Setting PM intervals that fit your fleet

Why a generic interval fails

Manufacturer intervals assume an average duty cycle that almost nobody actually runs. A highway tractor at steady load and a city unit doing forty stops a day wear out completely different things at completely different rates.

Set intervals too long and you pay in roadside failures, which cost several times what the same repair costs in a bay. Set them too short and you pay for oil, filters and bay time you did not need.

The A/B/C structure

Most fleets are best served by three nested service levels, each including everything from the level below it. The value is in the nesting: routine visits stay short, and the deeper inspections happen on a predictable cadence.

Aligning the C service with the annual inspection is the highest-value scheduling decision available to you. The teardown overlaps heavily, so you pay for one visit rather than two and the unit is off the road once.

Reading your own duty cycle

Before setting intervals, characterise how the trucks actually run. Four numbers get you most of the way there.

• Average kilometres per unit per month, and the spread between your highest and lowest unit.
• Engine hours per month, and the ratio of hours to kilometres — a high ratio means heavy idling.
• Stop frequency, which drives brake, clutch and aftertreatment wear far more than distance does.
• Load profile and terrain, which drive driveline and cooling system stress.

A fleet where the ratio of hours to kilometres is high is an urban fleet, whatever its odometers say. Those units need brake and aftertreatment attention sooner and oil changes tied to hours rather than distance.

Common adjustments worth making

A few patterns come up often enough to be worth naming, because each one has a specific fix.

• Short urban runs with regen problems. Aftertreatment attention moves into the B service rather than waiting for C.
• Heavy stop-and-go work. Brake measurement moves to every A, not every B — it is fast and it prevents lining jobs.
• High-idle vocational units. Oil intervals set on hours, and cooling system checks pulled forward.
• Seasonal fleets. Deeper services scheduled into the slow season, so downtime happens when the truck is not earning anyway.
• Wide mileage spread. Do not use one calendar interval for the whole fleet; group units by actual usage.

Making the schedule survive contact

The best schedule is one that gets followed. That means it has to be visible, and it has to be booked ahead rather than remembered.

• One calendar for the whole fleet, showing PM level, unit and sticker expiry together.
• Slots booked in advance for the next quarter, not called in the week they are due.
• Driver-reported defects folded into the next scheduled visit where they can safely wait.
• Measured values recorded at every B and C so wear trends are visible over time.
• Intervals reviewed annually against what actually failed in the previous year.

That last point is what separates a schedule from a system. If a component keeps failing between services, the interval is wrong — and the failure record is the evidence you need to change it.