# Measurement of tire pressure from pressure on ground

I am a B.Tech student and working on a project.I want to measure the tire air pressure (condition is I can't mount anything in the tire). I have to create a platform on which the vehicle will move and the data will be collected. For the same, I am using the force sensors. So, now I have the data: Force acting on ground and area of contact. But as it is said in (https://physics.stackexchange.com/a/119791/147435) pressure on the ground is slightly higher than the pressure inside the tire. But I am not able to measure the tire deformation force. Can you please suggest me any way available to measure them.

It would be a great help sir if you can spare some time for this.

Thank you, Ashwin Sundarka India

Call myself "Pigheaded Dutch Selfdeclared tirepressure specialist"nowadays. Story began when I got hold of the official European formula , and went running wiht it.

What I found out is that a normal car tyre AT 2.5 bar/36psi filled has aproximately 20% deflection of free flexible part of sidewall. This then gives 15% of the maximum load of the tire to be wore by the construction of the tire. An LT/C- tire with for instance AT 4.5 bar/65psi would then have at 20% deflection , about the same weight carried by the construction of tire, but because higher maximum load for same sise tire, this is a smaller percentage.

The rest is caried by the pressure X surface story.

You can determine the construction load ( as I babtised it) Lc, by letting all the air out of the tire when off the ground , so zero pressure in tire, then push it back on the scale giving it the same deflection , the this weight is the construction load at the given deflection.

but this only for laboratory purposes, you cant use this for individual cars .

The special energy saving tires , to my conclusion, have a smaller construction load at the same deflection, because of the less rigid material, especialy the sidewals. But have at same deflection a larger surface length on the ground, because the overgoing curve from unloaded radius to flat on the ground is less then a non energy saver with same sises and specifications.

The deflection so is an issue in this story, more deflection gives more construction load but also more heatproduction.

If its only to measure the pressure of tire a different way, you can use the way they measure Eye-pressure. For that they push against the thinnest part of the cornea, ans see what pressure is needed to flatten a sertain surfacesise.

For a tire you could press against the middle of sidewall, where it is the thinnest, and where the rigidity has the least influence. You can also put somekind of shissor shaped device wich pusches inner and outer sidewall at the same time.

In fact a perfection of pushing with your fingers at a bycicle tire to estimate if pumped up hard enaugh.