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Sram Quarq under reading


Jbr

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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)

post-139805-0-17702300-1598382477_thumb.png

 

And this is what Zwift recorded from the Quarq

post-139805-0-85386000-1598382510_thumb.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...

Edited by Jbr
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This article explains power meter accuracy well.

 

https://roadcyclinguk.com/how-to/fitness-nutrition/power-meter-really-telling-think.html

 

Its not about being relatable to other power meters but accurate to within 2% of itself over and over again.

 

Hope this helps.

 

Train low race high :)

 

What you are asking about is precision not accuracy, they do not disclose this in the marketing blurb.

Edited by Pure Savage
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Not saying it's not possible but I would not trust the flow as accurate power.

 

One reasonability check is to weigh yourself accurately with your bike and cycle up a longer hill with a relatively constant grade with no wind at a steady power a few times. Compare your times with a few of the online calculators available. You wont pick up if its say 1 or 2% out but probably will pick up 10% out

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Not saying it's not possible but I would not trust the flow as accurate power.

 

One reasonability check is to weigh yourself accurately with your bike and cycle up a longer hill with a relatively constant grade with no wind at a steady power a few times. Compare your times with a few of the online calculators available. You wont pick up if its say 1 or 2% out but probably will pick up 10% out

How would he take his flow up a hill outside a few times?

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How would he take his flow up a hill outside a few times?


I think he means to check the quarq this way.

I wouldn't trust the tacx flow power readings. Wheel on trainers give widely variable numbers. 
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I don't, but I do trust my good old rotor, and with that one I know what I could do for 5, 10 and 20 mins, and I'm not anywhere near those numbers on the new bike, yet I'm faster on lots of segments, so I really suspected that Quarq before I did my test today... I was expecting a few watts difference but not 30w difference on an hour !

 

Unfortunately that rotor stopped working a few weeks ago and I can't go out on my old bike to confirm by doing a 10mins effort on both bikes to compare ????

Edited by Jbr
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I think he means to check the quarq this way.

 

I wouldn't trust the tacx flow power readings. Wheel on trainers give widely variable numbers. 

Think the point is the quarq will always under read. His tacx will always be higher and constantly so. 

 

Just adjust zones depending on what bike going to use I guess. Obviously tell your mates the Tacx value though.

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I don't, but I do trust my good old rotor, and with that one I know what I could do for 5, 10 and 20 mins, and I'm not anywhere near those numbers on the new bike, yet I'm faster on lots of segments, so I really suspected that Quarq before I did my test today... I was expecting a few watts difference but not 30w difference on an hour !

Yeah in that study of the power meters they found pretty massive differences between brands and for some even within the same models. 

 

Hence why power data from pro's should be taken with a little pinch of salt. 

 

It could be a case of you have 2 power meters which are both off my 5% of whats correct but either side. 

 

If the results are constant then its not "really" a problem.

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Put your bike on a friends (or your lbs) proper direct drive trainer and compare the readings on two headunits. Most the new trainers are within 2% accuracy so you'll be able to tell where the problem is.

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first I'm gonna take it appart and put it back in at torque, then yes I'm going to try this. I didn't work this hard to get my FTP above 300 to now be on 290 avg for an hour ????

 

When you check the DC rainmaker's test the readings are always withing 2/3 watts from the garmin vector, his tacx and the unit he's testing... I'll read that study this morning nonetheless

Edited by Jbr
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I was in the same boat not too long ago.

 

Went from Cycleops Powerbeam "smart" wheel on trainer to Elite Direto X.

The cycleops was over reading quite a bit, some cases by 30-40w average over an hour. Its also much easier to hold power on the wheel on trainers vs direct drive, well thats from my experience.

Tested different bikes with different power meters and outcome was the same.

 

Direto X was within a few watts when tested with Specialized and 4iii powermeters.

 

Rather just use the numbers to track progress on the Flow.

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The flow drops all the time on zwift so I can't race with it, I've been racing using my power meter for as long as I had one, also makes more sense as when I'm outside I use my power meter's data so there's more consistency.

 

When I was using the rotor on the old road bike I also had a stages on my MTB and my 1min and 5 mins power were consistent on both bikes, and the flow would also read more or less the same. I never ever worried too much about power consistency as I do now with the Quarq. Now I'm actually thinking it would be stupid to invest on a stages for my new MTB if the numbers end up meaning nothing. It's only 10% but in W/kg it's massive (4,16 vs 4,61)... Let's see after I've reassembled everything to torque. If it's still reading low then so be it, I'll make peace with the fact that my FTP is now barely in the 300 but at least I'll have new figures to pace myself in races or as a reference for training/intervals.

 

Unfortunately I'll always be penalised on Zwift but who cares, the real racing is about to resume  :drool:  :drool:  :drool:

Edited by Jbr
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The flow drops all the time on zwift so I can't race with it, I've been racing using my power meter for as long as I had one, also makes more sense as when I'm outside I use my power meter's data so there's more consistency.

 

When I was using the rotor on the old road bike I also had a stages on my MTB and my 1min and 5 mins power were consistent on both bikes, and the flow would also read more or less the same. I never ever worried too much about power consistency as I do now with the Quarq. Now I'm actually thinking it would be stupid to invest on a stages for my new MTB if the numbers end up meaning nothing. It's only 10% but in W/kg it's massive (4,16 vs 4,61)... Let's see after I've reassembled everything to torque. If it's still reading low then so be it, I'll make peace with the fact that my FTP is now barely in the 300 but at least I'll have new figures to pace myself in races or as a reference for training/intervals.

 

Unfortunately I'll always be penalised on Zwift but who cares, the real racing is about to resume  :drool:  :drool:  :drool:

It also allows you to be that dark horse. "How is that oke still here only smashing 240w???"

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Unfortunately I would suggest that the Quarq is probably the most correct.

 

Left only powermeters (like the Rotor In-Power and stages) is seen as the less accurate type of powermeters and a wheel on trainer is very difficult to get absolutely correct.

 

I would suggest one of the following to try and gauge your current powermeter values.

 

1. Borrow a set of powermeter pedals (dual not just left), a powertap hub or a direct drive smart trainer like a tacx neo. (some LBS will have a trainer as demo on the floor, ask them if you can come around with your bike to check)

2. Go ride with a similar build friend that weighs close to your weight (+-1kg), riding next to each other your values should be the same.

 

You can contact the guys that import Quarq and ask them if the can do a "factory" calibration for you as well, just to make 100% sure that the unit is set up correctly.

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Unfortunately I would suggest that the Quarq is probably the most correct.

 

Left only powermeters (like the Rotor In-Power and stages) is seen as the less accurate type of powermeters and a wheel on trainer is very difficult to get absolutely correct.

 

I would suggest one of the following to try and gauge your current powermeter values.

 

1. Borrow a set of powermeter pedals (dual not just left), a powertap hub or a direct drive smart trainer like a tacx neo. (some LBS will have a trainer as demo on the floor, ask them if you can come around with your bike to check)

2. Go ride with a similar build friend that weighs close to your weight (+-1kg), riding next to each other your values should be the same.

 

You can contact the guys that import Quarq and ask them if the can do a "factory" calibration for you as well, just to make 100% sure that the unit is set up correctly.

as far as I know the quarq is also a left only that only estimates the right side power, it's not a real dual sided (I think)

 

Best thing would be yes to compare with pedals and/or direct drive trainer, easier said than done though :D

Edited by Jbr
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as far as I know the quarq is also a left only that only estimates the right side power, it's not a real dual sided (I think)

 

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.

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