Handbook

These articles are written once, not generated from the car register. Model charts link here for method.

• What tyre pressure actually is

  Tyre pressure is the gas load that carries the car. Why the door-pillar placard beats the sidewall, in bar and PSI.

• Bar versus PSI

  How UK and European placards use bar while garage hoses still shout PSI — and why 2.3 is not twenty-three.

• How to read the tyre placard

  Where the yellow or white door-pillar sticker lives, what the two columns mean, and why laden figures exist.

• Sidewall maximum versus recommended pressure

  The number moulded on the tyre is a carcass limit. Recommended operating pressure is the vehicle placard.

• How to check tyre pressure

  A cold-gauge routine that does not depend on a supermarket air-and-water machine.

• Cold tyre pressure

  What “cold” means in a UK climate, why the M6 reading is the wrong one to set, and how frost fools TPMS.

• How temperature changes tyre pressure

  About 1 psi per 5–6 °C. Why a January frost lights the lamp, and why you must not bleed a July afternoon.

• What under-inflation does

  Low pressure builds heat in the shoulders, raises rolling resistance, and is the usual path to a belt separation.

• Risks of over-inflating tyres

  Too much pressure shrinks the contact patch, wears the centre rib, and turns potholes into liner bruises.

• TPMS in the UK and EU

  Direct versus indirect systems, the 25% warning rule, and why the dash is not a substitute for a gauge.

• Nitrogen versus air in tyres

  Nitrogen leaks a little slower and is drier. It does not freeze, run cooler by magic, or replace the placard.

• Winter tyre pressure

  Snow tyres still use the door placard. Cold snaps drop the gauge. Do not run 4 psi low “for grip.”

• Electric-vehicle tyre pressure

  EVs are heavy, often use low-rolling-resistance tyres, and can list different targets by wheel size.

• Plus-size wheels and estimated PSI

  Lower-profile plus-sizes usually stay at or slightly above the placard, not below.

• Load index, C-type and LT tyres

  What the number after the size means, and why a 195/75R16C is not a Golf tyre.

• Speed rating and pressure

  A V-rated tyre still wants the vehicle placard. Speed symbols are not an inflation chart.

• Spare tyre pressure, including space-savers

  Full-size spares follow the higher axle. Compact temporary spares are often 4.1 bar.

• Run-flat tyre pressure

  Run-flats still need the placard. Stiff sidewalls hide a low tyre from your eyes. TPMS is doing more work, not less.

• Van tyre pressure

  Transits, Trafic and Crafter vans often split front and rear and live on C-type rubber. Empty and laden are different jobs.

• 4x4 and SUV tyre pressure

  Crossovers often share a car band; body-on-frame 4x4s may not. Roof boxes are load. Airing down is off-road only.

• MOT, legal tread and inflation

  The MOT looks at tyres; it is not a pressure-setting service. Bald, damaged or mixed-axle tyres fail regardless of a perfect gauge.

• Tyre pressure, rolling resistance and fuel use

  Correct placard pressure is the mpg setting. Over-inflation buys a little resistance and spends it on centre wear.

• Wet grip and pressure

  The contact patch in rain is a pressure story as much as a tread-compound story.

• Front versus rear tyre pressure

  Why some cars print two numbers, why FWD eats fronts, and why a van’s rear is not a Fiesta.

• Tyre pressure myths

  Sidewall-max, “add 5 for the motorway,” nitrogen magic, bleeding hot tyres, and filling until it “looks round.”

• Monthly tyre-pressure checklist

  A short driveway list: cold soak, four corners plus spare, TPMS, valve caps, and when a 0.3 bar miss means a nail.

• Forecourt compressors versus a proper gauge

  Pay machines are convenient and often optimistic. Use them to add air, then finish with your own instrument.

• Kilopascals (kPa) explained

  100 kPa is 1 bar. Why some stickers use kPa, and how to set a gauge that only speaks SI.

• Towing, nose weight and tyre pressure

  A hitch is load. Use the laden column if it exists. Trailer tyres have their own spec.

• Motorway running and pressure

  Sustained high speed heats tyres. The placard already assumed that. Do not bleed at the services.

• Summer heat, tarmac and pressure

  Hot tarmac raises the gauge. Do not dump air in a heatwave. Recheck on the next cool morning.

• Valve cores, caps and slow leaks

  Most “mystery” pressure loss is a core, a cap, or a corroded rim, not a haunted tyre.

• When to replace a tyre rather than inflate it

  Pressure will not save cords, bulges, or 1.6 mm in the wet. Know the difference between a fill and a scrap.

• Staggered fitment and split pressures

  Wider rears can have a different target. Do not average front and rear. Square versus staggered is a placard reading.

• Tyre pressure, handling and braking

  How a 0.3 bar miss changes turn-in, stopping distance and ABS behaviour on a wet British roundabout.