RE: Mercedes tyre 'skipping' - official statement
Discussion
Kenny Powers said:
So I'm sure those ever-so-clever bods at Mercedes COULD do it better, most probably if they had the budget...which Merc clearly chose to spend elsewhere...
Fair enough. You're entitled to your opinion. But that's all it is, an opinion. As I've said, this behaviour is not especially abnormal. Plenty of cars exhibit the same, admittedly undesirable trait. I can only presume, through your rationale, that they all had inadequate development budgets or were designed by fools. I suppose it could be because not everything in life is black & white, but that would be just my opinion 
- It's apparently more severe on RHD cars;
- It appears to be more severe on 4wd cars.
...which leads very quickly to the conclusion that there are more compromises in the geometry than just 'not being quite Ackermann'. And it's a case of a car engineered for a certain layout (LHD RWD) then being cheaply butchered for RHD / 4WD...so as I said, lack of engineering budget / attention to detail)
...and for reference, I've not driven a single car which does this...so exactly how big a % is 'plenty'???
Cyb3rDud3 said:
Dr Interceptor said:
They don't do it when you go round corners.
They do when manoeuvring at very slow speed on full steering lock.
Have you got one? You sound like Mercedes, they keep on telling me when I experience this. Funny how I actually drive the vehicle and have a different experience.They do when manoeuvring at very slow speed on full steering lock.
...and as above I've got a Transit Sport on 18" wheels that does the same thing.
This is not a Mercedes issue, it's physics.
My Lexus is220d used to do this. I put it down to the angle of the wheels when it was on full lock - it was very similar to how a Mercedes locks. Instead of the wheel being vertical it kind of goes out about 20 odd degrees. The juddering was more apparent if the surface was wet or slippy.
Mr2Mike said:
dvs_dave said:
All permanent awd (particularly performance orientated) cars will have a tendency at full lock to grumble a little due to slight transmission windup.
All permanent AWD systems without a centre diff or viscous coupling will suffer from windup, but surely the Merc has a center diff? I wouldn't have thought they be using plate LSDs either, which can also cause tyre skipping.dvs_dave said:
It's part of the compromise between the optimal Ackerman geo and the awd system.
Ackerman is a separate issue. Windup is causes by the front and rear axles traversing different distances during cornering. Imperfect Ackerman causes increased slip angles on the inner wheel.The Ackerman plays its part because on the 2wd versions, the front wheels freewheel at whatever speed they need to, minimizing any NVH as a result. If that wheel is now attached to an awd system it can no longer freewheel at whatever speed it needs to, only the speed the driveshaft will allow it to.
This obviously has the effect of increased NVH, especially as the center diff is locking itself up in those conditions.
As I've said before, as this only seems to be an issue on RHD 4Matic's, there is clearly something up with the RHD implementation of the AWD system. Be it a different transfer case/diff setup (unlikely), or a bodged steering rack location to accommodate the RHD. Need to compare a RHD with a LHD to see what the differences are.
GranCab said:
I've had 54 different cars since passing my driving test in 1973 and my C43 is the only car to have shown this trait.
i can't claim to have had 54 cars ... but 'only' passed my test in 1982 ... so have had 21 (as best I can remember) in that time ... and my Facelift A45 is the only car which has done it ! I am guessing it is a lovely MB trait !! So long as they all do it I can cope - odd though it is !
I bet the C43 is great btw ... I miss the sounds with only my little 2L after a Z4 35iS !
dvs_dave said:
The Ackerman plays its part because on the 2wd versions, the front wheels freewheel at whatever speed they need to, minimizing any NVH as a result. If that wheel is now attached to an awd system it can no longer freewheel at whatever speed it needs to, only the speed the driveshaft will allow it to.
The whole point of the centre diff is to allow the front diff to turn at a different speed to the rear diff, and the diffs in the axles allow the wheels on each axle to rotate at different speeds. Ackerman should not be causing transmission windup in this case.Mr2Mike said:
dvs_dave said:
The Ackerman plays its part because on the 2wd versions, the front wheels freewheel at whatever speed they need to, minimizing any NVH as a result. If that wheel is now attached to an awd system it can no longer freewheel at whatever speed it needs to, only the speed the driveshaft will allow it to.
The whole point of the centre diff is to allow the front diff to turn at a different speed to the rear diff, and the diffs in the axles allow the wheels on each axle to rotate at different speeds. Ackerman should not be causing transmission windup in this case.
LaurasOtherHalf said:
Happens on my mate's 911 GTS, it's only rear wheel drive so isn't a diff issue on that car.
I surmised it was more to do with castor as it only happened on full lock at parking speeds when the front wheels were angled right over.
Autocorrect? I surmised it was more to do with castor as it only happened on full lock at parking speeds when the front wheels were angled right over.
I thought camber helped in this case, as you turn tight you get a significant difference in speed not only in each wheel but even on one wheel inside vs outside, the wider the tire the more this comes into play. Camber would solve this by making the contact patch at slow speeds a lot slimmer.
Gassing Station | General Gassing | Top of Page | What's New | My Stuff