If there's one five-minute job that saves you money at the bowser, extends the life of your tyres and makes your car safer all at once, it's checking your tyre pressures. Yet it's the job most of us put off for months at a time. Here's why it matters more than you might think, and how to get it right.
Why underinflation costs you fuel
A tyre that's low on air flattens out where it meets the road. That bigger contact patch creates more rolling resistance, which means your engine has to work harder to keep the car moving. The effect is small per kilometre but adds up quickly across a tank of fuel — and with fuel prices being what they are, it's money quietly leaking out of your tyres.
It's not just fuel, either. An underinflated tyre flexes more as it rolls, which builds heat in the sidewall. Heat is the enemy of tyre life: it accelerates wear on the outer edges of the tread and, in extreme cases, can contribute to tyre failure at highway speeds. Underinflated tyres also respond more sluggishly when you steer or brake, and they're more prone to aquaplaning in the wet.
Finding the right pressure for your car
The correct pressure isn't printed on the tyre itself — the number on the sidewall is the maximum pressure the tyre can hold, not the recommended one. Your car's recommended pressures are on the tyre placard, usually a sticker inside the driver's door frame, in the fuel filler flap or in the glovebox. The owner's manual lists them too.
Most passenger cars sit somewhere between 30 and 38 psi, and many placards give two sets of figures: one for normal driving and a higher set for when the car is heavily loaded or towing. If you're heading off on a road trip with a full boot and passengers, use the loaded figures.
How to check pressures properly
- Check when the tyres are cold — ideally before you've driven more than a couple of kilometres. Driving heats the air inside and raises the reading, so a tyre checked hot can look fine when it's actually low.
- Use a reliable gauge. Servo air machines vary in accuracy, so a small gauge kept in the glovebox is a worthwhile investment. Check the servo machine's reading against it now and then.
- Do all four, plus the spare. A spare that's been sitting for a year is almost certainly low, and it's no help flat.
- Refit the valve caps. They keep dirt and moisture out of the valve, which helps prevent slow leaks.
How often is often enough?
Tyres naturally lose a small amount of pressure every month, even with no puncture. A monthly check is a good habit — picking a regular trigger like the first fuel stop of each month makes it easy to remember. It's also worth a quick check before any long highway trip, and any time a tyre looks visibly lower than its mates.
What if one tyre keeps going down?
If you're topping up the same tyre every couple of weeks, something's wrong. It could be a slow puncture from a screw or nail, a leaking valve, or corrosion where the tyre seals against the wheel rim. None of these fix themselves, and a slow leak can turn into a sudden flat at the worst possible moment, so it's worth having it looked at promptly.
If you'd rather have a professional cast an eye over things, the team at Global Tyres Geelong in North Geelong can check your pressures, track down slow leaks and make sure your tyres are wearing evenly — drop in any time you're passing along Thompson Road.