at the start of a work out and was at 180 watts on both power meters, after a maybe 30 minutes, I was at 180 watts on the Tacx but my power meter showed only 160 watts. I assume this has to do with heat and as the trainer warms up the resistance will drop. To reduce this effect, I suggest calibration well into your workout at least 10 minutes after you've started. If you want even best results re-calibrate every so often during a workout.
Besides the power drift, there's also an inconsistency in the power curve. The wattage difference is not linear so at 100 watts it might be only 1% off but at 200 watts it's 20% off, and then at 300 watts its maybe only 5% off etc. This will be even more exaggerated if you are shifting gears and trying different cadences.

Sorry to not have any better news but if you want consistent power for training you'll need a real power meter and use powermatch with TrainerRaod in ERG mode.

If you don't or can't get a power meter then you can still use the Tacx for good workouts with TrainerRoad but then with those few suggested methods above to cut down on the inconsistencies.

mcorn
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Re: Tacx Flow T2240 - Trainer Road problems / power limits

Post by mcorn » Tue Mar 20, 2018 5:29 pm

In order to achieve best possible accuracy, calibration after a warm-up has been a long-standing recommendation for all Tacx trainers as well as maintaining consistent tire pressure. Tire pressure affects the tension on the roller, which is part of the drag in the system and part of what calibration measures.

The idea of recalibrating multiple times during a workout is overkill and not really very useful. You have to be realistic in terms of expectations from this inexpensive and reasonably reliable brake. This unit is not a laboratory grade instrument, nor is it intended to be. It is mostly about getting a decent workout and getting your heart rate up. So, if it does that, it is pretty much doing its job.

Zarch
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Joined: Tue Oct 31, 2017 11:58 am

Re: Tacx Flow T2240 - Trainer Road problems / power limits

Post by Zarch » Tue Mar 20, 2018 5:37 pm

tomschlong wrote:
Tue Mar 20, 2018 1:57 pm
Sorry to not have any better news but if you want consistent power for training you'll need a real power meter and use powermatch with TrainerRaod in ERG mode.
Thank you for your detailed reply Tom, very much appreciated.

So if I buy a power meter and enable powermatch, will the brake on the T2240 Flow in ERG work right from 70w upto 400w?

Ie, I leave my 50/34, 11/32 setup in the small ring, middle cog and i wont ever have to worry about changing gears again?

Will both problems i've had above be resolved by using the power meter as the source of power?

My worry is buying the powermeter and then finding the Flow still unable supply adequate resistance.

tomschlong
Posts: 3
Joined: Tue Jan 30, 2018 11:23 am

Re: Tacx Flow T2240 - Trainer Road problems / power limits

Post by tomschlong » Tue Mar 20, 2018 6:34 pm

Zarch wrote:
Tue Mar 20, 2018 5:37 pm
So if I buy a power meter and enable powermatch, will the brake on the T2240 Flow in ERG work right from 70w upto 400w?

Ie, I leave my 50/34, 11/32 setup in the small ring, middle cog and i wont ever have to worry about changing gears again?

Will both problems i've had above be resolved by using the power meter as the source of power?

My worry is buying the powermeter and then finding the Flow still unable supply adequate resistance.
Well I can't say for certain that it will work from 70 W up to 400w with out needing to shift gears, even on my Vortex I have to shift into the big ring for stomps or sprints etc, because the resistance takes too long to ramp up.
You will need to find a gear that will allow for the lowest resistance necessary in the rest intervals and then still deliver enough resistance for the work intervals. This might not be the middle cog on your cassette. For me on 11-32 it's the 3rd smallest cog.

What I think a power meter will eliminate is the inconsistency. So when you are hitting 200 watts on your power meter you can be sure its 200 watts each and every time. It will also eliminate the discrepancies with power drift and that feeling you were talking about of 180 feeling harder in different gears. Because the power data comes from the power meter and then sends the resistance signal to the smart trainer in ERG mode, it will be irrelevant which gear you are in. (as long as you use a gear that allows for the range you need)

IMHO a power meter is never a bad investment because you can then use it outdoors consistently as well.

mcorn
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Re: Tacx Flow T2240 - Trainer Road problems / power limits

Post by mcorn » Wed Mar 21, 2018 3:32 am

I have a Flow Smart brake that I got recently for a good price. I put it on a trainer that also has a Power Tap hub. The power meter does insure that reasonably accurate power readings are reported. However, the Flow brake has significant limitations. I'm not sure it makes much difference what gear you are in, however. If you look at the Flow power curves, you will see that in order to obtain maximum resistance, your wheel speed needs to be high and you need to be on a course that has higher slopes. So, I'm not sure that cadence or gearing is all that important as long as you end up with a high wheel speed on a hill, which may be difficult for ordinary riders to achieve. Maximum wattage output requires speeds on uphills in the 30+ mph/50+ kmh range.

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