Bushido power vs Powertap P1

Anything about Power (watts)

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gzinga
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Bushido power vs Powertap P1

Post by gzinga » Wed Sep 23, 2015 6:34 pm

Hello

just got a bushido and i am comparing it with the power tap P1 pedals. There is a substantial difference in power. both trainer and pedals were calibrated properly.

Basically the bushido shows a 20% less power than the P1 pedals.

Any thoughts?

Gabe

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ms6073
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Re: Bushido power vs Powertap P1

Post by ms6073 » Wed Sep 23, 2015 7:38 pm

gzinga wrote:bushido shows a 20% less power than the P1 pedals.
Since there is no method for 'scaling' the power output of the Bushido to reduce the disparity, your best bet is to set aside 20-40 minutes and work with the Bushido calibration to adjust roller tension, increasing as required until the Bushido power output is as close as possible to your Powertap powermeter.
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gzinga
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Re: Bushido power vs Powertap P1

Post by gzinga » Wed Sep 23, 2015 8:40 pm

gotcha, do you mean just adjusting the knob so that there is more contact between the roller and the tire?

Gabe

Mark Hewitt
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Re: Bushido power vs Powertap P1

Post by Mark Hewitt » Thu Sep 24, 2015 10:17 am

But; does it matter? The P1 is likely to be the correct figure as the Bushido is affected by so many elements. So take the power figure from the P1 and ignore the Bushido power numbers. That's what I do, power readings come from my Stages, the only thing I connect to the Bushido for is changing the resistance through ANT+FE/C.

I appreciate not all apps play nicely in this way of course.

gzinga
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Re: Bushido power vs Powertap P1

Post by gzinga » Thu Sep 24, 2015 3:33 pm

well it does matter for 2 reasons:

1) we all paid for that feature, thus i want to use it
2) i have more than one bike and not all have P1s on it nor i want to move the pedals

according to Tacx tech support power is loss due to the drive train and roller. I guess i buy that to a point, i wish the app would let you amplify or offset the power

thank you

Gabe

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ms6073
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Re: Bushido power vs Powertap P1

Post by ms6073 » Thu Sep 24, 2015 4:31 pm

gzinga wrote:bushido shows a 20% less power than the P1 pedals.
Agree that there will be a difference in power output based on the point at which the measurement occurs but that would account for maybe 1%-3%, not 20%!
TTS 4.19.1 | T2800 NEO Smart [formerly Bushido & Fortius]
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gzinga
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Re: Bushido power vs Powertap P1

Post by gzinga » Thu Sep 24, 2015 8:25 pm

so i did an experiment today and tighten the friction between the roller and the tire. calibrated bushido and the difference in power went down but also the thing become un-ridable because of the tire compression. I then loosened the screw but did not recalibrate, the power output was very high.

1) calibrating the thing does something
2) tightening or loosening the knob changes your power output

Ultimately, the bushido power meter is off and while P1 has a tolerance of +-2.5%, even if both they were at the opposite side of the spectrum I would expect to see 10 watts or so at 200 watts average not 30 watts

I will keep messing with it but ultimately it is a disappointment

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ms6073
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Re: Bushido power vs Powertap P1

Post by ms6073 » Thu Sep 24, 2015 8:43 pm

gzinga wrote:1) calibrating the thing does something
Calibration should be done on a warm tire as a calibration on a cold tire will cause the power discrepancy to increase since the rolling resistance changes as the tire heats up.
gzinga wrote:2) tightening or loosening the knob changes your power output
More accurately, tightening/loosening the tension knob varies the amount of pressure the roller exerts on the tire. Given the same air pressure of the (we run 120 psi +/- 5 psi), increasing roller pressure will result in increased resistance, thus requiring more either higher cadence or more torque to spin the wheel at a given speed.
TTS 4.19.1 | T2800 NEO Smart [formerly Bushido & Fortius]
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Milkfloat
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Re: Bushido power vs Powertap P1

Post by Milkfloat » Thu Sep 24, 2015 8:44 pm

I have exactly the same with a vortex smart. I see about 25-30% less power than I should. It kills me on the RLVs and makes Zwift and other apps unusable. I have not worked out how to compensate for this. I will try the calibrate then loosen method you describe. I was also wondering if changing the roller into a position for a different size wheel would work?

Milkfloat
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Re: Bushido power vs Powertap P1

Post by Milkfloat » Thu Sep 24, 2015 8:46 pm

ms6073 wrote:
gzinga wrote:2) tightening or loosening the knob changes your power output
More accurately, tightening/loosening the tension knob varies the amount of pressure the roller exerts on the tire. Given the same air pressure of the (we run 120 psi +/- 5 psi), increasing roller pressure will result in increased resistance, thus requiring more either higher cadence or more torque to spin the wheel at a given speed.
But the big question is - will that higher resistance result in less watts being reported?

gzinga
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Re: Bushido power vs Powertap P1

Post by gzinga » Thu Sep 24, 2015 9:16 pm

it probably will but it will also make for an uneven ride. my suggestion is for the Tacx to provide a way to add an offset to the power in software, it will be so much easier than all the b...hit we are doing

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ms6073
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Re: Bushido power vs Powertap P1

Post by ms6073 » Thu Sep 24, 2015 11:55 pm

Milkfloat wrote:But the big question is - will that higher resistance result in less watts being reported?
No, a higher electrobrake resistance will require more torque from the rider which will in turn increase the powerout put. One thing to check is the electrobrake mounting in the position block.

Image

While some have had good results using mounting positions other than the slot recommended for 700c road wheels, my experience with both Bushido legacy and Smart trainers is when I try to use other slots, braking resistance is artificially inflated such that the trainer will not allow riding below ~125-130 watts no matter the setting in the TTS.
TTS 4.19.1 | T2800 NEO Smart [formerly Bushido & Fortius]
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ttelmah
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Re: Bushido power vs Powertap P1

Post by ttelmah » Fri Sep 25, 2015 8:18 pm

The 'silly' thing is that TTS used to have a power factor you could input after calibration, offering up to +/-20%. They got rid of it when they added the ability to display the figure from ANT+ pedals, but like you though I have such pedals I want to use these on one bike that is not the one used with the Tacx. It was nice to be able to have a reasonably close display so that training on the Tacx agreed roughly with the real bike. I actually have two brakes, and these differ by around 20%, so it shows the necessity for such an adjustment....

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ms6073
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Re: Bushido power vs Powertap P1

Post by ms6073 » Fri Sep 25, 2015 9:30 pm

Yeah, I miss the ability to set 'scale factor' as well. While fine tuning the calibration/roller tension will help, I don't think this is going to totally address the issues those with the power pedals are experiencing. Typically improper calibration results in the trainer resistance being artificially inflated so power output of the trainer reads higher than an external powermeter. In this case, since the external powermeter is recording higher higher power values than the trainer, sounds to me like the slope of the power pedals is not correct. For an SRM, I check the offset and use my Garmin Edge 520 to adjust the slope of the SRM but I do not think this can be done for the Garmin or PowerTap pedals.
TTS 4.19.1 | T2800 NEO Smart [formerly Bushido & Fortius]
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gabriele_ti
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Re: Bushido power vs Powertap P1

Post by gabriele_ti » Sun Oct 04, 2015 2:45 pm

it could be nice to have the possibility to calibrate the bushido's resistance with the powermeter's data.
now it's impossible to follow a workout made with garmin.

waxwobbler
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Re: Bushido power vs Powertap P1

Post by waxwobbler » Mon Oct 12, 2015 1:27 pm

I have the same issue with Vortex and Powertap hub. Around 20% higher at 260 Watts on the Powertap. Shame there is no way to offset the slope. I guess you need to spend more on a Kickr to get meaningful data.

Must be a lot of people going round thinking they have over inflated numbers for FTP tests. That's ok until you try to recreate that on the road with another meter.

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ms6073
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Re: Bushido power vs Powertap P1

Post by ms6073 » Mon Oct 12, 2015 4:01 pm

waxwobbler wrote:Must be a lot of people going round thinking they have over inflated numbers for FTP tests. That's ok until you try to recreate that on the road with another meter.
Ironically, TrainerRoad and Zwift offer the option to control SMART trainers (ANT+ FE-C enabled) based on an external powermeter instead of the trainers calculated power output. The long term solution would seem to be for Tacx to implement similar functionality in TTS.

As a side note, past experience testing legacy Bushido firmware that integrated powermeter control of the trainer, was somewhat problematic. While never actually expressed, I think this was primarily due to limitations of the ANT communication protocol used by the Bushido T1980 handlebar controller.
TTS 4.19.1 | T2800 NEO Smart [formerly Bushido & Fortius]
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doggled
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Re: Bushido power vs Powertap P1

Post by doggled » Sat Feb 20, 2016 5:27 pm

Ironically, TrainerRoad and Zwift offer the option to control SMART trainers (ANT+ FE-C enabled) based on an external powermeter instead of the trainers calculated power output.
Do you have any info on how we go about doing this?

My problem is I'm using TrainerRoad to control the Smart trainer but the reported watts coming from the trainer and reported on T/Road differ wildly from what my Garmin Vortex power meter is saying. If T/Road could pick up my Vortex watts and control the trainer accordingly, I'd be a happy Tacx user again.

Any advice gratefully received.

doggled
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Re: Bushido power vs Powertap P1

Post by doggled » Sat Feb 20, 2016 5:50 pm

Actually, just found it on TrainerRoad site. Here it is for anyone else. Apparently there are issues but TR are trying to fix these...

http://support.trainerroad.com/hc/en-us ... c-Trainers

pauldmorgan
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Re: Bushido power vs Powertap P1

Post by pauldmorgan » Wed Mar 09, 2016 10:04 pm

I really hope Tacx work out how to get their Smart trainers putting out a ball-park correct value for power as at the moment it's a long way off the readings on my Stages (-50W at 300W effort as measured on the PM). The inaccuracy appears to be non-linear so a straight offset figure of x Watts won't work, I guess it's also possible that the discrepancy not only changes with speed but also with the amount of resistance/slope set by the electronic brake. Not beyond their ability to do some measurements and model the power curve you would've thought.

For me it's not a deal breaker or a reason to send my Bushido back but in the end it will hurt them if the competition get this right and they don't. It's good that Zwift and Trainer Road allow for external PM input but I'd like to be able to use a different bike on my trainer and not to have to keep swapping my PM from bike to bike and taking tyres on and off and I suspect others feel the same.

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