Correct tyre pressure

[v8sam]

I have recently purchased a C clas AMG estate 2009 and noticed the tyres seemed low.
I inflated them to 2.8 41 front and 2.9 42 rear reading from the petrol cap
Tyres front 235/40/18
rear 255/35/18
Now you can feel every bump in the road it does not feel very comfortable is this normal for a AMG?
Any advice welcome.

Rickey

 

[Dieselman]

Can you post a picture of the information in the fuel flap as it sounds like you have inflated them to the maximum pressures.
Typical pressures would be 2.1Bar front, 2.2Bar rear.

 

[DSM10000]

I have recently purchased a C clas AMG estate 2009 and noticed the tyres seemed low.
I inflated them to 2.8 41 front and 2.9 42 rear reading from the petrol cap
Tyres front 235/40/18
rear 255/35/18
Now you can feel every bump in the road it does not feel very comfortable is this normal for a AMG?
Any advice welcome.

Rickey

Do you have AMG suspension? that is usually firmer than standard. You also have rather low profile tyres so it is never going to absorb bumps particularly welll. Those inflation figures seem high, are you sure they are not for when fully loaded and have you checked with another pressure gauge in case the one you used is reading incorrectly?

 

[MicB]

The optimum pressures do not change with tyre/wheel size. As above those pressures are surely too high.

Mic

 

[markjay]

I don't have the details for your model, but from what I can see the pressure for the C-Class Estate is in the region of:

Unladen and non-Motorway use:
2.1 - 2.2 front
2.3 - 2.5 rear

Laden and/or Motorway use:
2.3 - 2.5 front
2.9 - 3.2 rear

So your figures of 2.8 front and 2.9 rear are probably too high, at least at the front anyway, and most likely at the rear as well. But as others said, best to check the info on the sticker in the fuel flap and adhere to it.

 

[John]

I did my tyres this morning which are that size.

I think the 41 ball park is when you are likely to have 5 people and tons of luggage on my sticker.

For 3 people and moderate luggage, it is 35 all round.

 

[jefrs]

You also need to observe tyre wear, especially wide lo-pro. Recommended pressure is just that, recommended.
If you are wearing out the centre then you need to lower pressure, If you are wearing the edges, then raise it. Tyre wear should be even.

Tyre pressure also dictates the ground contact footprint area. Assume 400-lb on each corner and 40psig, then footprint is 400/40 = 10-sq.in. If 30psig then 400/30 = 13-sq.in (more contact area). Obviously a certain area is optimum and will vary with load, hence the pressure adjust for load.

 

[v8sam]

I have enclosed a picture and the tyres are low profile

 

[grober]

My first question would be how accurate is your tyre pressure gauge you measured the new pressures with?

As an additional comment Mercedes recently amended [ raised ]some of their recommended tyre pressures for their E class 4 cylinder diesels after owner complaints that they could not achieve published MPG figures. Its possible MB recommend these high tyre pressures in anticipation that C63 models would be routinely used for high speed journeys rather than slower A road work.

 

[rhud]

My first question would be how accurate is your tyre pressure gauge you measured the new pressures with?

As an additional comment Mercedes recently amended [ raised ]some of their recommended tyre pressures for their E class 4 cylinder diesels after owner complaints that they could not achieve published MPG figures. Its possible MB recommend these high tyre pressures in anticipation that C63 models would be routinely used for high speed journeys rather than slower A road work.

There seems to be a widespread trend these days towards higher tyre pressures - mainly, I suspect, so that manufacturers can claim better mpg figures vis-a-vis the competition. In MB's case it seems mostly the BlueEfficiency models. My A Class has been upped from 29psi all round to 32 front, 38 rear for all load circumstances, a substantial increase. Ride is consequently harmed.

 

[v8sam]

My first question would be how accurate is your tyre pressure gauge you measured the new pressures with?

As an additional comment Mercedes recently amended [ raised ]some of their recommended tyre pressures for their E class 4 cylinder diesels after owner complaints that they could not achieve published MPG figures. Its possible MB recommend these high tyre pressures in anticipation that C63 models would be routinely used for high speed journeys rather than slower A road work.

The gauge is a Benbow one that the aircraft industry use but this one is made for car usage and is very accurate.
I will decrease the pressure to suit as the majority of the time I am the only person in the car until we go away up north several times a year when it becomes fully loaded with family and 2 dogs.

 

[BTB 500]

Hmm .. running under-inflated (compared to the book figures) isn't usually a good idea, so I would go very carefully.

I have the opposite problem with the Vito, twice it has come back from a service with the tyres set way higher than the plate figures

 

[BTB 500]

There seems to be a widespread trend these days towards higher tyre pressures - mainly, I suspect, so that manufacturers can claim better mpg figures vis-a-vis the competition.

I thought this was usually in conjunction with different tyres?

 

[grober]

I thought this was usually in conjunction with different tyres?

E-Class W212 2009 | Mercedes-Benz | Car Reviews | Honest John

 

[kamalpatel12448]

I settle for 42psi. Same size tyres

 

[John]

Tyres front 235/40/18
rear 255/35/18

I have enclosed a picture and the tyres are low profile

I notice 'up to' on your sticker and yours are larger... i.e. yours are lower profile as they are 40% of 235 and 35% of 255.

I think I'd be dropping them a little personally and seeing how you get on - especially as I doubt you travel 3 up with 3 suitcases...

 

[jefrs]

I have enclosed a picture and the tyres are low profile

225/40R18 are not low-pro as commonly understood.
The pressures shown on your flap are more like those on a van than a car - how heavy is this vehicle?

 

[ringway]

I have the opposite problem with the Vito, twice it has come back from a service with the tyres set way higher than the plate figures

Me also, Bill.

I had my Vito serviced at a MB commercial dealership and was greeted with "Do you know you have been running with the tyres way below the recommended pressures?"

After tyre pressure adjustment by the dealership, the ride home was boneshaking, resulting in me (after consulting the handbook) adjusting the pressures to what feels comfortable.
I also looked at the way the tyres were sitting to the road surface as a guide.

There is so much ambiguity with regard to tyre pressures and the calibration of air lines at forecourts, garages, tyre dealers etc,.

If involved in a serious accident, things such as tyre pressures are checked, and someone (most likely the driver who is unable to obtain a difinitive answer for pressures) will carry the can. Sheesh..

 

[v8sam]

I notice 'up to' on your sticker and yours are larger... i.e. yours are lower profile as they are 40% of 235 and 35% of 255.

I think I'd be dropping them a little personally and seeing how you get on - especially as I doubt you travel 3 up with 3 suitcases...

I have dropped the fronts to 39 psi and rear to 40 psi the car feels and drives a lot better.

225/40R18 are not low-pro as commonly understood.
The pressures shown on your flap are more like those on a van than a car - how heavy is this vehicle?

It is an estate not sure of the weight. I will look in the owners manual later today.

 

[The _Don]

I have recently purchased a C clas AMG estate 2009 and noticed the tyres seemed low.
I inflated them to 2.8 41 front and 2.9 42 rear reading from the petrol cap
Tyres front 235/40/18
rear 255/35/18
Now you can feel every bump in the road it does not feel very comfortable is this normal for a AMG?
Any advice welcome.

Rickey

Does your c63 have the performance pack ? (alcantara on the steering wheel)
If it has this option then the suspension is considerably stiffer than the non performance pack cars.