[Spridgets] Air Pressure & Lug Nut Torque

Tue Aug 28 08:28:32 MDT 2018

Thanks, Rick. You're the best! (But I tell everybody that.)

Here is some info from TireRack. I may be incorrect about the 32 degree
thing, but basically they explain it better than I. Read more at
TireRack.com.

"The rule of thumb is for every 10° Fahrenheit change in air temperature,
tire pressures will change about 2% (up with higher temperatures and down
with lower). This means that light-duty, standard-pressure tires (typically
inflated to 30-50 psi) used in applications on cars, vans and light trucks
will change by about 1 psi; ...

"In most parts of North America, the difference between average summer and
winter temperatures is about -50° Fahrenheit...which results in a potential
loss of about 5 psi as winter's temperatures set in...

"Additionally, the difference between cold nighttime temperatures and hot
daytime temperatures in most parts of the country is about 20° Fahrenheit.
This means that after setting tire pressures first thing in the morning,
the vehicle's tire pressures will be almost 2 psi higher when measured in
the afternoon (if the vehicle was parked in the shade). While that is
expected, the problem is when you set your vehicle's tire pressures in the
heat of the day, their cold pressures will probably be 2 psi low the
following morning.

"And finally, if the vehicle is parked in the sun, the sun's radiant heat
will artificially and temporarily increase tire pressures.

"We put some of these theories to the test at the Tire Rack. First, we
mounted two tires on wheels. We let them sit overnight to equalize and
stabilize their temperatures and pressures. The following morning we set
them both to 35 psi. One tire and wheel was placed in the shade while the
other was placed directly in the sun. We then monitored the ambient
temperatures, tire temperatures and tire pressures through the day. As the
day's temperatures went from 67° to 85° Fahrenheit, the tire that was kept
in the shade went from our starting pressure of 35 psi to a high of 36.5
psi. The tire that was placed in the sun and subject to the increase in
ambient temperature plus the sun's radiant heat went from our starting
pressure of 35 psi to a high of 40 psi. In both cases, if we had set our
tire pressures in the afternoon under the conditions of our evaluation,
they would have been between 2 and 5 psi low the following morning...

"It's important to remember that your vehicle's recommended tire pressure
is its cold tire inflation pressure. It should be checked in the morning
before you drive more than a few miles, or before rising ambient
temperatures or the sun's radiant heat affects it.

"And by the way, if you live in the North and park in an attached or heated
garage you will lose pressure when you leave its warmth and venture into
the real world outside during winter. Add 1 psi cold tire pressure to
compensate for each 10° Fahrenheit temperature difference between the
temperature in the garage and outside."
So I guess what they are saying is that you should check your tires
pressure every few minutes whilst driving.

Allen Hefner
Norristown, PA

*Current:*
2016 Subaru outback somewhere
2006 Chebbie
*Former:*
1963 Sunbeam Alpine Series III
1967 Triumph TR4A IRS
1964 VW Type I
1967 VW Type II
1967 Rover 2000TC
1977 MG Midget (Sniff!)

On Tue, Aug 28, 2018 at 8:39 AM Rick Fisk <refisk at chartermi.net> 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
>
> *Current:*
> 2016 Subaru outback somewhere
> 2006 Chebbie
> *Former:*
> 1963 Sunbeam Alpine Series III
> 1967 Triumph TR4A IRS
> 1964 VW Type I
> 1967 VW Type II
> 1967 Rover 2000TC
> 1977 MG Midget (Sniff!)
>
>
> On Tue, Aug 21, 2018 at 1:40 PM John Farley via Spridgets <
> spridgets at autox.team.net> wrote:
>
>> I am running 175/70 R13s on my 1275+ Bugeye with front disc brakes.  What
>> are folk’s recommendations for tire air pressures & lug nut torque?
>> The manual  seems low for both.
>> Thanks,  John F.
>> ------------------------
>>
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