The question of what is equal to 1 bar in kilograms arises for every motorist, when only a pressure gauge with one scale is at hand, and the instructions for the car indicate completely different figures. Confusion between technical atmospheres, bars and the usual "kilograms" per square centimeter can lead to the wrong pressure in the tires. This, in turn, affects fuel consumption, rubber wear and traffic safety.
For quick calculation, drivers often use a simplified rule: 1 bar is approximately equal to 1 atmosphere. or 1 kgf/cm2. However, with accurate adjustment of the wheels of a sports car or truck, such an error is unacceptable. The difference is small, but it exists and is about 2%.
In this article, we will analyze the physical essence of differences, give accurate formulas for recalculation and create a convenient table for the garage. You will understand why engineers use different measurement systems and how to convert values quickly without a calculator.
Physical Difference Between a Bar and a Kilogram
To understand, 1 bar is how many kilos.It is necessary to refer to the definitions of units of measurement. Bar is a non-systemic unit of pressure equal to 105 Pascal (Pa). It is widely used in meteorology and engineering, as it is close to normal atmospheric pressure.
At the same time, when we talk about the pressure in tires in “kilograms”, we mean kilogram-force per square centimeter (kgf / cm2). This pressure exerts a force of 1 kilogram per 1 cm2 area. Technically, this is called the technical atmosphere (at).
The exact mathematical ratio is as follows:
- 🔹 1 bar = 1.0197 kg/cm2
- 🔹 1 kg/cm2 = 0.9806 bar
As you can see from the figures, the difference between these values is less than 2%. That is why in everyday life, pumping the wheels of a passenger car, these values are neglected. However, in hydraulics or when working with high-precision equipment, such an error can be critical.
Use the 1-to-1 rule for a quick check of road pressure, but when preparing for track days or expeditions, use an accurate recalculation for perfect balance.
Exact formula for translation and calculation
If you need high accuracy, for example, when setting up slug-suspension or gauge gauge, an exact conversion factor should be used. The formula for converting bars into kilograms (kgf/cm2) looks like this:
P(kgs/cm2) = P(bar) × 1.0197
For the reverse translation, when you need to know the value in bars, knowing the pressure in the atmospheres, the formula changes:
P(bar) = P(kgs/cm2) × 0.9806
Let's take an example. For example, the manufacturer recommends a pressure of 2.2 bar. Translating this into "kilograms", we get: 2.2 × 1.0197 ≈ 2.24 kgf / cm2. If the instructions indicate 2.5 atm, then in bars it will be: 2.5 × 0.9806 ≈ 2.45 bar.
⚠️ Note: Do not confuse the technical atmosphere (atm) with the physical atmosphere (atm). The physical atmosphere is 101325 Pa, which is slightly more than 1 bar. For car tires, the technical atmosphere (kgf/cm2) is always used.
Tyre pressure translation table
For ease of use in garage conditions, we have prepared a summary table. It will help you quickly orientate if the scales on your device do not match the recommendations on the door rack of the car.
| Bars (bar) | CHS/CM2 (at) | Fiz. Atmospheres (atms) | PSI (pounds) |
|---|---|---|---|
| 1.0 | 1.02 | 0.99 | 14.5 |
| 1.5 | 1.53 | 1.48 | 21.7 |
| 2.0 | 2.04 | 1.97 | 29.0 |
| 2.5 | 2.55 | 2.47 | 36.3 |
| 3.0 | 3.06 | 2.96 | 43.5 |
The PSI column shows values in pounds per square inch. This measurement system is often found on American cars and imported tires. Knowing the basic ratio, you can easily convert any values.
Where did the PSI come from?
The unit of measurement of PSI (pounds per square inch) is widely used in the United States and the United Kingdom. 1 PSI is approximately 0.069 bar. To convert the PSI to bars, divide the value by 14.5.
Impact of pressure on safety and resource
The right tire pressure is not just a recommendation from environmentalists, but a safety issue. Insufficient pressure leads to overheating of the tire frame, especially at high speeds. Sidewall deformity when riding on flat wheels can cause cord stratification and sudden rupture.
On the other hand, over-pumped tires have a smaller spot of contact with the road. This impairs grip, especially on wet asphalt, and increases the braking distance. Comfort also suffers: the rigid suspension transmits all the blows to the body and suspension of the car.
The main consequences of improper pressure:
- 🔸 Reduction of the protector resource (wear of the central or edge part).
- 🔸 Increased fuel consumption due to increased rolling resistance.
- 🔸 Deterioration of controllability and exchange rate stability.
- 🔸 The risk of aquaplanning on a wet road.
Regular pressure checks, at least every two weeks, allow you to maintain the optimal characteristics of the car. Remember that the pressure is measured only on cold tires, that is, after a downtime of at least 2-3 hours or a journey of less than 2 km.
☑️ Pressure check
Measurement features on different types of cars
Owners of passenger cars are most often faced with the range of 2.0-2.5 bar. However, for SUVs, vans and trucks, the requirements may differ significantly. Here's the translation accuracy. 1 bar in kilograms It's becoming more important.
For example, for a passenger truck ("Gazelle" or "Sprinter"), the rear wheels often require a pressure of 3.5-4.5 atm. The error of 0.5 bar is already noticeable here. In such cases, it is better to use a digital pressure gauge with the ability to switch units of measurement.
When pumping wheels in the cold, temperature dependence should be taken into account. When the air temperature drops by 10 degrees Celsius, the pressure drops by about 0.2 bar. Therefore, in winter it is recommended to pump the tires slightly more than normal, but not exceeding the maximum value indicated on the sidewall.
⚠️ Warning: Never release pressure from hot tires immediately after a long trip. The readings will be overstated and you may lose your wheels, which is dangerous if you continue driving.
In winter, check the pressure more often, as temperature changes greatly affect the volume of air in the tires.
Choosing the right gauge
To accurately control the parameters of your car, you need a high-quality tool. Cheap mechanical pressure gauges often have a large margin of error, especially at the end of the scale. Electronic devices are usually more accurate, but require replacement batteries.
When choosing a device, pay attention to the range of measurements. For cars, 0-5 bar is enough, for freight cars, a scale of up to 10-12 bar will be required. The price of division is also important: optimally, if it is 0.05 or 0.1 units.
Popular types of pressure gauges:
- 🔹 Mechanical (shooting) - reliable, do not require power, but are afraid of blows.
- 🔹 Electronic - high accuracy, backlight, but depend on the charge.
- 🔹 Built-in compressors are convenient, but often have low accuracy and are calibrated for a specific hose.
Check the accuracy of the pressure gauge can be compared with the reference device at the gas station or in the tire assembly. If the discrepancy is large, the device is better to replace, since your safety depends on its readings.
How do you extend the life of a pressure gauge?
Keep the pressure gauge in a protective case, avoid falls and do not leave in direct sunlight or in the cold in the car. The mechanism is sensitive to sudden temperature changes.
Why is tire pressure measured in bars and not in Pascals?
Pascal is a very small unit of measurement. The tire pressure would be about 200,000 Pa. Operating with such large numbers is inconvenient, so bars (1 bar = 100,000 Pa) or atmospheres are used.
Can you pump nitrogen instead of air?
Nitrogen is less susceptible to volume change when heated and does not contain moisture, which prevents disk corrosion. However, for normal driving, the difference with normal air is minimal and noticeable only in extreme racing conditions.
How often should I check my blood pressure?
Recommended frequency - every two weeks or before each long trip. Also, checks are required in case of a sharp change in ambient temperature.
Does the load in the trunk affect the pressure?
The load itself does not change the pressure in the resting car, but when driving under load, the tires warm up more strongly, and the pressure increases more than usual. For full load, manufacturers often recommend increasing the pressure norm.