WHAT IS TPMS & HOW DOES IT WORK

The purpose of the tyre pressure monitoring system (TPMS) in your vehicle is to

warn you that at least one or more tyres are significantly under-inflated, possibly

creating unsafe driving conditions. The TPMS low tyre pressure indicator is a yellow

symbol that illuminates on the dashboard instrument panel in the shape of a tyre

cross-section (that resembles a horseshoe) with an exclamation point.

That indicator light in your vehicle has a history. It’s a history rooted in years of

uncertainty about proper tyre pressure and many serious car accidents that might

have been avoided had drivers known their air pressure was low. Even now, it’s

estimated that a substantial number of vehicles hit the road each day with

underinflated tyres. However, proper tyre maintenance with the aid of a TPMS can

and does help prevent many serious accidents.

Before this indicator light became commonplace, knowing whether your air pressure

had reached unsafe levels meant getting out, crouching down, and using a tyre

gauge. With few exceptions, this was the only pressure-checking tool ordinary

consumers had at their disposal.

Then, in response to a surge in accidents due to underinflated tyres, the US

government passed the Transportation Recall Enhancement, Accountability, and

Documentation (TREAD) Act. One of the outcomes of this legislation is that most

vehicles sold in the United States since 2007 include a tyre pressure monitoring

system of some kind.

Not every TPMS works the same way. The illumination of the low tyre pressure

indicator represents the final step in the process of either an indirect TPMS or a

direct TPMS.

INDIRECT TPMS: WHAT IS INDIRECT TPMS & HOW DOES IT WORK?

An indirect TPMS typically relies on wheel speed sensors that the anti-lock brake

system uses. These sensors measure the rate of revolution each wheel is making and

can be used by on-board computer systems to compare with each other and to other

vehicle operation data such as speed.

Based on the rate of revolution of each wheel, the computer can interpret the relative

size of the tyres on your vehicle. When a wheel starts spinning faster than expected,

the computer calculates that the tyre is underinflated and alert the driver accordingly.

So, an indirect tyre pressure monitoring system doesn’t actually measure tyre

pressure. It’s not electronically processing the same kind of measurement you might

see with a tyre gauge. Instead, an indirect tyre pressure monitor simply measures

how fast your tyres are rotating and sends signals to the computer that will actuate

the indicator light when something in the rotation seems amiss.

ADVANTAGES OF INDIRECT TPMS

Relatively inexpensive compared to a direct TPMS

Requires less programming/maintenance over the years than a direct TPMS

Less overall installation maintenance than its direct counterpart

DISADVANTAGES OF INDIRECT TPMS May become inaccurate if you purchase a bigger or smaller tyre

May be unreliable when tyres are unevenly worn

Must be reset after properly inflating every tyre

Must be reset after routine tyre rotation

DIRECT TPMS: WHAT IS DIRECT TPMS & HOW DOES IT WORK?

Direct TPMS uses pressure monitoring sensors within each tyre that monitor specific

pressure levels – not just wheel revolution data from the anti-lock brake system.

Sensors in a direct TPMS may even provide tyre temperature readings. The direct

tyre pressure monitoring system sends all of this data to a centralized control module

where it’s analyzed, interpreted, and, if tyre pressure is lower than it should be,

transmitted directly to your dashboard where the indicator light illuminates. A direct

tyre pressure monitor usually sends all of this data wirelessly. Each sensor has a

unique serial number. This is how the system not only distinguishes between itself

and systems on other vehicles, but also among pressure readings for each individual

tyre.

Many manufacturers use proprietary technology for these highly specialized systems,

so replacing a TPMS in a way that’s consistent and compatible with your vehicle

will require an experienced, knowledgeable technician.

ADVANTAGES OF DIRECT TPMS

Deliver actual tyre pressure readings from inside the tyre

Not prone to inaccuracies because of tyre rotations or tyre replacements

Simple resynchronization after tyre rotation or tyre replacements

Batteries inside the sensors usually last for about a decade.

May be included in a vehicle’s spare tyre

DISADVANTAGES OF DIRECT TPMS More expensive overall than an indirect TPMS

Though simple, resynchronization may require costly tools.

Battery rarely serviceable; if the battery is drained, the whole sensor must be changed.

Proprietary systems make installation, service, and replacement confusing for consumers and

auto shops.

Sensors are susceptible to damage during mounting/demounting

TYRE PRESSURE AND SAFETY

Although the methods may be different, both systems serve the same purpose and

activate the same indicator light. Even though a TPMS can deliver accurate alerts

when properly maintained, it’s not a replacement for manual air pressure checks,

consider it just another item in your car maintenance toolbox.

Source: http://www.bridgestonetyre.com/

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