Tyre Pressure, I know that again!!!

[mike102]

Dear Members.
I know, I should check out old Forums regarding tyre pressure but i have in the past had conflicting opinions.
I drive a 1990 300 E, Very good condition and the tyres have full tread.
Thing is, I have been told by a Merc Mechanic to set my tyres as this: FRONT 32 POUNDS, and REAR 35 POUNDS.
Well did as advised and found the car skating the road, especially round the bend, and seems like the wheels kind of find themselves following any track on the road, For example, If theirs work or resurfacing on the road where your kind of half on or half off the new too old piece of road, i get the front wheels being dragged along that course, A bit like i'm on a tram rail.
Respond for advise even if you think i'm going bonkers.
Very hard to explain less you come out with me.
And would like to know the correct tyre pressure, The MB settings in the petrol door are missing so have nothing to go on.
Regards.
Mike.

 

[mike102]

You All.
Least by now Television would have come up with some advice!
Has no one got anything.
Come back Malcolm, all is forgiven!!!
Disgruntled.
Mike.

 

[Xtractorfan]

The pressures sound about right, have you tried googling tyre pressures for your model.. tramlining is to my mind a bit of a problem with the 300e and some of the cheaper tyre brands dont help..

 

[brianbrian]

Am I correct that you have 195/65/15 tyres, the tyre makes do make a huge difference try 30 all round on your 124 If your not carrying a full load ,Hope this helps.

 

[SQ_W211]

I dont think you need 35 at the back either, Try the safer options at 32 at back and 30 at front and see if it makes any difference. Because you have higher profile tyres, your car doesnt really need all that air if you not going around with fully loaded car.

 

[mike102]

Sound Advice from you all, Will have a play around with the pressures youv'e given.
Much appreciated.
Regards.
Mike.

 

[S.Speed]

I know my car is a different model (C270 CDI) but I have been running 30psi front and rear and so far the treads are wearing nice and evenly..
I disregarded the fuel cap recomendations because my rears were wearing the centre down very quickly indeed.. So in my book that says over inflation..
So far all 4 tyres are wearing just fine..
Hope this helps.

 

[Alex M Grieve]

I know my car is a different model (C270 CDI) but I have been running 30psi front and rear and so far the treads are wearing nice and evenly..
I disregarded the fuel cap recommendations because my rears were wearing the centre down very quickly indeed.. So in my book that says over inflation..
So far all 4 tyres are wearing just fine..
Hope this helps.

There are those in the trade who never bother consulting charts when fitting new tyres to saloon cars and just go for 30 all round. Seems to be effective in most cases, but excess wear will of course not become obvious for quite a while, by which time more precise inflation might have overtaken the situation during servicing.

 

[Number_Cruncher]

I know my car is a different model (C270 CDI) but I have been running 30psi front and rear and so far the treads are wearing nice and evenly..
I disregarded the fuel cap recomendations because my rears were wearing the centre down very quickly indeed.. So in my book that says over inflation..
So far all 4 tyres are wearing just fine..
Hope this helps.

The *difference* in pressure between front and rear is important for vehicle handling, and should not be disregarded.

Reducing rear tyre pressures, and/or increasing front tyre pressures move the vehicle towards a dangerous instability, and should certainly not be recommended.

 

[turbopete]

I know my car is a different model (C270 CDI) but I have been running 30psi front and rear and so far the treads are wearing nice and evenly..
I disregarded the fuel cap recomendations because my rears were wearing the centre down very quickly indeed.. So in my book that says over inflation..
So far all 4 tyres are wearing just fine..
Hope this helps.

dad had this problem on his 203 c220 cdi. switched from goodyear to michelin tyres, problem seemed to stop!

 

[Number_Cruncher]

Tyre pressure recommendations are always show as if the vehicle is fully laden. ie. four passengers and a loaded boot.

If none of the above applies, always ride with much lesser lbs.

The tyre pressure recommendations I've read don't specifiy a fully loaded car - in fact they usually show higher pressures for fully laden cars.

Reducing tyres, pressures, especially in conjunction with high speed usage can cause catastrophic tyre failure via excessive sidewall flexing.

>>much lesser lbs

That's not a safe recommendation IMO.


For cars without staggered sizes, it's far better to somply rotate the tyres than fiddle about with the MB recommended tyre pressures - it's even included in the service schedule, where the expected wear patterns are also described.

 

[rf065]

The *difference* in pressure between front and rear is important for vehicle handling, and should not be disregarded.

Reducing rear tyre pressures, and/or increasing front tyre pressures move the vehicle towards a dangerous instability, and should certainly not be recommended.

I cannot agree with that at all.
My rears were wearing in the middle, so I reduced them to 30psi.
My fronts wear at the edges, so I increased them to 33psi.

The tyres now appear to wearing evenly front & back and the handling has not suffered one bit.

Russ

 

[Number_Cruncher]

>>I cannot agree with that at all.

The vital point of my post is that you move towards an instability, not that your car becomes unstable. A driver possessing rare and sensitive skills would be able to detect that the handling balance of the car had shifted in the unstable direction.

MB do this deliberately to give their cars safety margin against the instability, and recommend that, where possible, wheels and tyres are rotated to even the uneven wear that they know is going to happen.

The quickest and best way to impart the technical detail which informs my posting is to recommend you to a book "Fundamentals of Vehicle Dynamics" by Gillespie - particularly the chapters on tyres and handling. It's not a cheap book, you may prefer to see if your library has it in stock.

 

[wireman]

I think Number cruncher has a valid point.

Perhaps a 190 owner may help you by looking at the makers data on his fuel filler flap.

In my owners book (1989 124) it suggests that the front and rear tyres are swapped at 5 - 6,000 mile intervals keeping them on the same side of the car as they were fitted such that they always rotate in the same direction throughout their life.

 

[brianbrian]

The reason I suggested 30 all round, it suits my 124 as the car only has my wife and I in the vechicle, if I put an extra 2lb in my tyres they wear in the middle also if the road is wet I noticed on round abouts at normal driving the car was not as stable. Hope this helps

 

[Number_Cruncher]

>>I have the quals, knowledge and expererience to supercede these books.

Sadly, that's clearly not the case.

 

[Number_Cruncher]

>>Basics are, you did not serve your apprenticeship as a mechanic.

That is not true.

In fact, it was a national prize winning apprenticeship, where I won and was awarded a medal by City and Guilds.

However, I did not stop there, and the book I recommended was one I used in study at a much higher level than an apprenticeship - in fact, it was recommended to me by a professor of vehicle dynamics who consults for Ford among others.

I see that you're one of the types who sneer at those who learn from what they read in books, and what they learn from more learned people. Does this mark you out as a knowledgable person, or an ignorant one?

 

[turbopete]

if anyone actually bothers to read the label inside the fuel filler cap corectly they will see that the pressures are based on 2 situations. a normal, then a full load, with high speed (over 100mph) variations for each. in the uk, there is obviously no need for the high speed variations. your friendly plods or speed cameras have made sure of that, as has your fuel bill! the standard, every day setting i use is the lower one. this is for an EMPTY CAR with 3 OCCUPANTS. ive had the car a year, done about 8k miles in it (just myself mostly) and have no wear issues with the tyres at all, and they werent new tyres when i got the car! the higher pressure is for 5 OCCUPANTS AND LUGGAGE! so unless you regularly run loaded to the max, i see no point in altering from the standard pressures! especially if 3 of your occupants are your kids etc! i am willing to admit that i dont check my pressures every week but unless you have a slow puncture etc, theres no need to really, in my experience!

 

[Alex M Grieve]

>>Basics are, you did not serve your apprenticeship as a mechanic.

That is not true.

In fact, it was a national prize winning apprenticeship, where I won and was awarded a medal by City and Guilds.

However, I did not stop there, and the book I recommended was one I used in study at a much higher level than an apprenticeship - in fact, it was recommended to me by a professor of vehicle dynamics who consults for Ford among others.

I see that you're one of the types who sneer at those who learn from what they read in books, and what they learn from more learned people. Does this mark you out as a knowledgable person, or an ignorant one?

You need a bit of both really. To paraphrase Sir William Osler, a famous physician:

"To practice without books is like going to sea with out charts.
To work purely from books, without practical experience is like not going to sea at all".

 

[turbopete]

You need a bit of both really. To paraphrase Sir William Osler, a famous physician:

"To practice without books is like going to sea with out charts.
To work purely from books, without practical experience is like not going to sea at all".

this is also quite true. the mechanics course when i did mine (1992-1995) was day release with 4 days on the job. now you can qualify in a year as its a full time course with no practical experience. IMHO this is not a good move. anyone that followed Alfiebeard's threads about his SBC pump fitment and related problems can see where im coming from with that. cross threaded brake pipe unions that leak fluid? qualified mechanic? possibly. competent? i wouldnt say so. id rather have unqualified, competent people than qualified incompetent people. at least competent people know how to do the job, even if they dont understand why its done the way it is!