I have 2001 s-type 4.0 just put winters on. did not realize the set had two different sizes the fronts have pirelli P245/45/R17 the back has P245/50/R17. The car has always had 245/45/17 with no issues. Now the car speedo is different then my in dash speedo/navigation system about 6-7 kms different then the dash, but also the traction light keep flashing when i drive off and on. Also the shop also said the Two tires in the back were chopped/choppy. What would be the cause of all this jibberish? also the car runs nice and smooth no vabration just a humming coming frome rear wheels i believe the choppyness. All tires have 80-90% tread
Thanks in advance

sounds like you awnsered your own question. replace the rear tires with new ones that are the right size. your front tires are spinning faster then your rears causing issues and as you said the rear tires have flat spots.

You have front/rear tire diameter difference 3,6% Thats too much!. Try to keep it under 3%, better even less. Traction control measures speed diferences between all 4 tires...

Jack