The ETRTO standard sets a maximum pressure of 73 psi (5 bar) for tubeless-ready hookless rims. For most cyclists — gravel riders, MTB riders, or road cyclists on 28 mm+ tyres — this limit is never reached. It only becomes a constraint for lightweight road cyclists on narrow (25 mm) tyres whose setup would otherwise want 80+ psi.
Why the 73 psi cap exists
Hookless rims use a straight-walled bead seat without the hook profile that traditional hooked rims use to retain the tyre. The hook on a conventional rim provides a mechanical stop that prevents the tyre bead from seating incorrectly or blowing off under high pressure.
Without that hook, the tubeless bead relies on tyre/rim interface fit geometry and the tension created by the inflation pressure to stay seated. Above a certain pressure, the lateral force on the bead seat exceeds what the hookless interface can safely contain. ETRTO (the European Tyre and Rim Technical Organisation) set the standard at 5 bar / 73 psi for tubeless-ready hookless rims after testing failures in the 6–7 bar range.
The cap is absolute for road use. Gravel and MTB hookless rims have their own lower limits (typically 30–35 psi) due to the lower rim height and different bead geometry, but road hookless rims are capped at 73 psi across all brands that comply with the ETRTO standard. Some manufacturers add their own lower limits based on specific rim geometry — check your rim's documentation.
Which riders actually hit the ceiling
To hit 73 psi, you need a combination of narrow tyre width, high rider weight, or high-speed road riding that drives pressure high. The calculator tools show which setups approach the limit:
A 90 kg rider on 25 mm road tyres without the hookless cap would want approximately 95–100 psi rear. With the cap, SRAM clips this at 73 psi — a reduction of 22–27 psi from what the unconstrained formula would recommend. This is significant enough to affect ride quality and rolling resistance.
A 70 kg rider on 28 mm road tyres wants approximately 75–80 psi rear. The hookless cap clips this at 73 psi — a small reduction of 2–7 psi. Most riders in this range won't notice the difference.
A 75 kg rider on 32 mm or wider road tyres calculates to 60–70 psi — comfortably under the limit. The hookless constraint is irrelevant.
The practical rule: if you're on 28 mm or wider tyres, hookless rims impose no real restriction. If you're on 25 mm or narrower with a hookless wheelset, check your setup with the hookless option enabled and see if the cap is binding.
How SRAM implements the cap and what Silca doesn't
SRAM's AXS pressure calculator applies the 73 psi cap directly. If you set rim type to hookless, any output above 73 psi is automatically reduced to 73 psi. This is visible in the calculator: for a setup that would normally yield 85 psi rear on hooked rims, the hookless version returns 73 psi rear.
Silca's calculator was originally designed for hooked rim geometry and does not apply a hookless cap. Their model computes a pressure based on weight, width, and surface, regardless of rim type. If you're using Silca with hookless rims, you must manually check that the output doesn't exceed 73 psi and cap it yourself.
Pirelli applies a small hookless correction (-2 to -3 psi) but doesn't hard-cap at 73 psi in the same way SRAM does. This means for edge-case heavy-rider-narrow-tyre setups, Pirelli can recommend above the ETRTO limit on hookless rims.
The safest approach with hookless rims: always use SRAM as one of your reference calculators and enable the hookless option. Its cap is the one that reflects the actual ETRTO standard most directly.
Practical implications and what to do at the ceiling
If your setup hits the 73 psi ceiling, you have three options: run the maximum safe pressure and accept the rolling resistance penalty; switch to a slightly wider tyre to lower the ideal pressure below the cap; or switch to hooked rims if your riding style genuinely requires more than 73 psi.
For most riders, switching from 25 mm to 28 mm tyres is the easiest solution. The wider tyre reduces optimal rear pressure to approximately 70–75 psi for a 90 kg rider — right at or just under the hookless limit. The rolling resistance penalty of 28 mm vs 25 mm at optimal pressures is essentially zero; the wider tyre at its correct pressure rolls the same speed as the narrow tyre at its correct pressure on smooth surfaces.
If your sport genuinely requires very high pressures (criterium racing on perfectly smooth tarmac), hooked rims remain the technically correct choice. Hookless rims are an excellent option for everyday road cycling, gravel, and MTB, but they were not designed for the extreme pressures that narrow high-speed road tyres require.