Originally Posted by
kenshireen
This was his GP5000 comparison: Continental Grand Prix 5000 Comparison: 23, 25, 28, and 32 mm Compared Published: 2019-02-19 by Jarno Bierman
I just looked at the chart with a
15% drop and it appears that the
rolling resistance between a 25 and 28 is almost identical when the 25 is at 100 psi and the 28 at 90 psi (even though the Butyl tubes weighs 30 grams more on the larger tire)
Is this true... to me this means that you can pump up a 28 at less psi and it will have a similar RR to a 25 which will be at a higher psi.
I always thought that a thinner tire with high pressure would have less RR than a wider tire with a similar psi
That was the theory back in the 1970s or so. There's been some learning since then. Higher pressure tires do transmit more vibration and this causes power loss. If you're a bigger guy (like me) it would be pretty impossible to get the tire pressure in a 21mm up high enough to avoid bottoming out on big bumps, and so the tire flexes, which is a major cause of power loss.
Here's something from Jobst Brandt:
https://sheldonbrown.com/brandt/rolling-resistance.html
Jan Heine, another knowledgeable bicycle guy, weight in
here. His take: inflation doesn't matter that much. Inflate your tires with enough pressure to keep you from bottoming out on bumps and to avoid the tires rolling in hard cornering, and ride. And don't worry about it.
Now I don't optimize stuff much. I probably would best like 28mm tires. I settled on 26mm because Bontrager R3s were on my wheels when I bought the bike, and I trust the previous owner's (Neko Mulally) judgement so I stayed with R3s, and R3s come in 26mm. Could I go to 28s and get a better ride? Maybe. Some cyclists being tech-wienies means we can't help but optimize. I've gotten better perspective as I've aged*. When I was a lad working in the bike shop, all these things mattered a lot. Now, more important to make a choice and go ride. Same with tire pressure. Signficantly more comfortable with 95psi in the front, and I think it vibrates less and is actually more comfortable.
But to the OPs point: I disagree: pressure gauges can give you a reliable, repeatable measurement. Figure out what that is for best performance and... get out and ride.
(looking at this as an optimist, if your tire pressure is a few psi low you'll have a more comfortable ride, AND you'll get more exercise!)
*Slower too. Shoot.