72 psi. 95 psi. “Hard enough that it feels fast.” Everyone carries a number in their head, usually picked up in a forum or from someone in the car park. The trouble is that four things decide your tire pressure. And one of them counts for more than almost anyone expects.
Four things decide it, nothing else
Tire width. The biggest lever by far, and the one that keeps getting overlooked. At 75 kg on tarmac: 25 mm wants 74 psi, 35 mm only 51. That is 23 psi of difference from the tire alone. Wider means more air volume, and more volume carries the same weight at lower pressure.
One catch: the number on the sidewall is a nominal width, measured on a narrow reference rim. On a modern rim the same tire builds one to three millimetres wider. Measure it once with a caliper and you know it for good.
Your weight. It matters, but less than you think. Going from 60 to 90 kg of rider on the same 28 mm tire is 11 psi, from 60 up to 71. So the rider laughing at his heavier mate’s pressure is usually further off himself, if he picked the wrong tire width.
The surface. This is where a lot of people have the direction backwards. On rough ground you run less pressure, not more. A hard tire skips over the bumps instead of swallowing them, and every skip is lost energy and lost grip. Between cobbles and fresh tarmac there are about 13 psi.
Tube or tubeless. With an inner tube you need 2 to 5 psi more, the rougher the surface the more. The reason is not rolling resistance, it is the pinch flat: in a snakebite the tube gets crushed between rim and edge, and the only thing that prevents it is pressure. Tubeless has nothing to crush, so it can go lower. Latex and TPU tubes sit somewhere in between and behave more like tubeless.
And one detail that hardly anyone bothers with: the front wheel wants about 6 percent less pressure than the rear, because less weight sits on it. The front wheel steers and brakes, which is where grip pays off most directly.
Which of them weighs the most?
I ran the factors against each other. The starting point is an average setup, a 75 kg rider on 28 mm tires on normal tarmac, and then I move one value at a time across its realistic range:
| Factor | Range | Difference |
|---|---|---|
| Tire width | 25 to 35 mm | 23 psi |
| Surface | cobbles to fresh tarmac | 13 psi |
| Rider weight | 60 to 90 kg | 11 psi |
| Tube instead of tubeless | depending on surface | 5 psi |
| Front instead of rear | fixed factor | 4 psi |
| Bike weight | 6 to 15 kg | 3 psi |
One piece of honesty about that: a ranking like this depends on the ranges you pick. Take the full span from 50 to 117 kg instead of 60 to 90, and weight jumps to the top with 26 psi. If you are very light or very heavy, you feel it accordingly.
What I find more interesting is something else. Tire width is the only big factor you get to choose freely. You cannot change your weight overnight, and the surface is wherever you happen to ride. So the biggest lever is the one decided at your next tire purchase, not at the pump.
And the last two rows tell you what not to worry about. Two kilos more bike, or a full bottle, move less than a single adjustment step.
And then the rim’s own ceiling
So far this has been about which pressure rides well. Now comes the pressure you must not exceed, and that one is down to the rim.
A conventional rim has a small lip on the inside, the hook. It grabs over the tire bead and holds it mechanically. Hookless rims do not have that lip, the wall runs straight up. The most honest reason for that: it is cheaper. Producing a clean hook in carbon is involved, a straight wall is not. There are real arguments alongside it, the wall gets thicker and more impact-resistant and tubeless seals more cleanly, but the saving lands with the manufacturer first.
Without a hook, only the fit holds. The tire sits so tightly that friction keeps it there. Like a cork in a bottle: it holds for a long time and then not at all. No hiss, no warning, the tire comes off in one go. A puncture you can roll out. This you cannot.
ISO 5775-1:2023 gives no single maximum for hookless at all. It recommends maximum pressures, banded by nominal tire width:
- 25 to 29 mm: 72 psi (5.0 bar)
- 30 to 34 mm: 65 psi (4.5 bar)
- 35 to 39 mm: 58 psi (4.0 bar)
- 40 to 44 mm: 50 psi (3.5 bar)
- 45 to 54 mm: 43 psi (3.0 bar)
If 72 psi is the only number you ever see quoted: that is the 25 to 29 mm band, the road bike row. It is why the figure sticks, and it is why it does not hold on gravel. A 40 mm gravel tire on hookless should not see 72 psi, it should see 50 at most. That is a 30 percent difference. The standard calls this a recommendation for the marking on the tire sidewall, not a hard limit: what binds you is always the lower of the tire sidewall print and your rim manufacturer’s approval. The table also runs further in both directions, from 18 mm up to 84 mm. And below 28 mm most rim manufacturers do not approve hookless at all: a 25 mm tire on it is not a question of the right pressure, it is the wrong combination.
Two more things. Whether you are on hookless is in your wheel’s spec sheet, usually as “hookless” or “TSS”. And above the standard sits your rim manufacturer’s compatibility list, because many approve only specific tire models. Incidentally, “it has been fine so far” is not an argument, it is a description.
What the calculator does with all this
Those four levers plus the rim limit are exactly what sits inside our tire pressure calculator. It works out front and rear separately, and on hookless it shows you the limit for your width before a result even appears.
If your demand goes over that limit, it caps and marks the value “at the limit”. If it goes more than ten percent over, you get no number at all, just a note that the combination is the wrong one. That is the less comfortable route, and the only honest one. More background sits in the YMC tire pressure guide.
The bottom line
There is no single number, and anyone who gives you one does not know your setup. Measure your real tire width, be honest about your weight, pick the surface you actually ride, and add a little if you run tubes. Going up, the maximum on tire sidewall and rim applies, and on hookless the bands above. Then work your way in from there in small steps, and when in doubt go up. Too little pressure is the bigger risk.
