Tire Pressure on 19" Wheels

breser · Mar 2, 2015

My 85D has the tire pressure listed on the door as 50 psi. I know my S85 had it listed at 45 psi. Both had 19" standard wheels with the Michelin Primacy tires and air suspension. The tires list the maximum pressure as 51 psi.

Today I was in for a service appointment to deal with some minor nits and I noticed that the courtesy inspection listed my tire pressures at 45 psi. I sent an email to service after I got home and noticed this asking for clarification. They said they'd double check in the morning but that they use 45 psi with 19" wheels on air suspension per Tesla documentation.

I'm curious of a couple of things.

1) What do other owners have as the recommend tire pressure on their door sticker. Particularly interested in recent S85 and P85D deliveries (please mention your manufacture date when posting, note month/year is listed on the sticker in the corner).

2) Anyone else experience this sort of mismatch between what service is saying and the door pressure listed. Service mentioned that they've had other owners point out differences in the listed pressure before from what they were using.

Not sure if this pressure change is for D vehicles only or is just an overall change in recommendation.

billarnett · Mar 2, 2015

My P85D was built I early Feb. I have 19" Michelin Primacy. The sticker says 50psi on all four tires. The tires say 51 max. It was delivered with 45 psi. I pumped them up to 50. I'll ask next time I have it in for service.

I'm speculating that the higher pressure is to increase range?

breser · Mar 2, 2015

billarnett said:
My P85D was built I early Feb. I have 19" Michelin Primacy. The sticker says 50psi on all four tires. The tires say 51 max. It was delivered with 45 psi. I pumped them up to 50. I'll ask next time I have it in for service.

I'm speculating that the higher pressure is to increase range?

Thanks for the data point. I'm assuming you have air suspension, at least I don't think any coil P85Ds have been delivered yet. I'm wondering if it's not due to increased weight. Wonder what recent S85s say.

Cottonwood · Mar 3, 2015

My P85D was built in December 2014 and was delivered with Michelin Primacy Tires. The door sticker lists the recommended pressure for the tire at 45 psi.

I wonder if going from 45 to 50 psi recommended tire pressure is part of tweaking out a little better EPA range...

breser · Mar 3, 2015

Cottonwood said:
My P85D was built in December 2014 and was delivered with Michelin Primacy Tires. The door sticker lists the recommended pressure for the tire at 45 psi.

So it's definitely a change they made sometime this year. Since we have two P85Ds with different pressures for the same wheel/tire configuration.

I wonder if going from 45 to 50 psi recommended tire pressure is part of tweaking out a little better EPA range...

Could be, but it doesn't effectively do that if the cars are delivered at 45 psi and the service centers maintain them at that.

stevezzzz · Mar 3, 2015

I had my snow tires rotated on the P85D last week and the shop used 45 psi. I made them check it, because I'd read here about the 'new' standard being 50 psi: but 45 psi is what the door sticker says on my 2014.

Cottonwood · Mar 3, 2015

breser said:
Could be, but it doesn't effectively do that if the cars are delivered at 45 psi and the service centers maintain them at that.

Service people get into habits, and you just have to heck them. I have a Cessna 421 where the main landing gear tires are supposed to be inflated to 80 psi. Almost all other twin Cessna's have a main landing gear inflation pressure of 60 psi. It is truly amazing how many times after I get the airplane back from some minor service that the main tires look a little squished. I check the pressure and it's 60. I've even had to pull out the POH (Pilot Operating Handbook) and show some mechanics that it the spec is 80 psi for a 421 before they would believe me. They just have it in their head that a twin Cessna should be 60.

I am afraid that it will be the same for 2015 85D owners if you want those last few miles from a charge.

This brings up a secondary question, when I am doing a range challenged route (like my regular Pagosa-Silverton run), should I push the pressure up towards 50. I wonder where the TPMS thresholds are for warnings.

evp · Mar 3, 2015

Cottonwood said:
Service people get into habits, and you just have to heck them. I have a Cessna 421 where the main landing gear tires are supposed to be inflated to 80 psi. Almost all other twin Cessna's have a main landing gear inflation pressure of 60 psi. It is truly amazing how many times after I get the airplane back from some minor service that the main tires look a little squished. I check the pressure and it's 60. I've even had to pull out the POH (Pilot Operating Handbook) and show some mechanics that it the spec is 80 psi for a 421 before they would believe me. They just have it in their head that a twin Cessna should be 60.

I am afraid that it will be the same for 2015 85D owners if you want those last few miles from a charge.

This brings up a secondary question, when I am doing a range challenged route (like my regular Pagosa-Silverton run), should I push the pressure up towards 50. I wonder where the TPMS thresholds are for warnings.

After I put the Hakkas on, the S85 seemed to "hunt" a little around centered steering. I had it in for maintenance at Tesla, and shortly thereafter two of the tires started reporting under-pressure (possibly cold was a contributing factor). I had them boosted to 47lb each; that seems to have also cured the handling issue without over-pressure warnings. Let us know if 50lbs gives out warnings.

Gizmotoy · Mar 3, 2015

Mine say 45psi and I keep them there. 50 is awfully close to the tire's max pressure (51psi). I wouldn't want to inflate to 50, have them get a bit hotter, and then be over-inflated beyond their specs.

breser · Mar 3, 2015

Gizmotoy said:
Mine say 45psi and I keep them there. 50 is awfully close to the tire's max pressure (51psi). I wouldn't want to inflate to 50, have them get a bit hotter, and then be over-inflated beyond their specs.

51psi max is a cold inflation max. The actual failure point of the tire is going to be much higher than that.

Gizmotoy · Mar 3, 2015

breser said:
51psi max is a cold inflation max. The actual failure point of the tire is going to be much higher than that.

Hmm. Good point. Alternatively: is my tire pressure gauge accurate to within 1 psi?

Edit: And to be clear, I'm not assuming the things are going to pop if they get a psi or two over max, but it is a heavy vehicle and over time, who knows. There are two things on a vehicle that deserve a bit of extra caution: tires, and brakes.

Isn't 50psi the recommended inflation for the 21"s? Maybe they just slapped the wrong sticker on.

breser · Mar 3, 2015

Gizmotoy said:
Isn't 50psi the recommended inflation for the 21"s? Maybe they just slapped the wrong sticker on.

They don't have different stickers for different tire sizes. They print the correct info on the sticker. So unless they managed to get 50 psi in for 19" wheels incorrectly I don't think so.

Here is a picture of the sticker.

jerry33 · Mar 3, 2015

Gizmotoy said:
Mine say 45psi and I keep them there. 50 is awfully close to the tire's max pressure (51psi). I wouldn't want to inflate to 50, have them get a bit hotter, and then be over-inflated beyond their specs.

This isn't correct. The pressure on the sidewall of the tire is what you can set it to cold, first thing in the morning. It's just fine if it goes over during the day after driving. Tires are designed to do this. Pressure does not kill tires, heat from lack of pressure does. Something to bear in mind is that the maximum inflation pressure is chosen to be reasonably safe throughout the life of the tire, meaning that at 80,000 miles inflating it to the maximum cold pressure is still a reasonably safe thing to do. (80,000 miles being about how many miles a passenger car casing has before it fatigues. Not that any Model S tire will ever see 80,000 miles

I really don't understand why so many people feel that pressure in a tire is evil.

- - - Updated - - -

breser said:
They don't have different stickers for different tire sizes. They print the correct info on the sticker. So unless they managed to get 50 psi in for 19" wheels incorrectly I don't think so.

If you actually look at the load/inflation table for this tire, you'll see the load maxes out somewhere around 40 psi and the pressure above that is to be able to run at higher speeds. I guess Tesla figures that most purchasers of a D will be driving faster than a non-D purchaser. Another alternative is that the higher pressure will result in less wheel damage.

Gizmotoy · Mar 3, 2015

jerry33 said:
This isn't correct. The pressure on the sidewall of the tire is what you can set it to cold, first thing in the morning. It's just fine if it goes over during the day after driving. Tires are designed to do this. Pressure does not kill tires, heat from lack of pressure does. Something to bear in mind is that the maximum inflation pressure is chosen to be reasonably safe throughout the life of the tire, meaning that at 80,000 miles inflating it to the maximum cold pressure is still a reasonably safe thing to do. (80,000 miles being about how many miles a passenger car casing has before it fatigues. Not that any Model S tire will ever see 80,000 miles

I really don't understand why so many people feel that pressure in a tire is evil.

Well mainly because, as already noted above, I forgot max pressure was specified cold.

breser · Mar 3, 2015

Response from Tesla (just copying and pasting from the email they sent me)

Thank you for bringing this to our attention. After checking with our engineers at the factory we have been told both PSI ratings are acceptable. Our service manual states 45psi and some vehicle placards say 50psi. We are happy to inflate the tires to 50psi if you prefer. Moving forward, we will likely adjust your psi to 50 to follow the door placard.
The car will alert you if your psi is too low, I believe 38psi is when the "Tire pressure too Low" alert will appear.

jerry33 · Mar 3, 2015

breser said:
Response from Tesla (just copying and pasting from the email they sent me)

Thank you for bringing this to our attention. After checking with our engineers at the factory we have been told both PSI ratings are acceptable. Our service manual states 45psi and some vehicle placards say 50psi. We are happy to inflate the tires to 50psi if you prefer. Moving forward, we will likely adjust your psi to 50 to follow the door placard.
The car will alert you if your psi is too low, I believe 38psi is when the "Tire pressure too Low" alert will appear.

Click to expand...

The SC has always set mine to 50 once I requested it the first time. The main difference between running 45 and running 50 is how hot the tire gets after a bit of highway driving.

billarnett · Mar 3, 2015

Slightly off topic, but as I was driving down CA 85 just south of I-280 today I noticed the car didn't seem to want to stay going straight. I think it was following the rain grooves. It's been a long time since I had a car that did that (though it's common on motorcycles). Do you suppose it has anything to do with the 50psi in my tires? Does anyone else here in Silicon Valley feel the same behavior?

jerry33 · Mar 4, 2015

billarnett said:
Slightly off topic, but as I was driving down CA 85 just south of I-280 today I noticed the car didn't seem to want to stay going straight. I think it was following the rain grooves. It's been a long time since I had a car that did that (though it's common on motorcycles). Do you suppose it has anything to do with the 50psi in my tires? Does anyone else here in Silicon Valley feel the same behavior?

Nothing to do with the pressure. Some tread patterns have a tendency to follow some pavement grooves. It depends on the spacing of the pavement grooves and the spacing of the circumferential tire grooves. Misalignment can make it worse.

AmpedRealtor · Mar 4, 2015

I have been running at 50 PSI for a few days on my 19" Primacy tires. No TPMS warnings and no noticeable difference in ride quality on air suspension. I know of a Honda Insight owner who runs his tires at 90 PSI and has done so for years without any harm. He does this for range, but I'd hate to think what it does for his ride quality and comfort.

Thud · Mar 5, 2015

breser said:
51psi max is a cold inflation max. The actual failure point of the tire is going to be much higher than that.

Unless you really really really overinflate, the dangers aren't really around tire failure but reduced traction (smaller contact patch) and uneven treadwear which can shorten the life of your tires.

Tire Pressure on 19" Wheels

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