Nitrogen in tyres tested — with disappointing results
The debate around filling tyres with nitrogen instead of compressed air is fast and furious, but we noticed no difference during our testing.
Many garages and tyre retailers will encourage the use of nitrogen, even charging extra for it, touting benefits such as reduced wear, less heating, and even less pressure change due to heat.
MyBroadband filled up two tyres on one side of a car with nitrogen. We went through a few inflation and deflation cycles to eliminate most of the compressed air.
We fitted the tyres with the monitoring system we tested previously.
We then used the car to run errands for the day, with some spirited driving to try and heat the tyres as much as possible, while taking regular notes of the pressure and temperature reported by each sensor.
After compiling the data, we looked for any noticeable difference between the tyres on either side of the car.
The most significant difference was the heating and pressure changes between the front and rear tyres. The front tyres heated up substantially more, and their pressure increased consistently with that temperature.
This is due to the vehicle having a front biased all-wheel-drive system, and the steering also being done with the front wheels.
However, the temperatures and pressures between the two sides of the vehicle were never far apart.
| Nitrogen in tyres | ||||
|---|---|---|---|---|
| Tyre | Left Front | Right Front | Left Rear | Right Rear |
| Filled With | Air | Nitrogen | Air | Nitrogen |
| Fill Pressure | 2.3 bar | 2.3 bar | 2.3 bar | 2.3 bar |
| Minimum temperature | 26 °C | 27 °C | 23 °C | 23 °C |
| Minimum pressure | 2.3 bar | 2.2 bar | 2.3 bar | 2.3 bar |
| Average temperature | 37 °C | 40 °C | 31 °C | 31 °C |
| Average Pressure | 2.45 bar | 2.40 bar | 2.41 bar | 2.39 bar |
| Max temperature | 44 °C | 46 °C | 37 °C | 42 °C |
| Max Pressure | 2.6 bar | 2.5 bar | 2.5 bar | 2.5 bar |
Ultimately, the difference in average temperature between the two sides was only 1.1 degrees Celsius — which is about the same as the measurement resolution of the sensors.
This may seem significant, but the higher average temperature was recorded on the side where we filled the tyres with nitrogen, so this does not prove any benefit.
The average measured pressure on the two sides of the vehicle only differed by 0.036 bar, while the measurement resolution of the sensors was 0.1 bar, which means that the difference can be considered a part of the measurement error.
The pressures in the tyres also rose consistently with the temperature in each tyre.
This is expected from the ideal gas law, which states that the pressure of a gas is directly proportional to the temperature if the volume remains the same, regardless of the gas.
The pressures in each tyre varied by as much as 0.3 bar during normal driving — a more significant change than the difference between the air and nitrogen.
Another stated benefit is that nitrogen-filled tyres will lose less pressure over time compared to those filled with normal compressed air.
This is partly true, as nitrogen will leak through the rubber slower than the oxygen in the air.
However, air comprises 78% nitrogen, which means this leakage difference is minimal.
Rather than relying on the slightly slower loss of nitrogen, check and rectify tyre pressures regularly — with nitrogen or air.
While filling nitrogen may have some benefits when used for racing where tyres reach extreme temperatures, it is not noticeable during day-to-day driving.
If inflation with nitrogen is offered for free, there are no real downsides, but there is also no reason to go out of your way to fill your tyres with nitrogen for a normal passenger vehicle.
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