That's a known problem with th cyclops fluid trainers:

http://forum.slowtwitch.com/...ring=fluid2;#3590711

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http://bikeblather.blogspot.com/

Tom, thanks for making me aware of this thread. I must admit, I struggled to follow a lot of the debate. It would be *huge* if you could help me better understand the top line take-away message that I am looking for...

Long story short, I do a lot of my very specific interval training (e.g., 5x5, 2x20, etc) indoors on the Cyclops paired with the Quarq Cinco. But, of course, we race outside. I guess what I would like to know is so long as I use the first 20 minutes on the Cyclops as a "warmup" (I guess both for me and for the trainer) then the power numbers I am getting for the main set thereafter should be pretty accurate in terms of not much variability from what I would get outdoors? I just don't want to be in a situation where I'm pacing threshold intervals on the the trainer at X watts and then trying to hold that same power outdoors when in fact there is a lot of variability. This all assumes a manual zero offset (e.g., pedal at 6 o'clock position with no torque) prior to every ride.

Many thanks in advance for the help.

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*********************************************
Brad Stulberg
Author, Peak Performance
http://www.BradStulberg.com

The power output will be correct, but your perceived exertion my still find that indoors is harder than outdoors. Mostly this is due to the poor cooling indoors. People that use a big industrial fan have typically found that perceived exertion in and out matches pretty closely.

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Styrrell

As long as the zero offset on your Quarq is stable (which yours is), the power reported is accurate from the get go no matter what gear you're in. As your fluid trainer warms up, you may need to shift gears to keep the same power.

Mieke
Quarq Technology

Hey Tom, can you confirm that I have the formula for "wattage drift correct"

• Delta "wattage" = Delta (Zero offset Units) x (1/32) N-m x 0.17m x RPM

(I put 0.17 m for my crank arm length, others would have to put in their crank arm length).

Is this correct?

On my ride today I experienced a temperature fluctuation of 14C, and had drift of 47 zero offset units from start to end of ride (I forgot to back pedal). According to this the drift would be 21W, which was in line with my perceived exertion. I'm really excited about the ability to just pedal backwards and re calibrate on the fly. I just totally forgot about this feature coming from "SRM land" and where I live mornings are much cooler than mid/late ride on weekend long rides.

Anyway, good maiden flight on the Elsa.

Dev

The variation in the load of the Fluid2 has nothing to do with the power reading on your CinQo. Just go by the CinQo. The varying load will just mean that you'll have to shift sometimes to get your preferred cadence for the interval at a given load. No biggie...wheelspeed on a trainer is meaningless anyway.

It would be a much different story if you didn't have a power meter and you were trying to judge your effort based on wheel speed with that trainer.

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http://bikeblather.blogspot.com/

Nope. First off, you need to input the rotational velocity of the crank in radians/sec, not rpm. Multiply the rpm value by (2*pi rad/rev) / (60s/min) and use that.

Also, since you're dealing with a torque already, you don't need the crankarm length.


What was your average cadence? If I assume it was 90 rpm, here's how you figure out the power difference:

Power = Torque x Angular Velocity = (47/32 N-m) x (90 rpm x (2 x pi /60)) = 14W

If your average cadence was lower, then the power difference was lower as well.

Make sure you do some "standing start" type efforts on your first few rides and you should see much lower offset changes going forward, even with large temp changes.

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http://bikeblather.blogspot.com/

man....I badly failed first year mechanics on that last post.....17 years working in marketing and my brain is hazy....

Thanks for the corrections. Looks like I failed on 3 counts....how the heck did I mix minutes and seconds, forget about radians since this is a rotating system, and also include the crank length, when the offset number was already in Newtons.....

By the way, I was riding around 85 RPM, so the delta is around another watt lower.

Already in Newton-meters ;-)

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http://bikeblather.blogspot.com/

Yeah, that's actually what I meant to SAY, but not what I typed. Failed on round 2.

So quick rule of thumb...every 10 points around 3W if riding 85-95 RPM.

Yup.

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http://bikeblather.blogspot.com/

Confused by this. If you "soft pedal" and you are still pedaling then Isn't the freehub going to re-engange, and if you are pedaling you are going to put out some amount of power (albeit low) so wouldn't you expect the the number to be a non-zero?

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Thanks for the reply, and sounds good. It still seems that my first 15 minutes (holding RPE constant) produced a power reading that is about 15-20 watts lower than the same RPE at minutes 20-35. That is what I am kind of befuddled by. Like I said, it's not that big of a deal at all because all my interval workouts begin with an easy warm-up anyways, but I'm just not sure what is going on that would cause the power to "jump up" at a certain point at the same RPE. I guess it could just be my body getting warmed, but I've paid close attention to this and I don't think that is the case.

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*********************************************
Brad Stulberg
Author, Peak Performance
http://www.BradStulberg.com

As I wrote a couple of months ago it's not a problem of fluid trainer.
1 watt is 1 watt, after trainer warm up you should see a lower power reading at the same cadence/gear...
What I have experienced is an offset difference of 20points in the first 20-30 minutes.
It's seems a Powermeter warm up! Not an indoor trainer warmup..

Is there anyone who experienced this? Could be an issue?

Sometimes I see this "quarq warm up" outdoor too, so in my rides I always autocalibrate (backpedaling) after 20 minutes in the ride....

Bringing this back from the dead. If there is a -32 point shift from -100 at the start and don't calibrate until the end of the ride and the offset then is -132, that means my power readings during some point in my ride were likely 9.42W too high since I waited till the end to calibrate and the curve shifted down during my ride(thinking mx+b here)? Or do I have that backward? Just trying to confirm that a more negative offset number, when compared to the start value, means my power readings are lower than at the beginning.

Thanks,
Andrew

The most recent firmware update (21), greatly reduces the zero offset changes in the new quarqs. My Elsa now changes by less than 5 counts over a ride, even with a large temperature change.

I'm still on an s975, so don't think I can take advantage of that update.

Nope, the opposite. When force is applied to the pedals the reading goes negative, so in the case you outline above the meter would have been reading high if the actual offset had drifted -32 points without being zeroed to the correct offset (i.e., the calculation was being done with an artificially large absolute delta).

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http://bikeblather.blogspot.com/

Sorry, I wasn't real clear in my post there. I think I was coming to the same conclusion in the first part of my post and then muddied it up (tried to clarify with the additions in bold). I was trying to compare the uncalibrated power reading that woudl be displayed (higher) to the true power value (lower) when not doing a recalibration. Without calibration I could be displaying 109W after a -32 shift, when my actual/true power would be 100W if I recalibrated at that point, right?

^^^ this

I would get a 30 unit drift after 20-30min of riding at a constant temperature. With update 20, it's very stable.
In the wattage group there was an explanation of why

"We discovered that the measurement electronics (not the strain gages or mechanical part) were contributing their own drift after they powered on, requiring a few minutes to settle out. I adapted an old analog electronics technique to continually measure this drift and subtract it out of the measurement.

It's a closed-loop correction. Nothing is being painted over or fudged. The remaining drift is from the strain gages and mechanical circuit.

Because the first few minutes after power-on coincide with taking your bike out of the climate-controlled garage, the initial drift was sometimes wrongly attributed to temperature changes."

Yes. :-)

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