Tachograph calibration: what every HGV operator needs to know

A tachograph is only as useful as its accuracy. If the unit isn't calibrated correctly, the speed and distance data it records is unreliable — and if DVSA discover that during a roadside check or depot inspection, you have a problem. Here's a straightforward guide to what calibration involves and when it's required.

What calibration actually checks

Calibration is the process of verifying that a tachograph accurately records vehicle speed, distance travelled and driving time. During calibration, a technician at an approved centre checks the unit against the vehicle's actual tyre size and confirms the parameters — the w-factor and k-factor — are correctly programmed.

If those factors are wrong, the tachograph could be recording distances shorter or longer than the vehicle is actually travelling. That affects everything from driver hours analysis to fuel economy monitoring.

When calibration is legally required

Under UK regulations, every tachograph must be calibrated at an approved tachograph centre at least every two years. You also need a new calibration after any of the following:

• A tyre size change — even a different brand with a slightly different rolling circumference

• A tachograph repair or unit replacement

• A change to the vehicle's final drive ratio

• A speed sensor repair or replacement

• Any accident that may have affected the tachograph's accuracy

This catches more operators than you might expect. A tyre change without recalibration is one of the most common oversights, particularly on vehicles where tyres are swapped between axles or replaced with a different specification.

How to check when yours was last calibrated

There should be a calibration plaque in the vehicle cab, usually near the tachograph unit or on the windscreen. It shows the date of the last calibration, the approved centre that carried it out, and the vehicle's recorded tyre size at the time.

If the plaque is missing, damaged or out of date, that's an immediate action point. DVSA roadside inspectors check for it. A missing or expired plaque during a roadside encounter is likely to result in a prohibition notice.

Digital vs analogue tachographs

Most vehicles registered after 2006 are fitted with digital tachographs, which store data electronically and require a driver card to operate. Older vehicles may still have analogue units that record on paper charts. Both types require two-yearly calibration at an approved centre.

Smart tachographs — the latest generation fitted to newer vehicles — also require calibration and have additional requirements around remote communication features. If you have newer vehicles in your fleet, check the specific calibration requirements for your unit type.

Who can calibrate a tachograph?

Calibration must be carried out by a DVSA-approved tachograph centre. It cannot be done by a general workshop or by the operator themselves. The approved centre issues a calibration certificate, which should be kept with the vehicle's maintenance records.

DCVS is an approved tachograph centre in Brigg. We calibrate digital and analogue tachographs and carry out tachograph repairs where faults develop. We cover operators across Brigg, Scunthorpe, Gainsborough and North Lincolnshire.

If you'd like to book your vehicle in, call us on 01652 656885 or visit us at Island Carr Industrial Estate, Brigg, DN20 8PD. We're open Monday to Friday from 6am to 6pm and Saturday from 6am to 1pm

What is a PMI inspection — and how often does your HGV need one?

If you hold a goods vehicle operator licence, planned maintenance inspections are not optional. They're a legal obligation, and the way DVSA judges whether you're running a safe and compliant operation. Yet for many owner-drivers — especially those new to holding their own licence — the detail of what's required isn't always clear.

Here's what you need to know.

What PMI stands for

PMI stands for planned maintenance inspection. It's a documented safety check carried out on every vehicle and trailer in your fleet at regular, pre-agreed intervals. The 'planned' part matters — DVSA expects your maintenance to be scheduled and recorded, not reactive.

When you applied for your operator licence, you declared how often you'd have vehicles inspected. That declaration is legally binding. If you said every 6 weeks, every 6 weeks is what DVSA expects to see evidence of.

What a PMI covers

A PMI is a thorough safety check of the whole vehicle, typically including:

• Brake performance across all axles

• Tyre condition, tread depth and inflation pressure

• Steering and suspension components

• All lights, reflectors and electrical systems

• Bodywork, chassis and load security points

• Exhaust and emissions

• Coupling gear (for artics and trailers)

Every inspection must be recorded on a vehicle inspection report. Any defects found must be noted, categorised as immediate or advisory, and signed off once repaired. Those records need to be kept for a minimum of 15 months.

How often do you need one?

The frequency is set by your licence maintenance declaration and depends on the type of work your vehicles do. Common intervals are 6, 8, 10 or 13 weeks. Vehicles doing intensive work — multiple shifts, rough terrain, heavy loads — typically need more frequent inspections than lighter-duty operations.

If you're not sure what your declaration says, check your licence documentation or call your traffic commissioner's office.

What happens if you miss one?

Missing a PMI, or failing to keep the records, is one of the fastest ways to damage your operator licence. DVSA roadside encounters, operator compliance risk score checks, and public inquiries all look at maintenance records. Gaps in the paperwork — even for vehicles that were actually well maintained — can result in licence curtailment or revocation.

It's also worth knowing that a vehicle with an out-of-date PMI is more likely to carry a defect into an MOT or a roadside check. The inspection process exists because it catches things before they become prohibitions.

Getting your PMIs done properly

Your PMIs must be carried out by someone competent to do them — either a qualified in-house fitter or an approved external workshop. The inspection report must be signed by the person who carried it out.

At DCVS, we carry out PMI inspections for HGVs and trailers at our workshop in Brigg, covering operators across North Lincolnshire. We issue a full inspection report for every vehicle and can retain copies as part of your maintenance record if that's helpful.

If you'd like to book your vehicle in, call us on 01652 656885 or visit us at Island Carr Industrial Estate, Brigg, DN20 8PD. We're open Monday to Friday from 6am to 6pm and Saturday from 6am to 1pm.