Tire pressure high on delivery

[jerry33]

What is the pressure COLD? If 45 psi it can reach 50 on a hot day. 45 is over spec but not that terrible. Also TPMS can be off a pound or two.

Set at 42 psi cold I hit 47 on hot days.

42 to 47 is 12% increase. That's a bit high but still acceptable (8% is considered ideal). I'd increase the pressure by a couple of psi.

 

[timk225]

18" wheels with MXM4's, I tune the tires to 42 cold. Seasonal adjustments to compensate for temperature changes.

 

[mswlogo]

42 to 47 is 12% increase. That's a bit high but still acceptable (8% is considered ideal). I'd increase the pressure by a couple of psi.

You said that’s high and then recommend increasing?

That delta from garage (cold psi) to a hot highway is pretty typical. I just do what the door tag says. On some ICE cars I might go a couple pounds high, Tesla already does that.

Tires can rise as much as 50F, that’s 9 psi rise. I went up 5 lbs from say 75F garage to highway on a 90F day (tire will be much hotter than 90F), tire could be at 120F.

Article on the topic

A Look Behind the Tire Hysteria

PSI Temperature rise Chart

Cold inflation pressure - Wikipedia

 

[jerry33]

You said that’s high and then recommend increasing?

The 12% increase is a bit high, not the pressure. And yes increase in ambient temperature will increase the pressure more. That's why the range is usually from 8 to 15%.

 

[mswlogo]

The 12% increase is a bit high, not the pressure. And yes increase in ambient temperature will increase the pressure more. That's why the range is usually from 8 to 15%.

I really don’t know what your getting at. I never think about it percent, nor do most people. I routinely fill to recommended Cold psi and that’s that.

 

[jerry33]

I really don’t know what your getting at. I never think about it percent, nor do most people. I routinely fill to recommended Cold psi and that’s that.

Basically, heat, not pressure, is what kills tires. Inflating so that there is minimal heat build up lowers the temperature of the tires which makes them last longer. It's expected that an 8% increase between cold and warm tires will occur. This can be as high as 15% if there is a large difference between the ambient temperature in the morning and afternoon. Because every tire pressure recommendation is based on a set of assumptions that may or may not be correct for your particular driving style and geographic location, it's normal to adjust the pressure to suit your driving conditions.

 

[vickh]

42 to 47 is 12% increase. That's a bit high but still acceptable (8% is considered ideal). I'd increase the pressure by a couple of psi.

that's my range as well in hot AZ. It's 42 in AM , but when i get to freeway it's mid 40s. I usually go a few PSI over recommended but in Tesla's case it is so close to tire max that i'm concerned

Discount tire guy said sometimes car TPMS isn't accurate. Should I re calibrate to their guage after check? or have mobile service do it?

 

[jerry33]

that's my range as well in hot AZ. It's 42 in AM , but when i get to freeway it's mid 40s. I usually go a few PSI over recommended but in Tesla's case it is so close to tire max that i'm concerned

Discount tire guy said sometimes car TPMS isn't accurate. Should I re calibrate to their guage after check? or have mobile service do it?

If it goes over the maximum due to heat build up, that's fine. The maximum is for cold pressure, not hot pressure.
The way I do it is to have a known good pressure guage and then check every so often to make sure the car's numbers are the same. If they aren't I will still know what the difference is. I don't trust any gauges at tire shops because you have no idea how many times they were dropped or when they were last calibrated. Longacre Racing makes some good ones, which is what I use, but they're not inexpensive.

 

[jadatis]

Here a temp/ pressure tabel.

Tmps sensors in the tire measure the absolute pressure , and software of unit in the car substracts a fixed outside pressure of most likely 1013 mbar.

 

[vickh]

If it goes over the maximum due to heat build up, that's fine. The maximum is for cold pressure, not hot pressure.
The way I do it is to have a known good pressure guage and then check every so often to make sure the car's numbers are the same. If they aren't I will still know what the difference is. I don't trust any gauges at tire shops because you have no idea how many times they were dropped or when they were last calibrated. Longacre Racing makes some good ones, which is what I use, but they're not inexpensive.

Thanks. Didn't know that about cold pressure, not hot pressure. So low 50's hot is ok? I would like the range gain, and don't mind unless the ride get's too rough.

Discount tire uses a large digital auto cut off guage.

 

[Bill Foster]

I have been driving my M3 LRAWD for a few days. What I noticed most is it is very bumpy and it seems to ride hard. So I decided to check the tire pressure. All four tires (19 inch) registered 50 PSI. The door sticker shows a recommended pressure of 42. Why did Tesla deliver car with incorrect tire pressure?

Obviously Tesla is selling cars with high air pressure so the tires wear out faster and they can make more money

 

[jerry33]

Thanks. Didn't know that about cold pressure, not hot pressure. So low 50's hot is ok? I would like the range gain, and don't mind unless the ride get's too rough.

Discount tire uses a large digital auto cut off guage.

Low 50's hot is just fine. People are far too worried about pressure. I always say they drive backwards (e.g. They use the speed limit as a kind of minimum and the vehicle placard pressure as some kind of maximum, when they should be doing the opposite). Unfortunately there is a lot of information about tires and tire pressures that is left over from the days of bias ply tires and has little application to today's radial tires.

Digital makes it easy to read but not necessarily more accurate. It's always a good idea to check your tire pressures with your own accurate gauge the morning after service of any kind. I use Discount Tire too, they don't always get it right.

 

[jerry33]

Obviously Tesla is selling cars with high air pressure so the tires wear out faster and they can make more money

This is not correct. While it's true that in the days of bias ply tires, high pressure did wear tires out faster, many of today's radial tires have an almost flat crown radius, so only low pressure wears out tires faster. (It would be true if the tire had a small crown radius, but that's not the majority of tires sold today). By keeping the tire cooler, they might actually last longer. But the real reason for high pressure on delivery is to avoid damage during transportation. In transit the car and tires receive bumps that they would not normally receive during operation. Normally, the SC would set the tires to the vehicle placard pressure, but I can see them skipping this step during a really busy delivery period.

 

[Bill Foster]

This is not correct. While it's true that in the days of bias ply tires, high pressure did wear tires out faster, many of today's radial tires have an almost flat crown radius, so only low pressure wears out tires faster. (It would be true if the tire had a small crown radius, but that's not the majority of tires sold today). By keeping the tire cooler, they might actually last longer. But the real reason for high pressure on delivery is to avoid damage during transportation. In transit the car and tires receive bumps that they would not normally receive during operation. Normally, the SC would set the tires to the vehicle placard pressure, but I can see them skipping this step during a really busy delivery period.

 

[jadatis]

In other topic on this forum, I read about centerwear with 42 psi, so ,though you can go pretty high in pressure before that happens, this border is reached.

And if on other cars with same weights, 32 psi gives a good ride, why would it not be for Tesla.

 

[jebinc]

In other topic on this forum, I read about centerwear with 42 psi, so ,though you can go pretty high in pressure before that happens, this border is reached.

And if on other cars with same weights, 32 psi gives a good ride, why would it not be for Tesla.

I wondered this myself. I suspect the higher pressure is required to reach the "advertised" range of each model.

 

[jadatis]

Been playing with excell for the actiradius of battery for speed and pressure
Filled in as reference that at 65mph constant speed and 42 psi pressure and 250miles actiradius, and spreadsheet gives list for other speeds and pressures.

Try to copy it , but can be messy.

pressure》
sp 20 25 30 35 42 45 50 55
35 571 583 597 614 641 654 679 705
50 290 302 316 333 360 373 398 424
65 180 192 206 222 250 263 287 314
75 140 152 166 183 210 223 248 274
85 114 125 139 156 183 197 221 248

In this you see that at 30 psi actiradius drops to 206 miles. But speed does more 30 ps and 75mph and it drops to 166 miles.

All an indication, dit rough calc in wich I did not include the less impotant factors.

 

[jebinc]

Been playing with excell for the actiradius of battery for speed and pressure
Filled in as reference that at 65mph constant speed and 42 psi pressure and 250miles actiradius, and spreadsheet gives list for other speeds and pressures.

Try to copy it , but can be messy.

pressure》
speed 20 25 30 35 42 45 50 55
35 571 583 597 614 641 654 679 705
50 290 302 316 333 360 373 398 424
65 180 192 206 222 250 263 287 314
75 140 152 166 183 210 223 248 274
85 114 125 139 156 183 197 221 248

Perhaps a "screen shot" of the actual formatted spreadsheet would be better? Attach as a photo?

 

[jadatis]

Made new calc, old was wrong, and it shows less loss at lower pressure.
Filled in reference 50mph , 25% of total energy used by rolling resistece, 32 psi, and made actiradius so that it became 250miles at 42 psi and 65mph.

In first version I did speed / speed squaire,and that is right for energy per timeunit. But then you also make more miles a timeunit , so now only calculated speed/ referencespeed.
Made pdf print, could not find screenshot on mobile, and cant find a way to show it directly

 

[jerry33]

Made new calc, old was wrong, and it shows less loss at lower pressure.
Filled in reference 50mph , 25% of total energy used by rolling resistece, 32 psi, and made actiradius so that it became 250miles at 42 psi and 65mph.

In first version I did speed / speed squaire,and that is right for energy per timeunit. But then you also make more miles a timeunit , so now only calculated speed/ referencespeed.
Made pdf print, could not find screenshot on mobile, and cant find a way to show it directly

Are you trying to say that the rolling circumference of the tire changes with tire pressure? That's really only true for bias ply tires. For radial tires, the circumference of the steel belts (and to a certain amount the tread depth of the tire) dictates the rolling circumference. Tire pressure has little to do with it.

Or am I not understanding what you're saying.