41 PSI: High isn't it?

[stuck24]

Hey R folks!

just got back from VW dealer. Had one nice CW R in the showroom. Had a good look, I liked the look overall.

I looked on the driver side door placard and saw the recommended tire pressures. 41 PSI !!!!
This is got to be the highest of any tire pressure I've ever seen.

my 07 GTI was recommended at 35, my 2010 is at 38 , now I see this... 41 PSI.

What's next? Why are these getting higher and higher and higher? Fuel economy regulations???
thoughts

 

[SwiftGTI]

What's next? Why are these getting higher and higher and higher? Fuel economy regulations???
thoughts

Cars are getting heavier, and sidewalls are getting smaller.

Tire pressures have to be increased to cope with the heavier loads and reduced volume of air in tires.

 

[DougDome]

PV=nRT

As volume decreases, pressure increases increase to maintain same rigidity.

 

[CW_GTI1]

From the title, I thought we were talking about boost levels :yikes:

 

[cbursten]

From the title, I thought we were talking about boost levels :yikes:

I did as well.

Disappointed

 

[JAG1]

I did as well.

Disappointed

X2

 

[Dybz]

PV=nRT

As volume decreases, pressure increases increase to maintain same rigidity.

way to completely misunderstand how that equation works.

 

[veedoubleme]

X2

Came in here looking for this, but left disappointed.

 

[stuck24]

ha ha... sorry to dissapoint overeager boost seekers.

Tire pressures are important ... obviously not as important as massively unrealistic boost increases.

 

[MetalBong]

PV=nRT

As volume decreases, pressure increases increase to maintain same rigidity.

Yup, as Dybz pointed out, the ideal gas law isn't really working here, that R is a constant, that n is # of moles, and that T is temp. so using the ideal gas law, as P decreases so does Temp. Rigidity has nothing to do with the ideal gas law.
Sorry to troll, Nice try though

 

[stuck24]

if anything, this thread has turned into refuting application of stated equation. Excellent stuff!

 

[BoomBoy]

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

 

[DougDome]

Yup, as Dybz pointed out, the ideal gas law isn't really working here, that R is a constant, that n is # of moles, and that T is temp. so using the ideal gas law, as P decreases so does Temp. Rigidity has nothing to do with the ideal gas law.
Sorry to troll, Nice try though

Maybe it was an overly reductive way of looking at it. By rigidity, I was referring to the desired outcome. As the volume of the inside of the tire decreases, the pressure necessarily needs to be higher to exert the requisite amount of force on the sidewalls to keep the tire inflated. For example, a 235/55 r16 tire would need less pressure within the tire to appear inflated, while bike tires need about 60psi.

I'm reasonably sure my understanding is correct, although my high school chemistry may be a little rusty.

 

[Dybz]

Maybe it was an overly reductive way of looking at it. By rigidity, I was referring to the desired outcome. As the volume of the inside of the tire decreases, the pressure necessarily needs to be higher to exert the requisite amount of force on the sidewalls to keep the tire inflated. For example, a 235/55 r16 tire would need less pressure within the tire to appear inflated, while bike tires need about 60psi.

I'm reasonably sure my understanding is correct, although my high school chemistry may be a little rusty.

 

[MetalBong]

Maybe it was an overly reductive way of looking at it. By rigidity, I was referring to the desired outcome. As the volume of the inside of the tire decreases, the pressure necessarily needs to be higher to exert the requisite amount of force on the sidewalls to keep the tire inflated. For example, a 235/55 r16 tire would need less pressure within the tire to appear inflated, while bike tires need about 60psi.

I'm reasonably sure my understanding is correct, although my high school chemistry may be a little rusty.

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?