[Fastfwd]

The temperatures here have largely been above average for the season, but it looks like there are some below freezing days ahead. I've got my all seasons installed and I'm ready for that.

I am curious what tire pressures others are running for the days that the temperatures get down below freezing? Seems like I've seen something that your 'cold tire pressure' is supposed to be some equation involving what it would be at 60 something (Fahrenheit) less so many pounds for every 10 degrees less than that.

I'm personally gunning for minimum tire pressures not much less than 32lbs however cold it gets. I'm not exactly sure how those 20" with 30 sidewalls will stand up to potholes, etc. with less than 32lbs in the tires.

So, my warm days pressures have been hitting up to 36lbs or so, but I know there will be days (like today) that temperatures may start out with the pressure at closer to 32lbs.

[Fastfwd]

Just took the M2 on a trip over to Arkansas to do some driving in the mountains. Cold mornings down to the upper 20s had my tire pressures dipping to 30-31 psi, but after driving a short distance I was seeing pressures up to 36-37 psi with tire temperatures reaching up to 90f under hard use.

It made me wonder if I was giving up any traction to those higher pressures, but if I was I couldn't tell. I usually carry a little Milwaukee battery powered tire inflation pump with me on trips to keep my pressures as close to recommended levels as possible. I didn't make any adjustments. It seemed fine.

Still not sure what sort of liability it might be to let the pressure get below 32psi with the 30 sidewall tires on these rims. I suppose I'll just have to be careful if they do dip below 32 while at ambient air temperatures down below freezing until they warm up a bit.

[RockCrusher]

Originally Posted by Fastfwd

The temperatures here have largely been above average for the season, but it looks like there are some below freezing days ahead. I've got my all seasons installed and I'm ready for that.

I am curious what tire pressures others are running for the days that the temperatures get down below freezing? Seems like I've seen something that your 'cold tire pressure' is supposed to be some equation involving what it would be at 60 something (Fahrenheit) less so many pounds for every 10 degrees less than that.

I'm personally gunning for minimum tire pressures not much less than 32lbs however cold it gets. I'm not exactly sure how those 20" with 30 sidewalls will stand up to potholes, etc. with less than 32lbs in the tires.

So, my warm days pressures have been hitting up to 36lbs or so, but I know there will be days (like today) that temperatures may start out with the pressure at closer to 32lbs.

I check tire pressures often and adjust tire pressures -- in winter this means adding air -- to ensure the tires are inflated so when the ambient air temperature drops to the expected low temperature the tires are at least inflated to 32psi.

This means when I air up the tires even though they are cold I inflate the tires above 32psi. While today's low is expected to be 33F by next Saturday the low is expected to be 16F. So if I set the tire pressures today I'd set the air pressures to 34psi so when it gets colder the tires are still inflated to at least 32psi.

I actually set the tire pressures the other day when it was in the mid 40s and I set them to 35psi cold. So when the tires cool to 16F they'll of course lose about 1psi per 10F drop in temperature and thus lose about 3psi but this should still have the tires at 32psi at an ambient temperature of 16F.

[RockCrusher]

Originally Posted by Fastfwd

Just took the M2 on a trip over to Arkansas to do some driving in the mountains. Cold mornings down to the upper 20s had my tire pressures dipping to 30-31 psi, but after driving a short distance I was seeing pressures up to 36-37 psi with tire temperatures reaching up to 90f under hard use.

It made me wonder if I was giving up any traction to those higher pressures, but if I was I couldn't tell. I usually carry a little Milwaukee battery powered tire inflation pump with me on trips to keep my pressures as close to recommended levels as possible. I didn't make any adjustments. It seemed fine.

Still not sure what sort of liability it might be to let the pressure get below 32psi with the 30 sidewall tires on these rims. I suppose I'll just have to be careful if they do dip below 32 while at ambient air temperatures down below freezing until they warm up a bit.

While the tires will of course warm up and the tire pressure will climb that is not what you should do.

I strive to avoid driving on under inflated tires. At their coldest I never like to see the tire pressures below in the case of my M2 32psi.

To avoid this I may inflate the tires to some pressure above 32psi (cold) knowing that the car will be exposed to colder temperatures at some point and the tires even though they lose some pressure due to the colder temperature will still be at least inflated to 32psi.

[Fastfwd]

Originally Posted by RockCrusher

While the tires will of course warm up and the tire pressure will climb that is not what you should do.

I strive to avoid driving on under inflated tires. At their coldest I never like to see the tire pressures below in the case of my M2 32psi.

To avoid this I may inflate the tires to some pressure above 32psi (cold) knowing that the car will be exposed to colder temperatures at some point and the tires even though they lose some pressure due to the colder temperature will still be at least inflated to 32psi.

Thank you for your input on this..... I have traditionally set my tire pressures to whatever the recommended spec is while cold in the mornings and tried to monitor it as seasons change and periodically within seasons. These are the smallest sidewall tires I've dealt with so far, however. So, it seems a little more critical to be mindful of the pressure so I don't bend a rim inadvertently.

I did catch some reference within the last few years of this 64 (?) degrees ambient temperature being a factor that I'm not sure I (still) completely understood the relevance of. I might understand using that temperature as a reference point of how much air your tires will lose at 1psi per 10 degrees below 64, but it still confuses the issue imo.

Performance driving becomes possibly another matter and this probably gets amplified more in summer than winter as the tires heat up. To be clear, I wasn't heading out in the mornings that dipped into the 20s while the roads where at freezing temperatures. I was generally waiting until it warmed up a little with daytime temperatures hitting 50 degrees on some days.

The more I'm looking for information on this I'm seeing that maybe 37psi could be optimal when the tires get up to temperature, but there is no hard and fast rule. I was watching it closely as I was driving hard to see what happened. Even as ambient temperatures rose into the 40s if the tires cooled off to the 60s after driving relatively hard on them I might see the tires get down to 33psi.

This is also the first car I've owned that reports the temperature of the tires. So, that's just interesting for me to observe the relationship of ambient temperatures and reported tire temperatures during various driving conditions.

I have seen one Youtuber reference searching for the 'Goldilocks' tire pressure for a particular application, use case, etc. This may be a more personal discovery journey than anyone else can answer for me.

[ttaidapos]

Isn't the recommended 32psi on as cold tire?

[Fastfwd]

Originally Posted by ttaidapos

Isn't the recommended 32psi on as cold tire?

The short answer is yes.

[Fastfwd]

I don't mean to beat a dead horse with this, but I think my original sentiment if I can summarize it was more along the lines of what absolute minimum tire pressure would others run on these particular wheels.

Take this scenario into consideration. You've done your homework and you've calculated what pressure your tires should be for upcoming colder weather. Ok? So, you get caught by surprise and it's not 25 degrees out it's 15 degrees. Are you going to get out your tire pump and air up all 4 tires 1psi in the 15f weather to run your tires at exactly 32psi?

[ttaidapos]

Mind you I'm on 19x45x40 square, alpine 5. 29psi is the absolute lowest I'm comfortable with. At the same time, anything over 34, feels like I'm driving on cement tires.

[Fastfwd]

Originally Posted by ttaidapos

Mind you I'm on 19x45x40 square, alpine 5. 29psi is the absolute lowest I'm comfortable with. At the same time, anything over 34, feels like I'm driving on cement tires.

Appreciate your input. I have also wondered if I'm sacrificing some ride quality to run higher than needed tire pressure. I'm more concerned with bending the rims though.

These concerns may not be as pertinent for those in climates that maintain a more consistent seasonal temperature. Where I am it seems to vary wildly in the winter and it's been unusually warm so far this year, but bitter cold is coming soon.

[ttaidapos]

Originally Posted by Fastfwd

Appreciate your input. I have also wondered if I'm sacrificing some ride quality to run higher than needed tire pressure. I'm more concerned with bending the rims though.

These concerns may not be as pertinent for those in climates that maintain a more consistent seasonal temperature. Where I am it seems to vary wildly in the winter and it's been unusually warm so far this year, but bitter cold is coming soon.

2 or 3 psi is not going to save your wheels hitting something substantial. However, your concern with swinging temperatures is real. Snow tires are not as sensitive to temperature changes as performance tires, at least in my experience. The best that you can do is just be prepared for the temperature swings. The M2 has a rough ride IMO, and you have it lowered, even more pronounced. I get it, you feel like you're breaking something, but you're not. Try to stick to 32 and no lower than 30. I have a cable less, compact tire inflator add it's quick enough to adjust tire pressure. I've also noted that the car is off by 1-1.5 PSI (lower) than my other instruments (multiple readers).

[Fastfwd]

Originally Posted by ttaidapos

2 or 3 psi is not going to save your wheels hitting something substantial. However, your concern with swinging temperatures is real. Snow tires are not as sensitive to temperature changes as performance tires, at least in my experience. The best that you can do is just be prepared for the temperature swings. The M2 has a rough ride IMO, and you have it lowered, even more pronounced. I get it, you feel like you're breaking something, but you're not. Try to stick to 32 and no lower than 30. I have a cable less, compact tire inflator add it's quick enough to adjust tire pressure. I've also noted that the car is off by 1-1.5 PSI (lower) than my other instruments (multiple readers).

No lower than 30 has been my goal. Good to know that I might want to watch how my tire pump gauge reads vs the car's tpms sensor. Appreciate the tip. My tire pump tends to lose its calibration, but I did just find out how to reset it. I may have to find a backup to verify them both.

I realize that some people might just wonder why not inflate the tires to anything under the maximum inflation pressure that can accommodate any cold tire temperature for the season. I'm just trying to find the balance of ride quality and traction/performance, etc. without damaging the wheels/tires in the process.

I know this must sound super nitpicky. The BMW R1250RS motorcycle I bought a couple years ago reports tire pressures down to 1/10th psi. Which makes exceeding 1-2psi from recommended pressure seem like an even bigger deal. It can be a chore to keep them within spec.

[izzyM2]

Am I to follow the forums or the app?

[aerobod]

Originally Posted by izzyM2

Am I to follow the forums or the app?

It depends on the winter conditions you are driving in. I would always ensure a minimum pressure is maintained at the lowest anticipated temperature, bearing in mind the approximate rules of 0.1 bar pressure loss per 10C temp drop / 1 PSI per 10F.

When I left our unheated garage today the tyre pressure was 2.3/2.5 bar (33/36PSI) front/rear in our Macan, dropped to 2.1/2.3 bar (30/33PSI) while outside at the drug store for 30 mins in -32C ambient, then rose to 2.5/2.7 bar (36/39PSI) while parked in the heated indoor parking at the mall for an hour.

I will probably put another 0.1 bar in the tyres before going out tomorrow, as the forecast is for -40C Fri night and my target min pressures are 2.1/2.3 bar.

[Ravenseal]

You want low PSI in the winter to maximize traction. Nitrogen fill helps a lot with this, which is free with a Costco membership. Since nitrogen doesn't change in density with temperature changes, set the tires to 34 PSI and run with it.

[aerobod]

Originally Posted by Ravenseal

You want low PSI in the winter to maximize traction. Nitrogen fill helps a lot with this, which is free with a Costco membership. Since nitrogen doesn't change in density with temperature changes, set the tires to 34 PSI and run with it.

Nitrogen does change density the same as dry air with temperature, it closely follows the Ideal Gas Law. There is no advantage to using nitrogen in car tyres compared with dry air (assuming that there is no significant moisture in the air supply).

Aircraft tyres are the only place where nitrogen has a major advantage - to prevent rapid fire spread from the oxygen in the air if a tyre bursts and there is any fluid leak in the wheel bay that catches fire.

[M3SQRD]

Originally Posted by aerobod

Nitrogen does change density the same as dry air with temperature, it closely follows the Ideal Gas Law. There is no advantage to using nitrogen in car tyres compared with dry air (assuming that there is no significant moisture in the air supply).

Aircraft tyres are the only place where nitrogen has a major advantage - to prevent rapid fire spread from the oxygen in the air if a tyre bursts and there is any fluid leak in the wheel bay that catches fire.

Good points. Dry air is 80% Nitrogen so if it’s truly dry air then Nitrogen has a small benefit over dry Oxygen so it doesn’t justify the expense of using Nitrogen. However, if you’ve unknowingly used wet Oxygen instead of Nitrogen (this happened to a spacecraft once during integration in a clean room) then you’ll suffer the consequences. At least with a car the tires will survive the resulting change in pressure.

[fangelov]

Originally Posted by Ravenseal

You want low PSI in the winter to maximize traction. Nitrogen fill helps a lot with this, which is free with a Costco membership. Since nitrogen doesn't change in density with temperature changes, set the tires to 34 PSI and run with it.

Why would Nitrogen not change density with temperature changes?
By the way air is ~78% Nitrogen.

[fangelov]

Originally Posted by M3SQRD

Good points. Dry air is 80% Nitrogen so if it’s truly dry air then Nitrogen has a small benefit over dry Oxygen so it doesn’t justify the expense of using Nitrogen. However, if you’ve unknowingly used wet Oxygen instead of Nitrogen (this happened to a spacecraft once during integration in a clean room) then you’ll suffer the consequences. At least with a car the tires will survive the resulting change in pressure.

Why would you use Oxygen inside tires of any kind?

[M3SQRD]

Originally Posted by Carefree

Gas density, including nitrogen, changes with temperature. Every high school chemistry class teaches the pvt (pressure-volume-temperature) relationship.

Ok…temperatures will change and i do t disagree with that. I’m saying the difference between Nitrogen and dry Air isn’t worth it if you have to pay for it.

[Carefree]

Originally Posted by M3SQRD

Ok…temperatures will change and i do t disagree with that. I’m saying the difference between Nitrogen and dry Air isn’t worth it if you have to pay for it.

I agree with you 100% @32psi
That was for the edification of a chemistry/physics challenged individual not you.

[aerobod]

Originally Posted by Ravenseal

By the way nitrogen is 100% nitrogen.

It is easy to predict the pressure in the tyres when filled with nitrogen. Radial tyres are very predictable in volume when inflated to fully support the car and used within their speed rating. The volume stays constant within a very small percentage due to the steel belts in the tread and sidewall reinforcement, so don’t expand like cross-ply/bias-ply tyres do.

This means that P∝T.

It is then easy to compare absolute temperatures and pressures, bearing in mind the actual pressure is the measured tyre pressure plus atmospheric pressure, the actual temperature is relative to absolute zero, so is best calculated in Kelvin.

293K / 20°C / 68°F at an absolute pressure of 3.40bar (measured 2.40bar / 34.8PSI at sea level), equates to:

313K / 40°C / 104°F at an absolute pressure of 3.63bar (measured 2.63bar / 38.1PSI at sea level)

273K / 0°C / 32°F at an absolute pressure of 3.17bar (measured 2.17bar / 31.4PSI at sea level)

233K / -40°C / -40°F at an absolute pressure of 2.70bar (measured 1.70bar / 24.7PSI at sea level)