How much lag in displayed power from Quarq CinQo?

[mlennox]

In comparing the displayed power on the Garmin 705 and iAero (both coming fromt the CinQo), I'm noticing (I think) that the iAero is showing either a number that is lagging behind or a number that is smoothed over a longer period of time. This is especially noticeable when you stop pedaling and the 705 shows zero almost immediately whereas you can watch the iAero displayed power slowly make its way to zero over about a 5 second period. Can anyone shed some light on this?

[coachboyd]

I noticed this the past couple days. I was having a small problem in very humid conditions (right after a rainstorm) in where the Quarq's numbers would go all over the place. After talking with Jim at Quarq, he told me how to take about the Cinqo crankset (fun!) and to put dielectric silicone on the connectors to ensure that no water hits the plugs behind the battery. I'm not sure if I put too much on there, but the past couple rides there has definitely been some lag and times where the watts will get "stuck" at a higher wattage and not respond as quickly as from the iAero.

[travispape]

In the current FW, there is a filter on the ANT+Sport power signal (either the CinQo or the SRM wireless) that will be removed in the next release. You should find that there is a couple seconds of delay on the CinQo data that will be removed when we get that FW out.

Now if the delay that you are seeing is after you stop pedaling, every once in a while I see the same phenomenon. It is a different issue. The CinQo seems to be "stuck" on the last power reading from when I was pedaling. I still have an older FW in my CinQo. I think I remember Jim Meyer saying that they changed something in the CinQo FW that might fix that--you might ask him.

Travis

[travispape]

Or maybe not. Boyd posted at the same time as me and he had already talked to Jim.

[coachboyd]

The Quarq I have has the same older firmware as your Travis. I will be interested in seeing how it looks with the filters removed.
I am also seeing that the Cinqo reads higher than the iBike up steep hills when I am really pushing it. For the most part, I am getting great results, but when I am trying to hold about 350 watts, I notice that the Cinqo reads about 30 watts higher than the iBike. I need to do this test with a Powertap on as well, because I am leaning towards the iBike has the better numbers (based on online calculators and previous times up the climb with other power meters). I don't know if it's just might be my Cinqo unit that is overreporting the watts when it gets above a certain point.

[Russ]

Coach,
Don't forget that the Quarq at the cranks is before transmittion loss and the iBike is
after all such losses (including tire friction, which the SRM is also ahead of).

Besides that, just incase, I'd do a quick check for chain stretch and the like just incase
both meters are telling the truth!

Russ

[coachboyd]

I actually just changed my chain last week. It was off the chart stretched. Changing it made the bike feel a lot better, I didn't feel like I was doing 3 revolutions before it would engage anymore. So, I know it's not the problem of my chain is too worn out.

Looking at the power meter comparison, you can see that the Quarq reads just a bit higher than the iBike during the whole climb. There is a small climb leading into the main part that I didn't push it. The numbers matched great right there. During the climb (which starts exactly at 2:52), there were two points where I stood out of the saddle (One in between 2:54 and 2:55, and the other at the end where it gets really steep). And you can see one point where the Quarq kind of got stuck and read the same wattage for 5 seconds or so, despite me not pushing it. I have marked those areas (which can lead to part of the higher average)

Average for the iBike was 353
Average for the Quarq was 376
-----------min--avg---max
Aero-------0---30.8---950 W
Rolling----24---29.8---39 W
Gravity---108--285.0--517 W
Speed----10.1--12.5---16.5 mi/h
Wind------4.4---11.8---16.9 mi/h
Elev------1215---1584--1993 ft
Slope------2.1----6.88---14.3 %
Caden------72----85.5---102 rpm
HR---------128---161.7---172 bpm
Aero: 0.306; Fric: 8.38
CdA: 0.333 m^2
Crr: 0.0072
167 lbs; 8/10/2008 4:18 PM

[coachboyd]

Also, a couple of other notes. This picture is shown with no filtering. And looking at other parts of this same ride with no filtering, it matches up very well until the watts go above 330. That is when the Quarq starts to read higher. In this ride, I started off motorpacing behind my scooter. The data looks really good here between the ibike and the Quarq, even though some major drafting was going on at high speeds. There is one section where it's quite different, and that's where I was hanging onto the scooter for a moment of rest.
The ride file is located on our team's uploads, which you can get to by clicking on the homepage listed under my name. It's the one from 8/10/2008

Also, I should really say that although I wish differently, I think that the 353 is the better number. I have done this climb so many times I have lost count. And I know from other power meters (plus online calculators) that 350 gets you right at 10:30. Like I said, I will have to try this with a friends Power Tap just to get another verification, but I am leaning towards thinking the iBike gives better numbers here.

[Russ]

Coach,
Glad you got the new chain. But the fact that your power meters match at lower power makes me more suspicious!

Here is a quote from Sheldon Brown's web page on the topic:

"The worn chain has "stretched" so that it no longer matches the original pitch of the sprocket. The sprocket has worn so as to effectively increase its pitch to match the worn chain."

From about 2/3 down page here (with pictures of worn sprocket):
http://sheldonbrown.com/chains.html

Just checkin, bit me

Russ

[coachboyd]

I will have to slap my girlfriends brand new shimano cassette on my friends power tap wheel to do the ultimate comparison ride. . .but it's probably going to have to wait a couple days. I just did that same climb 6 times today, with all results similar to the one above (except the first where the Quarq had lost calibration). I was actually having a problem keeping it calibrated today, which might explain the difference. I will have to try and get it swapped out to see if that could be it too. I am not doubting I may be losing a little bit with a chain and cassette that don't match perfectly, but the cassette is still in great condition. When I start off in the 39-11, pushing hard at very low cadence, I can't get it to skip at all. Normally when a chain and cassette don't match, you can get it to skip when there is the most slack on the chain. In any event, I find it hard to believe that chain wear could be responsible for 30 watts difference.

By the way, in terms of precision (repeatability), the iBike rules!
Climbs time - avg watts
10:42 - 349
10:42 - 348
10:45 - 350
10:40 - 355
10:53 - 345
The 6th time was just riding up and over, including stopping to get water.

[Site_Admin]

Remember, Boyd still has a Beta, and the 'sticking' points could be due to the bushings. I had the same crank Boyd is using now, and there were times when road grime and sugar from bottles gummed things up a bit. Call Quarq if you have any questions and send them the file(s).

[coachboyd]

Actually I talked with Jim and we figured out what the problem was, and it had definitely been solved with the new production units. I am sending the one I have back and will post the comparison file as soon as I get the new one, and I'll make sure to get that power tap data in there as well. Those three way comparisons are great!

[Russ]

Ah... just as I should have suspected - -

A strange quarq !