Tyre pressures revisited

[pgkevet]

It makes no sense to me. Tyre pressures are advised to be set cold but if I put them at 45psi in the summer then from experience they will be as low as 40-41 on a frosty morning. If set at 45 on that frosty morning they go as high as 49 cold on a summers morning. Even in winter set at 45 cold they will hit 50+ on a long drive (which is the tyres rated max...but one assumes that is it's rated cold max).
I was at the garage this morning having a small puncture fixed (local guys are nice ..I was happy with the £10 charge compared to Tesla wanting to sell me a new tyre last week). Garage really didn't have any answer to the pressure question apart from 'we don't worry about it'.

 

[TheEVadvisor]

I believe it's 42psi

 

[MrBadger]

Is the TPMS as absolute as it seems in terms of tyre pressure or is it effectively calibrated from a certain starting point - bit like a shower mixer that assumes incoming water is the same temperature every time so set point is dependent on incoming water temperature.

 

[pgkevet]

I've been playing with the tyre pressures on my S for 15mths. TPMS seems to be absolute when compared to a digital pressure gauge (except that i can't lean out at motorway speeds to check the readings 'cos my arms aren't long enough and I lack the dexterity for following the valve round....) Recommendation for the S is 45psi although it has been suggested by Elon that the ride will be nicer at lower pressures albeit perhaps less efficient. Not sure whether it affects tyre wear. Also not sure about accuracy/repeatability of TPMS sensors in the tenths. I like to see all the tpms readings changing together as tyres warm up - just a silly game I play with myself fiddling with pressures to try get it spot on.

 

[Jason71]

You could always get them purged of moisture and nitrogen filled. This will minimise the variation with temperature as some of it is to do with vapour pressure of the moisture. The Nitrogen itself wont make any difference it's the fact that it is dry and does not leak as fast (larger molecule) so needs topping up less often.

 

[MrBadger]

You could always get them purged of moisture and nitrogen filled.

I get mine 78% nitrogen filled.

 

[webbah]

I bought a small battery powered air compressor I keep in the frunk. I set mine to 41 PSI cold and if the daily temps change in a big range (autumn) I can easily adjust accordingly anywhere. 41 PSI is my sweet spot for both comfort and handling with perfect tire wear.

 

[MOBB]

I get mine 78% nitrogen filled.

What a coincidence, I went for that exact percentage too

 

[Adopado]

I get mine 78% nitrogen filled.

Agree, and if you add a just a smidge of argon I find that gives a nicely balanced mix.

 

[pgkevet]

I bought a small battery powered air compressor I keep in the frunk. I set mine to 41 PSI cold and if the daily temps change in a big range (autumn) I can easily adjust accordingly anywhere. 41 PSI is my sweet spot for both comfort and handling with perfect tire wear.

I have a compressor in the barn so changing it isn't the issue. As to 45psi - well that's what's on the B pillar and I'm not going to get into an argument after any accident as to why i changed it. But the question still remains as to what it should be - you cannot have a set-point cold fill with no regard to ambient temp and expect the running temp to be the same and the running temp takes time to stabilise.

Of course if every vehicle tyre in the world was filled with captured C02......

 

[DJP31]

But the question still remains as to what it should be - you cannot have a set-point cold fill with no regard to ambient temp and expect the running temp to be the same and the running temp takes time to stabilise.

I’m absolutely not an expert, but why the expectation that the running temp should be the same? Is it not the case the the 45 lbs for the S on cold fill allows the running temp to rise to a level between known limits, irrespective of the ambient temperature?

 

[pgkevet]

I’m absolutely not an expert, but why the expectation that the running temp should be the same? Is it not the case the the 45 lbs for the S on cold fill allows the running temp to rise to a level between known limits, irrespective of the ambient temperature?

That may well be the case but it'd be nice to have the definitive answer. It also implies that one should re-adjust pressures depending on ambient temp.

 

[DJP31]

It also implies that one should re-adjust pressures depending on ambient temp.

It's been suggested to me in the past (although I can't remember who..) that around about the clock change, so a Spring and a Winter adjustment was a good yardstick to go by.

 

[ewoodrick]

Yes, tire pressure increases when they get warmer. That's why they are specified cold.
Yes, with cooler weather, most people will have to fill their tires a little. Did mine about a week ago.
This isn't a Tesla thing, all cars do it.

Go back to high School science and remember that warm air expands. Or even look at the evening weather and see what a "front" is.

 

[Mr Miserable]

Yes, tire pressure increases when they get warmer. That's why they are specified cold.
Yes, with cooler weather, most people will have to fill their tires a little. Did mine about a week ago.
This isn't a Tesla thing, all cars do it.

Go back to high School science and remember that warm air expands. Or even look at the evening weather and see what a "front" is.

A front marks the division between 2 different air masses.
Living in the UK we can get 2 or 3 frontal crossings in a day. It is why our weather is as it is.
The idea that we should adjust our tyre pressures everytime a front passes is an absolute non starter.

 

[Mr Miserable]

Go back to high School science and remember that warm air expands. Or even look at the evening weather and see what a "front" is.

Oh, and go back to school and learn how to spell tyre.

The pneumatic tyre was invented by Mr Dunlop. He must be clever because he could spell pneumatic. So the correct spelling is tyre.

To tire is to go weary.......ZZZzzzzz

 

[Dangerous Fish]

These days everyone seems to be so scared to change anything from the "manufacturer's recommended."
If it's to do with wheels and tyres, the reason given is usually insurance or extreme danger.

Tyre pressures are a variable. There is no magical 100% correct pressure. What you set your pressures at should and will vary with the weather, how hard you drive the car, the load, road conditions and other things.

Having TPMS seems to make people worry even more about it, because they are constantly looking at the numbers varying by a few PSI.

In my view, the pressures recommended by Tesla are a bit too high and are set there to improve range rather then give the best balance of ride/handling.

That's my view anyway. Feel free to ignore it and poke fun at me.

 

[pgkevet]

It;s perfectly possible to have temperature variations of 15C at this time of year between night and a sunny day. Add sun on parked black tyres or temp rises due to driving and that gets towards a 20C variation over 1 day. Between coldest winter temps where I am and hottest summer temps the variation is 45C

Tyres inflated to 45psi @ 0C will be at almost 50psi @ 20C
Tyres inflated to 45psi @ 20C will be about 41psi @0C

I'm not going to be checking and changing pressure every time I get in the car. From experience monitoring this car I know that a cool summer morning 12-15C with tyres at 45psi gives me motorway temps of 48/49psi. My best answer is to do ocassional checks of TPMS on long journeys and if the running temp changes outside 48/49 due to a change in seasons or a long term forcast the change the tyre pressure from whatever it is by the difference in running temp.

 

[GeorgeSymonds]

You have to (well you should) adjust the tyre pressures regularily throughout the year to maintain the pressure when the tyre is at the ambient temperature. Lots are aware in winter when pressure drops with the cold weather and flat tyre warnings get triggered, but few think about over inflation in the summer.

In use the tyre will increase in temperature above ambient and therefore pressure (ambient being what they mean by cold).

What your desired target pressure is and whether you want to run it differently to the manufacturer recommendation is another matter.

 

[rotor2k]

I bought a small battery powered air compressor I keep in the frunk. I set mine to 41 PSI cold and if the daily temps change in a big range (autumn) I can easily adjust accordingly anywhere. 41 PSI is my sweet spot for both comfort and handling with perfect tire wear.

Would you recommend the pump you have, and if so, which one is it? (Thanks).