I joined in the chat on the YouTube video a couple posts below yours. I’m sure you will recognize me! 
No…Because SCIENCE proves this work. Boyles Law.
And I told you what my personal experience was. I’ve done this experiment. So has my daughter…and I think my middle son has. Along with THOUSANDS and THOUSANDS of college and high-school physics students all across the country. You want to deny it happened? Fine. But your belief doesn’t disprove FACTS.
All that means is that no one has ever made a video of this experiment and posted it. Try going to a local college that teaches science/physics. Physics is NOT just sitting in a classroom and being taught formulas. Usually, 60% of your grade (some as high as 70%) is physics lab and doing experiments on what you were taught that week.
Boyles Law doesn’t account for all the non-linear affect of tire construction on this issue. Is the tire patch area proportional to load, and inversely proportional to pressure? Yes, but it’s not a simple linear relationship.
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I do not deny it happened. That was not my question. This was.
Data speaks volumes. A theory is just an idea until it is confirmed by data. I wanted your experience with how this method compares with actual data.
In the absence of data, the science is unproven. Boyle’s law is proven. But tire studies prove that the contact patch area indirectly related to the load, not directly.
The key piece of info in this link is this:
Further, the size of the contact patch cannot be simply calculated as load divided by inflation pressure, and the average contact pressure a tire has with the road surface is not equal to the inflation pressure. [4]
When driving over water, a tire that is underinflated by only 0.5 bar loses up to 20% of contact with an ideal tread depth. Now add to this an average wear, and you will lose 50%
On this site, actual data was obtained from Avon Tyres and posted here disproving the pressure vs contact patch relationship.
Key phrase being;
what is immediately obvious is that doubling the load does not double the contact patch area. I.e., the contact patch pressure does not remain constant.
Another study using truck tires containing data.
And the conclusions of the paper linked above on page 84 is the following;
Under normal combinations of wheel load and inflation pressure, the average contact pressure between the tire and the road will be less than the tire inflation pressure.
At constant inflation pressure, the contact pressure varies with load. A 100 percent
increase in load normally is associated with a 30 to 40 percent increase in contact pressure.
And physicists do not know how tires are made. Experimental physics would prove or disprove this with actual data.
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Why this doesn’t work. In theory it would work best with brand new tires inflated all to the same pressure, preferably at or near the pillar recommendation. But the issue even there is that you are trying to find the top of a curve.
As you go over the ideal pressure, the contact patch will get smaller, but very marginally. Over pressure would result in a longer contact patch where under pressure will result in a wider patch. But small variations in pressure have a very small difference in the total size of the patch. This means that the weight of the vehicle could vary by a pretty good percentage and result in a difference in the patch size that would be very small.
Now if you are using tires with some wear on them, it gets far more inaccurate. If the tires are driven chronically over or under pressure, the tires will wear in based on the pressure so the contact area will grow with wear. Over pressure will wear the center down to widen the patch and under pressure will wear the outer treads down to make the patch longer. That will result in a weight calculation over the vehicles actual weight.
If the air pressure is adjusted to the proper pressure as shown in the vehicle, and they have been driven for a significant time at a different pressure, the is going to result in a smaller patch, yielding a weight lower than actual.
But again, you are trying to find the top of a curve where the slope of the tangent line does not vary much for some distance on either side of the ideal.
BTW, the above is also taught in your physics class, and the math in your Calculus classes.
Wanna Bet? Firestone, Michelin, Goodyear, Cooper - ALL of them use MIT and other colleges for a lot of their research.
A WRONG…A scientific theory is an explanation of what is observed. It can be tested and either proved or disproved.
Dynamic change of tire contact is NOT the same as measuring a vehicle weight with static contact pressure points. They are completely unrelated.
Your ONE or two URL’s aren’t going to change my mind. I have no way of knowing the validity of the data (neither do you). I also never said it was 100% accurate. But in most circumstances - it can be used to estimate a vehicles weight. As I’ve said…I’ve done the experiment…So has my daughter. Along with everyone in my physics class and daughters physics class (separated by 40 years). And all had similar results. There were a bunch of different vehicles used in each class…
And as I also said…bicycle tire pressure needs to be CALCULATED based on the weight of the person riding the bike. My youngest son and I are the same height and ride the same size frame bike. But because I weigh 50lbs MORE then my son, we need to increase the tire pressure for me to ride his bike. Ask any bike shop on this.
My conclusion in time, is that not gaugepressure has to be used but absolute pressure, for calculating footprint (squaire inch) x psi( pounds per square inch) = pounds on tire.
And then a slight difference of the part that is carried by the construction of tire at the deflection.
A test to prove it is next.
Yack a tire up and lett of all the air, so absolute pressure is ambiënt pressure, wich you can measure, but also find on weather sites for your location.
Then use a personsweightscale and a piece of paper to make print of treathsurface on the ground.
Jack the wheel back down until for instance 100 or 200 lbs on scale.
Then screw the valve out, and measure what weight on scale left., thats the part carried by the construction of tire.
Substract that from first weight. Example
200 lbs set on scale, and with valve open 40 lbs on scale.
Then use 160 lbs for the calculation.
Then yack up to get the paper out, and measure as acurate as possible the surface in the contour of tireprint, and not rectangular, with pieces of paper determined, as I saw in one test.
Lets assume 14.5 psi ambiënt pressure so absute pressure in tire.
Then tireprint should have surface of 160lbs/ 14.5 pounds/sq inch = 11.034 squaire inch surface on ground.
If that surface is exact measured, it proves that absolute pressure carries the load, and here that 40 lbs carried by the construction of tire at that deflection.
Then science is in line with practice.
And that must be, that experiments are not in line with science only proves that the experiment is not complete.
The Nile was the longest river, also before it was discovered.
Go by the door sticker, check it often to maximize tire life. Every 10 degree shift in air temperature is a ~1 degree shift in air pressure.
30psi at 20 degrees will increase to 37psi at 90 degrees.
If you were inflating to 45psi cold, I’ll bet that was one rough ride…tires probably bounced their way down the road. Very hard on your suspension to drive overinflated…tires are designed to absorb some of the road impacts…overinflate and the road beating goes to all the suspension joints.
If you want to see your “Contact Patch”, wash the tire tread, take a short drive, the dusty area is the width of the contact patch.
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I looked over some links given.
Saw at site of capriracer about even larger surface on ground then calculated by weight and psi. Then this contradicts my statement of having to use absolute pressure, then surface even smaller
Then not the 11 sq inc on ground but for instance 12 or 13 sq inch.
Have to see how this can be get in line with rules of nature.
Does all this discussion apply to bias ply tires or radials tires??? lol
Cause tire pressure is way different for both on a drag strip which is where you want the MAX contact patch or footprint…
All things being even, with my radial street tires they hook about the best at 26 psi, but ride and wear better at 35 psi… If I was going to run drag radials then I would need to run about 20ish psi for best contact patch, if I was to run bias drag tires then you start around 10 psi for best contact patch… Doesn’t get anymore real world than that, just go to the track and talk to some top racers, they will have all the data you could want… including barometric pressure, humidity, ambient temp, and track surface temp… The Promods and Outlaws have more electronics recording data then the space shuttle… lol
Bias ply tires are ROCKS compared to radial ply. My rule of thumb is to add, when cold, 5-7psi to the original bias-ply pressures when converting a classic car to radial tires.
EG: That '63 Corvair speced at 15psi front and 26psi rear: with radials inflate at least to 20front and 31rear. Preserving that offset.
Yes, that is why my old junk says front 28psi and rear 30psi for the OEM D78-14 tires but I run 35psi in the front and they wear great, and the rears at 35 when driving normal and 26ish when not driving normal… lol… Of course they don’t wear great due to being on a full spool now and tend to spin from time to time (cough cough) but has worn great before the Spool somehow fell in it a few years back…
EDIT: 28F&R with reduced load and 30F&R max load… Been a while since I had looked at the sticker… sticker shown a few post down…
Is this on a Corvair? If so, you should run a ten PSI difference between whatever two pressures you run front and read. Front Rear 22, 32, or 25, 35, where ever you run them.
Remember, all of your power train(engine, transmission, is aft of the rear wheels in that design.
