Model 3 Tire Pressure

[jsanford]

Ours was delivered with 42. A friend of mine picked his up two days earlier with 45psi. Having ridden in both cars, I can’t discern a difference in the ride.

 

[SomeJoe7777]

18" Michelin Primacy MXM4 = 45 psi recommended (same as Model S). This gives max range, and you still get a good ride because the Primacy is a grand touring tire.

19" Continental ProContact RX = 42 psi recommended (similar to 21" Model S). This gives a less harsh ride than 45 psi, important because the 19" tires have less sidewall and less cushioning.

I believe these will be the pressures posted on the door jam of each Model 3, and it will reflect the tires/wheels that the car was ordered with.

For any tire, there are a range of pressures that are safe. Lower bound on the pressure range is generally defined by the maximum weight of the car + cargo, the car's top speed, and the load rating of the tire. Higher bound on the pressure range is usually the manufacturer's maximum cold tire pressure stamped on the sidewall. Any pressure within this range is safe for driving, but is not necessarily optimum for any particular task:

Max efficiency = higher pressures
Soft ride = lower pressures
Max traction = lower pressures
Best handling = somewhere in the middle

Usually, the car manufacturer tests various tire pressures within the safe range, and determines a pressure that balances the various needs of the car as best as possible.

 

[EV-lutioin]

45 psi was too harsh a ride for me so I dropped it to 40 psi and have kept it there for 4 months. I still get excellent range (the entire 310) and have averaged 249 Wh/m over 5,200 miles. I feel vindicated now that Musk says 39 psi is okay My only issue is that on cold mornings I get the low pressure warning on the screen that takes about 15 minutes to go away. I wish the tire pressure warning was synced with the external temperature sensor so that it did not give false warnings when cold.

 

[dhanson865]

45 psi was too harsh a ride for me so I dropped it to 40 psi and have kept it there for 4 months. I still get excellent range (the entire 310) and have averaged 249 Wh/m over 5,200 miles. I feel vindicated now that Musk says 39 psi is okay My only issue is that on cold mornings I get the low pressure warning on the screen that takes about 15 minutes to go away. I wish the tire pressure warning was synced with the external temperature sensor so that it did not give false warnings when cold.

You do know the 39 psi he is talking about is in the mornings when the car is cold on those coldest mornings? So is the 42 and 45 we are talking about. If you set it to 40 in the afternoon on a warm day it is too low compared to his recommendation of 39 cold and that is why the car is warning you every morning.

40 hot might be 35 cold for all we know. You have to test cold to be sure. If you say it is warning you at 39 cold you'll have to be more specific so we are sure you know the difference.

Here are the warnings about this in the Model 3 owners manual

Warning: Under-inflation is the most common cause of tire failures and can cause a tire to overheat, resulting in severe tire cracking, tread separation, or blowout, which causes unexpected loss of vehicle control and increased risk of injury. Under-inflation also reduces the vehicle's range and tire tread life.

Warning: Check tire pressures using an accurate pressure gauge when tires are cold. It takes only about one mile (1.6 km) of driving to warm up the tires sufficiently to affect tire pressures. Parking the vehicle in direct sunlight or in hot weather can also affect tire pressures. If you must check warm tires, expect increased pressures. Do not let air out of warm tires in an attempt to match recommended cold tire pressures. A hot tire at or below the recommended cold tire inflation pressure is dangerously under-inflated.

 

[smak]

I'm bring my car in to Tesla in the next few days, maybe I'll have them lower them to 42. Starting out cold here is pretty much a non issue

 

[eli_]

18" Michelin Primacy MXM4 = 45 psi recommended (same as Model S). This gives max range, and you still get a good ride because the Primacy is a grand touring tire.

19" Continental ProContact RX = 42 psi recommended (similar to 21" Model S). This gives a less harsh ride than 45 psi, important because the 19" tires have less sidewall and less cushioning.

I believe these will be the pressures posted on the door jam of each Model 3, and it will reflect the tires/wheels that the car was ordered with.

My door jam specifies 42 PSI and I have the 18" Michelin's. VIN range is 163XX. My old car (Acura TL) had the same tires and specified 32 PSI.

 

[camrunr]

I took delivery Jan 5th, #1727. 19's. Door sticker says 42 psi. Currently at 44.

 

[rtanov]

Elon says "Best way to improve ride is drop tire pressure to ~39 psi. 45 psi is best range, but lower comfort."

Elon Musk on Twitter

Last time I played with the tire pressure about a month ago I got the impression that the low pressure warning was being triggered at 40 psi - does anyone know if this has changed with the recent updates?

I am comparing the Model 3 to my beloved E39 540i I had, as they have similar size and weight (different F/R distribution in 3's favor), and I've always had the bimmer at 36-38 psi on similar type tires based on my and others' experience. My main objective is to optimize traction so I would like to go lower. At my first visit in February I asked the Tesla service folks at the local center whether the warning threshold can be lowered or the high recommendation reconsidered and they said no. Looks like Tesla has started moving down recently.

 

[EV-lutioin]

You do know the 39 psi he is talking about is in the mornings when the car is cold on those coldest mornings? So is the 42 and 45 we are talking about. If you set it to 40 in the afternoon on a warm day it is too low compared to his recommendation of 39 cold and that is why the car is warning you every morning.

40 hot might be 35 cold for all we know. You have to test cold to be sure. If you say it is warning you at 39 cold you'll have to be more specific so we are sure you know the difference.

Here are the warnings about this in the Model 3 owners manual

Excellent point! My son and I argued this for over an hour last week. Tire pressure drops ~1 psi per 10º F, so if you fill your tires at 40 psi at 70' F, it will read 39 psi at 60º, which will trigger the low tire pressure warning (Tesla psi warning is set at 39 psi). We researched this ad issue nauseam and could fine no standard temperature for "cold tire pressure". Does cold mean 50º, 60º 70º?? The standard temperature for "cold" tire pressure makes a huge difference because it could vary by 3-5 psi depending on what it is. That being said, the tire pressure warning should not trigger if the tires had the correct psi at the standard cold tire temp. (whatever that is), because it's giving a warning for a temperature that is lower than the official cold tire standard. The warning should be coordinated with the temperature sensor and only give a warning if the psi is too low for the corresponding change in psi as it relates to variation from standard "cold" tire temperature.

P.S: If you know what the standard temperature is for "cold tire pressure" please share!

 

[dhanson865]

Excellent point! My son and I argued this for over an hour last week. Tire pressure drops ~1 psi per 10º F, so if you fill your tires at 40 psi at 70' F, it will read 39 psi at 60º, which will trigger the low tire pressure warning (Tesla psi warning is set at 39 psi). We researched this ad issue nauseam and could fine no standard temperature for "cold tire pressure". Does cold mean 50º, 60º 70º?? The standard temperature for "cold" tire pressure makes a huge difference because it could vary by 3-5 psi depending on what it is. That being said, the tire pressure warning should not trigger if the tires had the correct psi at the standard cold tire temp. (whatever that is), because it's giving a warning for a temperature that is lower than the official cold tire standard. The warning should be coordinated with the temperature sensor and only give a warning if the psi is too low for the corresponding change in psi as it relates to variation from standard "cold" tire temperature.

P.S: If you know what the standard temperature is for "cold tire pressure" please share!

There is no standard temperature for "cold tires" so I set it at the coldest possible I can practically experience and/or adjust by the temp rule for my inability or unwillingness to do so.

I mean I could park outside and then the next morning lay or sit or squat by my car before sun up to set pressure in "outside cold" but I'd rather do it in the comfort of my garage.

So if it is going to be 30F low on the 10 day forecast and it's currently 50F in my garage I add a couple PSI to my "cold" targets. If the low on my 10 day forecast is going to be 60F and my garage is 70F I'll do similar

If my "target cold" PSI is near the sidewall max and my garage is sufficiently warmer I will set it above sidewall max at "garage cold" knowing that will put me at the target PSI "outdoor cold". For example if I want 48 PSI cold, sidewall max is 51, my garage is 40 degrees warmer than the expected low to come I'd set my tires at 52 PSI "garage cold" knowing my tires will cool off when I go outside.

If I see any sort of warning about a season high (heat stroke warnings, or similar) or a season low (freeze warnings, extreme wind chill warnings) then I visit my tire pressures again. In extreme cases I would actually let air out if my newly expected "outside cold" temp puts the current PSI over the sidewall max, but that would probably only happen once a year for a daily driver (around the time you first turn on the AC at your house).

If there aren't warnings I still check the TPMS reported PSI on a infrequent basis when I think about it.

If I was going on a road trip I'd check the expected low temps at both ends and consider the major (overnight or longer) stops along the way. Adjust as needed on a trip.

fwiw the Model 3 Owners manual has this glossary item

Cold Tire Pressure - The air pressure in a tire that has been standing in excess of three hours, or driven for less than one mile.

But as we discussed "cold" varies when the seasons change and by your local microclimate.

 

[T34ME]

My son and I argued this for over an hour last week. Tire pressure drops ~1 psi per 10º F, so if you fill your tires at 40 psi at 70' F, it will read 39 psi at 60º, which will trigger the low tire pressure warning (Tesla psi warning is set at 39 psi).

Hopefully, we will see another instructional video coming from son!

 

[SomeJoe7777]

We researched this ad issue nauseam and could fine no standard temperature for "cold tire pressure". Does cold mean 50º, 60º 70º??

There is no standard temperature for "cold" tire pressure. The meaning of the phrase is that the pressure should be set when the tires are at ambient temperature, before they have been driven on. After driving a few miles, the tire temperature has increased above ambient, and the pressure reading will have correspondingly increased.

Yes, you are correct that the cold tire pressure will indeed vary with temperature, and this will require that you adjust pressure seasonally so that the cold tire pressure is correct. You will need to bleed off air as the average daily temperature gets hotter in the spring and summer, and will need to add air as the average daily temperature gets cooler in the fall and winter.

The reason for this is that tire pressures are "gauge" pressure, meaning that the pressure reading is the difference between the internal tire pressure and the atmospheric pressure outside the tire. Both the internal tire air and the external air are affected by temperature, but there is a fixed mass of air inside the tire which also has a fixed volume. By the ideal gas law equation, PV=nRT, an increase in T will cause an increase in P, while V/n/R are constant. Outside the tire, the volume is not constant (air can use more space around the Earth), so increase in T does not cause an increase in P. Since absolute pressure inside the tire goes up but outside the tire doesn't, then the gauge pressure goes up. The pressure change due to temperature is approximately 1 psi for every 10 degrees F.

The bottom line is that if you want to set your cold tire pressure to 42 psi, you need to do this after the car has been sitting for several hours and the tires are at ambient temperature. The absolute temperature of the air doesn't matter. If the absolute temperature of the air changes radically (say a cold front comes through and average temperature drops from 80F to 50F), then you need to readjust pressure to 42 psi again, also after the car has been sitting for several hours.

For similar reasons, you may also need to adjust tire pressure if you make a large altitude change on a road trip. Increasing altitude increases gauge pressure, requiring you to bleed air at high altitudes to restore the correct pressure. Pressure changes about 1 psi for every 2000 feet altitude.

Sometimes you'll see temperature and altitude pressure changes offset each other. For example, drive from the Las Vegas strip (elevation around 2000 feet) to the Mt. Charleston peak to the west (elevation 11,400 feet). This would increase pressure about 3 psi. But the temperature might also drop from 80F at the strip to 50F at the mountain peak, reducing pressure 3 psi. Tire guage pressure would stay approximately constant.

 

[EV-lutioin]

There is no standard temperature for "cold" tire pressure. The meaning of the phrase is that the pressure should be set when the tires are at ambient temperature, before they have been driven on. After driving a few miles, the tire temperature has increased above ambient, and the pressure reading will have correspondingly increased.

Yes, you are correct that the cold tire pressure will indeed vary with temperature, and this will require that you adjust pressure seasonally so that the cold tire pressure is correct. You will need to bleed off air as the average daily temperature gets hotter in the spring and summer, and will need to add air as the average daily temperature gets cooler in the fall and winter.

The reason for this is that tire pressures are "gauge" pressure, meaning that the pressure reading is the difference between the internal tire pressure and the atmospheric pressure outside the tire. Both the internal tire air and the external air are affected by temperature, but there is a fixed mass of air inside the tire which also has a fixed volume. By the ideal gas law equation, PV=nRT, an increase in T will cause an increase in P, while V/n/R are constant. Outside the tire, the volume is not constant (air can use more space around the Earth), so increase in T does not cause an increase in P. Since absolute pressure inside the tire goes up but outside the tire doesn't, then the gauge pressure goes up. The pressure change due to temperature is approximately 1 psi for every 10 degrees F.

The bottom line is that if you want to set your cold tire pressure to 42 psi, you need to do this after the car has been sitting for several hours and the tires are at ambient temperature. The absolute temperature of the air doesn't matter. If the absolute temperature of the air changes radically (say a cold front comes through and average temperature drops from 80F to 50F), then you need to readjust pressure to 42 psi again, also after the car has been sitting for several hours.

For similar reasons, you may also need to adjust tire pressure if you make a large altitude change on a road trip. Increasing altitude increases gauge pressure, requiring you to bleed air at high altitudes to restore the correct pressure. Pressure changes about 1 psi for every 2000 feet altitude.

Sometimes you'll see temperature and altitude pressure changes offset each other. For example, drive from the Las Vegas strip (elevation around 2000 feet) to the Mt. Charleston peak to the west (elevation 11,400 feet). This would increase pressure about 3 psi. But the temperature might also drop from 80F at the strip to 50F at the mountain peak, reducing pressure 3 psi. Tire guage pressure would stay approximately constant.

This is very interesting, thanks for your detailed description. I'm still perplexed by the inaccuracy of the whole system though. For example it is not unusual to have temperatures above 105º F where I live and lows in the 60's. So with a 40-50º swing, my tire pressure will vary by 4-5 psi. It would not be realistic to change my tire pressure twice a day to account for ambient temperature swings. If tire pressure is so important (according to pretty much everyone), why do we have such an inaccurate way of calculating it? Frankly, I'm starting to think the psi is more about an average than a set number.... especially if my tire pressure can change 5 psi in one day just sitting in my driveway and change by as much as 10 psi when hot from driving. If it was really important to have an exact tire pressure cars would have systems that automatically adjust psi to maintain a constant number regardless of temperature. Which gets back to my point, the tire pressure warning on the Model 3 is pointless if it is not calibrated with ambient temperature. For example, if it's 20º F in the morning and my tire pressure has dropped to 40 to 36 psi, I'm not going to get out my compressor and top them off to 40 psi.... so why bother giving me the warning?

 

[dhanson865]

This is very interesting, thanks for your detailed description. I'm still perplexed by the inaccuracy of the whole system though. For example it is not unusual to have temperatures above 105º F where I live and lows in the 60's. So with a 40-50º swing, my tire pressure will vary by 4-5 psi. It would not be realistic to change my tire pressure twice a day to account for ambient temperature swings. If tire pressure is so important (according to pretty much everyone), why do we have such an inaccurate way of calculating it? Frankly, I'm starting to think the psi is more about an average than a set number.... especially if my tire pressure can change 5 psi in one day just sitting in my driveway and change by as much as 10 psi when hot from driving. If it was really important to have an exact tire pressure cars would have systems that automatically adjust psi to maintain a constant number regardless of temperature. Which gets back to my point, the tire pressure warning on the Model 3 is pointless if it is not calibrated with ambient temperature. For example, if it's 20º F in the morning and my tire pressure has dropped to 40 to 36 psi, I'm not going to get out my compressor and top them off to 40 psi.... so why bother giving me the warning?

Tire pressure goes up with heat, rolling resistance causes heat.

Driving faster increases airflow cools the tires as you drive to some extent preventing thermal runaway.

The higher your PSI the lower your rolling resistance making it a negative feedback loop in the range you will be concerned with.

Because of those reasons no matter what your hot rolling PSI won't go up as much as hot stopped PSI + the heat from rolling.

The engineers set max sidewall temp with all those temperature changes in mind. So you can set it at Cold and ignore the temp increase during the day and during the drive.

If For example, if it's 20º F in the morning and tire pressure has dropped to 36 psi, You should have put more air in the day before or you should put it in then when you noticed or put it in the next chance you get. The minimum pressure at the minimum temperature is all you have to worry about.

If the warning goes off, add more air. Ignore your PSI when tires are hot.

 

[TT97]

18" Michelin Primacy MXM4 = 45 psi recommended (same as Model S). This gives max range, and you still get a good ride because the Primacy is a grand touring tire.

19" Continental ProContact RX = 42 psi recommended (similar to 21" Model S). This gives a less harsh ride than 45 psi, important because the 19" tires have less sidewall and less cushioning.

I believe these will be the pressures posted on the door jam of each Model 3, and it will reflect the tires/wheels that the car was ordered with.

For any tire, there are a range of pressures that are safe. Lower bound on the pressure range is generally defined by the maximum weight of the car + cargo, the car's top speed, and the load rating of the tire. Higher bound on the pressure range is usually the manufacturer's maximum cold tire pressure stamped on the sidewall. Any pressure within this range is safe for driving, but is not necessarily optimum for any particular task:

Max efficiency = higher pressures
Soft ride = lower pressures
Max traction = lower pressures
Best handling = somewhere in the middle

Usually, the car manufacturer tests various tire pressures within the safe range, and determines a pressure that balances the various needs of the car as best as possible.

Manual says 42 psi for all sizes (including 20"). My door jamb has 42 psi with 18" wheels (no psi for the spare )

 

[dhanson865]

I'm starting to think the psi is more about an average than a set number

In case my previous reply wasn't clear on this point:

The PSI set point is about a minimum not an average.

 

[SomeJoe7777]

I'm still perplexed by the inaccuracy of the whole system though.

If tire pressure is so important (according to pretty much everyone), why do we have such an inaccurate way of calculating it?

It's not inaccurate, it just reflects reality.

The gauge pressure accurately and directly correlates with the internal force on the tire and the resulting stresses in the tire's rubber, steel, and nylon belts. The objective of the pressure selection is to have a constant amount of force on those items, as the tire can perform its desired functions with that amount of force on it.

Changing atmospheric pressure changes the gauge pressure and therefore the internal force on the tire materials.

As dhanson stated above, you should have enough pressure in the tire to clear the warnings (and preferably bring the tire to the recommended pressure) when the tire is cold (has not been driven in several hours). Additional pressure that shows up on the gauge after the tires are warm from driving does NOT need to be bled off -- this extra pressure due to driving temperature increases is already accounted for by the manufacturer, even if that pressure exceeds the maximum sidewall pressure value.

In short, do not worry about temperature swings during the day or temperature increases due to driving. Adjust your cold tire pressure once a month to the recommended pressure value on the door placard, and you will be fine.

 

[03DSG]

 

[EV-lutioin]

It's not inaccurate, it just reflects reality.

The gauge pressure accurately and directly correlates with the internal force on the tire and the resulting stresses in the tire's rubber, steel, and nylon belts. The objective of the pressure selection is to have a constant amount of force on those items, as the tire can perform its desired functions with that amount of force on it.

Changing atmospheric pressure changes the gauge pressure and therefore the internal force on the tire materials.

As dhanson stated above, you should have enough pressure in the tire to clear the warnings (and preferably bring the tire to the recommended pressure) when the tire is cold (has not been driven in several hours). Additional pressure that shows up on the gauge after the tires are warm from driving does NOT need to be bled off -- this extra pressure due to driving temperature increases is already accounted for by the manufacturer, even if that pressure exceeds the maximum sidewall pressure value.

In short, do not worry about temperature swings during the day or temperature increases due to driving. Adjust your cold tire pressure once a month to the recommended pressure value on the door placard, and you will be fine.

I appreciate your patience with my question and as a science teacher I am familiar with the science behind temperature and pressure, but what I don't understand is what the set point temperature should be for "cold" pressure. If I adjust my cold tire pressure once a month as suggested, should I do it in the morning when it is 50º or in the afternoon when it is 90º? That choice will result in a 4 psi difference. In science there always has to be a standardized base unit from which to compare your results. Based on the replies to my query it seems like most people agree that having low pressure in tires is more of an issue than high pressure, which is... "already accounted for by the manufacturer". If that is true, then in my scenario with a low of 50º and a high of 90º, it would make the most sense to adjust tire pressure to the lowest temperature of the day (50º). Does that seem correct?

 

[SomeJoe7777]

with a low of 50º and a high of 90º, it would make the most sense to adjust tire pressure to the lowest temperature of the day (50º). Does that seem correct?

Yes, that should be how you do it. Given that the low pressure warning is below 40 psi, and the max sidewall pressure is 50 psi, you have a 10 psi range that's safe for driving, even before driving temperature increases.

Set to 42 psi at the low temperature of the day (morning) and you should be in the proper range all day.

If the following week the daily temperatures end up with a low of 75F rather than 50F, then you might opt to bleed a few psi of pressure (back down to 42 psi @ 75F) just to soften the ride. However, if you don't, you won't hurt anything provided it's not hot enough so that the cold tire pressure is above 50 psi.