Tyre pressures in winter?

[ioweddie]

Hi
Probably a silly question.....inside my fuel flap it says....2.5bar all round....up to two occupants....cold

its a 2016 automatic model c220d premium plus estate.....I just thought that once the car is driving and warmed up the tyre pressures will rise with expansion.....It appears high...any thoughts!

 

[Edd1968]

I guess it will depend on your wheel and tyre dimensions. The lower the profile, the pressure tends to be higher. It has also to be remembered that it's not a lightweight car either.
I always lower might by maybe half a bar in winter anyway.

 

[Deletedmember130310]

A 20% reduction in your tyre pressues in quite a lot! What benefits do you think you get?

 

[190]

2.5 Bar does seem slightly high. I think MB are using tyre pressures a little higher than they used to for reduction in rolling resistance. Personally I run mine 5% lower than the fuel flap figures for a little extra comfort and that equates to only 0.4 % loss of fuel economy.

The only thing to be aware of in winter is if you last checked the pressure in warmer weather, when it gets cold the pressure will have reduced and you will need to add some air to bring them back up again. Tyre pressures fall 0.1 bar (1.5 psi) for every 8 Deg C reduction in ambient temperature.

 

[whitenemesis]

Use the pressures shown on the filler flap, filled and adjusted when the tyres are cold i.e. first thing in the morning. Manufacturer has calculated this to give the optimal pressures once the tyres have warmed up.

 

[Edd1968]

A 20% reduction in your tyre pressues in quite a lot! What benefits do you think you get?

I don't run this model of Merc and use much higher profile winter tyres on smaller diameter rim's.

 

[Edd1968]

I used to use Nitrogen in my motorcycle tyres for the track way back when. It isn't affected by tyre heat. (used on the racetrack for most motor sports for eons really)

 

[190]

I used to use Nitrogen in my motorcycle tyres for the track way back when. It isn't affected by tyre heat. (used on the racetrack for most motor sports for eons really)

Nitrogen has some benefits such as absence of moisture but it's still a gas and must obey the gas laws. It's pressure will change with temperature.

 

[Edd1968]

Nitrogen has some benefits such as absence of moisture but it's still a gas and must obey the gas laws. It's pressure will change with temperature.

Much less than air though at higher temps and my slicks were too hot to touch when they came out of the blankets and once up to temperature.

 

[190]

Yes the pressure change will be less due to the absence of moisture.

 

[MangoMan]

Hi. As Whitenemesis states, the "Cold" refers to cold tyres - ie sat for 12+hours at rest.
But at the Forecourt if you have driven more than a couple of miles add about 4-6 psi or 0.2 bar. on top of the recommended pressures.
On my clk320 I as a matter of course put 2.3 (F) & 2.5 (R).

NB. Another advantage of Nitrogen is that the molecules are larger so pressure loss is reduced over time.

 

[Edd1968]

NB. Another advantage of Nitrogen is that the molecules are larger so pressure loss is reduced over time.

...... And if you're sad enough you get to use green valve caps to indicate Nitrogen!!

 

[Oldlae]

I'm sad enough to use nice brass valve caps painted yellow.......they make my 'Munich Taxi' go like the corporate jet that they were fitted to, in their first life.
Tony

 

[Justintyme]

2.5 Bar does seem slightly high. I think MB are using tyre pressures a little higher than they used to for reduction in rolling resistance. Personally I run mine 5% lower than the fuel flap figures for a little extra comfort and that equates to only 0.4 % loss of fuel economy.

The only thing to be aware of in winter is if you last checked the pressure in warmer weather, when it gets cold the pressure will have reduced and you will need to add some air to bring them back up again. Tyre pressures fall 0.1 bar (1.5 psi) for every 8 Deg C reduction in ambient temperature.

And conversely, will rise by the same amount when the temp rises??

 

[Petrol Pete]

2.5 bar is 36 psi...that's not high. The lowest pressure shown on my fuel cap is 2.2 bar (32 psi) and the highest is 3.2 bar (46 psi). Not sure what makes OP think that 2.5 bar is high ?????

It's an AMG rolleyes Premier plus line, so it's probably got some 19/20 inch low profile tyres on it so it will need these types of pressure.

OP , what wheels and tyres are fitted. ?

 

[Edd1968]

.. Which is kind of what I'd said in my post..

I guess it will depend on your wheel and tyre dimensions. The lower the profile, the pressure tends to be higher. It has also to be remembered that it's not a lightweight car either.
I always lower might by maybe half a bar in winter anyway.

 

[CaptainChaos]

2.5 bar is 36 psi...that's not high. The lowest pressure shown on my fuel cap is 2.2 bar (32 psi) and the highest is 3.2 bar (46 psi). Not sure what makes OP think that 2.5 bar is high ?????

There seems to be an unwritten rule somewhere that all tyres should be pumped up to 32psi, regardless of what the manufacturer specifies. Seems to be something that is handed down from the first family member who had a car and if it was good enough for his Austin Seven, it's good enough for a two ton 150mph Mercedes.

 

[190]

And conversely, will rise by the same amount when the temp rises??

Yes they will rise with increased ambient temperatures. The basic point is that even if tyres lost no pressure at all through leaks you would still have to pump them up in the winter and let them down again in the summer. The winter check is perhaps more important. Pressures are always checked cold and will rise when the car is driven but inevitably they will rise a little less in the winter so best to have the correct cold pressure to start with.

Pressure changes are simply proportional to temperature but you have to use absolute temperatures and pressures which explains the 273's and the + 1's in this formula that calculates the temperature change needed to change the pressure by 0.1 bar.

8 Deg C =(-1+273)*(2.1+1)/(2+1)-273

 

[alzieboy]

I run the same pressure on Winter and Summer Tyres 33psi all corners, Two occupants , as listed on Door Jam.

 

[190]

I run the same pressure on Winter and Summer Tyres 33psi all corners, Two occupants , as listed on Door Jam.

That's exactly what you should do but the point I was making is, if you were set them at 33 psi in the summer and then check them in the winter the, pressure will have dropped below 30 PSI even with zero leakage