Date:         Mon, 19 Oct 2015 21:35:46 -0500
Reply-To:     mcneely4@COX.NET
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Dave Mcneely <mcneely4@COX.NET>
Subject:      Re: Nytrogen and tires
Comments: To: Dan N <dn92610@gmail.com>
In-Reply-To:  <CAFdLW6m-8+5tU0ib7HpBp8yqDnR_0Pi9Tqj4z24g3kbRwESf=w@mail.gmail.com>
Content-Type: text/plain; charset=utf-8

---- Dan N <dn92610@gmail.com> wrote: 
> I just give reference from a user manual, no research from my part
> 
> so I guess/interpret the process should be like this...
> 
> - let's say with cold tires (parked overnight), you check the tires and you
> want it at ie. 40psi.. you check your gauge and pump in air until you get
> 40psi
> 
> - let's say with hot tires (after a long run on highway), for some reasons
> you check the tires and you want it at ie. 40psi.. you check your gauge and
> pump in air until you get 43psi
> 
> which mean when the tires cool down you will have 40psi...
> 
> again my guess when hot, tires rubber expand and require 3 more psi...

Dan, when the AIR in the tires is hot, it expands, increasing the pressure inside the tire.    You should check the pressure when the tire is cool, not having been driven.  Set it at the pressure recommended for the vehicle (or for the weight being carried, but for most people, most of the time, the pressure on the door placard will do fine).  Don't check it again until the car has been parked and the tires cooled back to ambient.  If you check it hot, unless you know the temperature when it was cool, and now when it is hot, yoou won't know how much to inflate the tire.  David gave us the correction of 1 psi for each 10 F, and David is pretty good on this stuff.  But how do you measure the temperature inside the tire?  Perhaps, from the 3 psi figure that your owner's book suggested, the engineer who designed your SUV knows that the temperature of the tire increases 30 F when driven.  For me, I'd think that ambient temperature, speed, inflation level, and some other variables would contribute to the increase in temperature.

mcneely

--
David McNeely