https://silca.cc/...stance-and-impedance

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http://bikeblather.blogspot.com/

Hey Tom- quick question: which of these surface types does your "smooth to rough factor" correspond to? Is it something like "brand new asphalt"?

Look at the link in Tom's post. There are even pictures of the asphalt there.

I'm talking about the "rough to smooth factor" in Tom's CRR tests, so not the same as the article.

More like "New asphalt -aged"...brand new asphalt is apparently somewhat soft. It hardens a bit over time.

That said, remember that the blue "roller" and "on road" lines from my testing were from different tires (Vittoria Corsa KS) and a different rider/bike setup than the other lines...so things might not be directly comparable.

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http://bikeblather.blogspot.com/

Thank you so much Tom. Fascinating stuff

and new asphalt is "sticky" to a bike tire as well.

I think 'new' asphalt become mature, quite quickly, say in 1-2 months, then continues to age well (with lower rolling resistance for bikes), then after a few years, cracks can appear and the rolling resistance increases again.

I'm not sure about the medium asphalt but here in New Zealand, a high proportion of our road are "chip seal" (tar and gravel). In some areas they use stone about 4-6mm in size. It's not too bad to ride on once it's been flattened for a while by car use. There are some areas where they use large stones, about 10-15mm but the stones have rounded edges. They too get better with car use, but aren't as friendly to riders as the smaller stones. Worst of all, in our area, they use large 10-20mm rock, often basalt, that has sharp edges for a very rough ride. Worse yet, basalt is so hard, that it retains it's horrible riding qualities for many years.

There is one section of extremely course chip seal, that I (somewhat) joking say I can identify individual rocks, from year to year! They are so large and wear so slowly they are permanent. And not to mention the noise of passing cars at 100kph. It's insane. I have fond memories of riding on quality Canadian roads. I've never been fortunate enough to ride on German roads, but when I win lotto, I will head straight there!

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TriDork

"Happiness is a myth. All you can hope for is to get laid once in a while, drunk once in a while and to eat chocolate every day"

This is great information.

Does the breakpoint pressure increase with a heavier rider?

One of the reasons Roth is so fast. Best roads I've ever cycled.

How is the road surface in Hawaii?

Yeah - I set my PB there
Everyone is obsessed with the elevation gain on a course as its measurable. But its hard to account for wind conditions, and even harder on road surface
You can do a good ride on a windy day on terrible roads and average 20 mph
You can do lower NP on great roads and do 23 mph....
Courses should have a weighed average road surface index !

That's a great article that somehow I hadn't seen before, so thanks for posting!

I'll second Anachronism's question, how does rider weight affect the break-point pressure?

I don't know for certain (i.e. haven't tested it), but an inspection of various models relating to the effect imply that it could increase with increased mass. No idea on the size of the effect though.

With increased rider mass, you'd probably be more concerned about the pressure on the other end though (i.e. going too low), where you'd start bottoming the tire and suffering pinch flats.

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http://bikeblather.blogspot.com/

So the range of pressure that seems to yield the lowest rolling resistance for a typical road surface (yellow line) is approx. 90-100 psi using rather large 4000s 25mm tires? It seems kind of high to me, but I have no data, so who am I to argue!

I've been running my 4000s 23mm tires at approx. 78psi, and my roads are likely similar to the yellow line surface. It looks like I may actually be running them too low!

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Just don't forget, "Tis far better to err on the side of too low of pressure, than too high"...plus, if 78psi is more comfortable for you, you aren't giving up much speed to gain that comfort. Make sure you look at the range of the y-axis ;-)

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http://bikeblather.blogspot.com/

Yeah, there certainly isn't much crr to give up being a bit low - I find the comfort factor to be quite noticeable from 80psi to 90psi. I can't imagine being at 100 or more! Thanks for the response.

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I've never ridden the Kona course, but I've been to Maui many times, and the roads are very, very good for the most part.

I should add... when they are bad.... they are very, very bad. Like Paris-Roubaix bad....

Do you mean in Kona for racing?

Or in various places in Hawaii for training/riding?

The Ironman bike course.

I'm about 175 at my racing weight and I run around 100 PSI in 23 mm tires without any trouble even though most of the charts I see recommend higher pressure. It looks like I should be below the breakpoint on most roads.

Most likely :-)

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http://bikeblather.blogspot.com/