Lower said:
Sounds like the tyres have slightly different diameters, hence the pulling one way under acceleration. The diff will do weird things if this is the case.
Do the tyres have the same model code? Were there any model specific oem issue versions of this tyre for specific cars? This used to be a common problem with the honda s2000 as they had their own version of the s02, as did a Porsche and even though the tyre size codes were the same they were actually different sizes.
I checked the tread depth today and across the tread, one is 7MM, the other 6MM - WTF. They turned up looking new with chalk marks round them.
Do ALL makes of new tyre have 8MM tread? Even with the M LSD, I am surprised that this small margin of difference would make the car pull over the road under power but it seems it does.
Not sure on the model code, I will check tomorrow but as said previously they are a year apart in date of manufacture.
Earlier today I spoke with a knowledgeable chap at a tyre place I have used many times before (Micheldever Tyres):
The load rating on my Goodyears is 99. This is apparently the OEM Mercedes figment and means they have a different sidewall loading than the car is set up for and the OE Conti M3's on the front.
He said they have seen before on performance cars, a non uniform load rating on front and rear axles throwing the car out of kilter as the axles are then reacting to the road at different rates.
He gave an example of their experiences with the 1M being extremely sensitive to tyres. They have fitted a few well known brands and models of rubber for owners to return a couple of days later saying the car feels dangerous and to change all the tyres over. He is of the opinion that some cars are set up to tight margins.
He suggested that I either get some Goodyear 99 load ratings for the front to match it all up or better, change all the tyres to something more suitable.
It seems that what are to most people minor details on tyres can really screw some cars up. I have never experienced tyres making a car feel so bad, you live and learn I guess.
A sincere thank you to everyone who has contributed to this thread. There are some very knowledgeable chaps on this forum.
I hope the information in this thread helps others.