New and used tires on 4Matic

[Norse]

Hi all.
I have just bought a 2014 E350 CDI 4Matic that came with two new and two used summer tires. The circumference differs with 4-5 mm. Is this within acceptable tolerance? Or do I need to have all new tires?

 

[rf065]

They will be fine.

Russ

 

[markjay]

In theory if you don't have the same make and model of tyres and same thread wear all around, this could confuse the ESP/ABS.

In reality this will only happen in very extreme circumstances.

 

[Norse]

Well, I was more concerned about damage to the transfer gearbox. I don't want to risk anything. Measured again a little more precise, and the difference is 3-4 mm on average. Maybe a little more air pressure in the used ones would increase the size a little?? ;-)

 

[T5R+]

Are they different on each axle or simply front and rear.

Also many E Classes have different wheel offset front/rear which when you run the maths is a few mm.

Not enough experience of 4Matic so unsure if affects gearbox.

 

[Norse]

They are the same on each axle. I will put the new ones on the front axle, and the used ones on the rear.

 

[190]

I thought the question was in relation to the historical issue with the 4WD transmission fighting unequal tyre diameters. I've no idea if that is still a problem but you would think that it has been resolved by now. If was still an issue there would be guidance in the owners manual.

 

[Norse]

One thing got me thinking.. I know the newer high performance AMG cars with 4WD have the possibility to enter drift mode. This will disconnect the front wheel drive for as long as this mode is selected. I would assume drifting would wear down the rear tires considerably faster than the front ones. Have not heard that you must change tires after an hour of fun.......

 

[rf065]

Well, I was more concerned about damage to the transfer gearbox. I don't want to risk anything. Measured again a little more precise, and the difference is 3-4 mm on average. Maybe a little more air pressure in the used ones would increase the size a little?? ;-)

You're overthinking this, just keep the pressures you always use. Do you not think Mercedes have spent millions testing this already?

Russ

 

[jon.english68]

To answer your question, yes your tyres should be of equal ware front to rear, left to right. To understand why, first you need to understand how the transfer box works, the rear axle is driven all the time, the front axle is not, a computer applies a clutch inside the transmission to connect the front axle to the output to give 4WD, the computer is the part that does all the work by monitoring wheels speeds of all 4 wheels and as soon as it detects a wheel rotating faster than the others it sends a signal to the transfer unit to apply the clutch, giving 4WD, when in 4WD there is no differential in the transfer box so the front axle and rear axle drive at the same speed, that’s ok on a straight road but not great on the corners, if the tyres are worn sufficiently enough so the computer sees a difference in speed it can cause issues, the speed signals come from the ABS unit so you can also get transfer box issues if you have an ABS fault too.


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[PobodY]

I've said it before, but it's a pretty terrible AWD system that can't cope with different tyres (of the same size) on the front and rear axles. - I can assure you that a 25-year old Nissan with viscous centre coupling (that in theory would over-heat and be destroyed by a constant slip) copes just fine with different brands and ages of tyre. In fact it managed to run the front axles to near-slicks with plenty of tread left on the rear.

I would expect that a fancy computer controlled system would be even less bothered by the difference in axle speeds, especially when the car is biased to 80% RWD (as an example). - Don't forget that unless it's a locked differential, the front and rear axles can already happily spin one wheel faster than the other... although there is that annoying crabbing thing that the Mercedes off-roaders complain about, so maybe they're not so happy about it.