Rules for Tire Pressure Calibration (Summer and Winter)

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Given that the tires are our only contact patch to the road, it is wise to know how to properly calibrate them for any given season, temperature, road course.

Now in order to properly calibrate your tires (guidelines below) you'll need a few basic tools:

a digital or professional (w/ dial) tire pressure gauage.
a calculator
a thermometer (or meteomedia if parked outside)
a pen and paper
an air pump (wall plugged is fine).
recommended air pressure for light load (4 person) and in some cases season (BMW has pressures for summer and winter).

Given the importance of tires, I recommend you check the pressure once a week. It's a hassle I know, but for the 2 minutes it will take you to check and adjust pressure, it's worth it.

Next, check pressure and adjust when the tire is cold. According to the litterature, a cold tire is one that has not been driven in 4 hrs. I personally prefer overnight.

Now, the pressure that is indicated in the manual is calibrated at a certain temperature, which for some odd reason manufacturers refuse to divulge. However, seek and ye shall find that the OEM calibration temp is 21C.

On to the nitty gritty. Pressures are measured in psi (for the most of us) and temperature is measured in Kelvin.

1 Celsius = ? Kelvin
1 Celsius = 1 + 273.15K = 274.15K

25 C = 298.15K

-10C = 263.15K and so on.

I mention this because pressure calculations are ALWAYS done in Kelvin.

According to this formula. (this is high school math so no excuses to not be able to do it).

(P1/T1) = (P2/T2)

Where.....

P1 is the RECOMMENDED pressure in the book.
T1 is the CALIBRATION TEMPERATURE, so in the winter time: 263.15

T2 is the TEMPERATURE WHERE THE CAR IS STORED, outside, garage, etc.

P2 is the PRESSURE YOU WILL PUT IN

Alright, in case you're really bad in algebra:

(P1*T2)/T1 = P2

i.e. i am calibrating my front tires for -10C (since it's the winter time). I know that recommended pressure is 32psi, and that it is 15C in my garage. what Pressure do I need to put in my tires to have calibration for -10C?

1) convert to Kelvin

-10C = 273.15 - 10 = 263.15K

15C = 273.15 +15 = 288.15K

(32/263.15) = (P2)/288.15

(32/263.15)*288.15 = P2 = 35psi.

so by putting 35 psi in my front tires, i know that when it will be -10C outside they will be perfectly calibrated for that temperature.

Calibration is important because for ever 5-10C difference in temperature you lose 1psi of pressure.

I chose -10C as the calibration temperature for winter because i figured that it is the average cold temp outside. if the weather network says -20C for a given week, i'll calibrate in consequence.

Summer Time:


Calibrate for 21C sounds fair, since it is our ambient summer Temperature.

However, here are some bonuses for better handling.

once you have determined P2, add 2 psi to this value. This extra 2psi will cause a slight flattening out of the outside edge of the tire which will give you better grip in curves, and overall better grip in all conditions.

If you are going to track the car or will driving on a curve-rich road, like one that i have planned for this summer, then you add 4psi instead of 2psi.

adding 4psi is only for the duration of the event. while adding 2psi is throughout the summer.


Remeber now, rotate the tires every 5000km at the same time as an oil change, and check your tires once a week for gravel and other crap stuck in the sipes. Get rid of it because they are a cause for structural failure (premature).

Enjoy the info, and if you're not sure of how to calibrate pressures, just post and i'll do the math for you.