Typical for this type. Change it if you know yours.
Uses the 35 mm Brompton tyre and its printed 65 to 110 psi range.
Printed on the sidewall, for example 700×32c or 27.5×2.0.
No inner tube
Cobbles, towpaths, potholed roads
Carbon rims without a bead hook
Optional. Leave at 0 if unknown.
Front tyre
49 psi
3.4 bar, carrying 39.6 kg
Rear tyre
62 psi
4.3 bar, carrying 48.4 kg
How the pressure is worked out
The tool starts from the weight on each wheel, not the weight of the rider. Your weight, the bike and any load are added together and split front to rear by bike type, using the splits Bicycle Quarterly measured on real bikes: 40/60 for a racing position, 45/55 for a touring or hybrid position, 35/65 for an upright city bike.
Each wheel load then goes into Frank Berto's tyre drop data. Berto measured how far 50 tyres sagged under eight loads and seven pressures and drew the pressure that gives a 15% drop, the figure tyre makers recommend. The tool uses a power-law fit to his chart, psi = 153.6 × load in pounds ÷ width in millimetres to the power 1.5785, minus 7.17, which reproduces his published examples within a few psi from 20 to 54 mm.
Adjustments are shown, never hidden: tubeless tyres run 10% lower, rough surfaces 10% lower, hookless rims are capped at 72.5 psi, nothing goes below 18 psi, and a Brompton's 16 inch tyres run 15% higher within the 65 to 110 psi printed on them. The sidewall range on your own tyre always wins.
Berto's curve keeps climbing for a heavy rider on a narrow tyre, well past what the tyre can take, so the tool holds the answer at a conservative maximum for the width and tells you it has. That is a typical rating, not yours: read the sidewall. If the calculator is capping you, the fix is a wider tyre rather than more air.
Tyre pressures for common London set-ups
Worked from the same method. Your own weights will move the figures, so use the calculator rather than the nearest row.
| Set-up | Front | Rear |
|---|---|---|
| Road bike, 25 mm, 77 kg rider, 9 kg bike | 65 psi (4.5 bar) | 101 psi (7 bar) |
| Road bike, 28 mm, 77 kg rider, 9 kg bike | 53 psi (3.7 bar) | 84 psi (5.8 bar) |
| Hybrid, 32 mm, 77 kg rider, 13 kg bike, 3 kg bag | 52 psi (3.6 bar) | 66 psi (4.6 bar) |
| Hybrid, 38 mm, 77 kg rider, 13 kg bike, 3 kg bag | 38 psi (2.6 bar) | 48 psi (3.3 bar) |
| Dutch city bike, 42 mm, 77 kg rider, 16 kg bike, 3 kg bag | 24 psi (1.7 bar) | 51 psi (3.5 bar) |
| E-bike, 50 mm, 85 kg rider, 23 kg bike, 3 kg bag | 20 psi (1.4 bar) | 44 psi (3 bar) |
| E-bike, 55 mm, 85 kg rider, 23 kg bike, 3 kg bag | 18 psi (1.2 bar) | 37 psi (2.6 bar) |
| Front-loader cargo bike, 55 mm, 80 kg rider, 35 kg bike, 30 kg load | 32 psi (2.2 bar) | 41 psi (2.8 bar) |
| Long-tail cargo bike, 60 mm, 80 kg rider, 30 kg bike, 30 kg load | 19 psi (1.3 bar) | 41 psi (2.8 bar) |
| Brompton, 75 kg rider, 12 kg bike | 65 psi (4.5 bar) | 65 psi (4.5 bar) |
| Brompton, 95 kg rider, 12 kg bike, 5 kg bag | 65 psi (4.5 bar) | 79 psi (5.4 bar) |
Pressure is the puncture lever
A tyre that has quietly lost a bar since last month sinks further over every kerb and pothole, and the tube gets pinched between rim and road. That is the snakebite puncture, two small holes a few millimetres apart, and the right pressure is what prevents it.
Too much pressure has its own cost: less grip on wet London tarmac and a harsher ride with no gain in speed. The 15% drop figure is the point where the tyre rolls well and still absorbs the road, which is why tyre makers recommend it.
Flat anyway? Our puncture guide covers the fix, and a mechanic can come to you for puncture repair from £30, 9am to midnight, seven days a week.
Tyre pressure questions, answered
Where the numbers come from
- Frank Berto, All About Tire Inflation (2006) The 15% tyre drop measurements and the road and mountain bike inflation charts.
- Jan Heine, Optimizing Your Tire Pressure for Your Weight, Bicycle Quarterly Berto's chart by wheel load and the measured front and rear weight splits.
- Rene Herse Cycles, Tire Pressure Calculator 3.0 The 72.5 psi (5 bar) limit for hookless rims.
- Schwalbe, Inflation pressure Monthly pressure loss, tubeless and small wheel guidance, stay inside the sidewall range.
- Brilliant Bikes, Schwalbe Marathon Racer 35-349 The 65 to 110 psi range printed on the standard Brompton tyre.
Puncture already? We come to you.
Mobile puncture repair from £30, at home, work or roadside anywhere inside the M25.