45 psi in tires on Forester from factory?

Question

My Forester is 3 months old and going in for free first oil change Wed. In checking wife's tires today I checked mine and found the G900 Yokohoma Geolanders to all be at 45 psi. Thought gauge was defective and checked with 2 others and got same reading - wife's tires were 32 lb as expected on her Nissan. Dealer says maybe all three of my guages defective! No harm anyway since only result would be higher mileage. I'm not letting air out until I see him Wed. and have a little tete-a-tete ;) Frank

Edward Hayes · Accepted Answer

Typically tires when first mounted and shipped are pressurized to 45-50psig. It was the dealer prepping the vehicle who is expected to set tires tothe correct pressure. You do check then overnight cold? as expect a onepound increase for every ten degree in tire temperature. If you check aftera high speed run they can be up 10 psi easy. Eddie

someone · Answer

I used to work at a Subaru dealership a couple years ago. It was very common for the cars coming from the factory to have 45+ PSI. Part of the "pre-delivery inspection" is checking/setting tire pressure. Don't know if they still do or not, but when I was working in the dealership, the tires even have BRIGHT green stickers on them stating something to the effect of "Dealer set tire pressure" Sounds like whoever did the PDI on your vehicle didn't do a very good job of it.

Frank Logullo · Answer

Thanks for the comments. Don't know who I spoke to at the dealership but it was not the service manager. I'll set them straight tomorrow and have them reset pressures. Car has been fine. It replaced '98 Forester that was totaled in an accident, but ride not any smoother than '98. Maybe this will improve it. Frank

Richard Chang · Answer

Checked my '03 Forester after the first week at home and all four tires were at 38psi, which is about 10psi higher than they should be. (Yes, I checked the tires cold.) I don't think changes in ambient temperature could account for this much difference in tire pressuer. I suppose they could have filled it to 29psi when it's way below freezing.

-R.

Ken Gilbert · Answer

oh yeah, it will be smoother, no doubt, but expect to wallow around a bit more too as you get reintroduced to sidewall flex!

i run 42 psi (cold) in all 4 corners of my wrx. treadwear is BETTER than at stock suggested numbers, which are ridiculously low imho.

jm2c ken

Edward Hayes · Answer

I presume you used P1XT1=P2XT2 where T = the absolute temperature??? Pleaserecheck calculation.  Eddienews:...

David or Jo Anne Ryeburn · Answer

P1/T1 = P2/T2 is more like it. Your formula would have the pressure

*decreasing* as the temperature increases.

If you assume a pressure of 29.3 lb/in^2 at a temperature of +20 C (+68 F), his calculation of 1 lb/in^2 increase for every 10 degrees C increase is right on. And it agrees very nicely with my experience in checking tire pressures at various temperatures (front tire pressure for my 1997 Legacy Outback is 29 lb/in^2).

David

Frank Logullo · Answer

No, I start with gas law which is PV=nRT. I never remeber the differences between Boyles and Charles law (which is which). T of course is in degrees Kelvin (-273 deg. C). Since the volume of the tire is essentially constant, and n and R are constants for the same gas the ratios of temperature and pressure reduce to: P1/T1=P2/T2 Frank

Edward Hayes · Answer

I stand corrected and thank you. It has been a few years. Eddie

45 psi in tires on Forester from factory?

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