Why does this calculator charge a penalty instead of showing the capped optimum?

Because a wheel that cannot reach its optimum rolls worse, not equally well. Comparing setups as if their optimum were available distorts the result exactly where it matters most.

Guides · Hookless

Hookless rims: the 5 bar limit and what exceeding it costs

Q: Can I inflate above 5 bar on a hookless rim?

No. The limit is a safety rating (ETRTO): without a bead hook, an excessive pressure can unseat the tyre while riding.

Q: Does the 5 bar limit apply if I use an inner tube on a hookless rim?

Hookless rims are designed for tubeless and their bead profile corresponds to that limit. If you systematically need higher pressures, the answer is a hooked rim, not an inner tube.

A hookless rim has no bead hook: the tyre bead seats flat against the flange. It is easier to manufacture to tight tolerances and lighter, but the industry — via ETRTO — caps it at 5 bar (72.5 psi) for safety: excessive pressure can unseat the tyre while riding.

The problem is that the optimal pressure knows no limits. The loss minimum follows p = C · load / width^1.5, so the heavier you are and the narrower the tyre, the more likely your optimum exceeds 5 bar — especially at the rear wheel, which carries more load, and on smooth asphalt, which pushes the optimum up.

What the cap costs, in watts

Penalty for being unable to inflate to the optimum: tubeless, normal asphalt, 22 mm internal rim, 35 km/h, 45/55 load split. «—» means the optimum fits below 5 bar and nothing is capped.

Tyre (labelled)	60 kg	70 kg	80 kg	90 kg	100 kg
25 mm	—	+0.0 W	+0.4 W	+1.2 W	+2.6 W
28 mm	—	—	+0.0 W	+0.3 W	+0.8 W
30 mm	—	—	—	+0.0 W	+0.3 W
32 mm	—	—	—	—	+0.0 W

How to read the table

The first surprise is capped cells that cost +0.0 W. Not a bug: the loss curve is flat near its minimum. If your optimum is 5.2 bar and you settle for 5.0, the cost is negligible. The ceiling only truly hurts when the optimum lies far above it: a 100 kg rider on 25 mm tyres pays 2.6 W — more than separates many premium tyres from each other.

Most calculators, when the optimum exceeds the ceiling, simply show the capped value — as if the wheel rolled just as well. It does not: it rolls worse, and a comparison should charge that difference. That is exactly what the PsiBike calculator does: it evaluates rolling resistance at the pressure you can actually run, wheel by wheel, weighted by each wheel's load.

What to do if the ceiling bites

Go wider. The most effective lever: moving from 25 to 28 mm drops the optimum sharply, and the tyre measures wider mounted. Check the pairing with your rim first.
Accept the penalty knowing its price. If it is 0.3 W, change nothing. If it is 2.6 W, you have your argument.
Hooked rim + inner tube. No 5 bar ceiling (the model's sanity cap is 9 bar). The classic option for heavier riders.

Model honesty: the impedance terms depend on the asphalt and are a reliable trend, not an exact measurement. Differences below 1 W fall under its noise.

Frequently asked questions

Can I inflate above 5 bar on a hookless rim?

No. It is a safety rating of the rim + tyre system as homologated for hookless: without a hook to retain the bead, overpressure can unseat the tyre mid-ride. It is a ceiling, not a suggestion.

Does the limit apply with an inner tube?

Hookless rims are designed for tubeless, and their bead profile corresponds to that limit. If you systematically need higher pressures, the answer is a hooked rim, not an inner tube.

Why charge a penalty instead of showing the capped optimum?

Because a wheel short of its optimum rolls worse. Treating it as if it were at its optimum would make the narrow tyre win systematically exactly where it stops being the best option.

Check your exact case

The calculator flags every combination with its real hookless penalty, next to all the other watt-level differences.

Open the calculator