Pictures on the internet and judging the wear by the lip is not an accurate way to determine whether the rotor needs replacing. The service manual states the following, if you do not have a caliper tool go to Harbor Freight and get a micrometer.

http://www.harborfreight.com/catalog...t?q=micrometer
*pick one that has the horseshoe shape so you can clear the lip

Service manual info, I would think you have the Alcon system in your XKR which says your minimum is 26mm:

Disc thickness (new) 20 mm (0.78 in)
Minimum disc thickness (service limit) 18 mm (0.70 in)

Disc thickness (vehicles fitted with Alcon braking system new) 28 mm (1.10 in)
Minimum disc thickness (vehicles fitted with Alcon braking system service limit) 26 mm (1.02 in)

 

Alex, based on the pictures you uploaded, your brakes are standard XKR not Alcon. I have attached the specs for the brakes.

 

Hey JackJohn, what you posted is the spec's on the FRONT rotors, I posted the spec's on the REAR which is what his post said he was thinking were below the limit. FYI, in the service manual the front rotor's have a specific spec for the XK, XKR and Aclon. For the rear there is just one spec for just the XK and the Alcon which leads me to believe the XK and XKR share the rear rotor (at least for the 4.2 liter).

Anyway, in case he is not aware of this, there are two different spec's for front/rear rotors, combine my post and JJ's and you have the front and rear specs for the rotor wear.

 

Thanks for the catch Mark, since the first four pictures he posted were the front, I just posted the front specs. Should have checked closer.