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#16
02-19-2019, 09:10 PM
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I recently switched from 23mm GP4000S2's to 25mm GP4000S2's.
I use 17c (internal) wheels exclusively (Zonda, Shamal and Bora) and tubes are always Michelin A1 Aircomp butyl. I always ran 85PSI on the 23mm tyres, and interestingly, after multiple rides on the 25mm trying both lower and higher pressures I ended up settling on the exact same pressure for the 25mm tyres. I felt this gave me the best combination of grip, speed and comfort. The marketing told me I should be able to drop pressure by 10PSI or more, but notably the tyre felt unstable and slow right up to that 85PSI mark. 
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#17
02-19-2019, 09:27 PM
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Zipp still recommends 23's as the fastest tire size, on the front wheel at least.
It's the combination of aero and rr. Anecodally, the fastest clinchers I've ridden are Sworks 24's. Waiting to try GP4000IIs (late to the party) when my Schwalbe 1's wear out.
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#18
02-19-2019, 10:23 PM
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Quote:
Josh
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#19
02-19-2019, 10:29 PM
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Quote:
Either way, look at Schwalbe's recommended pressure differences from 23mm to 25mm - it's 13 to 15psi reduction: https://www.cyclingweekly.com/news/p...ressure-270668 I'd read similar elsewhere and seen the same thing repeated on YouTube videos from GCN and others... So of course having always run my 23's at 85psi, I pump up my 25's to 60psi and out I go for a test ride and think... holy sh*t this is cr*p! And it contines to be crap until I arrive at 85psi... Last edited by robertbb; 02-19-2019 at 10:34 PM.
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#22
02-20-2019, 06:22 AM
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Quote:
__________________
Chisholm's Custom Wheels Qui Si Parla Campagnolo
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#23
02-20-2019, 06:32 AM
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Take my above comments with a grain of salt.
I've loved my 23mm tires on wide (20mm interior width) rims for several years and may start going to 25mm due to my seemingly ever expanding waistline and the fact that the roads are crappy where I live. I do run lower pressure and have found it to be nice, with no apparent loss of speed. Just increased comfort. The reason I mention the lower pressure and people saying it decreases rolling resistance is that supposedly a rock hard tire will deform less over the texture of the road surface. Lower pressure will allow the tire to deform more and actually provide lower rolling resistance overall. I don't know the science. But I run my 23s at about 80 PSI and 25s a bit lower and they ride very nicely. In fact, I've found a cotton clincher on wide rims like I use now to be close enough to the ride of a quality tubular that my tubular usage has gone down dramatically in the past few years. I'm speaking here only about paved roads and road tires. Tires and pressures for unpaved roads are a whole 'nuther ball of wax.
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#24
02-20-2019, 06:45 AM
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Run latex for the biggest difference, regardless of width.
__________________
chasing waddy
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#25
02-20-2019, 07:07 AM
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#26
02-20-2019, 07:32 AM
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Way too much thought for this guy. I have always run 23's inflated to the proper sidewall squeeze pressure and off I go! Never owned a pressure gauge for bikes. Now the cars are another matter, they get the pressure onthe door jam twice a year.
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#27
02-20-2019, 07:42 AM
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Quote:
__________________
chasing waddy
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#29
02-20-2019, 08:15 AM
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Quote:
__________________
Chisholm's Custom Wheels Qui Si Parla Campagnolo
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#30
02-20-2019, 08:28 AM
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Quote:
As the guy who develops and has developed tire pressure strategies for 10+ years for guys like Cancellara, Wiggins, Sagan, and so many others, I can tell you that this chart is straight up wrong from a performance point of view. Now for most people, doing most things, it's probably fine, but if you are after optimizing for performance this isn't it. Optimal pressure will be different for different surfaces, but if you have a number a safe rule of thumb is that equivalent small bump stiffness of the tire can be achieved at ~2% per millimeter of width change.. so every mm larger in measured casing size you need 2% lower pressure, but again, for the same surface.. as surfaces increase or decrease in roughness, your baseline pressure changes Part 1 of our episode on Asymmetry starts to get into this topic and brings some context from racing: https://marginalgainspodcast.cc/asymmetry-part-1/
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