In recent decades, car manufacturers have started to include tire pressure monitoring systems in their cars. This means that these cars automatically indicate that at least one of the tires is subject to pressure issues. The official name of the system is Tire Pressure Monitoring System, abbreviated TPMS, and its purpose is to make drivers aware of the potential risks associated with tire misbalances. This system indicates an error on the dashboard screen not only when a tire is under-inflated, but also when it has too high pressure in it.
Symbolically, the indicator appears in a shape reminding of a cross-section that lights up in yellow and is accompanied by an exclamation mark. 1
How was it before the TPMS automatic system?
With the integration of this automatic system, drivers breathed a sigh of relief. The rate of road accidents caused by tire issues is very high. But unfortunately, this was not known some time ago. Respectively, the drivers used to check the tire pressure occasionally, not realizing that high or low pressure was a high-risk factor. In this context, the integration of the automatic TPMS system in vehicles brought a substantial reduction in road accidents.
Until the automation of this system, drivers had to manually check the pressure, basically "guessing" whether it was high or low. The most popular tool for pressure measuring was the tire gauge which was found in almost every garage.
With the increase in accidents due to incorrect pressure, road traffic regulatory bodies requested some changes. Following them, it was decided that most vehicles should be equipped with an automatic pressure monitoring system. Respectively, starting with 2007, drivers became more aware, and the number of accidents became substantially lower.
While the main purpose of the TPMS is the same for all cars, not all have the same principle of activity. Respectively, in this article, we will discuss the entire process of the TPMS system. At the same time, we will also cover the direct and indirect types of TPMS, which are the 2 basic types of TPMS mechanisms. Last but not least, we will compare them, highlighting their benefits and disadvantages. Let's begin then, shall we?
Indirect TPMS: What is it and how does it work?
The indirect TPMS system takes into account the wheel speed sensors. Based on these sensors, the computer system calculates the rotation speed of each wheel. Further on, the system compares this data with the speed data, as well as other indices. Following the calculations of the rotation speed of each tire, the internal technology assumes an average dimension of the tire. At the same time, the computer deduces if a wheel is spinning faster than it should. In this context, this means that the tire is inflated less than necessary and indicates the respective error on the panel.
What is important to understand is that the indirect pressure measurement system does not mean that the system measures the tire pressure itself. That is, the operating principle is not the same as that of measuring pressure with the help of a pressure gauge.
What this type of system does is calculate the rotation speed of each tire and overlay the data between the 4 wheels to detect that there is an imbalance between them that suggests certain pressure issues. 2
Pros and cons of an Indirect TPMS
Of course, like any other system, indirect TPMS has its advantages and disadvantages. It's good to know them because when you buy a car, they might influence your decision. Let's start with the "bad news" first.
Cons of the Indirect TPMS
- Indirect TPMS can cause inaccuracies when changing tires to something slightly larger or slightly smaller. They could indicate false data and you could visit the technical service center much more frequently and pointlessly;
- unevenly worn tires are a disaster for the indirect TPMS system. These tires can generate erroneous data in the system, which can increase the degree of risk. Sometimes the system can indicate the error when in fact the pressure is within the norm, or on the contrary, it can avoid indicating the error when there are pressure divergences;
- every time you inflate the tire according to the guidelines, you will have to reset the system;
- every time you rotate the tires, you have to reset the system.
That's it for the shortcomings. Let's move on to the advantageous aspects.
Pros of Indirect TPMS
- this system is usually more cost-effective and will help you save some money compared to its Direct TPMS counterpart;
- its setting and long-term maintenance are very intuitive and do not require great effort compared to its Direct counterpart;
- its installation is less hustle. 3
Direct TPMS: What is it and how does it work?
The main difference between Direct and Indirect TPMSs is that the Indirect one operates with data from the anti-lock brake system level. That is, in this system, some sensors inform the computer about the wheel revolution. In contrast, the Direct system relies on sensors within each tire and not those coming from the anti-lock brake system.
In addition to the fact that the sensors of the Direct system talk about pressure, they also inform about the temperature of the tires. These data are collected by the computer, then read, and interpreted. If the computer detects deviations in the tire pressure, it will notify you on the car's dashboard.
The transmission of information within the Direct TPMS system takes place wirelessly. In this context, manufacturers assign a unique serial number to each sensor. Consequently, the system perceives the error not at a general level, but at an individual level for each individual tire. At the same time, the fact that each sensor has its own mechanism and number makes it difficult to replace the TPMS system from one car to another. In this context, such procedures must necessarily be performed with the help of an expert in the field. Otherwise, the system could transmit erroneous data.
Unlike the Indirect TPMS, the Direct one comes with 2 types of sensors. These can be external and internal. The difference between them lies in their location. The external ones are found on the outside of the tire, while the internal ones are placed within it. 2.1
Cons of a Direct TPMS:
- expect a slightly higher price for this system compared to its indirect counterpart;
- resetting and resynchronizing requires more effort, even if the system seems quite simple;
- the system battery is very "capricious". If for some reason the battery runs out of service, it is most likely that you will replace the entire sensor and not just the battery;
- the sensors of the Direct TPMS system are much more sensitive. They can be easily damaged during their assembly or disassembly.
However, don't rush to draw hasty conclusions, because not everything is as bad as you might have imagined. For that, let's see the advantages of Direct TPMS.
Pros of Direct TPMS:
- this system indicates the pressure of each tire;
- it is much more accurate than Indirect TPMS because it is not based on tire rotations, but on pressure indicators directly from the tire;
- the synchronization and reset process after a possible tire rotation is not rocket science;
- even if the batteries are capricious and require the replacement of the entire sensor together with their damage, they serve up to 10 years. Respectively, it is unlikely to cause you head-bashing.
As you can see, both have both advantages and disadvantages. So it is somewhat complicated to say which TPMS system is better. What really matters is that both have the same purpose: to inform you about possible errors in tire pressure. And the rest, it's your job to take the car to the service and balance the pressure according to guidelines.
The essential reason why you have to react to the TPMS indicator is first of all your safety as a driver. So, don't neglect this marker and take immediate action. 4
To sum up...
I leave here a quick Q&A list regarding the two types of TPMS systems. These refer to the most frequently asked questions and might be helpful for you.
Which of the Direct and Indirect TPMS systems is better?
Both have advantages and disadvantages. It depends on your priority as a driver. If the priority is to save money, then the indirect TPMS will be more suitable. However, if your goal is increased accuracy, then experts suggest that Direct TPMS would be more appropriate. The explanation is that Direct TPMS is based on tire inflation level calculations. This calculation is more direct. In contrast, the Indirect TPMS shows data according to the calculations of the ABS sensors. Respectively, the calculation is a little more estimative and deductive.
External VS Internal TPMS: which is optimal?
As with the previous question, both types have pluses and minuses. But overall, experts recommend the internal option because it is less prone to theft. On the other hand, turns out that internal sensors are much more likely to get damaged during tire changes than external ones.
How can you reset the TPMS indicator on the dashboard?
Each car manufacturer installs an individual TPMS system. For this reason, there is no rule of thumb for all cars. The reset is not complicated, but it requires a bit of education. You will find the necessary instructions in the instruction book of your car, where you will find the exact steps depending on the specific model of the car.