Why 42 PSI ?

[rpiotro]

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

My wife's Mercedes 2012 SLK 350 (R172) had PS4S for the last tires. Traction was f'ing awesome. At least on dry pavement with temps at room temperature or better. If the temperature was in the 40s F and wet they were very slippery. But yeah, 22K miles on the fronts and about half that on the rears. Just switched to AS4s last fall. Not to drive it in snowy weather but more to extend the driving season. I don't feel we gave up an awful lot in traction. A pretty good tire.

 

[enemji]

https://www.toyotires.com/media/pxcjubjs/application_of_load_inflation_tables_20200723.pdf

That's a much better question with actual answers! Here, read this 37 page pdf for your answer!

Purely for load capacity, probably all the way down to 24 PSI for 18" and 32 PSI for 20" if your Model 3 is unloaded. But this isn't recommended of course, because that kind of PSI brings all sorts of other issues like pot hole protection, uneven grip level, sidewall folding over in corners, tires being too hot on highways etc etc...

Basically, the recommended PSI is a compromise for many reasons. You're probably safe to go +/- 3psi, but beyond that, other factors could come into play and ruin your day in extreme situations.

Excellent link!

So for the GVWR of 2447 & 2771, for the Hankook Kinergy GT 94V, 32 PSI front is a good starting point and 35PSI for the rear.

 

[Apprunner]

My wife's Mercedes 2012 SLK 350 (R172) had PS4S for the last tires. Traction was f'ing awesome. At least on dry pavement with temps at room temperature or better. If the temperature was in the 40s F and wet they were very slippery. But yeah, 22K miles on the fronts and about half that on the rears. Just switched to AS4s last fall. Not to drive it in snowy weather but more to extend the driving season. I don't feel we gave up an awful lot in traction. A pretty good tire.

I've had some variation of Pilot Sports for 20 years now but the Tesla tends to just murder them. I'm pretty sure constant take-offs don't help. I'm not willing to give that up so hoping to get to a more durable tire so I don't keep spending $1200 a year on tires

 

[enemji]

I'm just gonna chime in and say that Tesla set the pressure for the least rolling resistance -

If you own a road bike - and this is a simple explanation - take it out and put the max pressure noted on the sidewall and go ride 10 miles. check your time - then - go ride the same route at the bottom recommended pressure - I'd be willing to bet your time will be longer at the lower pressure because of higher rolling resistance - its a real world easy test you can prove to yourself - and it will repeatable day after day to take into account you being stronger or weaker on any given day. . . .

Without any regards to the load rating of the tire itself is what started the bee humming in my brain.

Either someone was not doing his/her/it’s job or there are calculations that we are not privy to. So which one is it?

 

[XPsionic]

Without any regards to the load rating of the tire itself is what started the bee humming in my brain.

Either someone was not doing his/her/it’s job or there are calculations that we are not privy to. So which one is it?

Tire pressures isn't simply for load, or for efficiency. At the minimum pressures of around 26-32PSI (depending on tire and rim size) that's appropriate for the load of a Model 3, the tire sidewall will be quite soft and will probably roll over quite a lot in extreme maneuvers like a moose test, thus reducing grip and stability.

Check out how close the rim is to touching the road and how much the sidewall folds at factory 42PSI.

 

[kgvickers]

Well I wasted some time searching around ye olde net and the consensus among the mom's basement experts and the some of the more academic types is that increasing automotive tire pressures does reduce energy consumption - yeah, duh, I know. But the point of diminishing returns is about 45psi. Maybe that's why Tesla initially recommended 45.

If you dig deep enough you'll find hypermilers that claim to run 70 psi. Wow. I've actually tried 60 psi in the past in my 2013 Chevy Volt. The ride was so bad I couldn't endure it long enough to get any useful consumption data.

I've always been of the "go for max pressure on the sidewall" mindset so I drove my 3 for some time with the tires at 50 psi cold. After a few years I got tired of the jarring ride and I started reducing pressure. Turns out, after the 50 psi rough ride, the 45 psi ride is pretty good, so that's what I'm running now.

 

[DP26]

Tire pressures isn't simply for load, or for efficiency. At the minimum pressures of around 26-32PSI (depending on tire and rim size) that's appropriate for the load of a Model 3, the tire sidewall will be quite soft and will probably roll over quite a lot in extreme maneuvers like a moose test, thus reducing grip and stability.

Check out how close the rim is to touching the road and how much the sidewall folds at factory 42PSI.

Show me the test using a Tesla with the lower cg.

 

[stopcrazypp]

Without any regards to the load rating of the tire itself is what started the bee humming in my brain.

Either someone was not doing his/her/it’s job or there are calculations that we are not privy to. So which one is it?

You seem to be assuming the "correct" setting is the minimum necessary for the load rating. That seems to be an incorrect premise from the start. As others shown, 42 psi is well above what is necessary to support the load (while still being well below the max pressure of the tires), so that is not an issue at all.

If instead it has been demonstrated that 42 psi is below what is necessary to support the gross weight of the vehicle, then I would agree that might be incorrect, but so far none of the analysis shows that. That you can safely set a lower pressure does not mean it is "wrong" to set it at 42 psi. Others have already brought up why a manufacturer might want to set a higher pressure (unrelated to load capacity).

 

[enemji]

You seem to be assuming the "correct" setting is the minimum necessary for the load rating. That seems to be an incorrect premise from the start.

I am not ass-u-me-ing. I am merely trying to identify the psi level that is unsafe. How much can I reduce before it turns into another Ford/Firestone Exploder incident

 

[enemji]

Check out how close the rim is to touching the road and how much the sidewall folds at factory 42PSI.

The sidewall is much softer for the Hankook Kinergy GT at 94V, and that is why it has a more quiet ride as well as a more disconnected ride compared to the Michelin MXM4 98W, or even the Hankook Ion Evo AS 98W. Even then it is at 42PSI.

The GT has polyester sidewall vs Polyamide for the MXM4 or the Ion Evo AS. FYI.

 

[Msjulie]

FWIW (not much probs) we keep our 2018 Model 3 at 45lbs cold, same for the 2023 Model Y - ride is fine in both for our tastes and for the Model 3 the range difference is notable. Model Y too new to prove that but seems reasonable

 

[DP26]

Tire pressure at the track: what do you run?

What kind of tire pressures do people use while running autocross or track? I'm planning on around 35 PSI for my RE71Rs

teslamotorsclub.com

These folks seem to agree with the load charts (me) and are not reporting any roll off the bead issues (moose test). Racers know as they will do anything for a hundredth… and they likely are not going to get to bead issues like dirt cars (who then use bead locks, or in my day, screws).

 

[XPsionic]

Tire pressure at the track: what do you run?

What kind of tire pressures do people use while running autocross or track? I'm planning on around 35 PSI for my RE71Rs

teslamotorsclub.com

These folks seem to agree with the load charts (me) and are not reporting any roll off the bead issues (moose test). Racers know as they will do anything for a hundredth… and they likely are not going to get to bead issues like dirt cars (who then use bead locks, or in my day, screws).

What are you even trying to achieve @DP26? I think you should start off by clarifying that. If your question is "What is a safe lowest PSI I could run on my street tire? Then the link you posted is literally comparing apples to oranges. I'll explain.

That thread is talking about running RE71-R, semi slick street legal tires on the race track, with very stiff sidewalls compared to the stock all seasons non run flat tires. You could definitely run closer to 30psi cold for tires like that, because 1. it has much stiffer side walls 2. they're running the tires way hotter on the track than a normal person would ever drive on the street = Hotter tire = higher hot pressures. And you know why the tires are hotter than you'd get it on your all seasons on the street? Because the compound is much softer, generating more heat, they're cornering much harder, generating more heat, they're not cooling the tires down by driving slowly, and the lower cold tire pressures allow the tire to flex more, generating more heat.

Run your stock all seasons at 26 psi cold as recommended by 1 of the comments in that thread and you'll be driving on the sidewalls of the tires in extreme hard cornering, reducing grip and response and safety. No one said anything about tires rolling off the bead, you invented an argument for yourself. I said rolling onto the sidewalls, which is not the same thing.

Let's clear some things up. If your goal is to soften the ride quality and run as low PSI as you dare and still be safe, go ahead, drop it down to the low 30s PSI as per the load charts. If you're running an all season tire, in terms of achieving even tire wear, pot hole protection, energy efficiency, and grip in extreme emergency cornering, you're better off staying close to the recommended 42PSI.

 

[DP26]

Even Tesla agrees at least as low as 38 (based in my own experiment) does not require a warning as their TPMS warning is lower. If 42 was the magic number for safety, the warning would be at 42. Thus, those who INSURE tesla are allowing 38 or less as being safe. Given our society, it is also as likely a lower number is still more than safe, as there is likely a cushion built in. TPMS was one Firestone result and no manufacturer likely sets there warning below what the suits demand.

I am of the opinion the 42/45 often given is for epa/range purposes ONLY. There are pros who say 38 is not normally noticible in range to the average driver. Would I run 26/28 based on load only? Too soon to tell. But on a Jeep with oversized tires and low weight, I run 15 as it is more than enough for the load and safety. When we are towing it behind our MH, I bump it up to 20 as it follows a little better and reduces the odds of death wobble. Same Jeep has a shift light which lugs the 4 banger, but such a light tells the epa test driver when to shift. Such is what makers have to do to meet their epa numbers. Even a tenth mpg from a way to early shift light, or extra inflated tires, means $ to the makers.

 

[AZAV8R]

Even Tesla agrees at least as low as 38 (based in my own experiment) does not require a warning as their TPMS warning is lower. If 42 was the magic number for safety, the warning would be at 42. Thus, those who INSURE tesla are allowing 38 or less as being safe. Given our society, it is also as likely a lower number is still more than safe, as there is likely a cushion built in. TPMS was one Firestone result and no manufacturer likely sets there warning below what the suits demand.

I am of the opinion the 42/45 often given is for epa/range purposes ONLY. There are pros who say 38 is not normally noticible in range to the average driver. Would I run 26/28 based on load only? Too soon to tell. But on a Jeep with oversized tires and low weight, I run 15 as it is more than enough for the load and safety. When we are towing it behind our MH, I bump it up to 20 as it follows a little better and reduces the odds of death wobble. Same Jeep has a shift light which lugs the 4 banger, but such a light tells the epa test driver when to shift. Such is what makers have to do to meet their epa numbers. Even a tenth mpg from a way to early shift light, or extra inflated tires, means $ to the makers.

"

"There are pros who say 38 is not normally noticible in range to the average driver."

That's what I've followed through this entire thread waiting to see. I've been running 42 and want to see how much softer the ride is at 39. Thanks!

 

[enemji]

Well I’ll be damned.

So I tried out 3 different PSI on the Hankook Ion Evo AS, starting with 42, then going to 36, and then 38 and back to 42.

42 psi provided the best ride quality not only in terms of steering response but also road noise.

 

[DP26]

Well I’ll be damned.

So I tried out 3 different PSI on the Hankook Ion Evo AS, starting with 42, then going to 36, and then 38 and back to 42.

42 psi provided the best ride quality not only in terms of steering response but also road noise.

Makes sense to you then it is good!

For me, no manner of explaining feel based on racing experience trumps SWMBO’s ride quality sensor. More pressure in a stock setup may feel better to some. Quieter too especially if it lifts the tire off shoulder blocks and center has few or no blocks.

 

[vogz]

Not true. Max pressure is max COLD pressure.

What's not true? The max pressure of a tire is the max it should be set at. It will only go up from there as it heats up, which would put tires well over 50psi. At that point ride quality would be total garbage and the tire might even start to wear unevenly.

Yup, cold
View attachment 922646

42 isn't max pressure. It's the manufacturer recommended set pressure for cold tires. I think you guys completely misinterpreted my post.

 

[stopcrazypp]

I am not ass-u-me-ing. I am merely trying to identify the psi level that is unsafe. How much can I reduce before it turns into another Ford/Firestone Exploder incident

Yes, I know you are trying to find the lowest psi that is still safe, but you say "someone was not doing his/her/it’s job" as if that is the goal for the manufacturer also. There is nothing that indicates putting the lowest psi possible is a valid goal for a manufacturer. As you find out later, you don't even gain better ride quality in your specific case, so it's pointless.

 

[blackT3$!@]

42 psi provided the best ride quality not only in terms of steering response but also road noise.

This discussion I think covered all possible reasons and explanations about Model 3 tire pressures. It all came back to the door sticker recommended psi for the OP. Elon for the win!