Straddle Carrier TPMS: Eight or Sixteen Wheels Under Load

It is not a truck with a tall body

A straddle carrier drives over a container, picks it up inside its own portal frame, and

carries it with the load hanging between the legs. That geometry changes what tire pressure

means. On a truck, pressure is mostly about tire life and fuel. On a straddle carrier the

pressure changes:

• Portal clearance. The frame height above the ground is set by the tyres. A soft tyre

lowers one corner, and the clearance the driver relies on when straddling a stack is no

longer what the drawing says.

• Wheel load distribution. Four or eight wheels per side carry a load that includes the

container and the machine. A pressure split moves load onto neighbours that were not

designed for it.

• Tracking in a narrow lane. These machines work in aisles with very little margin. A soft

tyre makes the machine pull, and the driver corrects all shift.

How many positions, and where they are

Typical straddle carriers run eight wheels (four per side); larger terminal machines can

run sixteen. Each side is a separate load path, so the wheel map has to be written by

side and by position along that side, not by "front left" — the machine moves in both

directions all day and has no meaningful front.

That is the same rule we apply to RTGs: name the mapping geometrically, keep the same

names on the display, in the register map and in the maintenance record. A wheel map that

changes its naming between shifts is worse than no map.

Where the receiver goes

Most straddle carriers have a 24 V electrical cabinet and a controller network. The receiver

mounts in the cabinet, takes DC 10–30 V, and puts the data on **CAN 2.0B (11-bit or

29-bit extended frames)**, RS485, RS232, Modbus RTU, PROFINET or UART. One receiver covers

up to 256 wheel positions, so even a 16-wheel machine uses a fraction of that capacity —

the design question is radio coverage around a steel portal, not capacity.

Two practical points from port work:

1. Antenna and repeater placement is the whole job. The portal is a shield. On larger

machines a repeater inside the frame is often needed; on smaller ones it is not.

2. Alarm ownership has to be decided in writing. The driver needs a fast leak now, on the

machine; the terminal planner needs trend data. Usually that means a local alarm plus

telemetry to the terminal system, not one screen trying to do both.

What to ask before buying

• Which wheels, and what does the supplier call each one? (Ask for a filled wheel map, not a

blank template.)

• Does the receiver support the protocol the terminal controller already speaks, and is the

point table documented?

• What happens when a sensor is lost — is there a distinct status bit, or does the value just

freeze?

• What is the IP rating of sensor, receiver and display separately, and what is the wash-down

procedure?

Honest limits

A TPMS tells you pressure and temperature per wheel. It does not tell you wheel load, it does

not do stability calculation, and it does not replace the inspection the driver does before a

shift. What it changes is that the pressure part of that inspection becomes recorded data

instead of a memory.

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