It depends on what wheels your cougar came with. If you have the 15 inch, six spoke fan blade wheels, you need 205/60 tires, if you have the 16 inch, sport package wheels, you need the harder to find, 215/50 tires. 17 inch wheels were not available in '99 to the best of my knowledge. If you have trouble finding the 215/50/16 tires, both the more common 225/50 tires, and the 215/55 tires can be used without much problem.
215/50r16
Pretty sure its 34mm
215 75 r15 The correct tire size is listed in your owner's manual and on the driver's door post.
For a 1999 Mercury Cougar, you typically need a 32mm socket to remove the axle nut. However, it's always a good idea to double-check your vehicle's service manual or specifications, as variations can occur based on the specific model and drivetrain configuration. Using the correct size will help prevent stripping the nut and ensure a proper fit.
For the 1999 cougar they have 2 different size brake rotors it sounds like you need the 276mm size
my tire sizes for my cougar are P215/50R16 or go here so you can find your size http://www.dragtimes.com/Mercury-Cougar-Tires-m31-n237.html
5X7 all around
What is the motor size? Run1
6 x 8
205/75R14
What is the motor size? Run1
5x7 or 6x8, either or