scrubbing front tyres.

[Glenn Smith]

Hi, hope you all had a merry Christmas, we're just back from a trip to the outlaws over in Holland, again the Mercedes C230K did a good job of hauling far too much "stuff" across complete with full roof box. One thing i have always noticed with the car is a tendency to scrub the outside tyre on tight locks, this has been more noticeable in the cold weather and especially on the BF goodridge tyres now they are wearing down. On some of the brick type road surfaces in Dutchland the effect was to grip and slip creating quite a noise (and leading to fatheroutlaw condeming the springs?) Obviously i need to check the suspension and tracking, but believe these to be fine. any one else experience this on the C class (mine is Esprit model with sport suspension) also has 16" rims with 205/55 tyres and i did wonder if the offset was correct.

 

[stats007]

This is usually down to the castor angle - modern Mercs have always had this trait.

 

[Glenn Smith]

Yeah, i'm not too worried about it, my old porsche did the same, and, as the Merc, had a very tight turning circle which obviously makes matters worse.

 

[television]

I would have thought that with the car being fully loaded it would be the inside that would wear more

 

[Glenn Smith]

this happens loaded or not, it' not the wear that bothers me it's the scrubbing of the tyre as if the ackerman angle is all wrong, this is very noticable in multi storie car parks with constant squealing as you turn sharply, in our local multi, now it's wet and slipery you can feel the outside wheel skidding across the surface.

 

[stats007]

It's possible you have worn bushes which could exaggerate the effect from the already worn tyre.

 

[television]

this happens loaded or not, it' not the wear that bothers me it's the scrubbing of the tyre as if the ackerman angle is all wrong, this is very noticable in multi storie car parks with constant squealing as you turn sharply, in our local multi, now it's wet and slipery you can feel the outside wheel skidding across the surface.

Thats an interesting point listening to some cars that squeal in car parks and others that dont when going the same speed.


Amazing to go all of these years without giving it a thought

 

[280gee]

Can certainly lead to false assumptions I'd imagine, like "why are they going so fast it's a car park?"

 

[kth286]

As stats says, the Mercs have traditionally had very large castor angles of the order 10 degrees verses normal 5 degrees on other cars.

This contributes to the relaxed steering feel at very high speeds with very little driver input required to keep correcting the steering inputs.

You can see the effect of this on the front wheels when you park with steering on full lock. Get out of the car and you will see very pronounced lean on each front wheel - tops of wheels actually leaning into the turn.

 

[television]

As stats says, the Mercs have traditionally had very large castor angles of the order 10 degrees verses normal 5 degrees on other cars.

This contributes to the relaxed steering feel at very high speeds with very little driver input required to keep correcting the steering inputs.

You can see the effect of this on the front wheels when you park with steering on full lock. Get out of the car and you will see very pronounced lean on each front wheel - tops of wheels actually leaning into the turn.

Do bare in mind that when cars are leaving car parks, all makes are on the same lock.

 

[kth286]

If another car is on the same lock as a Merc the wheels of the Merc will be leaning more for the same lock.

I will qualify all my remarks on this subject and say thet my facts are for the mid 90's cars.

I am not sure whether latest generation of modern Merc still stick with the high castor angle.

I mention this because high castor does have a negative in that the car is not normally so manoevereable (agile) when moving from turning one way and then turning the other way quickly.

Merc seem to be stressing how agile the new C204 car is.

If you think about high castor and how the wheels lean on lock, the effect of the leaning wheels actually lowers the body of the car.

So turning quickly from one lock to another means the car is lowered one way and then has to be raised again and lowers on the opposite lock.

All of this take a lot of expended energy on the steering gear of the car, and the car is therefore less agile than it's competitiors.

Anyone know the castor angle of the latest C204 car ???????????

 

[Glenn Smith]

Some very interesting comments all round, the castor on the C class is just under 5 degrees, so not quite so severe as some older larger models, which are around 10 degrees. does anyone else experience similar on their C class or should i be looking for a fault?

 

[280gee]

An interesting thread as one immediate problem noticed with my recent acquisition was that of the o/s front tyre's outer edge being scrubbed even though the toe-in proved to be set correctly.
Maybe an excess of left turns in a carousel type car park was to blame?

 

[television]

Interesting what kth286 says, the angle is measured in the straight ahead position and can change dramatically when on lock

 

[280gee]

Yes, I was thinking perhaps along similar lines in that it seemed to be a trade-off or maybe even tradition to have that ocean liner feel for those long cruises.

Dodging around town centres and using multi story car parks with their tight turns maybe just isn't what the cars are ideally suited for given the geometry settings?

 

[Glenn Smith]

Interesting what kth286 says, the angle is measured in the straight ahead position and can change dramatically when on lock

Correct, the bigger the castor the more dramatic effect it has when you turn the wheel, if you want to visualize this then of a chopper style motorcycle with long forks and a large castor angle (ie the angle between the forks and an imaginary vertical drawn up through the centre of the wheel, now imagine the wheel being turned, it effectively tips rather than turns this leads to slow but stable steering, compare to a sports bike which has a much steeper (smaller castor angle) the bike will be quick to turn but less stable

 

[280gee]

Using something similar to your description I attempted negotiation on castor settings during a recent geometry check/adjust. The response was "oh castor is preset and doesn't affect anything".

I obviously won't be shopping there again! (names supplied upon request)

 

[television]

Using something similar to your description I attempted negotiation on castor settings during a recent geometry check/adjust. The response was "oh castor is preset and doesn't affect anything".

I obviously won't be shopping there again! (names supplied upon request)

Only an outfit with MB jigs can do this work, that was an excuse they gave you

 

[280gee]

I hadn't realised that, many thanks for the info! I know that my local indy doesn't have them so it's likely to be main stealer only?

 

[kth286]

Castor angle is NOT adjustable on most cars. It is a fixed angle that is built in from the design stage.

To explain: a large castor angle causes large changes in CAMBER on wheel lock. CAMBER is when the wheels lean in or out at the top.

IF they lean IN at the top it is negative camber, and visa versa.

So at full left lock, the inside wheel is leaning so that only it's outer tyre edge is mostly touching the ground, whereas the outer wheel has only its inside tyre edge mostly touching the ground. On full right lock it would be reversed.

Therefore on those high castor Mercs the natural tyre wear configeration is for the both front tyres to wear on both outer edges more.

That is why the recommendation to swap them from front to back wheels and visa versa.

So, it is slightly complicated for those Mercs, because we have always been led to believe that wear on tyre edges mean the tyres are too soft, and wear in the middle of the tyre means tyres are pumped too hard.

Interesting eh !!!!!!