Why 42 PSI ?

[Perscitus]

Rule of thumb is to 1. stay below max cold inflation pressure of a given tire, with some margin of safety baked in, then 2. refer to the door sticker, manual for OEM recommendation and 3. perhaps strike a balance between the two based on many many different factors (with varying degrees of importance for each driver, climate, car use) including observed tire wear, set alignment, tire used, etc

MPP, for example, openly recommends raising the cold inflation tire pressure to 48psi all around for stock Ys and 3s, with either OE or fairly heavily modified suspension setup and ~ OE spec tires.

 

[GreenCoffee]

Tires on a sedan, coupe, crossover or minivan are usually unmarked because they have a standard 4-ply rating and do not require higher load carrying abilities. However, you may find these tires marked as Standard Load (SL) or Extra Load (XL or Reinforced). Both have a 4-ply rating, but the Extra Load can support additional load at up to 42 PSI while the Standard Load is 36 PSI.

Load index is another way to further describe a tire’s carrying capacity. The load index explicitly indicates the max load a tire can carry. To find your tire’s carrying capacity, look for the load index number on the sidewall. Load index is a more precise method of measurement than load range which focuses mostly on construction.

The load index number indicates a tire’s carrying capacity when inflated to maximum load sustaining pressure. It further explains the tire load range measurement by adding more specifics to the rating.

These paragraphs above are copied from a tire store site.

I personally believe that the reason Tesla does not make adjustments for inflation pressure is for maximum range numbers, I could be wrong but my pick up has a 275/60/20 load range 115 or 2,679 at 51 psi, now my sticker in the door panel says 33psi, why is that? because its adjusted for the weight of the vehicle is why. Interestingly I just put those numbers in on the tire pressure calculator and 33 psi only drops load on these tire to 2,485.

 

[MY-Y]

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

According to this Load Table for the weights you gave: 26 PSI, however, my sticker says:
Front GAWR: 3004, 1502lb/tire = 29 PSI
Rear GAWR: 3606, 1803lb/tire = 36 PSI (extrapolated as this table doesn't have an XL 255/45r19)

With a GVWR of only 5302, those GAWRs are quite generous.

I wouldn't go below 36 either way with the stock tire size

 

[zoomer0056]

Because the answer is 42?

Ha, good one!

 

[enemji]

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 ).

The Hankook Kinergy GT is 94V. Is that still XL?

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

 

[enemji]

Popcorn:
Audi Q4 e-tron® Tire Pressure: 32 psi
Hyundai Ioniq 5: 33psi

 

[philip295]

Because the answer is 42?

6 x 9

 

[kgvickers]

The Hankook Kinergy GT is 94V. Is that still XL?

Well, truth is I don't know. Hmmm .... my previous answer might not be totally correct.

 

[Willy’sEV]

I kept my tires at 42……and I was blessed with replacement at 22K miles.
Shortest life on tires ever for me.

 

[dafish]

OP:
I looked at this in some depth. There is a lot of belief and myth associated with your question, more than a little FUD, and some "I only follow the manual" baked in. Attached is the result of my thinking. It may not be the last word on the matter, but if you review it and the links associated I think you'll find it's reasonable well supported. I have, BTW, modeled it a few different ways. Bottom line is there is little air pressure difference needed as a result of different in modeling.

I would particularly encourage you to look at the rolling resistance difference's. Yep, pretty solid difference between 25 psi and 35 psi. But not much between 35 and 45.

I'm keeping mine at 36-37 and hoping not to bend a rim.

YMMV

Link

 

[dafish]

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.

This is all true. Some might get the wrong idea though - An XL tire is certified to hold more air pressure, not weight. Weight comes with it, but is only a function of air pressure and volume. In fact a "regular" tire and an "XL" at 36 psi carry the exact same weight.

 

[Apprunner]

I kept my tires at 42……and I was blessed with replacement at 22K miles.
Shortest life on tires ever for me.

I wish I got 22k. I barely got 11k on my last set of PS4S. I switched to PS All-Seasons 4...hoping for at least 20K on these

 

[GreenCoffee]

OP:
I looked at this in some depth. There is a lot of belief and myth associated with your question, more than a little FUD, and some "I only follow the manual" baked in. Attached is the result of my thinking. It may not be the last word on the matter, but if you review it and the links associated I think you'll find it's reasonable well supported. I have, BTW, modeled it a few different ways. Bottom line is there is little air pressure difference needed as a result of different in modeling.

I would particularly encourage you to look at the rolling resistance difference's. Yep, pretty solid difference between 25 psi and 35 psi. But not much between 35 and 45.

I'm keeping mine at 36-37 and hoping not to bend a rim.

YMMV

Link

Damn! this is some detailed info, looks to professional to question I would have to assume all is correct here, haha.

I always step up in width 2 section sizes if there is room and that does add some height with extra rim protection, I just like the way these heavier cars drive with a little bit higher load range tire, I went to a 275/40/20 from the stock 255/40/20 increasing height 0.7" and width 0.8" so now my sidewall is 4.35" vs. the stock 4" of course you will suffer at least 7 or 8% range loss over the life of the tire (at least I did on my model 3)

 

[3sr+buyer]

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.

And also for enough of a margin of safety against neglectful drivers not keeping the tires at the needed pressure.

Remember the Ford Explorer with Firestone AX, ATX II, and Wilderness AT tire failures? At the time, the Explorer had a 26psi recommended tire pressure, which did not give much margin of safety against driver neglect of tire pressure. Those tires (with only a C temperature rating on the UTQG scale) did not need much underinflation from 26psi to greatly increase the risk of failure.

Also note that major safety incidents can have lasting effects on maintenance procedures. All car dealers (and Tesla service centers) now check tire pressure on any car that enters a service bay. Toyota dealers now check floor mat installation when cars enter their service bays due to the floor mat unintended acceleration incidents.

 

[Benito1283]

6 x 9

close ...

 

[Perscitus]

Some good info here below this calculator.... Tire Pressure Calculator

 

[enemji]

Some good info here below this calculator.... Tire Pressure Calculator

My gut told me that if Hankook 94v needs 42psi then the MXM4 would need 37psi. This link says the same


.

 

[DP26]

Every motorhome board has the same discussion over and over. There is a tire expert who shares and educates. For a mh, a 15% safety factor is reasonable. For a car, likely 10 or even 5 is reasonable because of less load variation. The key is real corner weights and the tire manuf load inflation chart.

For real popcorn, read the debates on LT vs ST for travel trailers.

Tpms is the result of the blowout debacle.

 

[UserAnon99]

until late 2019 tesla actually recommended 45 psi.

According to my Service Center, still is. I just took delivery a few months ago and the tech that did the walkthrough recommended 45PSI, I guess he is old school. ¯\_(ツ)_/¯ I can't imagine the difference between 42 and 45 is even noticeable. M3P 20" wheels, for reference.

 

[E90alex]

My gut told me that if Hankook 94v needs 42psi then the MXM4 would need 37psi. This link says the same


.

View attachment 922831

View attachment 922836

Except the Michelins were the original factory tire and the Hankooks were the alternative/backup option.

In this case if you swap them, website says the Hankook is not recommended for use.

Do you trust the website or trust Tesla?