Strangest Tire Question EVERRR...

On 5/2/2020 7:50 PM, wrote:
> Arlen Holder:
>
> So rounded off we'll just say 270 sq. inch of area inside the avg. passenger
> tire. I think something was wrong with that online calculator I was using last
> night to convert square mm to square inches. For a similar tire I was getting,
> if I recall,1,220-something square inches? I suspected something was off!
>
> So the air inside the tire inflated to 35psi is pressing down on each one of
> those 270 square inches with 35 lbs of force. So a more sane 9,450lbs of
> total pressure on the inside wall of that tire. Probably closer to 7,000ish if
> you consider that side of the rim which completes the inside of that total air
> cavity at each corner of our daily vehicles.
>

I don't know but it cannot be 270 square inches ( which is
roughly 10" x 27". I can see a ten inch width bead to bead
but the circumference is way beyond 27 inches.

Regardless of arithmetic, the pneumatic (or hydraulic,
formulae are the same for these purposes) pressure at every
place within a closed figure is equal and all of it will be
35psi.

--
Andrew Muzi
<www.yellowjersey.org/>
Open every day since 1 April, 1971

AMuzi:

1,270 square inches. My tablet for some reaaon is not transmitting every character I
type, and is also changing some words and characters.

wrote:
> Strangest Tire Question EVERRR...
>
> Has anyone ever calculated or estimated the area, in square inches/square cm, of the *surface of the inside* of a tire?
>
> Does at least an average exist out there, for broad categories: passenger car, SUV-light truck, and commercial truck?
>
> Just curious, Thanks!

Entering footprint into the argument.
My car's GVW is 3800 lbs so each tire supports 950 lbs (ideally).
If a my tire has a footprint of 6"x6" = 36" sq, and if each sq in has a
pressure of 36 psi, then the psi total of the footprint is 1296 lbs.
Oddly enough my car tire's max load rating is 1295 lbs. Push on it with
an area and it will push back equally.
The rest of the tire area is at 36 psi and is irrelevant since it does
not support anything.

Paul in Houston TX wrote:

>The rest of the tire area is at 36 psi and is
>irrelevant since it does not support anything.

_______
Oh really? Last time I checked, a tire is a complete unit, with all of
its parts working together to support the vehicle, help maintain
traction, and help bring it to a stop.

That 36psi is pressing against every square inch of the inside of the
tire and the outer circumferential face of the wheel or rim.

On 4/5/20 3:28 am, Paul in Houston TX wrote:
> wrote:
>> Strangest Tire Question EVERRR...
>>
>> Has anyone ever calculated or estimated the area, in square
>> inches/square cm, of the *surface of the inside* of a tire?
>>
>> Does at least an average exist out there, for broad categories:
>> passenger car, SUV-light truck, and commercial truck?
>>
>> Just curious, Thanks!
>
> Entering footprint into the argument.
> My car's GVW is 3800 lbs so each tire supports 950 lbs (ideally).
> If a my tire has a footprint of 6"x6" = 36" sq, and if each sq in has a
> pressure of 36 psi, then the psi total of the footprint is 1296 lbs.
> Oddly enough my car tire's max load rating is 1295 lbs.Â* Push on it with
> an area and it will push back equally.
> The rest of the tire area is at 36 psi and is irrelevant since it does
> not support anything.

Lower the tyre pressure and see what happens to the sidewalls.

--

Xeno


Nothing astonishes Noddy so much as common sense and plain dealing.
(with apologies to Ralph Waldo Emerson)

Xeno:

Of course the tire sidewalls will slowly buckle! Common sense! They're the vertical
component of a tire. But what you seem to want to believe is that the only part of a
tire that matters is that which touches the ground. In your world, sidewalls don't exist.
In your world, a vehicle drives by and all you see are the treads and the rims.

It doesn't work that way. A tire - all of it - and the wheel or rim it's attached to, are
together a SYSTEM: of support, of absorption, of compliance, and of traction during
a variety of vehicle dynamics.

And whether a fully mounted, inflated, and balanced wheel/tire combo is sitting, waiting
to be put on a car, or is between that car and the road already, the air inside places
pressure on ALL interior surfaces of the cavity created by tire plus rim. Science!

On 4/5/20 10:11 pm, wrote:
> Xeno:
>
> Of course the tire sidewalls will slowly buckle! Common sense! They're the vertical
> component of a tire. But what you seem to want to believe is that the only part of a
> tire that matters is that which touches the ground. In your world, sidewalls don't exist.
> In your world, a vehicle drives by and all you see are the treads and the rims.

You have me 100% wrong. I was not disagreeing with you. My point was
that the sidewalls also have pressure acting on them and that helps
keeps them where they need to be. As well, the poster to whom you
responded omitted to mention, in his detailing of pressure acting at the
contact patch, is that it also acts in the upwards direction on the
inner rim surface opposite the inner rim surface. Tyres are not designed
by just looking at the contact patch to determine the inflation pressure
hence the load carrying capacity.

> In your world, a vehicle drives by and all you see are the treads and
> the rims.

Having been a mechanic for over 50 years, my view of a tyre is very
different from yours. I look at it as a sub-component of the vehicle,
its relationship to steering and suspension and, most importantly,
handling.

Two primary factors determine the load carrying capacity of a tyre, the
load and the inflation pressure. If you want to increase the load, you
need to increase the pressure. This is well known and is included in
vehicle owners manuals. The rub here is that there are many other forces
acting on tyres, lateral and centrifugal forces being just two, and each
needs to be considered, especially in relation to speed. Therefore the
service use of the tyre becomes important as well.
>
> It doesn't work that way. A tire - all of it - and the wheel or rim it's attached to, are
> together a SYSTEM: of support, of absorption, of compliance, and of traction during
> a variety of vehicle dynamics.

See above.
>
> And whether a fully mounted, inflated, and balanced wheel/tire combo is sitting, waiting
> to be put on a car, or is between that car and the road already, the air inside places
> pressure on ALL interior surfaces of the cavity created by tire plus rim. Science!
>
Well aware of that. Not my point. BTW, a tyre waiting to be put on a car
is *different* to a tyre on a car at 100 mph. Think heat and what that
does to a tyre and the pressure inside it.



--

Xeno


Nothing astonishes Noddy so much as common sense and plain dealing.
(with apologies to Ralph Waldo Emerson)

In response to what Xeno > wrote :

> Think heat and what that
> does to a tyre and the pressure inside it.

I have never been a mechanic (I'm an engineer & scientist), but I do agree
with Xeno, that heat is (almost) everything when it comes to rubber tires.
o Speed is heat
o Load is heat
o Inflation is heat
etc.
--
Rubber melts.

Xeno, Arlen:


My postulation is more a matter of wording:

We do not put "33 pounds of air" in a given tire. We put 33 pounds PER SQUARE INCH in
that tire. Ergo, that volume of air is applying 33lbs of force to EVERY SQUARE INCH of
the inside of that tire & rim face combination.

wrote:
> Xeno, Arlen:
>
>
> My postulation is more a matter of wording:
>
> We do not put "33 pounds of air" in a given tire. We put 33 pounds PER SQUARE INCH in
> that tire. Ergo, that volume of air is applying 33lbs of force to EVERY SQUARE INCH of
> the inside of that tire & rim face combination.
>

Correct, it applies 33 PSI of force to every square inch. However that
is the total force per square inch that the air applies. You cannot add
each inch up and say that number is the total pressure applied.

It is no different than atmospheric pressure which is around 14.696 PSI.
Using your version of physics every human being would be crushed to
death by that pressure if you consider the average human male has
22.173 square feet of surface area.

https://chem.libretexts.org/Bookshel...ts_Measurement
--
Steve W.