do you have to change all 4 tyres at the same time Ml

[mpgrant70]

I have a ML where the fronts tyres are getting near to the wear bars on the tread. But the rear set has about 4mm on them do I have to change all of the tyres at the same time or can i just replace the front ones ?

 

[trapperjohn]

I have only ever heard of this relating to a Volvo 4X4 Estate.

ML owners will be along soon with the real answer. I'm sure you will only need to change the front set.

CHEERS

 

[renault12ts]

I'm sure you must (where can I pick up the rear ones?).

 

[djm17]

I read on the honest john forum that its best to change all four because of the difference in the rolling radius generated by mixing new and old on 4x4's. But then there is some debate as to whether this is a fairy tale or something that has some basis in science. I also read that whatever the drive system newer tyres should always be on the front. This seems to make sense as that is where the steering is done.

Cheers

Dave

 

[renault12ts]

But when the fronts are down to the minimum and the rears have 4mm, there is already a difference.

 

[djm17]

Well yes that is so but we are talking about changing 2 or 4 and I did point out that there is some debate about this being bogus science. Here is the link to Honest John

2 or 4 New Tyres on 4WD? | Motoring discussion | Back Room Forum | Honest John

 

[grober]

The modern 4matic system depends on the ABS wheel sensors to monitor for wheel slippage i.e.speed differences side to side and front to back. It then applies the brakes on the fly to stabilise the situation. The system has built in speed difference " thresholds"that must be breached before intervening of course but I think the "change all 4 tyres" = [to maintain the correct wheel to wheel speed ratios] is why this is recommended if perhaps not essential.

 

[Deleted member 37751]

I change my tyres when they're at 3mm anyway, so if I was you I'd just replace the full set and get it out of the way.

 

[DSM10000]

I also read that whatever the drive system newer tyres should always be on the front. This seems to make sense as that is where the steering is done.

Cheers

Dave

Conventional wisdom is that regardless of the car being front or rear wheel drive new tyres should be fitted to the rear. Worn front tyres cause understeer and that is generally progressive and is easier for most people to deal with. Putting new tyres on the front will cause the front grip to exceed the rear causing rapid oversteer in certain conditions that is much more difficult to catch.

 

[markjay]

Ideally...

Buy all 4 tyres in one go, then rotate them rear to front to ensure even wear.

Second best...

Buy 2 new tyres of same make and model as the ones you currently have, the new tyres (as said above) go on the rear.

Third...

Buy two new tyres of different make to the one you have now, and again put them on the rear.

Personally, I always change tyres in sets of 4, to ensure even grip all around (particularly important with modern cars with ESP).

 

[m2287]

If you can afford to, change all 4, you will get decent money of ebay to sell your old rear ones as part worns

 

[Bobby Dazzler]

I only replace in sets of fours on our ML. There is a suggestion that differing rolling radius on each wheel can damage the diff - referred to as "win up". That's a good enough reason for me. If all is well then they tend to wear evenly too.

 

[bolide]

I only replace in sets of fours on our ML. There is a suggestion that differing rolling radius on each wheel can damage the diff - referred to as "win up"

Surely wind up only occurs if the centre diff is locked. The function of a diff is to negotiate the difference in rotational speeds between the two outputs

Nick Froome

 

[Rory]

I have a ML where the fronts tyres are getting near to the wear bars on the tread. But the rear set has about 4mm on them do I have to change all of the tyres at the same time or can i just replace the front ones ?

Assuming you're in the UK then bearing in mind we're going into winter it would probably be best to change all four anyway, unless the car does very low mileage.

Get the next set rotated a bit before the rears are half-worn.

 

[jaymanek]

Im sorry but ill go against the grain and say there is no good reason to throw away over 2.4 mm of useful tread.. thats over 30% of the tyres life.

The ESP/Diff issues arent true. The systems are designed to cope with much bigger tolerances than a few mm of tread! Just look at the people who go fitting staggered and larger wheels... the car doesnt suddenly implode.

Replace the two that are worn and replace the others at around 2.5mm.

Obviously tyre companies and fitters will tell you to replace the four but thats how they sell double the amount of tyres.

Just look on ebay for part worn tyres and you willl see how many people get conned into changing perfectly good tyres.

Today i bought a set of 235/45/17 continental Sport Contact 3 for £180. These are all with 6mm + with no repairs or cuts etc.
I couldnt even buy cheap chinese ones for that.

 

[Brian WH]

Im sorry but ill go against the grain and say there is no good reason to throw away over 2.4 mm of useful tread.. thats over 30% of the tyres life.

The ESP/Diff issues arent true. The systems are designed to cope with much bigger tolerances than a few mm of tread! Just look at the people who go fitting staggered and larger wheels... the car doesnt suddenly implode.

Replace the two that are worn and replace the others at around 2.5mm.

Obviously tyre companies and fitters will tell you to replace the four but thats how they sell double the amount of tyres.

Just look on ebay for part worn tyres and you willl see how many people get conned into changing perfectly good tyres.

Today i bought a set of 235/45/17 continental Sport Contact 3 for £180. These are all with 6mm + with no repairs or cuts etc.
I couldnt even buy cheap chinese ones for that.

I agree entirely.

Replace the worn front ones and put the new ones on the back for more grip.

 

[jaymanek]

Holy Batman, where did you back come from?

 

[Deleted member 37751]

Im sorry but ill go against the grain and say there is no good reason to throw away over 2.4 mm of useful tread.. thats over 30% of the tyres life.

It's not that simple though, is it?

As a tyre wears, so does your stopping distance. So the 1.6mm isn't a target, it's what the 'minimum' requirement is.

I have always replaced at 2.0-2.5mm because those four bits of rubber are the only thing keeping you on the road and if I'm ever that hard up that I have to squeeze every last 0.1mm out of a tyre, I'd rather walk...

 

[developer]

Lots of techical answers here - mine is more simple.

I replace those that are worn and continue to drive on those that aren't.

The only caveats to that are:

I always replace in axle pairs - whether front or back.

I always replace at (around) 4mm which is what MB recommend, I suspect as much for noise intrusion/handling as deterioration of grip.

 

[jaymanek]

It's not that simple though, is it?

As a tyre wears, so does your stopping distance. So the 1.6mm isn't a target, it's what the 'minimum' requirement is.

I have always replaced at 2.0-2.5mm because those four bits of rubber are the only thing keeping you on the road and if I'm ever that hard up that I have to squeeze every last 0.1mm out of a tyre, I'd rather walk...

1.6mm is where all of the tyre manufacturers have the wear bars set to, this is the useful life of the tyre - and yes its also the point at which it becomes illegal in this country.

Note that I would never recommend going that low, this is why I said above that I would replace at around 2.5mm.