41 PSI: High isn't it?

[DougDome]

lol, thanks. I'll stop now, I promise.

Good thing I'm an accountant.

 

[MetalBong]

Just to really be a dick about this (since I'm in that kinda mood today)

The ideal gas law does have an application in pressure theory when it comes to racing

since pressure is related to temp. changing tire pressure is how you control heat in the tire which in turn can effect grip or wear. I'm not a Nascar fan but they even have very strict rules about tire pressure so people won't compromise wear for traction.

OK I'm a troll, apologies

 

[DougDome]

Just to really be a dick about this (since I'm in that kinda mood today)

The ideal gas law does have an application in pressure theory when it comes to racing

since pressure is related to temp. changing tire pressure is how you control heat in the tire which in turn can effect grip or wear. I'm not a Nascar fan but they even have very strict rules about tire pressure so people won't compromise wear for traction.

OK I'm a troll, apologies

That's not really trolling, Trolling is the act of saying things to get a rise out of people, like what I try to do to jackgti every day. I appreciate the info :w00t:

 

[SwiftGTI]

Sorry, as much as I like your Adogg sig (which was a funny thread) the volume and pressure (in this case) of the tire is really only relative to itself (ie. it will feel softer or harder with pressure changes) due to the tires construction (sidewall, rubber compound, fiber weave, etc.) it doesn't relate to other tires or "volumes"
The bicycle tire is using a higher pressure because of its' construction not its' volume
The 235/55 16 (taller sidewall tire) if it's constructed the same as the lower sidewall tire would actually need more pressure to maintain its' rigidity because of the taller sidewall (think lever here, as in the distance from the rim to the tread)
The 41 psi thing could be due to the car being heavier, different tires with different construction, mileage, traction vs. wear, etc. who really knows their specific reason?

I think volume does come into play. The less volume the tire holds, the lower its load rating (given equal sidewall strength).

 

[myfastgti1]

PV=nRT has nothing to do with loads lol.
force=pressure*area is the basic eqn used to explain this

 

[webcrawlr]

Unless the wheels are 19", I'd consider 36 psi the sweet spot for 18" wheels.

I've tried 2 lb increases and decreases from 34 up to 48 and found 42-44 to be the best feeling setting for me. All models of cars will be different of course.

 

[Dybz]

I've tried 2 lb increases and decreases from 34 up to 48 and found 42-44 to be the best feeling setting for me. All models of cars will be different of course.

hot or cold?

 

[SwiftGTI]

PV=nRT has nothing to do with loads lol.
force=pressure*area is the basic eqn used to explain this

Yes, but volume has everything to do with load rating. The greater the volume of air the tire holds, the greater the weight it will support. If you want think of this in terms of the f=pa formula, then you can think of it as volume is directly proportional to area. What we're really talking about is the internal surface "area" of the tire and the pressure applied to that surface by external force (load).

 

[cbursten]

The amount of engineering expertise in this thread excites me. Somewhat.

 

[PandaGTI]

I forgot what the reasoning behind the higher pressure are... but even my Toyota FJ Cruiser had a TPMS recall done which was essentially to raise the tire pressures from 35psi to 45psi, replace the door stickers, and recallibrate the TPMS system for the higher pressures.

Maybe it's a tire safety issue, maybe it's to raise mpg... i dunno

 

[myfastgti1]

Yes, but volume has everything to do with load rating. The greater the volume of air the tire holds, the greater the weight it will support. If you want think of this in terms of the f=pa formula, then you can think of it as volume is directly proportional to area. What we're really talking about is the internal surface "area" of the tire and the pressure applied to that surface by external force (load).

psi= pounds per square inch, which by definition is irrelevant to the volume. what you are saying about the internal load area is correct, which means that pressure will vary with the tire width.

summary: higher pressure for low profile tires, so bumps dont hit the rim.
higher tire pressure=less contact surface with pavement, which means less friction. 255 width etc tires can run less pressure, as the contact surface is larger.

or so thats what i believe haha

 

[SwiftGTI]

psi= pounds per square inch, which by definition is irrelevant to the volume. what you are saying about the internal load area is correct, which means that pressure will vary with the tire width.

summary: higher pressure for low profile tires, so bumps dont hit the rim.
higher tire pressure=less contact surface with pavement, which means less friction. 255 width etc tires can run less pressure, as the contact surface is larger.

or so thats what i believe haha

The tire's contact surface with the ground is only one part of the equation though. There's also sidewall surface. That's why I was moving this to a debate about volume.

Think of the inside of a tire. The greater the internal surface area of the tire, the greater the area over which the force and pressure (of vehicle load, and say hitting a bump/pothole) are applied.

At least, that's what I believe. I ran this by a chem phd btw; he agrees with me in principle (but admittedly knows little about cars generally).

 

[myfastgti1]

The tire's contact surface with the ground is only one part of the equation though. There's also sidewall surface. That's why I was moving this to a debate about volume.

Think of the inside of a tire. The greater the internal surface area of the tire, the greater the area over which the force and pressure (of vehicle load, and say hitting a bump/pothole) are applied.

At least, that's what I believe. I ran this by a chem phd btw; he agrees with me in principle (but admittedly knows little about cars generally).

touche :clap:

 

[RacingManiac]

Contact area for tires at the same PSI is going to be the same, regardless if its wider, narrower, taller or shorter. But your tire "spring" rate will vary. Imagine a wider tire will require more normal force to deflect the same amount(displacement wise) as a narrower tire, at the same PSI. Since GTI and R has the same size tire, I am assuming VW is just taking up the weight difference between the R and the GTI, upping the PSI, you are upping the spring rate of the tire....

 

[stuck24]

as the thread OP, I now have a raging hard-on with all this volume/ pressure/ width talk... thx