Correct. The manual does not state the recommended cold tire pressure for street use. And I agree that it can be confusing because the manual does give pressures for sustained high speed use (starting page 286 in the 2024 manual, not to be confused with pressures for track use). And, in the Track Events and Competitive Driving section of the manual, that starts on page 159 , you will find some tire pressure settings on page 168 that is still in that Track section. You can find yourself in that section and not realize it, if you are not familiar with the layout of the manual.

Anyway, on page 173 of the manual, it does clearly direct the reader to the door sticker, explains where to find it, and what will be found on it. It is the "cold" inflation pressure for street use. Cold means that it is set at the ambient air temperature. That is, the manual does not indicated any need to adjust the "cold" setting for temperature for street use. If the ambient temperature is 40 degrees F, set it to 30 psi. If the ambient temperature is 90 degrees, set it 30 psi. I get it that some will adjust this a bit to compensate for changes in ambient temperature throughout the day - I usually don't worry about that. I think there is a good bit of tolerance in the acceptable psi range for a fully warmed up tire in street use. And yes, if there is a significant change in ambient temperature - yes it needs to be adjusted when the tires are cold. I find that when I set the pressure in the Summer months, and then we have significant drop in temperature, the cold pressure drops enough to trigger a low tire pressure warning while sitting in my garage.

 

No it's not. Cold tire temperature is measured at ambient temp. That's why you need to add more air to the tire in the winter, when the air is colder, and let some out again when the weather warms up. If you adjust your pressure to be 30 psi at 68F, and it's only 20F outside, your tires are going to be underinflated.

 

Now you're just talking nonsense I don't know why it's so difficult for some to just follow the sticker. And to another comment, the sticker is not only for the specific tires the car came with either.

 

Bad logic. It is indeed 30psi at the standard temp, (cold) which is 68 deg. I take it you have not had any science classes in your schooling. It is correct that at a lower temp the tires pressure will be lower and at a higher temp the pressure will be higher.

 

You inflate to 30 psi cold no matter what the ambient temperature (for street driving), you don't compensate for the difference between the current ambient temperature and standard temperature. The colder the ambient temperature the colder the tires will be at the stabilized running temperature. The cold inflation pressure is intended to be measured at ambient temperature conditions.

 

This true except you have to understand that in a location where there is a 30-40 degree ambient temperature change from morning to afternoon there will be a profound effect on the tires pressure. If you set your tires cold pressure at 40F in the morning and then it warms up to 70F by noon the tires pressure will be out of range. Now driven at higher speeds as in normal freeway/high way driving the tire pressure would definitely be excessive. Conversely if you start out in an area that is very hot drive to an area that is much colder the pressure will decrease and this could also cause an out of range condition.

It used to be the tire manufactures recommended the cold pressure was defined to be 68F, which is the standard temp (STP). It got too complicated for the lay and they changed to just cold temp. It is totally acceptable to set the pressure at a nominal value. Using this method will usually half the change in pressure variation. Now if you want use ambient regardless of the extreme you should check your tire inflation every time you drive or every time there is substantial change in the ambient temp. This might include after every static interval which would be another argument of how long, 4hrs, 8hrs overnight etc.

It is hard enough to convince most people to check their tire pressure let alone make it more complicated. The best rule of thumb is to check it during a nominal daily ambient temperature. This would not be in the morning before you drive if it is very cold out. Rather check it when the tire is cold or acclimated to the ambient temperature during the average of the day.

 

The most important fact to keep in mind is that cold pressures are set so that the tire reaches the "correct" operating pressure under normal driving conditions. In other words, we don't really care about the cold pressure and we really do care about the operating pressure. That means we need to understand what we want the operating pressure to be and adjust the "cold" pressure accordingly. I like to see ~35 psi in normal driving and 38 to 39 psi during spirited driving. If I am just driving down the road like I would commuting, and I see pressures in the 37 to 40 psi range, I know the cold pressures are too high. If you set cold pressures at 40 degrees F to 30 psi. The pressure will be higher than idea at 70 degrees F just driving around.

 

40F to 70F is roughly 3 PSI. Won't make a bit of difference.

 

The C8 owner's manual says to check tires when cold:

How to Check
Use a good quality pocket-type
gauge to check the tire
pressure. Proper tire inflation
cannot be determined by looking
at the tire. Check the tire
inflation pressure when the tires
are cold, meaning the vehicle
has not been driven for at least
three hours or no more than
1.6 km (1 mi).
Remove the valve cap from the
tire valve stem. Press the tire
gauge firmly onto the valve to
get the pressure measurement.
If the cold tire inflation pressure
matches the recommended
pressure on the Tire and
Loading Information label, no
further adjustment is necessary.
If the inflation pressure is low,
add air until the recommended
pressure is reached. If the
inflation pressure in high, press
on the metal stem in the center
of the tire valve to release air.
Re-check the tire pressure with
the tire gauge.
Put the valve caps back on the
valve stems to keep out dirt and
moisture and prevent leaks. Use
only valve caps designed for the
vehicle by GM. TPMS sensors
could be damaged and would
not be covered by the vehicle
warranty.

There is no mention of adjusting cold inflation pressure to compensate for when the ambient temperature deviates from standard temperature. I have never seen a car or tire manufacturer recommend compensating cold inflation pressure for street driving when ambient temperatures deviate from standard temperature. Do you have a source from a car or tire manufacturer that recommends compensating for ambient temperature when inflating cold tires?

 

Our disagreement is that cold tire pressure doesn’t mean the coldest part of the day. I’m not saying that you’re recommending to perform the check during the coldest part of the day, but it gets encapsulated in the ambiguity of the recommendation. This is a common topic. People need to be practical and use common sense. Check the tire pressure with the tires cold at a reasonable ambient temperature. Ideally close to the nominal for the day.

 

Main goal of tirepressure determination is to give tire a deflection warm that wont overheat any part of tire-material, when driving the speed for wich cold pressure is determined.

Keeping this in mind, you have to fill at 104 degr F /40 degr C ambiënt temperature, a higher cold pressure then at 68 degr F /20 degr C.
This because cooling down is also worse at 104 degr F ambiënt.
The lesser deflection the higher pressure gives, gives then lesser heatproduction at same speed. So heating up and cooling down of tire-material stays in line so tire-material still wont reach 120 degr C/248 degr F.
A man from Nokian (norwegian tirebrand) wrote me that that is the critical temperature, at wich tire-material hardens and little cracks are made, wich tear further in time, until, mayby after 2 years that far that tire blows or treath seperates, and then other factors are blamed.

So this overheating is only allowed "ZERO" times in tires use.

General idea is to fill determined best pressure at ambiënt temperature, be it 20 or 110 degr F.

But I dont agree with that, and in about 20 years I will be proven right.
So I am in the camp of calculating cold measured pressure back to an index temperature, as Rimex calls it, a company for earthmovers tires.
They use 20 degr C/68 degr F as index temperature, but I have read 65, 68, 70 degr F.

Can give you text I wrote about it for an RV forum, using 80 psi cold pressure as example, but it goes for lower pressures the same.

So opinions are devided about this.
That people with autority write things, dont always mean they are right.
The earth proved to be not flat.

Made a list using index temperature 70 degr F/21 degr C.
In that search your determined cold pressure, and it gives howmany degr F change per 1 psi change.

70degrF./degrF/psi

20 psi/ 15,5F/psi
21 psi/ 15F/psi
22 psi/ 14,5F/psi
23 psi/ 14 F/psi
24 psi/ 13,5F/psi
25 psi/ 13,5F/psi
26 psi/ 13 F/psi
27 psi/ 12,5 F/psi
28 psi/ 12,5 F/psi
29 psi/ 12 F/psi
30 psi/ 12 F/psi
3 1psi/ 11,5 F/psi
32 psi/ 11,5 F/psi
33 psi/ 11 F/psi
34 psi/ 11 F/psi
35 psi/ 10,5 F/psi
36 psi/ 10,5 F/psi
37 psi/ 10 F/psi
39 psi/ 10 F/ps
40 psi/ 9,5 F/psi
42 psi/ 9,5 F/psi
43 psi/ 9 F/psi
45 psi/ 9 F/psi
46 psi/ 8,5 F/psi
49 psi/ 8,5 F/psi
50 psi/ 8 F/psi
53 psi/ 8 F/psi
54 psi/ 7,5 F/psi
58 psi/ 7,5 F/psi
59 psi/ 7 F/psi
63 psi/ 7 F/psi
64 psi/ 6,5 F/psi
70 psi/ 6,5 F/psi
71 psi/ 6 F/psi
77 psi/ 6 F/psi
78 psi/ 5,5 F/psi
86 psi/ 5,5 F/psi
87 psi/ 5 F/psi
96 psi/ 5 F/psi
97 psi/ 4,5 F/psi
109 psi/ 4,5 F/psi
110 psi/ 4 F/psi
126 psi/ 4 F/psi
127 psi/ 3,5 F/psi
148 psi/ 3,5 F/psi
149 psi/ 3 F/psi
177 psi/ 3 F/psi





​​​​​

 

Once you add another 3-10psi on top of that from use it might. Usually it will wear out the centers of the tread prematurely. My point is checking a cold tire could be at any ambient temp. It would be ideal not to use the extremes. Checking them at 40 or 70 is less than ideal. I don’t actually target a specific temp with a thermometer, I just check them somewhere in between and not at the extremes.

 

It hard to believe this crazy thread continues over something as trivial as minor differences in tire pressures that are essentially meaningless.

 

Which is why the poster that said we are told to check them cold to uncomplicate what can be made complicated was spot on. There is a lot of good info if slightly trivial.

 

Maybe not to you....but I don't want to run around with my tires at 38 psi instead of 35 psi...again, the operating pressure is the important pressure...not the "cold" pressure.

 

Yes. Besides the owners manual, I found two other sources that say to check set cold tire pressure when the car has not been driven for at least three hours, with no mention of adjustment if the ambient temperature deviates from a reference temperature in any of those. Those two sources are Michelin and tiregrade.com. I believe the intent is to just set it at ambient. I always thought this made sense because the final warm/hot tire temperature will be lower for lower ambient, and higher for high ambient temperatures.

However, I did find a source that discusses a reference temperature of 68 degrees.
https://www.rimex.com/wp-content/upl...n-pressure.pdf
https://www.rimex.com/
If it was appropriate for this application, and you were setting the tire pressure at 40 degrees, but wanted it to result in 30 psi when the tire gets to 68 degree, then you would set the pressure low, by about 2.32 psi, to 27.67+/-. Yeah - i wont be doing that. But I don't that this particular source is applicable anyway. It is by RIMEX and the context appears to be for extreme heavy equipment. RIMEX is an international company that manufactures TyreSense which is "a tire (tyre) Temperature and Pressure Monitoring System (TPMS) designed for mining and industrial operations of all sizes from single operator-driven vehicles to large autonomous fleets." They also appear to make heavy duty wheels for those applications as well.

Bottom line is I believe that the intent is to set the cold tire pressure at ambient temperature and it will result in an acceptable warm/hot tire pressure in street use.

The next three are the Owners Manual, Tiregrade, and Michelin statements:

 

" My" system of calcuating back to a reference or index temperature is easyer in use.
Once filled to this system, you can let the cold pressure flow with ambiënt temperature, and not maniacally let of and fill up when large temperature swings.

And the list I gave, can be used to calculate by head accurate enaugh for the goal.
Yust for checking, so you dont worry.

That Rimex pdf comfirms my idea, and is also an autority to my opinion.

But even autority's in the field can make mistakes.
RIMEX uses absolute pressure in their example, and not gauge-pressure wich is 14.7 psi/1.013 bar lower then absolute pressure.
Their example is high pressure, so ambiënt pressure is relatively small part, so error is marginal.

But when used for 29.4 psi gauge-pressure the ambiënt is 1/3th of absolute pressure, and error gets serious.

I wrote Rimex about this, but conversation mostly goes into the twilight zone.

I made a temperature/tirepressure calculator myself.
A spreadsheet that calculates pressure change for temperature in tire change, and the other way around. For absolutely dry gascompound in tire, like Nitrogen lobby claims, but also for if enaugh water in tire, and I think I am first in that.

​​​If you mail me at my hotmail. com adress with username jadatis, I can send it in return.
Like this cripted so spamm machines cant figure it out, so combine yourselfes.

Now cars often have tmps, people worry more about pressure swing. And using the calculations can ease their minds.
After a while you understand the system, and dont calculate or worry anymore.

 

Adding to post 36, the RIMEX discussion of cold tire pressure says

"The cold inflation pressure is the contained air pressure of a tire that would occur at an indexed temperature,
usually 20°C or 68°F. This indexed temperature is based on the ideal ambient operating conditions for
the tire. There is ambiguity in the definition of cold inflation pressure among tire manufacturers. Some
manufacturers index cold inflation pressure to 18°C or 25°C, or have another definition altogether."
https://www.corvetteforum.com/forums...post1607685666

Since each manufacturer sets it, how does Michelin say to set cold tire pressure for their passenger car tires? Like this:
"For best results, check your tire pressure when tires are cool– before driving the car or if it has covered less than 3 miles at low speed. If the tire is hot, add 4-5 psi to the car manufacturer's recommended pressure value (0.3 bar) or wait until it has cooled down, which is an average of three hours after parking the car." No mention of a reference pressure or any need to make special adjustments.
https://www.michelinman.com/auto/aut...tire-care-tips

What could be simpler than just checking/setting the tire pressure before you drive the car to the psi on the door pillar at whatever the ambient temperature happens to be? Its what I do, and give it no further thought. The available tire temp display tile is useful for track use, but to me its just a novelty for street use.

 

Hello? They're called run flats because you're supposed to run em flat! I don't put any air in mine and it's a really smooth ride.

 

We need to email this thread to every tire shop in the country. I cannot tell you how many times I have had tire shops put the maximum pressure in the tires and then tell me "That's what it says on the sidewall" So frustrating. On all my vehicles I now stipulate the specific tire pressure when the shop wrights the order. A guy I know who was a Goodyear tire engineer always recommended "OEM tire pressure on the door sticker for street use".