How this number is calculated
Most tire pressure advice is a number and a shrug. This is the whole method behind ours — what it is built from, what it is checked against, and the four places it rests on us rather than on anything published.
It starts from a number you can check. This page is the checking.
Pick a rider. Watch the number get built.
There is no single equation with your answer hidden inside it, so rather than say so, here it is happening. Every figure below is the engine’s own trace for the setup you choose, and the two empty rows at the bottom are as honest as the five above them.
It is layers, not a formula
That is the whole engine, in the order it runs. Each layer does one job you can name, and nothing happens anywhere else — read down this list and you have read it.
The clamp is last on purpose. Every layer above it is an opinion about how you like to ride. The clamp is not an opinion — it is the tire, the rim and the ground, and it wins.
Things that must stay true
The engine is held to a set of fixed anchors and invariants — statements that have to hold no matter what else moves. A wider tire can never ask for more air than a narrower one at the same weight. Rougher ground can never ask for more. The front wheel can never come out above the rear on an even weight split.
Every release is checked against all of them. A change that breaks one does not ship, however much better it makes some other case look. That is the part worth knowing: the number is not tuned until it feels right, it is held inside rules that were written down first.
Four things you are trusting us on
Two are figures we picked with nothing published behind them. One is a setting we refused to build. One is a question we still do not ask. Nothing outside this project backs any of them, and all four are in your number — two by being there, two by being missing.
The tube figure is ours
A butyl tube firms your number by 9% here. We could not find agreement on that figure anywhere — not on the size of it, and not even on the direction. So we picked the firmer one, because being slightly over on a tube is the safer way to be wrong. Latex and TPU are the same story with less daylight between the answers.
How rough is rough
Every ride style starts from a roughness value we picked. Nobody published it and no fixture anchors it, and it is the path every percentage on the ride cards runs through. It is the single number on this page we would most like to replace with a measurement.
There is no soft-ground setting
None at all, which is why you will not find cyclocross or fatbike in the list. Snow, sand and deep mud are not a rougher kind of gravel, and treating them that way would print a number we could not stand behind.
How hard you ride is not asked
On a road tire it is worth around 8 psi at the middle of the range, and there is no control for it — everyone gets the middle setting. A steady commuter and a racer on the same bike get the same answer. That is a gap, not a decision.
What it takes to move a number
A constant here does not change because it feels better. It changes when the data that set it changes, or when a measurement arrives where there was not one — and the anchors and invariants have to still hold afterwards. A number that moves for any other reason is a number nobody can check, which would undo the only thing this page is for.
The last layer is your hands
Everything above gets you to a starting point. Then you ride it and say how it felt — harsh, just right, squirmy — and the number moves toward you. Three rated rides on one kind of ground start to shift it; six and it is dialled in. Each surface learns on its own.
The math gets you close. Your hands finish it.