Of all the tyre maintenance tasks available to drivers, maintaining correct pressure offers the best return on investment. It costs nothing but a few minutes of your time, yet proper inflation affects every aspect of tyre performance: safety, longevity, fuel efficiency, and driving comfort. Despite this, studies consistently show that the majority of vehicles on Australian roads are running with at least one under-inflated tyre.
The Physics of Tyre Pressure
To understand why pressure matters, it helps to understand what's actually happening inside your tyre. The air (or nitrogen) inside the tyre bears the vehicle's weight—not the rubber itself. The tyre casing is simply a container for that air, which pushes outward against the inner surface, creating the structural rigidity that supports your vehicle.
When a tyre is correctly inflated, the entire designed contact patch—the area of rubber touching the road—meets the surface evenly. This distributes forces across the full width of the tread and allows the tyre to perform as its engineers intended.
Under-inflation causes the sidewalls to flex inward, reducing the effective contact area and concentrating load on the outer edges of the tread. Over-inflation has the opposite effect, causing the centre of the tread to bulge outward and reducing contact at the edges. Both conditions compromise grip, accelerate wear, and affect handling.
Consequences of Incorrect Pressure
Under-Inflation: The Silent Killer
Under-inflation is far more common and more dangerous than over-inflation. A tyre running 20% below its recommended pressure—a deficit that's difficult to detect visually—experiences significantly increased internal heating. This heat buildup degrades the rubber compound and weakens the internal structure, potentially leading to sudden failure.
The consequences extend beyond catastrophic failure:
- Increased fuel consumption: Soft tyres have greater rolling resistance, requiring more energy to move. Studies suggest a 1% increase in fuel consumption for every 10 kPa of under-inflation.
- Accelerated edge wear: The concentration of load on the tyre edges wears these areas prematurely, potentially halving tyre life.
- Compromised handling: Under-inflated tyres respond sluggishly to steering inputs and provide less predictable grip, particularly during emergency manoeuvres.
- Increased braking distance: The reduced contact patch and decreased tyre rigidity extend the distance required to stop.
The internal heat generated by an under-inflated tyre at highway speeds can exceed 120°C—hot enough to literally cook the rubber and break down the structural cords. Most tyre blowouts result from this heat-induced failure, not from running over sharp objects. Maintaining correct pressure is your primary defence against blowouts.
Over-Inflation: Less Common but Problematic
While less immediately dangerous than under-inflation, over-inflated tyres present their own issues. The bulging centre of the tread wears faster than the edges, reducing tyre life. More critically, the reduced contact patch decreases available grip, particularly in wet conditions where water evacuation is already challenged.
Over-inflated tyres also provide a harsher ride, transmitting more road irregularities through the suspension. This additional stress can accelerate wear on suspension components and reduce passenger comfort.
Finding Your Correct Pressure
Every vehicle has a manufacturer-specified tyre pressure, developed through extensive testing to optimise that vehicle's performance characteristics. You'll find this specification in one of three places:
- A placard on the driver's door jamb (most common location)
- Inside the fuel filler flap
- In the owner's manual
The specification typically provides different pressures for front and rear tyres, as weight distribution differs. Many vehicles also list two sets of pressures: one for normal loads and another, higher pressure for when the vehicle is fully loaded or towing.
- The pressure moulded on your tyre sidewall is the maximum safe pressure for that tyre
- The pressure on your vehicle's placard is the recommended operating pressure
- Always use the vehicle manufacturer's specification, not the tyre's maximum rating
When and How to Check Pressure
Tyre pressure should be checked when the tyres are cold—that is, before driving or after the vehicle has been stationary for at least three hours. Driving heats the tyres and the air inside them, increasing pressure by 15-30 kPa or more. Adjusting pressure based on a hot reading will leave you under-inflated once the tyres cool.
For accurate measurement:
- Check pressure in the morning before driving, or after the car has sat for several hours
- Use a quality gauge—cheap pencil-type gauges can be inaccurate
- Check all four tyres and the spare
- Don't forget to replace valve caps—they protect the valve from dirt and provide a secondary seal
Most service station air compressors include built-in gauges, but these are often less accurate than a personal gauge. Consider carrying your own digital gauge for reliable readings.
Temperature Effects on Pressure
Australia's temperature extremes significantly affect tyre pressure. For every 10°C change in ambient temperature, tyre pressure changes by approximately 10 kPa. This means a tyre inflated correctly on a 35°C summer afternoon may be 15-20 kPa under-inflated on a 15°C winter morning.
This thermal relationship works both ways. Tyres inflated on a cold morning will run higher pressure as the day warms, and higher still after highway driving heats them further. While this temporary over-inflation is generally safe, it's why manufacturers specify cold pressure—it provides a consistent reference point.
As seasons change, recheck your tyre pressure. Many drivers find their tyres read correctly in summer but fall 10-15% below specification during winter. A few minutes of adjustment prevents months of accelerated wear and reduced safety.
Nitrogen vs Air
Some tyre shops promote nitrogen inflation as a premium service. Nitrogen molecules are larger than oxygen molecules, leading to slower pressure loss over time. Nitrogen is also moisture-free, reducing internal corrosion and potentially providing more stable pressure across temperature ranges.
However, the benefits for typical passenger vehicles are marginal. Regular air is 78% nitrogen already, and the performance difference is minimal for drivers who check pressure regularly. Nitrogen makes more sense for applications with infrequent access (spare tyres) or extreme conditions (racing, heavy commercial use).
If you choose nitrogen, remember that topping up with regular air when nitrogen isn't available is perfectly acceptable—far better than running under-inflated.
Tyre Pressure Monitoring Systems (TPMS)
Many modern vehicles include tyre pressure monitoring systems that alert drivers when pressure drops below a threshold. While TPMS provides valuable peace of mind, it's not a replacement for regular manual checks. These systems typically warn only when pressure is significantly low—often 25% or more below specification—by which point considerable harm may already be done.
Use TPMS as a backup alert system while maintaining your regular checking routine. If your TPMS light illuminates, address the issue promptly rather than driving until you find convenient time.
Establishing a Checking Routine
The key to consistent tyre pressure is building a sustainable habit. Some approaches that work well:
- Check pressure every fuel fill (or every second fill for frequent fillers)
- Set a calendar reminder for the first of each month
- Check before any journey over 200 kilometres
- Keep a small gauge in your glovebox for convenience
Whatever schedule you adopt, consistency matters more than frequency. A monthly check performed reliably is better than weekly intentions that slip into sporadic action.
Your tyres are the foundation of your vehicle's contact with the road. A few minutes invested in pressure maintenance pays dividends in safety, economy, and tyre longevity—a small effort for significant returns.