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I want to calculate the tyre pressure of a car from OBD parameters. I don't want to take TPMS or any custom PID for this. One of the indirect method is the calculate:

((w_LF + w_RR) - (w_RF + w_LR)) / ((w_LF+w_RR+w_RF+w_LR)/4)

where w_LF is the angular velocity of the left-front wheel. Now the problem I am facing is how to calculate w_LF, w_RR, w_LR, w_RF and how to find what is the actual angular velocity at that instant while driving.

I want to point that there is a reduction in tire pressure by this method

costrom
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Soumya Sen
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1 Answers1

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This approach is fundamentally flawed for a few reasons:

  • There's a circular definition here; to know angular speed you need to know wheel radius, but you're trying to infer the wheel radius from the angular speed.

  • I don't know of any OBD-II PID which will tell you wheel radius.

  • Even if such a PID exists, how will you cater for vehicles where a custom wheel size has been fitted?

  • For v = rω to work for each wheel, you need a measurement of speed for each wheel. This data might be available if the vehicle is fitted with ABS and has 4 wheel speed sensors. Don't assume that all vehicles are like this though; some vehicles rely on just a single speed sensor embedded in the transmission housing to measure vehicle speed.

  • The formula shown is an attempt to evaluate differences in angular speed that are normalized by the average of the four readings. It might be an acceptable qualitative check, but it wouldn't tell you which wheel is low on pressure.

Pᴀᴜʟsᴛᴇʀ2
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Zaid
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