Winter Car Care 101

[hans611]

BUT this is the surrounding air temp when you test your tyres with the tyres at the same temp as the air...so if you are testing your tyres inside the garage its that temp..not the temp outside the garage...

OK so here you are saying when you set your tire pressure inside a warm garage, to set it higher than normal if its cold out...

So if you are setting the pressure outside in the cold, early morning... then you would agree to just set it at the normal recommended pressure, right?

Thats not what you are saying here however....?

Regarding altering the tyre pressure...DON'T!!

The tyre pressures for the cars are quoted nominally at 20C......when the temp drops to 0C the same tyre should be 0.1bar less..DO NOT inflate the tyre to the normal setting as when the tyre warms up through use it will be over inflated!!

so if 2bar at 20C...then set to 1.9bar at 0C....& 1.8bar at -10C....& 1.7 bar at -20C...that is the correct inflation !!

It seems you are suggesting to set you tire pressure lower during cold weather because it will over inflate when it reaches operating temperature......?

Thats the first time i hear that... This is usually the way to go:

Yes, also wait till you get the first cold day that hits your average winter temp and adjust tire temps then, once.

From what i understand, outside temperature doesn't matter* as long as the pressure is correct... in fact, better heat dissipation in colder weather leads to lower than desired operating tire temperature and thus lower tire pressures when driving.... if anything, manufactures recommend higher pressures for winter tires, for that reason and the softer compounds....

*(not taking into consideration rubber compounds, winter tires, etc)

 

[golfdave]

OK so here you are saying when you set your tire pressure inside a warm garage, to set it higher than normal if its cold out...

So if you are setting the pressure outside in the cold, early morning... then you would agree to just set it at the normal recommended pressure, right?

Thats not what you are saying here however....?



It seems you are suggesting to set you tire pressure lower during cold weather because it will over inflate when it reaches operating temperature......?

Thats the first time i hear that... This is usually the way to go:




From what i understand, outside temperature doesn't matter* as long as the pressure is correct... in fact, better heat dissipation in colder weather leads to lower than desired operating tire temperature and thus lower tire pressures when driving.... if anything, manufactures recommend higher pressures for winter tires, for that reason and the softer compounds....

*(not taking into consideration rubber compounds, winter tires, etc)

STOP!!!!!

When the car is parked up & has not been driven for several hours, you set the tyre pressures taking into account the temp of the tyre.

If the car is parked outside & its -10 C you set the pressure for -10C, as the tyres will be at -10C

If the car is parked inside a heated garage to 20C ..the tyres will be at 20C temp so set the pressure for that temp...

The quoted pressures from VW are for 20C...temp.....

in the example above the car outside at -10C would need the tyres set 0.2bar below the pressues for 20C.....this is to stop over inflation when the tyres reach operating temps...

P.S. I did not follow the strict deduct 0.1 bar per 10C drop...as from 20C to -10C is 30C drop & thus 0.3bar..reason is that the tyres I find are too low pressure & cold only really starts to affect at 0C & below....

 

[hans611]

The quoted pressures from VW are for 20C...temp.....
in the example above the car outside at -10C would need the tyres set 0.2bar below the pressues for 20C.....this is to stop over inflation when the tyres reach operating temps...

Show me some evidence / link me a source that this is the normal suggestion... not that the recommended (min) pressure on the door sill is for 20C, i know that, but that you are expected to set your tire pressure at different pressures depending on how far you are from 20C...... " to prevent over inflation" (You know the danger is under inflation, right? more friction?)

GO!!!!!!!!!

 

[torga]

You've never heard that you shouldn't top off your air after a drive because the air inside your tires is too warm? And if you do, you'll have them under-inflated because the pressure will go down after your tires cool down?
He's talking about the exact same principle, but in the cold. When air gets warm, the molecules get more excited and move around more quickly, hitting the walls of their container at a faster rate - that's the literal definition of contained fluid pressure. Hot air molecules hit the walls like mad, meaning high pressure; cold air molecules are slower and hit the walls more slowly, so slower pressure.
Every single car manufacturer sets their recommended air temps at room temperature, which is anywhere from 18-22C.

 

[swcrow]

Very cold climates, consider a sleeping bag over blanket. I keep a surplus Army three piece sleep system in each of our cars in winter. Blanket can go only so far, a proper -50F fart sack can save lives.

the ECWS is totally legit. I've slept outside in the dead of winter in CO in this and been warm. If you can get this at a surplus, get it. It slams anything commercial in the dirt. I usually keep extra hat/gloves/energy bars in the car, but nothing more since I'm in VA.

Regarding salt and washing off....I'll only take my car to a DIY power wash station if it's warmed up, middle of the day and the salt/snow/ice is basically melted and gone. It allows for the water to dry/get blown off before it refreezes that night.

 

[hans611]

You've never heard that you shouldn't top off your air after a drive because the air inside your tires is too warm? And if you do, you'll have them under-inflated because the pressure will go down after your tires cool down?
He's talking about the exact same principle, but in the cold. When air gets warm, the molecules get more excited and move around more quickly, hitting the walls of their container at a faster rate - that's the literal definition of contained fluid pressure. Hot air molecules hit the walls like mad, meaning high pressure; cold air molecules are slower and hit the walls more slowly, so slower pressure.
Every single car manufacturer sets their recommended air temps at room temperature, which is anywhere from 18-22C.

Yes of course i have heard that, thats not what I am asking.... im asking for evidence / a source saying how you are supposed to set your tire pressure Xbar less for each Xdeg C colder than 20c to prevent over inflation when reaching operating temp...

Thats because I dont think you do, the pressures listed on the door are the minimum recommended pressures... its the lowest pressure they expect the tires to be... if you set your tires 5 psi below the recommended because the car / tire / outside is 18F, 50F less than 68F (20C) then you just under inflated the tires bellow the manufactures recommended....

The 1psi for each 10F less is just a guide to see how your pressures will be affected.... Also the operating temp / pressure of the tires at 68F outside air temp will not be the same as 18F....

There is no solution, but to set your tires periodically during the mornings when its coldest... so you are never below their rec. min. pressures... and heaven forbid you dont over inflate either.... but like i said, the danger is under inflation....

Obviously pressures aren't set in stone of course, I run 33 psi in the GTI's 17in wheels because the coilovers kill me, 2 psi less than the rec. OEM 17 summer tires... while i run 40psi in the R's 19s in an attempt to save the rims..... 1 psi more....

Usually the recommended pressures are too low for a softer ride anyways, and a little higher can bring up the MPGs too.... also its OEM's summer tire vs all season, generally the A/S has a softer sidewall etc... you can adjust based on wear patters later too (over infalted if its wearing in the middle and vice versa) and get it right for your preference/set-up....

Like i said before, this is the best way to go:

Yes, also wait till you get the first cold day that hits your average winter temp and adjust tire temps then, once.

 

[golfdave]

Show me some evidence / link me a source that this is the normal suggestion... not that the recommended (min) pressure on the door sill is for 20C, i know that, but that you are expected to set your tire pressure at different pressures depending on how far you are from 20C...... " to prevent over inflation" (You know the danger is under inflation, right? more friction?)

GO!!!!!!!!!

There are masses of article on the web from tyre manufactures & many others..I picked this USA one"

""first, a quick science lesson: when the temperature drops, molecules in the air move slower and huddle together. When the temperature increases, molecules move faster and farther away from one another!

You can test this concept for yourself. Just set a basketball outside and wait! The ball will deflate in the cold morning air, then re-inflate in the heat of the afternoon.

When this concept plays out inside your tires, it can affect your tire pressure.

That’s because tires lose or gain 1-2 pounds per square inch (PSI) for every 10℉ change in temperature. So theoretically, your tires could lose 4 PSI over the weekend if the temperature drops by 20℉!

While your tire pressure should bounce back after the cold spell passes (assuming it does pass and your tires have no leaks or holes), low tire pressure shouldn’t be ignored.""


https://blog.firestonecompleteautocare.com/tires/should-i-inflate-tires-cold-weather/

So basically if you set your tyre pressures correctly to 2bar when the surrounding air temp is 20C & the tyres are cool & the same temp as the surrounding air......all ok

Park car outside & it drops to -10C ..measure your tyre temps again & they will show 1.7 bar...

You DO NOT re-inflate to 2bar as when the surrounding air temp "bounces back" to 20C those tyres will now be OVER-INFLATED....

 

[hans611]

Jesus Christ dude....

Nowhere in that article does it say to set your car tires to different pressures based on the temperature... it says to "measure your tire pressures before driving", set them to "the recommended pressure" and to be mindful of the tire pressure being affected by temperatures and then they list the 1psi per 10F we all know.....

If the car is parked outside & its -10 C you set the pressure for -10C, as the tyres will be at -10C
If the car is parked inside a heated garage to 20C ..the tyres will be at 20C temp so set the pressure for that temp...
The quoted pressures from VW are for 20C...temp.....
in the example above the car outside at -10C would need the tyres set 0.2bar below the pressues for 20C.....this is to stop over inflation when the tyres reach operating temps...
P.S. I did not follow the strict deduct 0.1 bar per 10C drop...as from 20C to -10C is 30C drop & thus 0.3bar..reason is that the tyres I find are too low pressure & cold only really starts to affect at 0C & below....

"in the example above the car outside at -10C would need the tyres set 0.2bar below the pressues for 20C.....this is to stop over inflation when the tyres reach operating temps..."

No dude, if the car is outside and its -10C, hasnt been driven yet, and its the coldest it will be, you set that tire at 2bar.

So basically if you set your tyre pressures correctly to 2bar when the surrounding air temp is 20C & the tyres are cool & the same temp as the surrounding air......all ok

Park car outside & it drops to -10C ..measure your tyre temps again & they will show 1.7 bar...

You DO NOT re-inflate to 2bar as when the surrounding air temp "bounces back" to 20C those tyres will now be OVER-INFLATED....

Here is my last attempt:

If your car is already parked outside and its -10C outside, its the early morning, etc....... and you plan to "set your tire pressure correctly to 2bar".... would you set it to 2bar at -10C?

if yes, then we are in agreement ..... however, do you see how that goes against your earlier posts? I hope i am making sense, because i dont know how else to explain it.....

edit: reading between the lines, trying to understand the reasoning.... are you suggesting to use lower tire pressures in the colder weather so as to not have to deal with adjusting tire pressures once the air temps "bounce back" ? So just to not have to let air out once the weather warms?

In that case its more of a preference thing, but you would be driving with under-inflated tires the entire time its cold... like i said, the operating temperature is a range, and if the temps are cold outside, the operating temps will be lower, and the pressure rise will not be as much.... you would be running them under-inflated....

Not to mention temperature swings of over 30-40 deg F are quite rare, so at most you would see a 3-4psi change... might as well set them at their correct pressure during the cold, over-inflation is much less of a problem than what is being made seem, under inflation is much more dangerous.....

 

[torga]

2bar at -10C is not 2 bar at 20C.

I fill my tires at around 36psi, which is roughly 2.5 bar. So I will use this number. If I want my tire to be at 2.5 bar at 20C, but I have to measure/fill it at -10C ambient, my tire will need to be at 2.25 bar.

Here are my calculations, using the proportional gas law (which relates gas pressure, gas temperature and gas volume, assuming both gasses are identical in molecular composition). This is also assuming an average tire volume of 10L, which is equivalent to 0.01 m^3.

Increasing pressures above 20C doesn't matter (within reason... that's why tires have speed ratings) because tire manufacturers have accounted for this, as long as the tire is adequately pressurized at 20C or equivalent.

 

[mk7_bk]

um i just fill my tires at 36psi, car usually sits outside, check em about 1 a month

 

[golfdave]

No dude, if the car is outside and its -10C, hasnt been driven yet, and its the coldest it will be, you set that tire at 2bar.

Here is my last attempt:

If your car is already parked outside and its -10C outside, its the early morning, etc....... and you plan to "set your tire pressure correctly to 2bar".... would you set it to 2bar at -10C?

if yes, then we are in agreement ..... however, do you see how that goes against your earlier posts? I hope i am making sense, because i dont know how else to explain it.....

edit: reading between the lines, trying to understand the reasoning.... are you suggesting to use lower tire pressures in the colder weather so as to not have to deal with adjusting tire pressures once the air temps "bounce back" ? So just to not have to let air out once the weather warms?

You don't get it do you???

As a tyre is driven it gets warm... the air INSIDE the tyre gets hotter (regardless of WTF is happening outside) & expands cause it to INCREASE in pressure.

IF you set the tyre pressure to 2bar (correct setting for 20C) when the car is outside at -10C.....what happens when you drive the car for 1hr & the tyre gets warm???

Thats correct....your tyre will be OVER-INFLATED by 0.3bar when the air inside the tyre hits 20C....

Basic laws of thermal expansion....

 

[hans611]

2bar at -10C is not 2 bar at 20C.

I fill my tires at around 36psi, which is roughly 2.5 bar. So I will use this number. If I want my tire to be at 2.5 bar at 20C, but I have to measure/fill it at -10C ambient, my tire will need to be at 2.25 bar.

Here are my calculations, using the proportional gas law (which relates gas pressure, gas temperature and gas volume, assuming both gasses are identical in molecular composition). This is also assuming an average tire volume of 10L, which is equivalent to 0.01 m^3.

Increasing pressures above 20C don't matter (within reason... that's why tires have speed ratings) because tire manufacturers have accounted for this, as long as the tire is adequately pressurized at 20C or equivalent.

I understand perfectly, believe me I have known that my whole life..... however nowhere is that the recommended way to set your tire pressure... that's my point in asking for an article.... seriously look around the web, no one suggests what you guys are saying.... it makes sense, yes.... its the norm, no....

You don't get it do you???

As a tyre is driven it gets warm... the air INSIDE the tyre gets hotter (regardless of WTF is happening outside) & expands cause it to INCREASE in pressure.

IF you set the tyre pressure to 2bar (correct setting for 20C) when the car is outside at -10C.....what happens when you drive the car for 1hr & the tyre gets warm???

Thats correct....your tyre will be OVER-INFLATED by 0.3bar when the air inside the tyre hits 20C....

Basic laws of thermal expansion....

Look at my response above... also you are still assuming that the tire will reach the same operating temps and pressures regardless of outside air temp... colder air molecules are more densely packed and they will dissipate heat from the tires faster than at warmer outside temps... so its literally impossible for the tires to reach the correct pressure when its colder....

So for sure there is more to this.....

 

[torga]

I understand perfectly, believe me I have known that my whole life..... however nowhere is that the recommended way to set your tire pressure... that's my point in asking for an article....

Dude..... it's literal physics. The Proportional Gas Law utilizes derivations from the Ideal Gas Law, and I guarantee you that is what tire engineers (and any engineer worrying about pressure deviation with respect to temperature variation) use to come up with ratings. What do you need an article for? So someone can anecdotally tell you stuff that their dad used to do? And on the flip side, any scientific article will be using these same equations for verification.
There shouldn't be any question anymore.... equations prove it.

 

[swcrow]

ya'll are making this waaaaaaaaay too hard. like mk7_bk said......fill 'em up at 36 after letting the car sit outside. check occasionally

 

[mk7_bk]

ya'll are making this waaaaaaaaay too hard. like mk7_bk said......fill 'em up at 36 after letting the car sit outside. check occasionally

I agree, I set to 36, check 1 a month unless it looks low or temp changes like 60 one day to 15