Tyre or ABS issue?
 

Have been running round and round in circles over this issue - I have 05 Boxster 987.
Have owned the car for about a month and it used to drive beautifully - stable and smooth.
Since changing the rear tyres OR when fast stopping behind car and ABS kicking in it has not been the same. I can't work out what the problem may be - there are no lights coming on in the car.

I purchased the car with Pirelli P Zero Rosso 235/40 ZR 18 N5 on the front and Michelin Pilot Sport 265/40 ZR 18 on the rear. The rear tyres were worn so had Goodyear Eagle F1 Asymmetric 265/40 R18 fitted a week ago. At around the same time had a sharp braking inceident and ABS came on.

Now when I drive the car in a straight line it feels less stable and trys to turn (similar to tracking out feeling) and going around medium sharp bends at about 40 mph upwards (mainly right handed) the car feels very strange and feels as if it is braking and if I touch the barke I can feel the ABS type braking - juddering feeling.

I have looked on many forums and have seen about Speed sensors getting dirty so but wanted to know if the tyres could cause sensors to have errors or whether the tyres causing this.

Any solutions or thought much appreciated.

Takes 500 or so miles to break in new tires. How many miles have you put on the new Good Years?

I just changed to new tires today and right off the bat the car drove differently. Take it easy for the first 500 to 1000 miles.

Two different types of tires with different wear could be part of your issue to start off. The other possibility is that you warped the rotors with the hard braking incident and that is only noticeable when braking at speed.