Winter Tire PSI

[4givingGuy]

After switching to my new 19” winter wheels and tires (see photo taken after my morning commute here in Minnesota), service had to stop by and get the LUCID TPMS registered to the vehicle. A $60 service fee FYI.

A couple of interesting/dubious points were brought up by the mobile tech:
1) The Stealth package vehicle somehow didn’t have 19” tire profile registered in the firmware/software. They had to apparently contact the mothership to get this pushed out to my car through a separate software update - though the version remained the same 2.1.33
2) He suggested they needed to be inflated to 49 PSI. As a longtime Tesla driver, this seemed high to me and @Bobby’s Lucid Update FAQ doesn’t note anything on this topic that I can verify.

For anyone switching seasonal tires, I thought both of these points may be of interest and if there are any counter-facts it would be good to know for future reference.

 

[hydbob]

The stock 19s at inflated to 49 so it makes sense yours would also to not trip the TPMS. I keep mine inflated to 52.

 

[Daniel2022AT]

49 psi sounds high but actually the car rides and handles nicely at that inflation.

Many years ago doing club racing with the BMW Car Club we would inflate tire pressure on race day up to the max limit which was 55 or 59 back in the day. Best traction and minimize sidewall deflection and temperature melt-downs/blow outs.

I do notice there is leakage at the higher pressure. I top off once a month.

 

[Volund]

The stock 19s at inflated to 49 so it makes sense yours would also to not trip the TPMS. I keep mine inflated to 52.

If you're at 52, which is jgijee than the max, if you drive hard and the tire warms up, won't you exceed 52 by a but? Maybe 55-56 psi?
I notice when my car is at 43 it makes it to 48-49 psi when the tires are warm

 

[TFCooper]

If you're at 52, which is jgijee than the max, if you drive hard and the tire warms up, won't you exceed 52 by a but? Maybe 55-56 psi?
I notice when my car is at 43 it makes it to 48-49 psi when the tires are warm

This protocol is incorrect. The tires should be inflated to 49 when cold, i.e. when sitting outside. After some freeway driving, they should be well above 50 psi.
I add air as the weather gets cold, since psi drops with temperature: very roughly, about 1 psi per 10°.

 

[lucidtouringman]

Sorry.. pleading ignorance here.. but I've always only followed the mfr recommended 42 PSI for 20" on Touring... do I need to bump it up a few psi during winters? If yes, why? I'm going to fill up my car tires today so would like to get it right . Thanks in advance!

 

[TFCooper]

Sorry.. pleading ignorance here.. but I've always only followed the mfr recommended 42 PSI for 20" on Touring... do I need to bump it up a few psi during winters?

No, just keep it at the recommended 42 psi. My point was that in cold weather you'll need to add air to maintain 42 psi.

 

[borski]

pV = nRT

That means pressure (p) is directly correlated to temperature (T) - as T drops, p drops, so you have to put air in to bring p up

 

[lucidtouringman]

PV = nRT

That means pressure (P) is directly correlated to temperature (T) - as T drops, P drops, so you have to put air in to bring P up

It would be interesting to plot the change in T correlating to a drop in P in PSIG.. so we know how many more Ps to add depending on how low the Ts get...a lookup table like that would be nice..cos right now I'd be guessing how many Ps to add based on dropped Ts....

I feel like a science project coming on..

 

[kurious]

I wonder how much the warm tire temperature (steady state on freeway) varies with ambient and road surface temperature.
How much colder (and lower pressure) is the air in our tires on a cold winter freeway vs death valley highway?
PV = nRT still applies, but I doubt a 100 degree difference in weather and road means the same 100 degree difference in tire temperature (and therefore pressure.)

 

[borski]

It would be interesting to plot the change in T correlating to a drop in P in PSIG.. so we know how many more Ps to add depending on how low the Ts get...a lookup table like that would be nice..cos right now I'd be guessing how many Ps to add based on dropped Ts....

I feel like a science project coming on..

Doesn't really matter, does it? If you're filling up air, you're gonna use a gauge to test whether you got it right anyway - I don't have a fancy compressor that I can be like 'TWO PSI PLEASE' and it will just dole out the right amount lol

 

[borski]

I wonder how much the warm tire temperature (steady state on freeway) varies with ambient and road surface temperature.
How much colder (and lower pressure) is the air in our tires on a cold winter freeway vs death valley highway?
PV = nRT still applies, but I doubt a 100 degree difference in weather and road means the same 100 degree difference in tire temperature (and therefore pressure.)

Yeah, that's the ideal gas law. It is so named because no such gas actually exists, but it's a good approximation. You're right that it's not exact, heh

"An ideal gas is a theoretical gas composed of many randomly moving point particles that are not subject to interparticle interactions."

 

[lucidtouringman]

Doesn't really matter, does it? If you're filling up air, you're gonna use a gauge to test whether you got it right anyway - I don't have a fancy compressor that I can be like 'TWO PSI PLEASE' and it will just dole out the right amount lol

Ummm...might wanna Google that.. I have a compressor that will give me exactly the psi I want... here... In which case a Temp vs PSIG chart would be helpful ..

Airmoto Tire Inflator

Amazon.com

 

[Volund]

Ummm...might wanna Google that.. I have a compressor that will give me exactly the psi I want... here... In which case a Temp vs PSIG chart would be helpful ..

Airmoto Tire Inflator

Amazon.com

I went off @Bobby recommendation and got the gooloo which is also $30 cheaper

 

[HES]

I have 19” Pirellis that came with the car, and I’m in a warm climate. I keep the tires at 49 psi as recommended, and they normally go up to around 52/53. When I drove up to North Carolina over Thanksgiving the tires seemed low, so I brought them back up to 49 cold (and it was COLD up there!). Driving back south at freeway speeds the tires went up to 55/56. I was nervous about being overinflated, but they handled beautifully. So I guess there’s a lot of wiggle room for expansion.

 

[TFCooper]

Here's what I do in the winter: I want my Pirelli 19" tires to be at the recommended 49 psi when it's 32° outside. My garage tends to be around 50°.
So I inflate my tires to 51 psi in the garage. Easy rule of thumb, huh?
If it's 10° or 20° outside, I'll live with the slight underinflation. If it's 40° outside, I'll live with the slight overinflation.
Keeps it simple.

 

[borski]

Ummm...might wanna Google that.. I have a compressor that will give me exactly the psi I want... here... In which case a Temp vs PSIG chart would be helpful ..

Airmoto Tire Inflator

Amazon.com

That’s… not what that does. That lets you set 49PSI and it will always bring it back up to 49PSI. You cannot set “2 PSI” and have it only add 2 PSI if you’re at 47. I have a very similar compressor.

The desired inflation does not change with weather. The actual inflation *in the tire* does. So just set 49 on that bad boy, check it with a good manual gauge, and you’re all set.

No chart needed.

 

[lucidtouringman]

That’s… not what that does. That lets you set 49PSI and it will always bring it back up to 49PSI. You cannot set “2 PSI” and have it only add 2 PSI if you’re at 47. I have a very similar compressor.

The desired inflation does not change with weather. The actual inflation *in the tire* does. So just set 49 on that bad boy, check it with a good manual gauge, and you’re all set.

No chart needed.

I think we're talking .. typing.. past each other.. perhaps a topic for when we meet in person someday.. I agree with your comments, but think I'm failing to get across the type of chart I'm thinking of .. no worries.. over a beer someday

 

[borski]

I think we're talking .. typing.. past each other.. perhaps a topic for when we meet in person someday.. I agree with your comments, but think I'm failing to get across the type of chart I'm thinking of .. no worries.. over a beer someday

Haha no worries! You’re probably right. Are you referring to the temperature delta between the garage and outside? That I hadn’t considered, since my garage is immensely uninsulated.

And in for beers!

 

[Worldwide Beagle]

So I guess there’s a lot of wiggle room for expansion.

Try 100%. So I was told by Conti lawyers. You should never be concerned about hot pressure while driving, unless your tpms shows 20 psi and something is really wrong. People have died letting air out of hot tires. 20 years ago, rumors were spread and people started checking hot pressure and reduced psi.

All settings are based on cold ambient temperature. @lucidtouringman makes a good point: if it 20 outside and your garage is heated to 70, then your garage is not the ambient temperature. Same if it's 120 outside and your garage is cooled to 75.

One last point: THERE IS NO ONE PERFECT TIRE PRESSURE. For any tire. Every tp is a recommendation and a compromise. Auto manufacturers have to balance safety, comfort and handling. You cannot, usually, get all three. @HES made a great point, at higher tp, the car handled better. At the track in PCA club racing, we always used max cold inflation. But never used that everyday. Our teeth would fall out.

What this means is, yes @HES, you have a ton of flexibility. I prefer the term: acceptable range of settings. Example. Our 21" summer Pirelli's have a Lucid recommendation of 42psi. Cold, ambient. I consider that a safe minimum. If you are careful, the car drives fine, but too much oversteer and do not get near a damn pothole. I believe Lucid chose that based in large part on comfort.

I use 45. And like it. The car handles noticably better with far less oversteer and more predictable turn in. Only a moderate change in ride comfort. To ME, it's worth the decrease in comfort.

The 21" tire is rated to max cold of 50, I think. I am sure the car would handle even better at 50, but at a loss of more ride comfort. In sum: for this tire, you can use 42 to 50. All are safe. None are wrong. What are YOUR tradeoffs?