Flatforkcrown

maybe it’s your tires, not the psi. I took a ride at lunch and pumped my veloflex robaix (25mm tubular) up to 100 psi and it was comfortable and fast. Rolling over rumble strip at 25mph+ wasn’t even bad. I’m also about 180lbs, and ride a steel frame.

Jrasero

I run GP5000 28mm w/ tubes at 90psi

PeteHski

At least some of the tyre manufacturers now have decent pressure guides for their specific tyres, taking into account both rider weight, rim width and comfort vs performance trade-offs. I’ve been using Pirelli tyres recently and their pressure guide is excellent.

But some others are not so good, often stating pressures that are clearly too high for anything other than their own ass covering!

GBK233

Just started riding a few months ago. Started on 23s….then tried 25s and 28s…..now I’m riding on 32mm tubeless. Loving the 32s.

terrymorse 

An observation:

The trend in 700c tire widths seems to be approaching from below 32mm, which is an interesting number.

During the "bicycle boom" in the 1970s, the most popular clincher tire size for a road bike was 27 x 1-1/4".

1-1/4" is about 32mm. Hmm.

Another size at the time (for the really high end road bike) was 27 x 1-1/8", and 1-1/8" is about 28mm. Also hmm.

After 50 years of "trying something different", we are converging to the popular tire widths from the 1970s.

VicBC_Biker

A pressure guide that I like:
https://axs.sram.com/guides/tire/pressure

PeteHski

Yeah I like this one too, although it comes out a little lower than Pirelli recommends for my specific tyres. But not by much. I think if you start with these sort of recommendations you can't go far wrong.

rm -rf

I hadn't seen this calculator. It accounts for tire type, rim width, riding surface, etc. Good.

At 170 lbs, with wide 20.5 mm internal width rims, GP5000 tires with tubes. On these rims, my tires measure an actual 29mm wide. (I was running GP4000 25mm, and those measured 28mm on these rims. It looks like the 25s are bigger than advertised, and 28s are accurate.)
The calculator says:
73-74 psi front, 78-79 psi rear.

I've been running 65 psi front, 75-78 psi rear. Lately, 68-70 psi front, 80 psi rear. Either set of pressures seems fast to me. I have a mix of super smooth new pavement and bumpy patched roads and chipseal

On my adventure/gravel bike, I can mount 38mm smooth tread tires that have flexible road bike sidewall construction. (Compass tires, now Rene Herse. One of them developed a bulge, and I don't recall hitting anything. I'll probably change to something else.)
They measured an actual 39mm.
The calculator says 51 psi front, 55 psi rear. That seems way high.
I used 38 psi front, 45 psi rear. That's quite amazing on rough chipseal roads -- it just floats over the gravelly surface. Coasting downhill, I was just as fast as road bike riders with 25mm tires. I think these are quite efficient. 200 grams heavier, though.

Pinch flats
I increased the 28mm from 65 front to (hopefully) slightly reduce the chance of pinch flats. I haven't had one in more than a year, but I do try to be careful. I rarely get pinch flats from potholes. It's usually from a piece of large gravel / small rock sitting isolated on an otherwise nice road. And speed is a big factor. I can roll over these at cruising speeds, but downhill speeds mash the tire flat against the rim, slitting the tube in a "snakebite".

rm -rf

Air volume
A tire and wheel inflated cross section is somewhat like a circle. So the air volume is that cross section area x the tire "length", the circumference. The more air volume, the less pressure is needed to keep the tire from flattening out.

It still surprises me how fast the area and volume go up: Area of circles = 3.1416 * (width/2) ^2. That's the forumula Pi * r squared.

Diameter vs area:
18mm: 254 sq mm. Heh, had to add this one. I saw a guy riding a classic 70s Italian road bike with 20mm tires. (Might have been 18mm?) Those look tiny now. The pressure calculator says 128 psi front, 136 rear.

23mm: 415 sq mm. 18% less than 25mm.
25mm: 490 sq mm.
28mm: 615. 25% more

32mm: 804. 64% more.
38mm: 1134. 231%
45mm: 1590. 325%

BlackWhite

Road bikes typically have a 700mm outer dimension, and widths that start at 23mm.Road tires are usually less than 30mm wide, although you can find tires up to 45mm for bikes designed for gravel roads.

Sy Reene

Every calculator seems to always miss something though. This one only has one type of "Road" surface. Also it presumably tries to guess the tire width for the rim width entered. OTOH, asking for rim type is nice as it's also presumably it's building in safety factors and ETRTO standards based on PSI combined with inner rim widths. Hence why if you switch between hooked vs hookless TL rim types, the resulting recommendation drops quite a bit (which from pure theoretical performance standpoint I don't think should be case).

VicBC_Biker

??
Do you mean actual tire width vs labelled tire width?

Doesn't the outer diameter of the tire change a bit with different rim widths? Perhaps this has an effect on the chances of rolling the tire off the rim or 'burping' a tubeless tire?

70sSanO

My understanding, and real life experience, is that a rim’s internal width is a factor in the tire’s inflated width.

The same tire on an 18mm internal width will measure wider than when it is mounted on a 14mm internal width rim.

I think this has played out in mfg’s more current offerings. GP4000 vs GP 5000 measured width on the same rim comes to mind.

John

Sy Reene

Yes. I mean that calculator takes the nominal width that's listed on the tire, and is likely using some sort of conversion factor to what actual inflated tire width to use in its calculations, based on the rim width entered. I would think it would be more accurate to ask for the actual measured width than trying to guess though. It's a known thing that different models/brands of tires inflate to differing actual widths for the same rim.

ofajen

Yes, the ETRTO took note of increasing rim widths and changed its standards for expected rim width to wider rims between the release of the 4000 and the 5000, so the same nominal size of 5000 expects a wider rim and will be smaller in width on the nominal rim spec’ed back when the 4000 came out.

Otto

ironwood

The tire's construction is more important than it's width. Jan Heine of Bicycle Classics has done a lot of testing rolling resistance of tires. He is selling a line of tires , "Rene Herse", formerly "Compass", made by Panaracer. I like them.

vane171

That's only true for racing, not for sporting rides where what counts is the thrill or feel of going fast even if you lace the ride with coffee stops. But if fast tire means flimsy light tire that punctures easily, that takes the fun out of being fast.

70sSanO

Agreed. I’m still running the older Rubino Pro III, which is okay; better than the newer ones. I still have a couple of pairs for future use. But this thread has prompted me to entertain going to a GP-5000 in my advancing years instead.

John

PeteHski

There’s nothing more annoying than settling into a nice fast group in a Sportive ride and then getting dropped because of a flat. So I generally choose to trade off a few watts of rolling resistance for extra puncture protection on long Sportive/GFs.

pgjackson

Funny how less than 10 years ago there were threads just like this with people scientifically proving that 23mm tires were ideal in virtually all conditions. Anything over 25mm was a grandpa tire...something only an old dude on a beach cruiser would use.