Automatic gearbox fault and wrong tyres

[Mandrake]

Yes rolling circumference would be more accurate.

Another way to test it would be to go for a test drive in a straight line with a Lexia connected - you can monitor the 4 individual wheel speeds from the ABS computer which should all be the same when driving straight ahead. If there is a difference of more than about 1-2mph between them especially between wheels on the same axle it would indicate differences in rolling circumference that might upset the computer.