Here's how ambient temperature and time affect a tyre's air pressure
Published On 06-Jun-2016
We have said many times that tyres are one of the most important yet neglected components of a vehicle. Imagine what happnes if the tyres do not have air inside them? The air pressure inside the tyres greatly affects how a vehicle goes down the road. In motorsports, you will often find drivers tweaking the air pressure in their race cars's tyres each time they go out on the track. They do this because finding the right pressure helps in finding a good chassis setup.
Whether you drive on a race track or on public roads, the laws of physics stays the same in both cases. This is why maintaining proper tyre air pressure should be an indispensable part of car maintenance. Many people think that if a tyre is losing air pressure then it is due to a puncture or valve leak. However, in reality, the air pressures can also drop over time and fluctuate due to changing ambient temperatures. Here's a lowdown on different factors that affects the air pressure inside tyres:
[caption id="attachment_1991" align="alignnone" width="450"] Ambient Temperature effect on Tyre Pressure[/caption]
Temperature Fluctuation- Air being a composition of various gases, expands when heated and contracts when cooled. The expanded air, in hot weather, exerts more pressure on the tyres from inside, hence increasing tyre air pressure.
In India, the effect of ambient temperature fluctuation on tyre air pressure is most evident in the northern region as both winters and the summers, the temperatures are extreme. In summers, the temperatures can reach up to 45 degree Celsius, while in winters, the temperatures can drop to 3 degree Celsius. Generally, for every 12 degree Celsius change in the ambient temperature, the tyre pressure changes by 2 per cent (up with higher temperatures and down with lower). Most of the car manufacturers recommend tyre air pressure in the range of 30-35 psi therefore, a change of 12 degree Celsius will change the tyre pressure by 1 psi. You can put together the rest of the equation yourself.
The tyre pressure of a typical passenger car can change by 4 psi between winters and summers. This is sufficient to alter the handling of a car and durability of tyres. Apart from the different seasons, the difference between day and night time temperatures also affects tyre air pressure. Moreover, the air inside the tyres gets heated due to tyre flexing during use. Tyre flexing under aggressive driving can have a far greater effect on the tyre air pressure as compared to the ambient temperature.
Mostly people drive their vehicles to nearby petrol station or tyre shop to get the tyre pressure adjusted. But, keep in mind the car manufacturers mentions the cold tyre pressures for the vehicles. Even driving for couple of minutes and then adjusting the air pressure can make the tyre pressure setting way off compared to what the manufacturer suggested. Considering how all these variables effect the tyre pressure, it is important to select optimal conditions to get the tyre air pressure checked and increased/decreased.
[caption id="attachment_1993" align="alignnone" width="650"] Oxygen molecules find it easier to Permeate Rubber wall[/caption]
Influence of Time- From the outside, a tyre looks like a solid structure of rubber, but actually it is strands of rubber stuck together by vulcanisation process. As a tyre rolls, these molecular strands of rubber stretch and return to their original state. There is constant air pressure inside the tyres trying to push out, and some of the air do manage to escape the tyre through the microscopic spaces between the rubber molecules.
To reduce the permeation of air from the tyres, pure nitrogen gas is highly effective. Air is a composition of 78 per cent Nitrogen, 21 per cent Oxygen and 1 per cent argon with traces of other gasses. Also, Nitrogen molecules are larger in size as compared to the Oxygen molecules therefore, it is difficult for nitrogen to permeate the rubber walls of tyres.
In order to maintain the tyres' air pressure, we should get them checked often. It is recommended that tyre air pressure should be at least adjusted once every month. However, the more often you can get it done, the better. This will also give you a chance to inspect the condition of the tyres as there could be a slow puncture due to a nail or even sidewall bubble that hints towards damaged internal structure.