Normal Running Tyre Pressures

[Scouser51]

Hi Everyone,
I own a 2018 E Class 220d and am a little concerned about what pressure I should maintain my tyres at. Obviously the car is fitted with run flats, I normally only have the wife in the car and occasionally my young grandchildren.
The data on the inside of the fuel filler cap indicates 32 psi on the front and 33 psi on the rear. The rims are big at 19 inch but I’ve never known such low tyre pressures is it because they are run flats?

 

[E55BOF]

My 2013 SLF Shooting Brake runs 33 psi front, 35 rear, for 19" rims. Just stick with what it says inside the fuel filler flap.

 

[whitenemesis]

I wouldn't say that is low. I have 19" wheels and my pressures are 24psi F, 26psi R. OK not an E class but indicative of a 'low' pressure.
If that is what is recommended on the fuel filler flap and the tyres and wheels are OEM I'd stick with it. How is the wear across the tyre?

 

[DSM10000]

Hi Everyone,
I own a 2018 E Class 220d and am a little concerned about what pressure I should maintain my tyres at. Obviously the car is fitted with run flats, I normally only have the wife in the car and occasionally my young grandchildren.
The data on the inside of the fuel filler cap indicates 32 psi on the front and 33 psi on the rear. The rims are big at 19 inch but I’ve never known such low tyre pressures is it because they are run flats?

What is low tyre pressure?

PSI or whatever units you want to use are merely an expression of force over area and I am unsure why you think this is low because the tyres are 19 inch diameter.

 

[tonysmb]

Those aren't low pressures; it is correct that there has been a move towards higher pressures in recent years but some of that is driven by the need to reduce fuel consumption (lower rolling resistance). You will often see that Eco models in a range have tyre pressures specified approx 4psi greater than the non-eco models.

I have one (light) car with pressures of 22/24 fr/rear.

 

[Scouser51]

I wouldn't say that is low. I have 19" wheels and my pressures are 24psi F, 26psi R. OK not an E class but indicative of a 'low' pressure.
If that is what is recommended on the fuel filler flap and the tyres and wheels are OEM I'd stick with it. How is the wear across the tyre?

I know what your thinking, I’m told inside tyre wear is a normal phenomenon on this car, the dealership put four new tyres on it after the car had completed 31000 miles! So providing I keep the tyre pressure correct I’m looking at replacing the tyres around the 60,000 mile mark.

 

[DSM10000]

I know what your thinking, I’m told inside tyre wear is a normal phenomenon on this car, the dealership put four new tyres on it after the car had completed 31000 miles! So providing I keep the tyre pressure correct I’m looking at replacing the tyres around the 60,000 mile mark.

Is this car new to you or did you cover the previous 31,000 miles in it?

I am assuming from your initial question that it is a new to you car.

If so then you cannot extrapolate tyre wear from a previous owner or the tyres are most likely diffeent the driving styles and usages may well be quite different. There are many variables that will affect the life of the tyres.

 

[Scouser51]

Is this car new to you or did you cover the previous 31,000 miles in it?

I am assuming from your initial question that it is a new to you car.

If so then you cannot extrapolate tyre wear from a previous owner or the tyres are most likely diffeent the driving styles and usages may well be quite different. There are many variables that will affect the life of the tyres.

Spot on, there was only one previous owner, I’m unlikely (being retired) to travel more than 7000 miles per year, so I’m expecting to replace the tyres after 5 years given my steady driving style!

 

[DSM10000]

Spot on, there was only one previous owner, I’m unlikely (being retired) to travel more than 7000 miles per year, so I’m expecting to replace the tyres after 5 years given my steady driving style!

I wish you good health to enjoy!

 

[Scouser51]

I wish you good health to enjoy!

Very kind of you to wish me that, much appreciated.

 

[Fastcar155]

Hi , I try to run my tyres at the recommended tyre pressure recommended by Mercedes.

On my car with two people and items in the boot that is 36 psi when cold.

I have had issues with my tyres in that the have started to internally fail.Upon inspection the tyre manufacture feels that the tyres pressure on the rear of the car should be inflated to 38 psi.

The reason is the camber introduced on my car by Mercedes.

Kwit Fit recommend 32psi all round.

I am keeping an eagle eye on my new tyres at the pressure recommended by Mercedes.

 

[ChrisHGTV]

Hi , I try to run my tyres at the recommended tyre pressure recommended by Mercedes.

On my car with two people and items in the boot that is 36 psi when cold.

I have had issues with my tyres in that the have started to internally fail.Upon inspection the tyre manufacture feels that the tyres pressure on the rear of the car should be inflated to 38 psi.

The reason is the camber introduced on my car by Mercedes.

Kwit Fit recommend 32psi all round.

I am keeping an eagle eye on my new tyres at the pressure recommended by Mercedes.

That's interesting - im on 17's and the filler cap psi is 38. I find this incredibly unforgiving and really spoils the drive. So i run them 4 psi below (whatever the filler cap states given load conditions). Makes a huge difference to the comfort and ive not seen any adverse wear or degradation, at least on the outside. The Fronts almost need changing so i'll have a look at the inside when i do.

 

[Gbrowncls55]

Hi Everyone,
I own a 2018 E Class 220d and am a little concerned about what pressure I should maintain my tyres at. Obviously the car is fitted with run flats, I normally only have the wife in the car and occasionally my young grandchildren.
The data on the inside of the fuel filler cap indicates 32 psi on the front and 33 psi on the rear. The rims are big at 19 inch but I’ve never known such low tyre pressures is it because they are run flats?

I certainly wouldnt call them low pressures. Anyway as said above just stick to what it says in the fuel cap for your wheel size. Why wouldnt you?

 

[JHS]

Hi , I try to run my tyres at the recommended tyre pressure recommended by Mercedes.

On my car with two people and items in the boot that is 36 psi when cold.

I have had issues with my tyres in that the have started to internally fail.Upon inspection the tyre manufacture feels that the tyres pressure on the rear of the car should be inflated to 38 psi.

The reason is the camber introduced on my car by Mercedes.

Kwit Fit recommend 32psi all round.

I am keeping an eagle eye on my new tyres at the pressure recommended by Mercedes.

After my experience with inner tyre wear, I am inclined to follow your reasoning. Keep us informed.

 

[190]

I certainly wouldnt call them low pressures. Anyway as said above just stick to what it says in the fuel cap for your wheel size. Why wouldnt you?

I agree they are not low pressures, MB will have ensured that the tyres will support the weight of the car and then some at those pressures.

That's interesting - im on 17's and the filler cap psi is 38. I find this incredibly unforgiving and really spoils the drive. So i run them 4 psi below (whatever the filler cap states given load conditions). Makes a huge difference to the comfort and ive not seen any adverse wear or degradation, at least on the outside. The Fronts almost need changing so i'll have a look at the inside when i do.

38 psi does seem high though and I would do the same and reduce them to improve the ride. It's a shame tyre load tables are not readily available that show load rating at different pressures, but we do know the load at one pressure. If I guess that your tyres are load rating 91 then we know that 4 tyres will support 2460 KG at a stated pressure usually 2.5 bar or 36 psi. I suspect your car isn't anywhere near that weight including passengers which suggests there is some scope for you to reduce pressure from 38 psi to only 2 psi below the load rating pressure. For such a small reduction in pressure, the load rating would be reduced in approximate proportion to the pressure change but it gets extremely non linear at much lower pressures.

The obvious question is why would MB specify a higher pressure than necessary to support the load. They could be thinking about maximising fuel economy or sharpening the handling at the expense of ride quality. There is probably no point in trying to understand their rational. There is no point putting form before function by fitting ultra low profile tyres in the first place but MB still sometimes do it.

 

[Smiley]

Kwit Fit recommend 32psi all round.

A*se and elbow springs to mind.
They probably recommend 32psi all round for all cars; saves them looking anything up.

 

[OneForTheRoad]

Use what mb recommend at 10% heat in the tyre , I think it states this on the fuel flap and not cold. I use a pump with kpa and tend to go within 5 units under.

 

[Bobby Dazzler]

Use what mb recommend at 10% heat in the tyre , I think it states this on the fuel flap and not cold. I use a pump with kpa and tend to go within 5 units under.

How do you know you’ve got 10% heat in the tyre, and 10% of what?

I’ve only ever noticed that the manual and fuel filler flap usually state pressures are for cold tyres, ie with no residual heat from driving.

 

[OneForTheRoad]

How do you know you’ve got 10% heat in the tyre, and 10% of what?

I’ve only ever noticed that the manual and fuel filler flap usually state pressures are for cold tyres, ie with no residual heat from driving.

No idea . Ask mercedes maybe. I'm going off what mine states. Saying to warm tyres . Unless it means warm tyres will add extra psi. ?????

 

[190]

No idea . Ask mercedes maybe. I'm going off what mine states. Saying to warm tyres . Unless it means warm tyres will add extra psi. ?????

It doesn't mean you should check pressures with warm tyres as a matter of course.

What it means is that should you need to check them warm them add 0.3 bar or 4 psi to the stated cold pressures in the table.

10% does have a wider rule of thumb significance for determining correct cold pressures. If you check them both cold and hot and your pressures rise by 10% then the cold pressures were in the right ballpark. If they rise more than 10% then they were too low when cold and vice versa.