Why 42 PSI ?

[enemji]

What is with Tesla suggesting the same tire pressure of 42psi regardless of the 18” tire it comes with?

Michelin MXM4 is rated at 98w

• Max Load:
  1,653 lbs
• Max Inflation Pressure:
  50 psi

Hankook Kinergy GT is rated at 94v

• Max Load:
  1,477 lbs
• Max Inflation Pressure:
  51 psi

What is the actual tire pressure based upon the GVWR?

Front 2447 lbs
Rear 2771 lbs

 

[blackT3$!@]

What is the actual tire pressure based upon the GVWR?

42 psi. Keep tires inflated to the pressures shown on the Tire and Loading Information label, even if it differs from the pressure printed on the tire itself. The Tire and Loading Information label is located on the center door pillar and is visible when the driver door is open. Tire pressures display on the touchscreen in the cards area on the car status display, or by touching Controls > Service. If your Model 3 is equipped with aftermarket tires that differ in size from those printed on the Tire and Loading and Loading Information Label (see Vehicle Loading), it is the driver's responsibility to determine the correct tire pressure. Model 3 Owner's Manual | Tesla

 

[vogz]

Recommend tire pressure is based on the vehicle, not the tire itself. That said, you can play with different pressures around the recommended and see what works best for you.

Max pressure is just that. Max pressure. You don't want to fill your tires to anywhere near the max pressure since pressure will increase when you drive the car and the temperature of the tires increase.

 

[GlmnAlyAirCar]

You don't want to fill your tires to anywhere near the max pressure since pressure will increase when you drive the car and the temperature of the tires increase.

Not true. Max pressure is max COLD pressure.

 

[zoomer0056]

Not true. Max pressure is max COLD pressure.

Yup, cold

 

[E90alex]

I don’t understand the question?

Every car manufacturer has various tire suppliers and recommends the same pressures for the same tire size. It’s mostly a factor of desired rolling resistance and rolling diameter and suspension tuning. But even then a couple PSI is not likely to make a noticeable difference.

It would be insane to have a different specified pressure for every brand of tire in that size because not everyone is going to replace it with factory tires, and the factory tires will eventually get discontinued at some point.

The end customer can vary the pressure up or down if they want depending on their own preferences (although not as much in newer cars due to TPMS wanting a specified pressure range).

 

[Candleflame]

until late 2019 tesla actually recommended 45 psi.

 

[heavyD]

It's all about tire longevity and rolling resistance. The higher the better with heavy EV's.

 

[m73b54]

I keep mine at 38psi. Noticeably smoother.

 

[comanchepilot]

Because the answer is 42?

 

[rpiotro]

It's all about tire longevity and rolling resistance. The higher the better with heavy EV's.

What about not so heavy EVs. My 2021 SR+ came in at 3616 lbs. My last two cars, sedans. Were at least 400 lbs. heavier. I don't believe either one called for tire pressures above 36 PSI

I run mine M3's tire pressures at 38-40 cold for comfort. I also ditched those awful MXM4s for CrossClimate2s. Not really seeing a hit in range.

 

[DP26]

If you can find the tire manufacturer’s inflation chart, you can figure the proper pressure for the weight (add a safety factor). This is the true min pressure for a given load. Need real 4 corner weights as axle weights are not accurate enough.

The vehicle manufacturer has a different need, usually to get best epa and for max load.

 

[UncleCreepy]

What is with Tesla suggesting the same tire pressure of 42psi regardless of the 18” tire it comes with?

Because what you want is basically a certain amount of rubber that is in contact with the street.

The following is dumbed down a bit but for the purpose of your question it's reasonably accurate.

Let's look at a car that weighs 4,000 lbs and has its weight evenly distributed, so each tire is carrying 1,000 lbs. A perfect tire is round, but since it's pushing down on the street, the area that touches the street is flat. The question is: how big is this area? With a pressure of 40 psi (pounds per square inch) it's 1000/40=25 square inches.
The tread width of a Model 3 is 235 mm or about 9.25 inches, so the length of the square footprint would be 25/9.25=2.7 inches.

If you reduce the tire pressure, the amount of rubber touching the street is bigger, causing the tire to flex more, thus causing more rolling resistance.

What car manufacturers do is that they try to find a pressure that is both good for fuel economy and comfort. The max cold pressure of the tire has nothing to do with it and neither does the make of the tire.

 

[NeverGoingBack]

Because the answer is 42?

Given the general attitude and personality of Tesla ……… I would not be surprised at all if that is why they chose that number

 

[heavyD]

What about not so heavy EVs. My 2021 SR+ came in at 3616 lbs. My last two cars, sedans. Were at least 400 lbs. heavier. I don't believe either one called for tire pressures above 36 PSI

I would imagine your last two ICE sedans didn't have the instant acceleration of your Model 3. I believe instantaneous acceleration alone is good for faster wear. There's lots of factors working against tire life when it comes to EV's.

 

[enemji]

42 psi. Keep tires inflated to the pressures shown on the Tire and Loading Information label, even if it differs from the pressure printed on the tire itself. The Tire and Loading Information label is located on the center door pillar and is visible when the driver door is open. Tire pressures display on the touchscreen in the cards area on the car status display, or by touching Controls > Service. If your Model 3 is equipped with aftermarket tires that differ in size from those printed on the Tire and Loading and Loading Information Label (see Vehicle Loading), it is the driver's responsibility to determine the correct tire pressure. Model 3 Owner's Manual | Tesla

Not only you but pretty much everyone here missed the real question, which I will repeat below:

What is the actual tire pressure based upon the GVWR? (Given the load carrying capacity is different ie 98W & 94V)

Front 2447 lbs
Rear 2771 lbs

 

[DP26]

see prior reply. Find the load/inflation chart if you can.

 

[RayK]

Given the general attitude and personality of Tesla ……… I would not be surprised at all if that is why they chose that number

Yeah, Elon probably would have preferred 69 psi but then you'd have to use truck tires.

 

[GreenCoffee]

Not only you but pretty much everyone here missed the real question, which I will repeat below:

What is the actual tire pressure based upon the GVWR? (Given the load carrying capacity is different ie 98W & 94V)

Front 2447 lbs
Rear 2771 lbs

I get it, not sure why your question was not answered but I have been struggling to understand this as well, for instance on the model Y there are 3 different load range tires for just the front axle.

Model Y performance front tire is 255/35/21 load range 98 or 1,653 max load
Model Y with 20" induction wheels are 255/40/20 load range 101 or 1,819 max load
Model Y with 19" gemini wheels are 255/45/19 load range 104 or 1,984 max load

using a tire pressure calculator

Tire Pressure Calculator

Easy to use tire pressure calculator. Use our tire pressure calculator to calculate the new tire pressure needed when changing tire sizes.

tiresize.com

and going by the tire mounted on the front of the performance model Y 42 psi on the front tire would equate to 38 psi on the Induction wheel tire and 34 psi on the gemini wheel tire.

I just switched tire size from stock to a 275/40/20 with a load range of 106 which would equate to 32 psi, I have been running 35 psi and setting off the tpms tire pressure warning, wish we could reset them to a custom psi like maybe 35 or 36.

 

[kgvickers]

If the tire is an "Extra-Load (XL)" load range tire, which the stock 18" tires are, then they meet the "Load Index" #98 rating of 1653 pounds load at inflation pressure of 42 psi (per info on this page from discount tire: Discount Tire | Tires and Wheels for Sale | Online & In-Person ).

I read somewhere that at less than 42 psi, an XL load index tire is no longer certified to the the load shown on the side of the tire. Per that same page, a "Standard Load" tire meets its max load carrying at 36 psi.

I've noted that my 2019 Model 3 Performance came with the 20" tires with a Load Index of 92 .... 1389 lbs. This is considerably less than the 18" Aero tires with the 98 Load Index .... 1653 lbs. Quite a difference.

Anyway, all that to simply say: I think it's 42 psi because that's what's required to meet the XL load index rating.