Tacx Basic- Trainers Accuracy In Measuring Power?

Pobre

Hi,

Have anyone tested the accuracy of Tacx- trainers in measuring power with e.g. SRM- Powermeter? I' m supposing it gives one little too small figures, opionions?

Regards,
Antti Träskelin
Turku, Finland

ric_stern/RST

i found that when i compared it to a Power Tap (which had previously been compared to an SRM) it tended to underestimate at low powers and over estimate at high powers. however, the difference in power was also affected by air temps and/or roll down calibrations.

ric

__________________
http://www.cyclecoach.com

BrianMartley

Hi folks,

Newbie here - any further details available on the high/low ranges Ric ? Most of my sessions are in the 230-260w range, with intervals at 300w-ish. I really struggle after that.

I'm using a tacx basic (about 4 yrs now) and would be interested to hear how it compared. I've always assumed it's inaccurate and just used it as a relative measure between sessions for comparison.

cheers

Brian

tuney

Hi Brian

A bit long:

I have a power tap and Tacx Flow which I upgraded to an Imagic.
The Flow is pretty similar to the powertap but shows higher values than the power tap and lower watts, i.e. below 200 watts, and over estimates at higher values, 290watts on Flow is 270 on the PT.

The one good thing about the Flow is that is has a calibration utility which can tell you if the current session has the same 'power' as any previous session, this is worked out similar to a kingcycle where you accelarate to a speed and then freewheel... the flow then calculates the power via the decelaration of the wheel.

The imagic is very different, for example 210watts on imagic is 250ish on the powertap... and I dont think there is any way to calibrate the imagic.

I feel its best to use everything as a relative. Do a test on your turbo (e.g. 20sec/5mins/30mins flat out) and use these for levels in your preceding sessions, and when looking for improvements!

The only value of having 100% accurate power levels would be if you can translate any tests you do on the road e.g. TT or a kingcycle test/lactic test to values on your turbo. I do this by using the Power Tap when I do a TT or a KC test, that way you can go home and calibrate the Turbo to the 'right' values.

Chris

tomUK

Chris -

I too have a Tacx flow, but no powertap (as of yet). What is the method you use to calibrate your tacx flow? The manual suggests a 3 minute warm up from cold. I usually ride at 100W and keep the speed between 12-13mph. Once I have done this 3 min warm up I then go through the calibration period.

Would you mind posting some figures for me? i.e. what the powertap says the watts are when the flow is indicating 100W, 150W, 190W, 210W and 330W.

I would REALLY appreciate it.

Many thanks.

BrianMartley

Hi Chris,

Thanks for your comments.

I agree that really the numbers are best used as relative values between sessions. I've kept a training diary for a few years now, so I do have a rough correlation between my road fitness and the turbo numbers, although I bet they don't line up with anyone else's !

Be interested in your views on the imagic. I don't know anyone who uses one and I was very tempted to buy one for this winter as the turbo I have is getting a bit tired now. Anything that improves the interest factor has got to be good for turbo sessions.

I also second TomUK's request - be very interested to see comparison figures in those ranges.

cheers

Brian

tuney

Hi Guys

Im on the turbo tongiht, so I'll post the files(IMagic and PowerTap) tommorow, maybe that will give you a feeling of what to expect.

I do like the IMagic, I dont use the 3d function but I like how I can program courses.

The flow is also very good as a simple turbo.

REMEMBER: You can t really take this to an event to warm up on, as it really needs to be plugged in. Its actually harder to pedal when there is no power due to the electomagnets!

Chris

tuney

I did some test last night while on the Tacx

I was using the Imagic for my first interval session and wondered what power to tap into the Course generator.


Oh and thanks Ric, I used your interval session from your website... and PHEW they are good!!! I was nearly sick after the last one and I only managed 4 and a half! Maybe I should increase the rest period to 2 or 3 mins!

Anyway.

Before I started I used the results from my MAP test to figure that 320-330 watts on the powerTap is 260 @ 95-100rpm on my tacx as it is currently set up... Therefore I created a course which allowed an interval session @ the right %MAP.

I did no calibration on the tyre pressure or force at which the roller is on the tyre... ill do this next time.

What was interesting was that if I lowered or increased the cadence the power would unsyncronise, i.e.

@~95 rpm @ 250w on the Tacx would be 310 on the powertap (avaraged 309watts on pt for 5min interval)

@~95 rpm @ 260w on the Tacx would be 320-330 on the powertap (avaraged 324 for 5 min interval)

@110 rpm @ 260w on the Tacx would be 315-320 on the powertap... a bit lower...

So... In conclusion.... If you are using a power based course on the IMAGIC, I suppose its best to calibrate the power your going to ride @ with a specic RPM (within a few rpm).

Otherwise use a slope based session and simply ride faster and user the Powertap as the power meter.


I know this is a bit clinical... but hey... we are here to improve.

Chris

ric_stern/RST

chris,
depending on when your main peak is going to be and what you're expecting to race, it maybe a little too early to be going flat out with those 4-min intervals...

ric

__________________
http://www.cyclecoach.com

tuney

Ric

Yeah.. I was thinking of taking the intensity down to about 290(just into zone 4 of 7 your zones) and doing 10 minutes ones with 1 min rest ... I was doing these before.. but had a bad Jan training.

Do you think that would be a better idea?

Oh I'll start racing next month... that was my proposed start of the 'BUILD' period for 2 months.. maybe Ill leave the Higher Int stuff until then.


Cheers
Chris

ric_stern/RST

i'd concentrate on zone 3 and 4 intervals at the moment, completing one to four x 15 - 30 mins, once + times per week

ric

__________________
http://www.cyclecoach.com

tuney

Back to the old routine then

Cheers

ric_stern/RST

the bad january bit, makes/made me think you hadn't done much (of these?).

ric

__________________
http://www.cyclecoach.com

BrianMartley

Hi Chris,

Thanks for posting those figures, I'm amazed how far apart the two bits of kit (tacx/PT) are in their measurements. Although you state that there's no checks on tire force, which I guess could increase the perceived effort and give lower readings (?) there's still quite a margin.

Still, it does help me and give me something to consider when reading other folks' suggested power training figures - so thanks again.

Oh - I've also tried similar intervals (4-5mins on) to the ones on your site Ric, and personally I found that when I could work up to doing a set, they did make much more improvement in my road-riding than any others I've tried. But I also feel ill trying 'em at this time of year.....

cheers

Brian