Drag, rolling resistance, etc

So from the IM Virtual thread @stenard raised the question of whether my results reflected reality which they don’t but it got me wondering if they do reflect the perfect virtual world - eg perfect roads/tyres, zero elevation change, zero wind etc.

So I took a 20km section from IMCH2019 (19.65km +38m) to be exact which I did in torrential rain.

Then I went to the aeroweenie calculator and on the left put in my weight, zero gradient, the speed and power from the above section, then reduced the drag until my time reflected real world result, 0.221.
Next, on the righthand side I put ideal rolling resistance for my tyres, 0.00321 for GP5000 at 100psi, and my higher power from the virtual ride, showing in the ideal world I’d ride about 3.1kph faster.

Lastly I upped the distance to 90km, to give what I think on the left is my projected real world best, and on the right my virtual world best…

Does that make sense?

I understand that heavy rain increases rolling resistance as in my IMCH ride but can’t find a site that says by how much.

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Interesting. Does any of that account for road surface? I’ve read quite a bit about rolling resistance and just bought a pair of Vitoria corsa speed isotech G+ tyres. Which I probably won’t get to race this year… Apparently they have the lowest rolling resistance. But I wonder about the tests - roads aren’t always ideal, and maybe different tyres would go better on different surfaces. And possibly in different temperatures too. And possibly the age of the tyres (will my tyres deteriorate by the time I get to use them in 15 months?) And psi is a dark art. I’ve heard it said I should run 65psi. And also 110… and then inner tubes will make a difference too. Trying to work up the bravery to try latex but have read quite a lot of negative points…
I’ve asked questions before about my speed versus my wattage. I got a 3:58 100 mile TT a few years ago - 265 watts and 165bpm. I had a decent bike, decent aero wheels, continue GP4000 tyres, aero helmet, and what I think is a decent aero position. The opinion was I should get more speed for the watts. But how…?!
I guess there’s always going to be a difference between the ideal theory and the real world and the question is how much can you minimise it?

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Crr is the value that handles the element of road surface and tyres - as I understand it 0.004 is a quality tarmac road, 0.00321 is a value I took from bicyclerollingresistance.com for GP5000 tyres at 100psi.

The great thing about cycling with power is training, imo.

Not so much using it to compare riders or predict real world times. 265W on your set up might be fine but you could get on my bike and have it read 250W or 280W who knows which is right?

I did FTP tests on my home set up and on a gym watt bike and as the results were only a few watts different, I took that as validation my FTP and power meter was reasonably accurate. Then I bought an Elite Zumo and it read 30-40W lower than my power meter…so I just don’t know.

I use those tyres and latex tubes on my race day wheels. Apart from the cost and having to pump the tubes up daily what other negatives are there for tubes?

Yep, sorry. I suppose the CRR will also depend on the type of wheel - some wheels may make the tyre sit a little flatter and wider, some will allow more deformity etc. Also I read a bit about the fastest tyre not necessarily being the one with the lowest CRR, but the one with the combined best aerodynamics and CRR together. I think the tyre/rim interface is pretty important and I think the GP5000s do well at this. Also yep you’re right, where on the bike the power meter is will make a difference. I guess pedal based meters will give the highest reading while rear wheel based ones the lowest due to losses through the drivetrain. I’ve a left crank stages on my road bike and tt bike so hopefully the numbers correspond and are repeatable. I suppose as long as it’s repeatable for you…!

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Have a look at podcasts by JP Ballard, CEO of Swiss Side, he is probably the best aerodynamisist in cycling at the moment. Apparently, above 30kph, aerodynamics play a much bigger impact than rolling resistance. If wheels are wider than rim, that can cost 10w per wheel. The drag on a GP4000 is actually less than a GP5000 as the tread pattern is more aerodynamic

Its a really fascinating area

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Agreed. Which is why enve et al either have to make a tire like Mavic do (with a 3rd party) or categorically say this is the tyre sku you need to run with our wheels for optimal performance

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