Talk Morgan Forums Morgan Sports Cars Morgan Aero 8, 2012< Plus 8, SuperSports, Coupe & Aeromax Choice of Tires

Over the years I’ve read much about tires and selecting the “best” tire for a particular car. To be honest I was a bit sceptical about the differences reported by buyers. It often seemed to be a justification of a decision, rather than an objective comparison. I'm planning new tires for Tarka next year and had been making my choice based on looks and price.

I am now convinced I was totally, completely, wrong and the difference a change of tyre makes can be simply enormous.

How so?

Last January we purchased a Mercedes AMG C43, as reported here. It came with Mercedes selected Dunlop Spot Maax, complete with the “MO” logo, indicating that they had been matched by Mercedes to the car.
We were really pleased with the car, other than the way the front tires crabbed at low speed and full lock, producing a pronounced judder and banging noise. We complained and were told that the problem would go away as roads warmed up and by the autumn Mercedes would have a solution.

As temperatures fell the problem returned, I contacted the dealer and on last Friday the car was called in for a recall, this involved replacing the tires with a newly developed Bridgestone Potenza s100 MO tyre and a software update.

I was told that these tyres are specific to the 4-Matic C43 and GLC43, they are not yet available through normal tire distribution, but only through Mercedes dealers. It was further explained that the structure and rubber composition was unique to that tire and had resulted from many hours testing by Mercedes and Bridgestone.

The difference is simply amazing: the crabbing has gone; the steering has a bit more feedback and the car feels more refined. There is also less road noise.

Thy tires look like any other Potenza s100 but the rubber on the shoulders seems quite sticky, also the sidewalls are very soft. It will be interesting to see how they wear, but the result is a much nicer car.

I am delighted that Mercedes has sorted the problem, but do wonder how Mercedes managed to get the tires supplied with the new car so totally wrong.

So, tire choice is really important: this makes selecting tyres for Tarka even more difficult…..the car has 19" wheels so tire choices are a bit limited.

Suggestions welcomed!!

Mercedes has so many different models, I assume that not all cars get everything completely tested and assumptions are made against similar models in the range.

That probably works 95% of the time and in that specific model it did not.

So Mercedes have sorted that issue but the majority of other models are probably working well.

Changed mine earlier this year over to Michelin Pilot Sport 4s and they have made a big difference to the rear end and steering feel as well. Far more confidence in the wet, abit too much if I'm honest. Even went out yesterday morning in the frost!

Peter, my A250 4Matic has similar symptoms but I would guess to a lesser degree. I notice the skipping on wet surfaces on full lock. I have tried to get it resolved by MB but all I get is a fob off along the lines “yes they know about it but it is not a problem”.
Your post has given me hope, off to MB tomorrow for another go.

Tires? You gone all Stateside on us, Peter?

I had the same problem on my Cayman. Not just that car but the two 911s I had as courtesy cars. I just put it down to the width of tyre and design of the tread. Can’t say it bothered me.

Jays,

this was not at al nice, the violence of the "lurch" and the bang that echoed through the car made me think, more than once, that someone had hit me or something had broken in the front suspension.

It only happened with cold roads, below 10C and if the ground was wet it was at its worst.

From April to September there was no skip, at all, so very much a tyre/road temperature issue.

I agree about the lurch/bumping you refer to which is quite disconcerting.

I always used the custom spec Bridgestones on the Skyline GTR33V I had. When I fitted some Michelins and Dunlops at different times on this the car roamed around hunting cambers and hard braking was uncomfortable.

I had the Audi RS6 which was 4WD with 21 inch wheels and 285 wide tyres. It arrived with Continental A0 spec tyres. I go to full lock both ways backing out of my drive and at first it did not do this bumping in a significant manner.

As the tyres got down to 3-4mm it did start to do this very noticeably. As the replacement Pilot SuperSports were put on it did not go away as I had expected. On full lock the contact patch changes shape as well as some differential activity which I was told caused it.

In the end I took it to a place near Oxford called Centre of Gravity. They are experts on wheel and tyre alignment. Not just toe and camber but full race car stuff with adjustable link skills level.

http://www.centregravity.co.uk/services/

I learnt a few things. Cars from the factory are not always setup correctly. They found my Audi was totally out of alignment. Dealers do not check this in the PDI. As tyres get thinner they do suffer more from this effect. I cannot remember the cause I am afraid.

On the highly controlled cars with the auto-brake, lane control, laser etc a full geometry change can result in the need for the systems to be reset to enable them and preserve warranty etc. This is not trivial and needs extensive equipment and one of the factory computer thingys.

Most road cars don't offer extensive change opportunities as the links have no adjustment but they can do a few things. If you have something with adjustable suspension (GT model Porsches etc) then they can do a lot.

Once the Audi had been to CoG it was a different car. Massively improved and I would recommend it to anyone who really enjoys the cars response.

The ML63 is now near to replacement tyre stage and I will be doing the same with them on it once the new tyres are in place.

I had not looked at the temperature issue, or how inflation settings might change this on the ML and so will see if I can get anything from these. I imagine the warmer sidewalls will let the tyre flex prior to skipping ?

The full lock bump/jump seemed to be a big issue last winter, I saw reports of it affecting lots of premium brand cars with low profile tyres a big wheels - its good to see Mercedes has managed to fix it.

I believe it was caused by the tyre skipping/hopping because the rubber is less compliant when cold, which would make sense if the new tyres have softer sidewalls.

With regards to tyres its always a difficult choice, Michelin have fantastic test facilities and are the only tyre manufacturer that I know to produce all the tyre production equipment (they supply this to most other tyre manufacturer's) which allows them to tailor the equipment/tyres to suit.
For instance a lot of cheaper tyres are molded and "stamped" with tread, whereas the Michelin tyres have different compounds spun onto the carcass to allow differing characteristics, such as harder sidewalls for steering direction and a softer centre for grip - etc.
Richard Hammond visited their test centre on an episode of the grand tour to learn about drifting.

I have also found Continental tyres to be very good, and Pirelli although they wear out at a rather ridiculous rate..

The C43 is 4WD, with 30% of the drive sent to the front, according to the "bumpf" from Mercedes.

The problem seems to occur with other 4WD C Class cars, to a much lesser degree. The AMGs have unique front suspension geometry. The 2 WD C Class AMGs do not have this problem at all.

The Plus 8 doesn't have this problem, even though the engine power and tyre sizes are similar to the C43.

My conclusion: applying power to front wheels whilst on full lock make a minor problem a lot worse.

Comment: MB did a major software upgrade when they changed the tyres. Did this alter the torque to the front wheels on full lock at low speed?