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Recommended tire pressure reverted for 18" wheels?

metaclass

Member
Oct 1, 2019
28
12
San Jose, CA
I've read some posts saying that the original recommended tire pressure for 18" wheels was 45 psi, and then it changed to 42 psi (door stickers).

My M3 SR+ was built and delivered 09/2019. However, the door stickers show 45 psi:
Tire Pressure.jpg


I checked owner manual and it shows 42 psi there. I believe the pressure was ~42 psi upon delivery, but I filled to 45 psi later for better range.

Any idea if Tesla reverted the number recently?
 

03DSG

Active Member
Apr 5, 2016
2,150
2,453
Ontario
Maybe you’d got an older door jam sticker in error? As you indicate the manual still specifies 42 lbs for both 18”, 19” and 20” for all tire types listed:

E24EB841-01D1-4BB6-90A8-CFEE051115DC.png
 

mreynolds767

Member
Jul 11, 2019
728
392
Boston
I just checked my door sticker, also have a 9/2019 build (AWD with 18's)
Door states 42 PSI for both front & rear

My car upon pickup was at 45 PSI though and still remains at that. I think I would prefer 42 but too lazy to change it myself.
 

XLR82XS

D M C
Jul 26, 2019
3,141
1,794
SWFL | Vegas
I believe that the door is required to be correct. It's what every tire shop is going to use.
Required by law? I always inform tire shops of cold pressure desired if I want it set a specific way. That 45 does seems odd as every 3 I've seen states 42 cold. FWIW I keep my 3 at 42 cold.
 

Sophias_dad

Supporting Member
Jul 29, 2018
1,245
1,198
Massachusetts
In the upper left of one of the OP's attached pictures you can see the mfg. date. Its clear its not a misprint... sometime recently(apparently in Sept) they moved it back up to 45psi. I've been at 45 pretty much the entire time I've had my AWD, and am quite happy.
 

ewoodrick

Well-Known Member
Apr 13, 2018
5,285
3,733
Buford, GA
Required by law? I always inform tire shops of cold pressure desired if I want it set a specific way. That 45 does seems odd as every 3 I've seen states 42 cold. FWIW I keep my 3 at 42 cold.
Not sure if law, but I suspect so. It's part of the ratings of the car, such as max load.
 

jadatis

Member
Dec 19, 2015
27
16
Holland ( Europe)
With the info on plates, I calculated pressures for GAWR's +10%, so enaugh reserve for fully loaded and 99mph. And no bumping.
Gave F 32 psi and R 38 psi.
The 42 and 45 is yust for actiradius of battery, and normal use axleweights is probably so 32 psi all around is needed.
Especially front then can give centrewear at 45 psi, and for that reason they lowered advice to 42 psi later.
 

Watts_Up

Active Member
Mar 4, 2019
3,457
2,357
In a galaxy far, far away
With the info on plates, I calculated pressures for GAWR's +10%, so enaugh reserve for fully loaded and 99mph.
And no bumping. Gave F 32 psi and R 38 psi.
The 42 and 45 is just for actieradius of battery, and normal use axle weightsis probably so 32 psi all around is needed.
Especially front then can give centrewear at 45 psi, and for that reason they lowered advice to 42 psi later.
Could you explain the formulat that you used for calculating the tire pressure, based on the vehicles gross axle weight rating (GAWR)?
 
Last edited:

jadatis

Member
Dec 19, 2015
27
16
Holland ( Europe)
I once got hold of the official European used formula for calculating tyrepressure for a load on tyre and system for speed used, and went running with it.

Now I use my own determined formula, and system for speed, to idea of an article of an american IR J.C.Daws.

I concuded in time that pressure advice is to give the tire a deflection for the speed, that wont overheat any part of tire when driving constantly the speed for wich the deflection is determined.

Can sent you the officiall formula and the link to mr Daws article , and more, if you mail me at my hotmail.com adress, with username jadatis ( combine yourselves, spamm-machines cant this way)

But I determined by reactions about bumping, that if real weight is 85% of weight the pressurevis calculated for for 99mph, that comfort and gripp is still acceptable. Verry subjective, and open for discussion. So I calculate for axleweight + 10% , wich makes if equally devided R/L, this load% , as I babtised it , to be 91%
Then if a little weight-difference R/L , lightest tire stays above 85% L%.

Can write a book about it, and call myself " pigheaded selfdeclared tirepressure-specialist" nowadays.
 
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davidk2213

Member
Jul 3, 2019
68
42
Waxhaw
July 2019 and 45 psi on door, was warned that in the sudden cold temps, tire pressure was too low (39 psi), so I put them up to 49 psi. Think that is too hard?

I recon, they would be set at 45 and run down to 39, to start at 49 and let them run down to 42 to get better wear out of them instead of running them all the time underinflated.
 

camalaio

Active Member
May 28, 2019
1,483
2,101
Vernon, BC, Canada
Odd. The maximum for XL rated tires at load is 42psi as far as I understand, I thought this is why they brought it down to 42psi.

For what it's worth, there are service bulletins for 2019 models with incorrect labelling. The bulletins do not outline what exactly is the wrong information though.

July 2019 and 45 psi on door, was warned that in the sudden cold temps, tire pressure was too low (39 psi), so I put them up to 49 psi. Think that is too hard?

I recon, they would be set at 45 and run down to 39, to start at 49 and let them run down to 42 to get better wear out of them instead of running them all the time underinflated.

If you are using stock tires, the tires are rated for a maximum of 50psi. Especially if it gets warmer while initially at that pressure, 49psi will be much too high.
 
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mswlogo

Well-Known Member
Aug 27, 2018
6,069
4,699
MA, NH
RWD door tags with 18” will show 45. AWD will show 42. Not sure what the 19” will show on RWD (I believe based on lower load rating on 19”) I suspect they will show 42 as well.
 

jadatis

Member
Dec 19, 2015
27
16
Holland ( Europe)
On normal car tires, only max allowed cold pressure is given on sidewall, between 44 and 51psi, and XL/ reinforced/ extraload, sometimes even 60 psi( Toyo) .
The cold pressure for wich maxload is calculated is called reference- pressure in official system, and for standard load is 36 psi , and XL// 42 psi( EUR system, since 2006 adopted by USA system.
Difference between reference and maxcold is used to highen up the reference-pressure for higher speed and camber angle above 2 degr( alignment wheels like this /-\ instead of this|-| )
And this all is cold measured so when inside and outside tire temp the same, and 65degrF.

On LT tires on sidewall reference-pressure is given, and nowadays is the maxcold, in earlyer days higher was allowed.

And when warm the pressure rises even above maxcold sometimes, and is all meanth that way by the tiremaker.

Once read that test-standard of tires, is that they must stand a pressure of 2 to 3 times the reference- pressure. This is for XL 84 to 126 psi.
 

vickh

Active Member
Dec 16, 2018
3,121
488
az
July 2019 Build here of a SR+ with 18 Aeros and mine says 45 psi on the door... I believe it was delivered with about 42 to 43.

+1 July 2019 Build here of a SR with 18 Aeros and mine says 45 psi on the door as well. Except mine was delivered with 50psi!

Rough ride @ 45 so I'll be dropping it to 42 and see how it goes w/ range efficiency. Any one notice a perceptible change?
 

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