Pirelli commercial tires are now produced and marketed by Prometeon Tyre Group, which uses the Pirelli brand under license and publishes a detailed range book for trucks and buses. Most of that book is product data, but pages 62 to 67 contain a surprisingly good short course in inflation: load and speed tables, the EU tire label, an inflation pressure chapter and rules for storage. This article distils the inflation guidance into practical rules for a fleet, and shows how to connect it to the load index printed on every Pirelli sidewall. For the wider subject, see our master truck tire pressure chart by axle load.
Why inflation is the factor that matters most
Prometeon’s manual opens its inflation chapter with a simple physical statement: it is the compressed gas in the tire that supports the load. The rubber and steel are a container; the air carries the vehicle. That means two things. If pressure is too high, the casing is over-supported and stressed, and the contact patch becomes too small. If pressure is too low, the casing is under-supported, flexes more and generates excessive heat that can end in tire failure. The manual illustrates three conditions: over-inflation with a contact area that is too small, under-inflation with a contact area that is too large, and correct inflation with the intended footprint.
The footprint point is the one fleets overlook. Even wear is a function of contact pressure. A correctly inflated tire spreads load across the full tread width, so wear is uniform and the rubber is used up evenly. A tire that is over-inflated crowns, wearing the center ribs. One that is under-inflated wears its shoulders. Our guide to steer tire wear patterns shows what each looks like on a worn tire.
Pressure must follow the real axle load
The most useful sentence in the chapter is that inflation pressure must always depend upon the actual load per axle, to guarantee the proper tire flexing. Flexing during service is a function of the load supported and of the inflation pressure, and it is set in the design phase to optimize the tire. The manual adds that overload leads to effects similar to under-inflation. In other words, an overloaded tire at the correct pressure behaves as though it were under-inflated.
This is why a single “fleet pressure” for all axles is a poor policy. A tractor steer axle, a loaded drive axle and an empty trailer axle need different pressures. The correct process is: weigh the axle, find the tire’s load capacity from the load table, and choose the pressure that covers the load with a margin. Our existing guides on 11R22.5 pressure by axle load and 315/80R22.5 pressure show the process in US units.
Never bleed a hot tire
Prometeon singles out one habit as a cause of under-inflation: bleeding hot tires. All tires generate heat in service because the casing deflects. The air warms and, being confined, its pressure rises. That increase is normal and tires are designed to withstand it. If a driver lets air out to bring the hot reading back to the cold figure, the tire is now working at too great a deflection for its temperature, which generates more heat. The tire may reach the higher pressure again, but it will be hotter still.
The practical rule is the same one Bridgestone and Hankook give in their own books: measure cold, correct cold. Prometeon defines cold as measured after the vehicle has been standing for several hours. It also reminds fleets to keep valve caps fully screwed on and to check the spare wheel, which is often forgotten until the roadside.
How the load index links to inflation
Every tire carries a load index and speed symbol, such as 156/150 L. The first number is the single-fitment index and the second the dual-fitment index; the letter is the speed category. Pirelli’s range tables show these indexes next to the EU label grades. A few examples from the fuel-efficiency range:
| Size | Load index / speed | Alternative marking | EU label notes |
|---|---|---|---|
| 315/70R22.5 | 156/150 L | 154/150 M | Grades A and B, 67 dB |
| 315/80R22.5 | 158/150 L | 156/150 M | Grades A and B, 71 dB |
| 385/55R22.5 | 160 K | 158 L | Grades A and B, 71 dB |
| 385/65R22.5 | 164 K | 158 L (HL) | Grades A and B, 71 dB |
The two markings on 315/80R22.5 (158/150 L and 156/150 M) show how a tire’s rating depends on the speed it is used at. The same tire can carry a slightly lower load index when it is rated for a higher speed category (M instead of L), because speed adds heat. We cover that trade-off in our upcoming guide to how speed changes load capacity. The 385/65R22.5 HL at 164 is a high-load wide-base tire, rated for single fitment only. The Goodyear data book lists the same index for an equivalent size, which makes it a useful cross-check; see our Goodyear load and inflation table guide.
A weekly inflation routine for a Pirelli fleet
Prometeon’s manual includes a “pressure check” frequency table keyed to use: radius of activity, kilometers covered per month, and on/off-road use. The principle is that the more kilometers and the harder the duty, the more often tires should be checked. For a typical regional or long-haul fleet that means at least weekly and, for high-mileage vehicles, before each long trip. A short routine:
- Park the vehicle for several hours, or check before the first run of the day.
- Remove each valve cap, check the valve for dust or damage, and read the pressure with a calibrated gauge.
- Compare with the target for that axle load, not the sidewall maximum.
- Correct cold, and fit valve caps again.
- Check the spare, and any tire on a liftable axle that is not in contact with the road.
- Record the readings and flag any tire that loses more than 0.2 bar (about 3 psi) between checks for inspection.
Tire age and condition matter as much as pressure
The manual ends with a reminder that tires age even if they have not been used or have only been used occasionally. Cracking of the tread and sidewall rubber, sometimes with carcass deformation, is evidence of aging, and old or aged tires must be checked by a specialist before further use. Correct pressure cannot rescue a casing that has hardened. For storage, Prometeon recommends cool, dry, moderately ventilated rooms, away from direct sunlight, at ideally 5 to 25 degrees Celsius and not above 35. Our storage guide later in this series covers the stacking rules in detail.
How inflation affects your cost per kilometer
Every inflation problem listed above has a cost. Under-inflation drives rolling resistance and fuel use up, wears the shoulders, and raises casing temperature, which reduces retreadability. Over-inflation shortens tread life. Overload accelerates both. Fleets that track tire cost per kilometer usually find that fixing pressure compliance saves more than changing brands. See our total cost of ownership guide and the article on low rolling resistance tires for the numbers, and hot retreading for the casing value you protect.
Common mistakes with tire pressure charts
- Using the sidewall maximum as the working pressure.
- Setting pressure by position rather than by axle load.
- Bleeding air from hot tires to hit a cold target.
- Not checking spares or lift-axle tires.
- Ignoring tire age when pressure looks correct.
A quick fleet scenario
Consider a regional fleet running 315/80R22.5 tires on a mix of Pirelli and other brands. During an audit, technicians find that the steer tires on three trucks are 0.4 bar below target while the drive tires are 0.2 bar over. Under the Prometeon logic, the first group is under-supported and generating excess heat, while the second is over-supported with a smaller footprint. Neither is an emergency, but both erode tire life every day. The fix takes ten minutes per truck: check cold, correct each axle to its own load-based target, and write the new values on the vehicle. Repeat the audit in a month. If the same trucks drift again, look for a leaking valve core or a driver who bleeds hot tires. The principle is the same one stated in the manual: pressure must follow the actual load per axle, and it must be measured when the tire is cold.
FAQ
Does Prometeon use bar or psi?
Its range book is metric, so expect bar and kilograms. Convert 1 bar to 14.5 psi when comparing with US tables.
Is Pirelli the same as Prometeon?
Prometeon Tyre Group produces and sells Pirelli-branded industrial tires, including trucks and buses, under license. The manual identifies the logo and several product names as trademarks used under license.
How cold is cold?
Prometeon says to measure after the vehicle has stood for several hours. The outside temperature is not the criterion; the tire’s own heat is.
Key takeaways
Prometeon’s inflation guidance can be summarized in four rules: pressure follows axle load, measure cold, never bleed hot tires, and treat overload as under-inflation. Add tire age to the inspection and you cover the main causes of premature failure. Continue with our pressure management hub for the complete cluster.
