On Tuesday, July 21, 2020 at 8:07:06 PM UTC+2, wrote:
On Tuesday, July 21, 2020 at 10:35:04 AM UTC-7, Lou Holtman wrote:
On Tuesday, July 21, 2020 at 5:10:32 PM UTC+2, Frank Krygowski wrote:
On 7/20/2020 8:10 PM, AMuzi wrote:
On 7/20/2020 6:34 PM, wrote:
I think we had this discussion before but it is time to revisit it.. I
have been riding Vittoria Corse G+ 25 mm tires. Somehow I had gotten
the idea that these were faster than the 28 mm tires I had been using
5 or so years ago. Well, Since I have been switching over to clinchers
again I got a set of Michelin Power 28 mm clinchers.

There is a sharp descent and a long slightly downhill section I travel
on regularly. There is a radar speed limit sign on this route so that
I can double check my speedo. My speed through this rough area is
normally 24 mph on the sign and about that on my speedo. I just
changed over to the 28 mm tires and did that section and the radar
reported 26 mph through this section. And the fatter tires at a 10 psi
less inflation pressure rode so much smoother that I cannot for the
life of me remember why I changed to the 25's.

Before I had 23's on my Time and you simply could not ride that Time
with 23's on it unless you had a butt of cast iron. When I changed to
the 28's on the Time it was and entirely different bike.

As you probably know, I am 6'4" and 190 lbs so I'm sure there is some
dividing point though I don't know where that might be since the Tour
riders are using 26 mm sew-up tires on their bikes. But I can tell you
I won't make that mistake again and I will be riding 28's from now on.



I don't know but there are more factors such as ambient air pressure and
humidity, wind etc. Also new tires are definitely faster than worn (flat
center) tires.

I wonder if there's data proving that. It's the kind of thing that's
really ripe for the placebo effect: "I put on new tires and they're SO
much better!"

Sort of related: I remember way back when some tires were sold with a
narrower center belt of rubber that protruded farther than the rest of
the tread surface. That center stripe might have been about 10mm wide on
a 32mm tire. As I recall, they were claimed to reduce rolling
resistance. It may have been Jobst who showed they increased it instead.

--
- Frank Krygowski

I ignore all claims comparing different tire widths if the tires are not the same make and type. Let alone the riding conditions and fitness. That is ridiculous.

Lou

Up to a point I agree with you. But the place where the radar speed sign is I have often gone by it and I am quite familiar with the speed I normally get there on several different bikes. And they are all comparable. In is in a canyon that blocks a great deal of the wind except at the very top of the climb.

Talking about same brand and model of tires is ridiculous when we have tire rolling resistance tests that show that my slower speeds were on faster tires. And high speeds on a slower tire. We know that the pro racers who are much smaller and lighter than I am are using tires much wider for their weight than I was doing.

I noticed this same rather surprising increase in speeds several years ago and wrote about it then. Again, I'm pretty convinced that it has to do with the vertical compliance instead of the rolling resistance. I will keep an eye on it and see. Do you think it could be that clinchers somehow roll faster than tubeless? Regardless of the various tests I didn't see any real decrease in rolling resistance with Tubeless so it must be pretty small.

At the moment I'm trying to compare Continental GP 5000 25 mm tires (7 bar pressure) on my Canyon Aeroad (7.2 kg) with Continental GP 5000 32 mm tires (5 bar pressure) on my Moots gravel bike (9.2 kg) both on the same Zipp rims. After several rides I still can't draw any conclusions. I only noticed and surprised that I am pretty fast on that tank of a gravel bike with aerodynamics of a hippo. I'm very pleased with that.

Lou