Tyre Pressures

[Greg4412]

Hi Guys

This is my 1st post so please dont shoot me down if its a bit basic

I have recently purchased a E350 Coupe on a 17 plate (not the new shape the older one)

Ok right well when I downloaded Mercedes me I noticed the tyre pressure section and also noticed it was in KPA not PSI so having previously owned a C250 i knew the pressures were on the inside of the petrol cap, so I looked and saw this was also in KPA, so I then looked at handbook which tells u to go to the petrol cap where u will find the tyre pressures. So i coverted the 270 KPA which converts 39.16 PSI.......So we are getting somewhere, however I have never put anywhere near this amount of pressure in any car and it seems very excessive ?????

Can anyone confirm the correct tyre pressures for my E350 Coupe I have the 19 inch rims on it

255/30/19 rear
235/35/19 front

I have contacted the dealer and they say the to check the petrol cap........

If this right then please accept my apoligies for not listening to the dealer, but I know from using forums
like this previously you guys often know more than the dealers

It also seems Strange that all my tyres are currently set to 235 KPA ....34 PSi

Thanks in advance

 

[kianok]

I thought the same but as I've never had 19's before I just went with the figures on the cap.

Don't quite understand what was wrong with using PSI as a measurement!

Welcome to the forum.

 

[markjay]

No idea... I have always pumped the tyres up to what the sticker on the fuel flap says.

The theory is as follows:

Use the higher figure within the range if (a) you have a fully-loaded car, or (b) you prefer a harder ride and more sporty drive, or (c) you drive mostly on Motorways, or (d) you want to achieve best fuel economy, or (e) you want the maximise the mileage you get out of your tyres..

Use the lower figure within the range if (a) you prefer a softer car with more cushioned ride, and don't care much about any of the above.

 

[Greg4412]

I thought the same but as I've never had 19's before I just went with the figures on the cap.

Don't quite understand what was wrong with using PSI as a measurement!

Welcome to the forum.

Yes I am going to pump them up as like you I have never had 19's so I am assuming because of the super low profile they must require this rather excessive 39 psi

 

[kianok]

Yes I am going to pump them up as like you I have never had 19's so I am assuming because of the super low profile they must require this rather excessive 39 psi

My thought exactly and so far so good.

 

[190]

As pressures vary even within the same model range I don't think you will find them anywhere but on the fuel flap.

Kilo pascals are the correct fundamental scientific unit if you wear a white coat and work in a lab but crazy for tyres pressures as the numbers are ridiculously big. Even if they didn't want to use PSI it's unforgivable that they didn't use the more convenient and widely used unit of Bars simply by dividing kPa by 100. It's the equivalent of the weather forecaster saying "it will be sunny tomorrow with a temperature of 293.15 degrees Kelvin". Scientifically correct but techno snobbish and stupid.

 

[markjay]

Did you know....?:

1 furlong per fortnight = 0.000166309524 m/s.

 

[kianok]

Did you know....?:

1 furlong per fortnight = 0.000166309524 m/s.

Of course, everyone knows that........

 

[clk320x]

No idea... I have always pumped the tyres up to what the sticker on the fuel flap says.

The theory is as follows:

Use the higher figure within the range if (a) you have a fully-loaded car, or (b) you prefer a harder ride and more sporty drive, or (c) you drive mostly on Motorways, or (d) you want to achieve best fuel economy, or (e) you want the maximise the mileage you get out of your tyres..

Use the lower figure within the range if (a) you prefer a softer car with more cushioned ride, and don't care much about any of the above.

Is the info in the fuel cap different depending on the wheel size you order?

 

[markjay]

On my car the sticker has info regarding various tyre sizes, so I am assuming that each model has the same sticker, showing the different pressures for the various optional sizes available for it.

 

[carnut]

What make of tyre do you have? Check their web site for the recommended pressures as a reality check. My car petrol cap has bar recommendations and as the pump supplied is in bar I use that , I also run 19s

I'm in Brisbane at the moment so I can't check what I use but I think it's more like 34 psi so I would be ,as you are, suspicious of your 39

 

[carnut]

What make of tyre do you have? Check their web site for the recommended pressures as a reality check. My car petrol cap has bar recommendations and as the pump supplied is in bar I use that , I also run 19s

I'm in Brisbane at the moment so I can't check what I use but I think it's more like 34 psi so I would be ,as you are, suspicious of your 39

Ps what does your handbook say?

 

[RonFleet]

The handbook for my C200 matches what's on the filler-flap sticker (250 kPa = 36.25 psi). The handbook also states that the pressure may be dropped to as little as 220 kPa (31.9 psi) for a more comfortable ride at the expense of fuel efficiency. I currently run them at 33psi.

 

[190]

The handbook for my C200 matches what's on the filler-flap sticker (250 kPa = 36.25 psi). The handbook also states that the pressure may be dropped to as little as 220 kPa (31.9 psi) for a more comfortable ride at the expense of fuel efficiency. I currently run them at 33psi.

There is a method of judging tyre pressures using tyre manufacturers load tables which give the maximum load per tyre at different pressures. It's what the car manufacturer does of course to determine the minimum safe pressures. When I looked into it, I concluded that in general car manufacturers are recommending higher than the minimum safe pressures probably for handling and economy reasons. If they allow 31.9 psi instead 36.25 psi you can be sure that the tyre will still adequately support the weight of the car at that pressure. In fact usually the car plus 3 passengers and some luggage.

For what it's worth my W204 on skinny tyres has recommended pressures of 31.9 Front 33.4 Rear so I can't see how a W205 which I think is a little lighter actually needs 36.25 PSI to support the weight.

I also looked into the relationship between pressure and fuel economy. It's not a simple linear relationship because it depends on speed but in general a 10 % increase in pressure produces 0.8% improvement in MPG. Personally I stick to the lower pressures and trade 0.8% MPG for comfort.