asgelle

You should never trust power data unless you are certain that the unit has been properly zeroed. Knowing it's been calibrated recently is also desirable. It goes without saying that one-legged data is useless for this application.

Doge

Do you have your overall air drag coefficient sitting around? I don't. I get I can pay money to get it. And it changes. From tucking your neck to elbow width or shaving your arms.

I just posted two teens solo speeds. One in a training ride, one in a TT. Both on TT bikes.
Both would give up about 2mph on a road bike.

I have not found an online calculator I can plug known parameters into that really works at high speeds. The competitive folks test a whole bunch. More popular now is using the Velodrome as they realize riding you learn things you don't in a tunnel (and it generally costs less).

Doge

I agree with you. I've been trying to say that.

asgelle

Yes, it takes some effort to get the parameters for the model. Again, that isn't the model's fault. If you aren't willing to put in the effort, don't blame the model for giving poor results.

And yes, I have plenty of drag areas sitting around (drag coefficient doesn't do you much good without frontal area). Robert Chung has described a protocol to do it yourself quite clearly, and you can do it just fine on the open road. A velodrome is not needed and may be counter productive since you won't get a realistic Crr. He and others have shown accuracy equivalent to a quality wind tunnel. All it takes is the desire and a little time.

So which is it? Do you have known parameters or don't you?

Seattle Forrest

I think it's the opposite: skinny tires can show less rolling resistance in an idealized, simplified lab setting ( spinning on a drum ) but have more rolling resistance outdoors, on the roads and trails.

But as with all things, it's a double edged sword. Skinny tires also weigh less and have slightly less frontal area ( think air resistance ).

Then you mate them to rims, air them up to taste, etc, and a small change in any one of those numbers might not be such a big deal anymore.

Doge

I have not seen the model. I think I posted that several times.
I doubt I have all the parameters it wants and I expect it does not have the parameters I want.
I have shoulder width, and rolled width and drop and neck tuck, but there are things you see like the head above the rider's back that are easy to fix, spot but I'm guessing may not be a parameter - neck / head gap. I can see it in a video riding behind. Also position changes a wee bit at speed, so seeing a rider at speed helps. So rolled solders at 20 may not be at 28. Is the rider nervous, are their tires too thin, pressure too high? I think you pick that up from the road, esp videoing from behind.

Really though, I'm not going to go through the work or take the time. We've been fine tuning for a while. On new equipment we test. Things like diet, sleep, mechanical mistakes, preparation have more bearing on outcomes, but the little stuff matters.

dmanthree

Well, this lab tests shows that fatter tires roll easier. But there's more to speed than a simple rolling resistance test, right?

https://www.bicyclerollingresistance...0s-ii-23-25-28

Anyway, I agree that less weight and less air resistance can be factors.

dmanthree

I didn't say the feel faster, I said I *was* faster. The numbers bear this out. And yes, I had some training time, but it's late in the season, so that's not a factor. I'm not going by feel, I'm going by average speeds over a two week period over the same courses under *very* similar conditions.

asgelle

Yet you repeatedly post how the model fails. Interesting.

Doge

Guess this was my point. You need to plug in Effective Frontal Area. Obviously they are trying to figure drag. But that number changes on how you tuck you neck, arm - shave your arms. I want to get that number from changing the angle of the foot, booties on or off and then compare to a Sub 6 shoe with sleeves.

That is the number I want calculated. I don't want to enter it.

So when I put in the lowest number in the range .4 it says about 50 more watts are needed to go the speed that was gone.
I expect slop etc is off or tires were too thin.

Capture.JPG

Doge

The work is getting the input parameter. It is barely a model.

Spoonrobot 

I just do a roll down test every now and again:

https://janheine.wordpress.com/2012/...ance-of-tires/

Doge

This one attempts to figure the effective frontal area out by position and ...tires?
Or maybe the tires are Crr. This calculator say Tubulars are better, drops are better.

Still off by 100 W or so.
Not a useful tool.

Capture.jpg

asgelle

You don't understand what the kinetic model is and does. If you want a model for CdA, that is something else entirely. There are some, but they don't provide the resolution you're asking for. Given how easy it is to measure CdA directly, there really isn't any reason not to measure it if you care enough. If you don't care to put in the effort, that's fine, but it isn't the fault of the model, that you choose not to get accurate inputs.

Doge

Very cool. Thank you.
You (I assume you) say:
"Very high tire pressures don’t roll much faster. Above an “adequate” tire pressure, the tire’s speed increases only very slightly with higher pressures. "

What is Very High? 120?

I thought they went faster too but was told a test said otherwise. https://www.bikeforums.net/19854496-post86.html

Doge

How do you measure (not calculate) CdA directly? That is the number I want.

The speed power falls where it does.

asgelle

Post #129

I'll even do the work to get you started. Start here https://anonymous.coward.free.fr/watt...direct-cda.pdf and follow the thread for later developments.

Doge

Well thanks for that.
It is estimating/calculating CdA . Points I likely have now.

I wanted measured CdA to calculate speed and power. If I need to estimate/calculate CdA I might as well just test and see what is faster - set course, set power, similar wind.

asgelle

Earlier in this thread I believe you wrote something to the effect that all things are never equal. That's true so what good is testing when conditions will be different on race day? The answer is that rather than testing and then have conditions change, we develop a model which allows us to input race day conditions and test to measure the unchanging parameters for the model.

(And virtual elevation "estimates" CdA the same way a scale "estimates" weight. This is clear from the Martin paper.)

Racing Dan

One thing I have often wondered regarding drumtesting is how well they represent reality. For one, as have been noted, their surface does not represent real roads well, second the drum pulls the wheel at a steady pace. > No real power transfer through the wheel/tyre outside of whatever power i required to spin the wheel, similar to coasting. > Would the results be any different if in stead the wheel pulled the drum at, say, an average of 200w and would it affect if the results if power was pulsed like a real pedalling motion. Im betting everybody on the forums have heard the "swish, swish, swish, ..." from a road bike tyre going at decent power. That is not accounted for.

Racing Dan

Off by 100w? Rally?

Abe_Froman

I dont THINK the power transfer thing matters. But I've wondered why nobody has taken a mold of an asphalt road, and made a roller out of it.

Doge

Good gob!

Doge

It is something that is noticeable, esp out of the saddle. Relative squishy-ness of the various rear tire setups can be felt. I wouldn't necessarily expect what is a low rolling resistant tire to also be the firmest when standing.

99Klein 

Until you get out of the saddle to climb