Tyre Pressure and Fuel: What Every Fleet Manager Should Know

Diesel is your biggest variable operating cost. Tyres are your second biggest. Most fleet managers treat them as separate problems. They're not.

Tyre pressure directly affects rolling resistance — the force your engine has to overcome to keep the truck moving. Get it wrong in either direction and you're burning more fuel, wearing out tyres faster, and increasing your blowout risk. Get it right and you can cut tyre-related costs significantly without spending a cent on new equipment.

Rolling resistance accounts for roughly 15–20% of total fuel consumption in a long-haul truck. Of that, tyre pressure is one of the most controllable variables.

The physics is straightforward: an under-inflated tyre flexes more with each rotation. That flexing generates heat and requires more energy — energy that comes from your fuel tank. An over-inflated tyre has less contact with the road, which reduces traction and causes accelerated centre-tread wear, but doesn't save as much fuel as you might expect because it increases road shock transmitted to the vehicle.

The sweet spot is the manufacturer's recommended cold inflation pressure for your load.

A tyre running at 20% below its rated pressure (say, 80 psi instead of 100 psi) will:

• Increase fuel consumption by 1–2% per tyre on that axle
• Reduce tyre life by up to 25% due to shoulder wear and heat buildup
• Increase blowout risk significantly, especially at highway speeds in summer heat

On a fleet of 20 trucks, each running four drive tyres at 20% under-inflation, that 1–2% fuel penalty adds up to thousands of rands per month in wasted diesel — before you account for the accelerated tyre replacement costs.

These are general guidelines. Always check your vehicle's tyre placard (usually on the door jamb or fuel cap) for the manufacturer's specific recommendation for your load rating.

Steer axle (single tyres):

• Light rigid (GVM under 8 tonnes): 80–90 psi
• Medium rigid (8–16 tonnes): 95–110 psi
• Heavy rigid / semi-truck: 100–120 psi

Drive axle (dual tyres):

• Typically 5–10 psi lower than steer axle
• Both inner and outer tyres must be checked separately
• Dual tyres must be within 5 psi of each other — mismatched pressure causes the higher-pressure tyre to carry more load

Trailer axle:

• Match drive axle specification unless the trailer placard specifies otherwise
• Refrigerated trailers often run slightly higher pressure due to load distribution

Tyre pressure increases with temperature — approximately 1 psi for every 10°C rise in ambient temperature, plus additional pressure from heat generated during driving.

In South Africa's summer, this matters. A tyre inflated to 100 psi at 7am in Johannesburg may read 108–112 psi after two hours on the N1 in 35°C heat. This is normal and expected — do not bleed pressure from a hot tyre.

Always check and set pressure when tyres are cold (before the vehicle has moved more than 2km, or after it has been stationary for at least three hours).

The most effective fleets check tyre pressure:

1. Before every departure — driver responsibility, part of the pre-trip inspection
2. Weekly — workshop check with a calibrated gauge, not just a visual
3. After any long stop — before resuming a journey after an overnight break

Invest in quality pressure gauges and calibrate them regularly. A gauge that reads 5 psi high across the fleet is costing you money in over-inflation wear without you knowing it.

For high-value fleets or long-haul operations, consider a TPMS. These systems monitor pressure and temperature in real time and alert the driver to deviations before they become failures.

The ROI on TPMS is well-documented: reduced blowouts, lower fuel costs, and extended tyre life typically pay back the system cost within 12–18 months on a fleet of 10 or more vehicles.

If you're finding that tyres consistently lose pressure between checks, the issue isn't your inflation routine — it's a leak. Common sources:

• Valve stem leaks — the most common cause of slow pressure loss
• Bead leaks — where the tyre meets the rim, often caused by corrosion or impact damage
• Punctures — not always obvious, especially slow leaks from small objects
• Rim damage — a bent or cracked rim will not hold a seal

If a tyre is losing more than 5 psi per week, it needs to be inspected by a professional. Call us on +27 079 294 4277 and we'll come to you.

Check pressure cold. Use the placard specification for your load. Check every tyre, including the inner duals. Do it before every trip. Record it.

That's it. The fleet managers who do this consistently spend less on tyres and less on diesel. The ones who don't call us at 2am on the N3.