[Spridgets] Air Pressure & Lug Nut Torque

Tue Aug 28 14:59:05 MDT 2018



    So like when the wheels on the bus go round and round.  In a front wheel drive world , 30-34 in rear and 36-38 in front to stiffen side walls ...although some white shoe polish on the sidewall so you can see how much roll the side wall has and a digital pyrometer and you read temperatures on both edges of the tread and the center to determine how hard your tire is being "worked".In my sports racer it's 10 up front and 12-13 in the rear tires for an 800 pound car...Chuck
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------ Original message------From: Ron Soave via SpridgetsDate: Tue, Aug 28, 2018 4:44 PMTo: Mike Rambour;Spridgets;Subject:Re: [Spridgets] Air Pressure & Lug Nut Torque
Heat. Your increased load causes heat. You want higher pressures for increased sidewall strength, btw. The math is simple - 
 PV=nRT. V is constant, so as T increases, P increases. Or, simplified, the density of air is 
2.7*P/T. As t increases, the air expands in a given volume and pressure increases. 
Ron Soave
On Aug 28, 2018, at 10:20 AM, Mike Rambour via Spridgets <spridgets at autox.team.net> wrote:

              
       I have to partially agree.  I also have never seen the 32 degree      specification and that would seem near impossible for any owner or      even tire shop to check the pressure at that point (maybe a few      lucky ones in the cold part of the country for a few months).
      
       But Tire pressure is not the same when hot or cold, check your      tire pressure in the morning before driving and then check it      again after 10-15 miles down the freeway and you will see it has      increased.  In my new truck, I have tire pressure monitors, I will      start at 35psi in the morning and average 39psi on the freeway.       Its interesting to see that the front tires will get to 40psi and      rears stay at 39psi, but when towing  a heavy trailer, the rears      will get to 41-42psi while the fronts stay at 39.  And this is      always starting at 35 cold, by cold I mean mid-60's ambient      temperature and before driving at all.  I assume the difference in      PSI is due to weight on the tire at the time, motor up front and      1-2psi then empty rear of truck, towing its the other way around,      more weight on the rear.  And no, I do not use my TPM to set my      tire pressure, I use a proper tire gauge, but the TPM is never      more than 1 psi off.
      
       Some people add PSI in the belief that they will get better      mileage, doubt its true after a certain point.  Yes, if your tires      are under pressured, then getting it to manufacturers specs will      improve mileage (by what, a few tenths maybe, assuming the tires      are not flat to begin with) but after you are in spec, I seriously      doubt it will improve the mileage more than a tenth of a MPG.
      
          Mike
      
      
      On 8/28/2018 5:39 AM, Rick Fisk via Spridgets wrote:
                    Allen,      
            Not wanting to start anything here,        but your tire pressure recommendations don't make sense to me.         I've never seen the recommended tire pressure is at 32 degrees        F spec in a manual anywhere.  ???  Seems to me the tire pressure        should be the same no matter what the temperature is.      
            For every 10 degree F rise in air        temperature the pressure in your tires will rise about 1 psi and        fall 1 psi for every 10 degree drop in temperature.  So to        maintain the car manufacturer's recommended tire pressure you        should reduce the pressure when the temp goes up and raise it        when the temp drops.      
            Why would you always add 5 psi to the        recommended pressure?  Seems to me the car manufacturer probably        knows best when it comes to recommended tire pressures for their        cars.        
            Rick      
        Sent from my keyboard      
        On Aug 27, 2018, at 10:39 AM, Allen Hefner via Spridgets <spridgets at autox.team.net>        wrote:
        
                              Don't forget that the recommended tire pressure            in the manuals is at 32 degrees. You usually add 1 PSI for            every 10 degrees above freezing. Nobody seems to know that            anymore. The manuals just say ## PSI cold. I always just add            5 PSI to the recommended pressure.             
                                                                                          Allen Hefner                      Norristown, PA                                             
                                                                                                                -- A gun is like a parachute, if you need one but don't have it,you'll probably never need one again.  ------------------------

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