Sram Quarq under reading

[Jbr]

If it is a spider based powermeter, then it is a total power measurement as it measures between both crank arms and the chain. Quarq does not produce single sided PMs.

 

Powertap is now owned by Quarq (SRAM) but is still sold as powertap. Their Powertap P1 s pdals are the only left side only powermeters that they sell.

Right that's what I thought as I posted my message... as it's is a spider system it doesn't make sense that it's a left only... I'm pretty sure I saw in a video someone saying it wasn't a real dual sided but yeah, must have been an error!

[Jehosefat]

In my experience a left-only vs dual sided can make a huge difference. Personally my L-R power balance is pretty consistently between 52 and 53% left (although it's been anywhere between 49 and 55 for a particular ride) which means that on a left-only power meter setup it would pretty constantly measure around 104 - 106% of my actual power output (and up to almost 110% in the "worst" case). This is across 2 dual sided power meters, a Power2max and a Stages LR, and both compare reasonably accurately with both my Saris H2 and my girlfriend's H1 (the two direct drive trainers read a few watts lower than the crank/spider PMs which is expected due to mechanical losses in the drivetrain).

Edited August 26, 2020 by Jehosefat

[Sprocket and Chain]

dont you wna share some watts with me? 320 ave....yassis!!!

[TNT1]

Hi,

 

I recently purchased a Giant TCR with a SRAM Force eTap groupset/Quarq power meter. Since I bought it I'm thinking I'm becoming very weak as my power data is super low compared to the one on my old bike with a Rotor InPower3D+ and Qrings, but on the other hand I'm smashing PRs everywhere... I started to believe it was just the new bike's stiffness and efficiency...

 

I also though maybe it was the switch from Qrings to round rings, didn't look into it too much.

 

Tonight I did that ZHR Masters race on Zwift and thought it'd be interesting to do it on my TCR instead of my old bike to compare readings between the Quarq and the Tacx Flow. Usually the Tacx reads a little bit less than what my old Rotor does.

 

Now today at the end of the race, this is the data I have from the Tacx Flow on the Garmin (I cropped both from the begining to the finish line)

Capture d’écran 2020-08-25 à 20.55.37.png

 

And this is what Zwift recorded from the Quarq

Capture d’écran 2020-08-25 à 20.55.53.png

 

Basically the quarq gives me 291w average and the Tacx 320, that's quite a discrepency... I calibrated both 1 hour before starting the race to be sure everything was in order.

 

Not sure what to think now... or to do ? Anyone noticed similar things ? They all say they are 1 or 2% accurate, now the two are 10% out...

There's something funny with the max power as well as the speed. The max and average speeds on the Quarq are very different to the Garmin, as is the max power. 

[Veebee]

There's something funny with the max power as well as the speed. The max and average speeds on the Quarq are very different to the Garmin, as is the max power. 

#Zwiftspeed

[Quagga]

Hi,

 

I recently purchased a Giant TCR with a SRAM Force eTap groupset/Quarq power meter. Since I bought it I'm thinking I'm becoming very weak as my power data is super low compared to the one on my old bike with a Rotor InPower3D+ and Qrings, but on the other hand I'm smashing PRs everywhere... I started to believe it was just the new bike's stiffness and efficiency...

SNIP

The best way to see if your Quark is accurate is to perform the proper home calibration.

 

You need a calibrated weight, or get something that is really close. 25kg

 

Hang that of the crank with rear wheel locked and look at the torque you get and compare that to the recommended from Quark. 

 

Then you can see if it is in limits. 

 

There are a few videos online, and it is also called calibrating the SLOPE

[Quagga]

Hi,

SNIP again

Rather than comparing it like this.

 

Connect your Garmin the the quark and lets say phone to the Tacx, then ride and watch them side by side.

 

This is what I did with my Tacx and the readings were very close.

 

Remember the Tacx show data every 1 sec. and my Garmin was set to avg of 3 sec. So remember to change your Garmin to 1sec.

[Quagga]

There's something funny with the max power as well as the speed. The max and average speeds on the Quarq are very different to the Garmin, as is the max power. 

It depends where he is getting speed data from, swift will record the "speed on decent" for excample

 

And I assume that the other graph is from a wheel mounted speed sensor sending the data to Garmin head unit

 

The best way to check data like this is with two Garmin devices, on recording the Tacx and one the Quarck

[Jbr]

#Zwiftspeed

Yeah I didn't really bother setting up the trainer in the garmin : wheel size, etc... so I assume that's why it always gives lower speeds and distance than zwift. But also Zwift is speed always is crazy high... And I'm not cheating on my weight (yesterday I was 69kg for 70kg in my profile )

 

When I'm zwifting I only use my garmin for the laps feature to track my avg power on the race duration, or 5 mins or 20 mins power

Edited August 26, 2020 by Jbr

[Spinnekop]

If it is a spider based powermeter, then it is a total power measurement as it measures between both crank arms and the chain. Quarq does not produce single sided PMs.

But....................

 

The spider measures power from both sides. The part that is estimated is left/right split, as the spider can’t completely isolate which side the power is coming from, but it’s definitely directly measuring total power.

 

Thus the stats on Left / right on the quarq is not 200% correct.............

[Quagga]

But....................

 

The spider measures power from both sides. The part that is estimated is left/right split, as the spider can’t completely isolate which side the power is coming from, but it’s definitely directly measuring total power.

 

Thus the stats on Left / right on the quarq is not 200% correct.............

It is not actually a estimated split.

 

The PM has an accelerometer in it so it "knows" when the right crank arm is producing power and the when the left is. 

 

The only "estimation" is when you are on the crank upstroke. 

[thisismyotherbike]

But....................

 

The spider measures power from both sides. The part that is estimated is left/right split, as the spider can’t completely isolate which side the power is coming from, but it’s definitely directly measuring total power.

 

Thus the stats on Left / right on the quarq is not 200% correct.............

 

Yes, Quarq is effectively a dual-sided power meter, in that it measures the total power from both legs accurately.  The L-R balance is basically unusable.

 

Only pedals report L-R balance accurately.  I ride a five bolt S-Works Dual powercrank. It is meant to be very accurate on L-R as five bolt is not plagued by the coupling issues that crank dual power meters suffer on Shimano four bolt cranksets.  However, the reading is clearly stupid.  It reads a 40-60 L-R vs the 51-49 L-R I usually get on my Favero Assioma Duo pedals.  On total power they are near identical.

 

Back to the OP's question, among his three power sources the Quarq is by far the most credible.  I'd get the bike on a Tacx Neo and check those two power sources against each other.  If the Quarq reads lower than a Neo I'd send it to Quarq for verification.

[Jbr]

A friend of mine has a kick4, I'll see if I can put my bike on there to try

[Schnavel]

Yes, Quarq is effectively a dual-sided power meter, in that it measures the total power from both legs accurately.  The L-R balance is basically unusable.

 

 

I don't agree with that statement - my quarq is very accurate with the L-R balance. As already mentioned, it uses the onboard accelerometer to determine whether the right or the left arm is measuring power.

 

I have compared it with pedals and it is very similar.

[Spinnekop]

I don't agree with that statement - my quarq is very accurate with the L-R balance. As already mentioned, it uses the onboard accelerometer to determine whether the right or the left arm is measuring power.

 

I have compared it with pedals and it is very similar.

But even when you pedal hard down with your right leg, you can ALSO pull with your left leg.  

In fact, there are coaches that actively does training sessions with their riders focusing on just that.

#justsaying

 

Most people (99.9%) including myself, the L-R split is pretty 50/50 or 51/49 and sort off useless measurement in general.

 

With regards to the OP question.  I will go with the Quarq readings and will only do FTP testing outside in the real world.  

I have seen too many riders use indoor power readings, base their training zones on that and then ride themselves into a coma or train like miss daisy.

Edited August 26, 2020 by Spinnekop

[Jbr]

Just in case someone experiences the same as me in the future, I would advise taking the crank out and losening all the bolts on the spider then applying the correct torque (4Nm and 12Nm on the chainrings).

 

It worked for me !

Edited September 2, 2020 by Jbr