LARS-m | mobile wheel contact force measuring system


The LARS-m wheel contact force measuring system (formerly wheel load or axle weigher) is a mobile and flexible measuring system used to calculate wheel contact forces on rail vehicles. By virtue of its special design, it can be used with almost all commonly used rail profiles and track gauges. It is extremely compact in build, thereby reducing set-up time to a minimum. Used in conjunction with the MARK data analysis software, it is an impressive high-precision instrument with the versatility to perform its measurements in various installation situations.

The new LARS-m wheel contact force measuring system was developed as a stand-alone system in response to market demands. It is designed in such a way that it can be used as both a stationary and a mobile measuring system. It takes just a few minutes to install and remove. No special tools are required for this purpose.

There are measuring amplifiers located downstream of the wheel load measuring systems. These are connected as CAN bus systems and their job is to supply the measuring bridges with a specific input voltage and to digitise the output signals received from the measuring bridges.

They communicate with a central measurement data controller, the WMV. The WMV has a TFT panel to display the readings therefore measurements can also be taken without the computer. The touch-screen input facility is also the means whereby commands can be sent to the measuring amplifiers.

The wheel-rail contact force is tested on the wheel flange. This means that faults related to the running surface are ruled out from the outset, such as faulty grip due to conical wheels and effects caused by the linear expansion of the rail.

The LARS-m wheel contact force measuring unit is supplied ready calibrated, obviating the need for any time-consuming and expensive adjustment on site. This calibration is undertaken by an independent accredited body in conformity with DIN 7500-1. This body is in turn accredited by the German national accreditation body (Deutsche Akkreditierungsstelle GmbH (DAkkS)) as conforming to DIN EN ISO/IEC 17025.

Measurement of a vehicle with two twin-axle bogies in bogie order 🔍
Stress test rig with eight measuring axes, consisting of LARS-m LT (in the foreground) combined with LARS-m 🔍
Stress test rig with four measuring axes for single-step measurements on four-axle vehicles 🔍
Stress test rig with six measuring axes 🔍
Stress test rig with 12 measuring axes for single-step measurements of entire trains 🔍

The LARS-m weighing system consists of a robust steel construction and inner tensioning element with locknuts. These are used to fasten the measuring system to the inside of the rails, ensuring that it stays securely in place, even over relatively long periods of time.

The height of the wheel flanges can be adjusted with shim plates without the need to remove the weighing system. The individual measuring points can therefore be adjusted to the same height as each other so there is no need for a zero-level track when measuring all the wheels on a vehicle at the same time. Consequently, with the help of the LARS-m measuring system, the user can actually set the measuring points to the required height tolerances (according to the measuring track quality) during the measurement process.

The weighing system is "deactivated" when the wear cover above the measuring bridge is removed and the wheel flange is no longer lifted out. Vehicles can run over it at relatively high speeds in this state.

The wheel need not be positioned in the middle of the measuring system in order to measure the wheel contact forces. The section in which the wheel can be positioned can be up to 350 mm, duly observing the required accuracy of ±0.5%. The general working section of measurements is 425 mm.

Special LARS-m LT variant



The LARS-m LT wheel contact force measuring system is a special variant of the standard LARS-m system and is used wherever the tare weight of the measuring system plays a decisive role.

Like the LARS-m system, the lighter LARS-m LT system consists of three components which can simply be connected together to form a measuring axis. The heaviest single part weighs just 35 kg. 

Despite the weight reduction, there is no change in the performance of the LARS-m in that high levels of reliability and accuracy are still guaranteed. The downstream electronic measuring equipment with the WMV measurement data controller is identical therefore both models can simply be connected together.

In addition to the individual wheel loads, it is also possible to calculate the respective axle loads and the gross weight of the vehicle. It is possible to connect two, three, four or more systems together to end up with a stress test rig to measure all the wheel forces of a complete bogie, vehicle or even an entire train. The measuring process on vehicles or whole trains therefore consists of just one step.

In the event of malfunction, it is possible, due to the modular design and the digitisation of the sensor blocks, to replace a defective sensor block with one that is working so that the measuring process can be continued without any major delays.

There is the option of linking the MARK data software module to the measuring systems. It conforms to DIN EN 15654, DIN 27201 and UIC V 660.

WMV measurement data controller

The WMV measurement data controller is supplied with the product and is the link between the sensors and the measuring software. It receives the digitised sensor data and displays them on a logical user interface. It is also possible to execute certain commands via its touch screen – such as resetting the sensors to zero.

The user can therefore carry out wheel contact force measurements without the need for a computer. If, for example, the measuring computer is out of order, the measurement can be continued immediately. At the same time, the WMV sends the data it has received to the measuring computer where they are processed by the database software MARK data.

  LARS-m features

  • High-precision mobile system for the measurement of wheel contact forces in  conformity with DIN EN 15654, DIN 27201, DIN EN 50215, EN 14363 and UIC V660

  • Extremely flexible system which can be quickly adapted at any time to different installation locations and to axle and bogie centre distances

  • Shim plates for establishment of own height reference (measuring track quality)

  • Measurements are taken on the outside diameter of the flange, thereby suppressing lateral forces which can affect the result

  • Measurements not affected by transverse offset of wheels

  • Facility for "deactivation" of the measuring system so that it can remain in the track when not in use

  • Compatible with all commonly used rail profiles and track gauges, including narrow gauge and broad gauge

  • Sufficiently versatile for use in different installation situations without the need for building work, e.g. inspection pits, elevated sidings, level concrete areas or other railway track systems

  • Patented force transmission process, preventing any potential distortion of the measurements by restraining forces

  • Minimal set-up time (a few minutes) requiring no special tools

  • Expandable and upgradeable at will thanks to modular design with digital connection via CAN bus and simple replacement of sensor blocks in case of defects

  • Interactive digital WMV measurement data controller

  • Optional MARK data software module conforming to DIN EN 15654, DIN EN 27201, EN 14363 and UIC V 660

  • Supplied as a calibrated and accredited measuring system approved as conforming to DIN 7500-1

  • Measuring accuracy exceeding the regulation ±0.5% laid down in DIN 27201 (±0.2% on request)

  • Also available in the LARS-m LT extra lightweight version

Technical specifications


Rail profile

Virtually all standard profiles

Track gauge

All standard track gauges, including narrow gauge and broad gauge

Sensor protection rating

IP 67

Sensor storage temperature range

-40 °C bis +85 °C

Nominal sensor temperature range

-10 °C bis +60 °C

Max. load / force per measuring point

Up to 15,000 kg / 150 kN

Above 15,000 kg / 150 kN on request

Min. load / force per measuring point

10% of measuring load / measuring force

Lower on request


2 kg / 0.02 kN

More on request

Measuring equipment class

0.5 under DIN 7500-1

0.2 on request

Measuring section in compliance with measuring equipment class 0.5

Up to 350 mm

Longer on request

General working measuring section

425 mm

Power supply

230 V / 50/60 Hz

Other supply voltages on request

Weight of heaviest single part LARS-m: 55 kg

LARS-m LT: 35 kg

Data transfer

Digital data bus




MARK data