He is not normally present in air
Sure it is. Just in VERY tiny quantities, in the PPB range. A sniffer detects in the PPM range.
wvmarle:
Take a tire, inflate it, measure the diameter. The exact brand and type of tire will matter.
Of course the tire gets bigger when inflated more but I don't think it's much. What will change more is how deep the weight of the vehicle compresses the tire.
ian332isport:
Tyres filled with Nitrogen are also less prone to pressure changes due to temperature.Ian.
TomGeorge:
Hi,
Because not all tyres are created equal would this sound plausible.You have a test vehicle, fitted with GPS.
For different pressures and temperatures you do runs in the car and compare car speedometer and GPS speed.
A smart bloke, Newton I believe, the apple and gravity character, many many years ago invented a thing called calculus that would help calculate the expanded wheel diameter.
If you have a chassis dyno or rolling road, then the difference between speedometer and road roller speed.
Just a thought.. Tom....
Thanks all for replying to this post. What I concluded is:
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Test test test and more test. Without testing I now know it is almost impossible to get the the most precise values to get the most realistic values from RPM sensor(Hall effect).
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It is possible that I might try with filling tires with Nitrogen.
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For testing I might use a GPS to compare speed values between RPM sensor and GPS. Also monitoring at the same time the pressure (I have to add the new sensor) and the temperature. I think that could help.
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I can contact the company tires provider, to know more information about how the pressure changes the size of the wheel. That could help too.
Thanks everyone, I'll keep trying hard on this, I'll keep you updated.
Regards.
Antomabu:
Thanks everyone, I'll keep trying hard on this, I'll keep you updated.
Those are not the messages I would take from this Thread. But I acknowledge that I have a vested interest 
Of course, testing can't do any harm.
...R
PV = MRT
Don't think so.
You mean PV = nRT whe n is the number of moles and R the universal gas constant.
Stuff is more permeable than you think. I did a design job a while back which looked at the concentration of hydrogen on the OUTSIDE of a 1 inch thick steel pipe carrying crude oil to estimate the internal corrosion rate.
It's measurable!
And the gadget is in production now ( Made by Ion Science, Fowlmere, England)
Allan
I would suggest doing an experiment comparing speed/distance with tires at various pressures and GPS.
allanhurst:
You mean PV = nRT whe n is the number of moles and R the universal gas constant.
I can't find immediately find it in my books so I am prepared to give the point to you in the interests of global harmony. I have a feeling that M is just a special case of n. It's a long time since I was familiar with that stuff.
However, whether n or M it won't affect the point I was making as that is not variable in the particular calculation.
...R
Measuring tires to that level of precision is useless outside of a lab and would be impossible to maintain in the real world. (tire wear, new tires etc.)
Calibration is best done using a GPS so you are on the right track there. this is how commercial aftermarket speedometers are calibrated. (dakota digital et al ). Before GPS we had to make measured marks on the ground or time it against mile markers on the highway or compare against another car. The point is that you will need to implement a way to calibrate your speedo.
None of these methods including GPS are precise enough to discern small difference's in tire size. It simply isn't necessary or realistic.
Just calibrate after installation and you'll be good.