Why 45 psi?

[Barry]

For what it's worth, the door jamb placard on my March 2015 build Model S with 19" Michelins calls for 50 psi. It looks like Tesla recommended 50 for a while, then went back to 45 psi. When Tesla did the annual service on my car, they went to the trouble to reduce my tire pressure from 50 to 45. I will set them back to 50.

Mine is the same. Placard says 50. However, it appears that Tesla reverted back to a 45 psi recommendation, so why fill it back to 50?

 

[msnow]

OK, I'll monitor. Could you check that Amazon link please when you get a chance. Nothing popped up for me.
I got the tire repair kit as swag...they said I'd need it being a Boston driver. But my blowouts so far have been out the sides and I didn't even try the kit. Used roadside and they've been outstanding. Thank you.

This is the one I got and it works well. I'm sure there are others as well.
Amazon.com: Tire Pressure Gauge Digital w/ Metal Body 150PSI: Automotive

 

[Deans]

Thanks for all the responses. Maybe I should rephrase my question a bit:

Why do similar ICE cars not recommend 45 psi? I have not seen any sedan ICE cars recommending anything above 36 psi.

The Audi A7 is very similar to the Model S in terms of acceleration, body design, suspension, and tire size. The recommended pressure is 34 lbs (average). The car weights 350 lbs less than the MS, which accounts for a 2 or 3 lbs of pressure difference.
I realize that all cars handle a little differently, have different weight distributions, differently braking properties, etc. However, I doubt these two cars have major differences in these respects.

Just to give you an idea of where I'm coming from with these questions:
At higher PSI, you may get a nice sporty feel on roads in California and Florida. In Colorado and the Midwest, the ride changes from "Sporty" to "Red Wagon". I have a dormant bulging disc in my neck. It only flares up when I jog too much or ski bumps. However, the MS seems to be triggering inflammation when I drive more than 10 miles or so on the highway. I need to find a solution to soften the ride, or have the disc replaced, or sell the car. I'd like to avoid the latter two options.

But again, I don't want to make a change without be fairly certain that I'm not sacrificing safety for comfort.

 

[msnow]

Thanks for all the responses. Maybe I should rephrase my question a bit:

Why do similar ICE cars not recommend 45 psi? I have not seen any sedan ICE cars recommending anything above 36 psi.

The Audi A7 is very similar to the Model S in terms of acceleration, body design, suspension, and tire size. The recommended pressure is 34 lbs (average). The car weights 350 lbs less than the MS, which accounts for a 2 or 3 lbs of pressure difference.
I realize that all cars handle a little differently, have different weight distributions, differently braking properties, etc. However, I doubt these two cars have major differences in these respects.

Just to give you an idea of where I'm coming from with these questions:
At higher PSI, you may get a nice sporty feel on roads in California and Florida. In Colorado and the Midwest, the ride changes from "Sporty" to "Red Wagon". I have a dormant bulging disc in my neck. It only flares up when I jog too much or ski bumps. However, the MS seems to be triggering inflammation when I drive more than 10 miles or so on the highway. I need to find a solution to soften the ride, or have the disc replaced, or sell the car. I'd like to avoid the latter two options.

But again, I don't want to make a change without be fairly certain that I'm not sacrificing safety for comfort.

I went for the fusion surgery, not because of tire pressure but because of a wider and longer term benefit.

 

[Deans]

I'm probably going to get the disc replacement surgery in the Spring. Trying to work it in after ski season and before golf season.
I've gained 10 lbs. in the last year since I can't run much.

 

[dgpcolorado]

FWIW, not all of the placards say 45. Mine says 42:

Why some say 45 and some have other pressures I couldn't say, but it might be due to the lighter weight of an S60. I tend to keep my tires at 45-46 psi for slightly better rolling resistance and the fact that when I leave home I descend to lower elevations.

 

[brec]

My Sep. 2015 85D's placard says 45 PSI; the original Michelin Primacy 19" sidewall says maximum pressure 51 PSI. I guess the latter also refers to "cold" (65F or so) temperature conditions.

 

[Deans]

My Sep. 2015 85D's placard says 45 PSI; the original Michelin Primacy 19" sidewall says maximum pressure 51 PSI. I guess the latter also refers to "cold" (65F or so) temperature conditions.

I think the reason they dropped the recommendation from 50psi to 45psi is beacuase 50psi leaves no room for error with a max of 51psi. You would have to let air out of the tires anytime the weather warmed up.

 

[TexasEV]

FWIW, not all of the placards say 45. Mine says 42:

Why some say 45 and some have other pressures I couldn't say, but it might be due to the lighter weight of an S60. I tend to keep my tires at 45-46 psi for slightly better rolling resistance and the fact that when I leave home I descend to lower elevations.

Did your car come with the Goodyear tires? My 60 did and had 42 psi on the placard. When I replaced the tires with Michelin Primacy last year the service center said 45 psi is recommended for those tires. They couldn't change the door placard but put a note in my service record to ignore the door placard and inflate to 45.

 

[dgpcolorado]

Did your car come with the Goodyear tires? My 60 did and had 42 psi on the placard. When I replaced the tires with Michelin Primacy last year the service center said 45 psi is recommended for those tires. They couldn't change the door placard but put a note in my service record to ignore the door placard and inflate to 45.

Interesting. I do have the Goodyear Eagle RS A2 tires and am pretty sure that they were original equipment.

 

[dandelot]

For a while the wife insisted on a softer ride, so we had 39-40 PSI. I could never get below 300 Wh/mile. Including some long trips. Switched to 45PSI at ambient and now routinely see 275 Wh/mi on longish drive on mainly flat land.
YMMV.

Tire pressure (when using air) does increase at least 2 PSI over a 20 degree F temperature change.
And A long trip will easily raise the pressure 4 PSI as the tire gets heated
by driving. Race cars often use dry Nitrogen ( instead
of moisture-laden air) to dramatically reduce the pressure increase with tire temperature.

 

[GSP]

Mine is the same. Placard says 50. However, it appears that Tesla reverted back to a 45 psi recommendation, so why fill it back to 50?

Lower energy consumption, more range, sportier ride and handling. After all, it is a high performance car.

GSP

 

[jerry33]

For a while the wife insisted on a softer ride, so we had 39-40 PSI. I could never get below 300 Wh/mile. Including some long trips. Switched to 45PSI at ambient and now routinely see 275 Wh/mi on longish drive on mainly flat land.
YMMV.

Tire pressure (when using air) does increase at least 2 PSI over a 20 degree F temperature change.
And A long trip will easily raise the pressure 4 PSI as the tire gets heated
by driving. Race cars often use dry Nitrogen ( instead
of moisture-laden air) to dramatically reduce the pressure increase with tire temperature.

Race cars use nitrogen because it's guaranteed to be dry so they can tune their suspension properly, and/or they use it because on some smaller tracks there is no electricity and nitrogen is a cheap and safe as anything else. It's of no practical value to normal driving. When driving, the combination of heat built up from flexing and the cooling down by air flowing over the tires after driving awhile causes them to reach a thermal equilibrium where the heat build up equals the cooling. Slowing this process down, just adds heat and shortens tire life. Pressure is not the enemy of tires, heat is.

 

[JRMW]

isn't the point of the alarms to alert you to low pressure in the tires?
AFAIK the easiest way to shut those alarms off is to inflate your tires to the correct psi.

Sigh. Yes I know that. I'm not sure where your confrontational points are coming from.

The OP opined about possibly using a lower pressure.

I told them that doing so would cause Tesla Model S alarms to go off, and that there was to my knowledge no way to turn said alarms off.
This was to give them one more piece of info that they might not have known (lowering psi will set off alarms that take over your screen, that cannot be turned off).

Given that, obviously
1. Discount Tire inflated to the wrong psi
2. The point of the pressure sensor alarm is to notify us that the tire pressure is low
And
3. The easiest way to shut off the alarm is to add pressure.

So I'm not exactly sure what point you're trying to make, that I haven't made already?

 

[JRMW]

Back to the original question...

I wonder of the high psi is needed due to the rapid acceleration and instant torque?

The torque specs for the wheel are much higher than comparable vehicles. Could be the same reason for higher tire psi?

What's the tire psi on a Bugatti veyron?

 

[Deans]

@JRMW : I understood what you were saying about the alarm status. You can actually dismiss the car status view by pressing and holding the button on the steering wheel underneath it (left side, usually). However, I don't think that would ever be a good idea as you would have no way of knowing whether your pressure got even lower. For example, in your case when the PSI was at 39, you could dismiss the car status view, but if you subsequently ran over a nail and the PSI dropped to 28, you'd have know what of knowing. So it would be wise to keep the car status up at all times and check it periodically while driving if you are intentionally driving with PSI less than 40.

 

[MorrisonHiker]

For example, in your case when the PSI was at 39, you could dismiss the car status view, but if you subsequently ran over a nail and the PSI dropped to 28, you'd have no way of knowing. .

If you dismiss it and the pressure goes down, it will pop up again...at least it did this for me. When my car was delivered, all tires were set incorrectly. I dismissed the pressure warning but it came up later on my drive home. If I added air or dismissed it, it would come on later as the pressure decreased. Eventually I went to the service center and found I'd had a nail in my tire since day 1.

We've also noticed that the pressure warning will come on frequently in the mountains when changing elevation. If we dismiss it at the top of one pass, it will come back on later if the pressure changes again.

 

[Mr X]

Well I don't know why but tire rack makes it very clear that inflation must be higher than 45psi
View attachment 210869

Because they are quoting what Tesla said. But its not entirely necessary.

 

[bxr140]

I wonder of the high psi is needed due to the rapid acceleration and instant torque?

It is not. That's coincidental, not to mention the 'slow' teslas have the same psi as the fast ones.

The pressure is largely due to loading (the weight of the car), which aggregates variables like safety, wear, and handling. Tesla likely folded in range as a secondary factor in there too.

For the record, I usually keep mine in the low 50s. Tire sensors go off at 57, fyi.

 

[sorka]

I was beginning to have excessive center wear at 50 psi. Tesla looked at it and agreed and lowered the pressure back down to 45 psi.