How skinny a tire should I run? There seems to be a trend towards fatter road tires. I like my 23s, but they are a little squirrely.
Choosing a tire width, 23, 25?
I wonder if the proliferation of mega stiff carbon frames has anything to do with cyclists seeking out wider rubber in an effort to increase comfort. My 23mm rubber feels fine to me but then all my road bikes are either titanium or steel.
Mega-stiff carbon? Generally not in the vertical plane. Hopefully laterally and torsionally though, as that gives greater efficiency - the reason to ride high quality carbon over titanium if you are racing.
A larger tire DOES NOT have a larger contact patch. 28 25 23 all have the same size contact patch if all inflated to the same pressure with the same load on the bike. Contact patch only increases when load is increased or pressure is decreased. Don’t argue with me over this like other people do. Google it, ask Boeing how they calculate tire patch contact on a runway.
A 25 tire has a wider and shorter contact patch than a 23 (same surface area). This is why it has a lower rolling resistance. The wide patch keeps the overall shape of the tire more round as it turns, instead of having a longer flat spot on the bottom.
It’s doubtful a larger tire has better aerodynamics than a smaller one, as the frontal area is larger. The wide rims are generally more aero because of the shapes they can be made into that resist cross wind forces at certain angles. That nice day when you doing a TT a 23 is going to be more aero.
That said, I feel the rolling resistance to aero advantage is minimal on either tire, my coach friend and I were estimating the crossover point is around 27mph. So if you are slower than 27mph run 25’s and if you are faster run 23’s. We based this on it always seemed like an extra 10watts to do 27 on 25c tires. We did not do this scientifically, it’s just an observation.
Buy the tire with the highest TPI and softest casing you can find if you want a nice ride. A 23c vittoria open corsa with a latex tube rides infinitely nicer and has more grip than some 60tpi piece of crap 28c hardcase gatorskin armadillo iron sided anchor. You’ll just need to learn to live with a few flats. And also it saves you about 40watts total.
I’m a fan of wider rims that make my 23’s more like 24.5’s so i save the weight, and have good aerodynamics at wider angles.
I think I just learned something. Thanks!
But isn’t half the point of a wider tire the option of running lower pressure without increased risk of pinch flats? And thereby a larger contact patch in practice? I run just over 7 bar in tubeless 23 Hutchinsons on the road bike, just over 6 bar in 28 Conti 4-seasons on my cx/commuter. I don’t know squat about aerodynamics, but it works wonders for comfort.
And one more thing: Is a larger contact patch always good? I half remember reading an interview with a pro mechanic who increased tire pressure for racing in wet conditions. The I understood it smaller contact patch, higher pressure between road and tire, and less water between tire and road surface.
By the way. PSI’s are for mountain bikers. 
I changed to 25 from 23 and IT DOES change the contact patch, because you do run them at lower pressure. I was putting 110 psi in 23’s now run the 25’s with front at 85 and rear at 90.
I weigh around 83kg and should have done this years ago; the overall handling of my bike is better, softer ride, more confidence cornering, etc.
Going to 25’s also gives you a slightly taller tyre which gives a bigger roll out.
Even a lot of the pro teams are realising this fact and changing to 25’s.
Aerodynamics also improve because the wider tyre breaks the air before the down tube on your frame.
Have a read of this article Why you must run wider tires on your road bike.
You obviously can’t read correctly. The article says this: “Bigger casing means a larger contact patch. Drop the tire pressure a bit and that contact patch just became even bigger,” which is just not true. The only thing that changes contact patch is the pressure + bike and rider weight. The size of the tire has nothing to do with it. I’m not debating that you run bigger tires + lower pressure hence the patch is bigger. I’m stating that what i quoted here is just not true, in regards to tire size = more contact.
You’re getting pretty excited over a detail mate. The article also says only use recommended pressure. That is lower for a start. Must be time you tried putting 100 psi in a mtb tire. It doesn’t work. Likewise with a fat road tire. No point even trying. My fatbike tire is hard at 20 and can ride great at 5psi. The article refers to a lower pressure below 80 odd. I’ve run mine in the 70s or less happily and I’m no lightweight.
I went from 23 to 25 mm and from 140 to 90 psi. I also went from treaded to slicks; less airborne and more control over manhole covers. Much more comfortable ride and more grip. 28 mm may be the next tire 
Btw I read your article on lower pressures and tried it and agree with going wider. I run Vittoria Rubino Pro slicks 120 tpi.