On Tuesday, July 21, 2020 at 1:10:44 AM UTC+1, 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.

--
Andrew Muzi
www.yellowjersey.org/
Open every day since 1 April, 1971

Not just a lot of factors, some of them of lesser importance than generally thought in cycling, some important only when weighed against the circumscribed power the rider can deliver through the pedals, but some counterintuitive to common sense (particularly in rolling resistance), and the huge amount of simply wrong street corner information purveys as gospel in cycling. (When I arrived on RBT I was amazed at the crap people who claimed to be engineers spouted on a TECH group. Some of the dealers then here also seemed to believe they had a god-given right to ask money for being stupid.)

Of course, I think of 25mm tyres as arse-splitters. A comfortable tyre starts at 50mm and is definitely adequate at 60mm, if designed for low pressure operation, which basically means it must have extremely flexible sidewalls and a stiff rolling surface until well over the shoulder to allow for all likely angles in cornering. On a bicycle tyre, where rolling resistance is thought to be important (I've never seen a truly convincing demonstration of rolling resistance being important outside the very top echelons of racing), it is fortunate that the general stiffening of anti-puncture bands are already "priced-in" not only to the money but the weight budget of the bike, because that Kevlar weighs plenty, yet without it the tyre will generally not work as a comfort generator because it also enables the low-pressure operation.

But regardless of what you define as a narrow or a wide tyre, for a roadie there's little sense in going wider unless he is also able to lower inflation pressure, because without the comfort and possibly lower rolling resistance that additional width and lower pressure in a correctly designed tyre can bring, there is no point in the extra cost and weight of a wider tyre. This assumes of course that the tyre isn't stupidly narrow to start with, a rolling blade rather than a suspension medium.

Sounds to me like you're heading to a golden meeting of bum with bike, Tom. I had the opportunity a few years ago on a manufacturer's site to see a whole bunch of serious cyclists, who'd believed the nonsense about narrow tyres, being convinced that wider tyres were better tyres not just for touring but for everyday sports cycling. It was an education.

Andre Jute
Hedonist