donheff

I guess I am an anomaly. I use the optimal tire pressure chart shown in a biking magazine article that several years ago introduced this topic. I weigh 162 and run my 28s at 60 psi. If I was more anal the front would be a few pounds less. My ride feels great. To understand the graphic, you need to break up your total weight - 55% back and 45% front. Then find your mark on the proper tire size and move left to see pressure.

StanSeven

Velonews produced similar results. But rolling resistance is only part of the equation. The aero benefits of narrower tires aren't considered here. When they are, it's just about a wash. Also there was a long thread of the comfot between 23 and 25 and most people admitted they couldn't tell any difference. For those that sad they could, it generally was because they used less pressure.

jimmuller 

The trouble is, a bike magazine may run a chart like this and so it is accepted as "truth". Personal experience: I weigh 160 and use 28's on one of my bikes set up specifically for commuting. I keep them at 100 to 105psi. Trying a new route on the return home once this past spring with the sun in my eyes, a traffic light ahead, and traffic around me so I couldn't pay enough attention I hit a hole with my rear wheel (but somehow not the front). I hit it so hard it flat-spotted a perfectly great vintage MA2 rim, but it did not flat the tire. Had I been running 60psi it would most certainly have caused a snake-bite puncture too, and probably have bulged out the rim sidewalls too. The rim was toast anyway but at least I could ride the rest of the way home.

FWIW, I can feel the difference in weight between it and my lighter, skinnier wheels and tires. More often than not I'm on 23s or 25s. Had I been on 23s that bump might have ruined that rim too, but I keep them pumped up higher in accordance with the smaller contact patch so as to provide greater cushioning distance between rim and road.

That pressure chart makes no sense to me.

But my real point in entering this discussion was to point out that there are three factors, not two: rolling resistance, aerodynamic drag, and moment of inertia. None by itself is terribly significant, especially compared to the rider's mass and wind resistance. We are talking about subtle differences. Do any of these three matter in non-competition? Not really, but the weight at least can be felt. The weight will not affect your top speed (for any given level of exertion), but it affects how quickly you get there. Rolling resistance may be speed dependent, and aerodynamic drag certainly is.

kingfishr

You're right those three factors are tiny compared to everything else, and you could always run a 23mm on the front, where there is less weight to support and use a 25 or 28mm back since there is much less aerodynamic cost of a wide tire in back. As far as moment of inertia, Continental GP4000S have the following weights:
approx. 205 gram (23-622)
approx. 225 gram (25-622)
approx. 235 gram (28-622)

I certainly can't feel the 30 gram difference on my 1600g wheelset...

Actually the most important feature of the Panaracer Grand Bois is the tan sidewall for that retro look on my steel frame

John E

A couple of you have mentioned that a tire's labeled callout size does not necessarily match its actual width. I have been very pleased with 700Cx28 Continentals on the Bianchi, 90 PSI front, 100 rear, but these tires are actually only about 25mm wide on my rims. Other "28mm" tires I have owned, such as Specialized Armadillos, run enough taller and wider that they won't clear my fork crown and chainstays. I suppose we should consider sidewall height and actual tire width in this discussion.

I remember the early 1970s race to smaller and smaller clincher tires, which seemed to start right after the Michelan Elan broke through the traditional 27x1-1/8 barrier. Over the years I have migrated back toward somewhat wider tires, as have several of you.

BlazingPedals

I'd be perfectly happy running 28s. Running 25s is almost the same. The difference between 23 and 25 is almost theoretical - I sure can't tell the difference.

donheff

I no longer have the link but the article I got the chart from detailed a technical test protocol done in a lab, along the lines of some of the studies reference here. It was pretty compelling that the standard recommended tire pressures are far higher than needed for comfort and good rolling. I followed the directions for my wife and my cyclocross bikes running 32s. We never got a snake bite and we hit some rough stuff over the years. You may be correct that your bump would have caused a snake bite at 60 psi but then maybe not. And maybe the more cushioned impact might have better protected your rim. Or maybe not.

ModeratedUser150120149

Wonder how many times this subject has been discussed? I know I looked at a bunch when a couple months ago I was deciding what size tires to put on my road bike. The conclusions I came to are:
-A few mm difference in tire width makes little or no difference for all but the most competitive riders.
-Tires are not very precisely sized. Armadillo 23's actually measured 25. A Gatorskin that was labeled 28 rubbed the bike frame where another did not.
-Lots of snake oil about tire pressure. Manufacturers aren't very forthcoming about actual strengths and recommendations. I found a manufacturer chart which I used.
-Tire quality as compared to airplanes, cars and motorcycles is very low. Manufacturers use weight requirements as an excuse not to make quality tires. Yet, in airplanes where weight has a direct effect on profits they can build tires that do not need to be pumped up frequently and are not prone to flatting.
-Lacking actual, meaningful operational testing and data each person arrives at a tire size and pressure they are comfortable with. But, this is really accepting a role as a test pilot. They may stoutly defend their decision because it seems to work. But, they haven't a clue why it works.

Seems to me customers ought to act less like sheep in demanding the manufacturers produce quality tires that are labeled with their operating parameters.

Zinger

+1