Tyre Pressure Monitoring Systems

I have been using an aftermarket Tyre Pressure Monitoring System (TPMS) on one of my cars. There have been times when I feel that one of the tyres feels a little flat and I bought the system to help me see what was going on.

Tyres can be affected by many things – the age and usage are obvious ones, however road conditions and the number of potholes and bumps that the tyre has to deal with can also affect the pressure in the tyre. Most people would consider a nail or puncture as the only way that a tyre could deflate, however general driving will also affect the tyre’s ability to perform. That is why I am keen to keep an eye on them as when you think about it – there are only four small patches of rubber keeping you on the black stuff.

In the US, the TREAD (Transportation Recall Enhancement, Accountability and Documentation) Act was implemented in 2000 to help with consumer safety and the heart of the Act was an early warning system for tyres thanks in part to the infamous Firestone/Ford Explorer issue where the tyres fitted to that model would have an unscheduled disassembly at high speeds. Nearly 300 deaths occurred in the Explorer, putting a dent in the reputations of both the car and tyre manufacturer involved. 23 million tyres had to be replaced under the recall. What came out of that was the legislation that meant that all new cars sold would have to have a TPMS fitted as the early warning system. Whether the systems actually save lives is another topic, however all cars in the US, Europe and parts of Asia must now have the equipment fitted as standard.

Typical systems measure the pressure and temperature of each tyre and can either be “direct” or “indirect”:

Direct Systems
These systems use sensors inside or mounted to each wheel and relay data back to the main control system for a graphical display in the vehicle. The sensors read the actual pressure and temperature of the tyre and the control unit has the ranges required for the vehicle to report whether a tyre is too hot or leaking for example. The sensors are designed to only send data when the wheel is moving to keep power usage as low as possible. These are the most common now in high end vehicles.

Indirect Systems
This type of system was really the first common iteration and measured speeds and other data from outside the wheel and tyre – from existing ABS or stability control systems. The data was then collected and analysed to give an approximate view of the tyre pressures. This was still OK to provide the driver an assessment of whether the tyre was in the boundaries that the manufacturer defined. Some of the larger European vehicle manufacturers still fit this type of system to their cars to conform to legislation. I think that is probably a cheap way of meeting expectations rather than fitting a proper direct system.

Aftermarket Solution: SteelMate TPMS
As my cars were both manufactured in 2013, they do not have a TPMS as standard – the European law came into effect a year later.

I bought the system from Davies Craig in Melbourne and is a simple but very accurate set of sensors. I have tested the pressure readings against a known digital meter that I know is accurate! Fundamentally the system consists of 4 battery powered sensors that are marked for each wheel and screw on to the top of the valve stem. These units also have a weather shield and locking nut.

In the car, a transceiver is plugged into the old cigarette lighter/power socket. A green glow tells you all tyres are within the prescribed range of pressure. Should a tyre get too hot or above/below a set range, then the transceiver turns orange and starts beeping.

The transceiver then connects via Bluetooth to a smart phone to provide a display and to set the preferred pressures. The display will also change colour when a tyre moves outside the preset boundaries and the corner affected will have a red background.

I put them on the car I use for track days and found that they worked OK to see the pressures and temperatures after each session however, two things got in the way. The first was that I couldn’t fix the phone in the car to be securely mounted. Normal car phone mounts don’t lock the phone in place, so there is a danger that the phone and mount could part company and move around the cabin. Secondly, with the locking nuts in place, it is a pain to remove the valve sensors to adjust the pressures.

After an afternoon at the track this week, I have decided to put the system onto my main road car as it probably will be more useful there. For track use, I will go back to the tried and trusted way of testing and adjusting the pressures between sessions – manually and with a quicker turn around.