[Spridgets] Air Pressure & Lug Nut Torque

Ron Soave soavero at yahoo.com
Tue Aug 28 11:35:50 MDT 2018


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
>>>  
>>> 
> -- 
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