Get it here:
https://www.simracing.org.uk/smf/index.php?topic=3356.msg54519#msg54519You need the 'Physics pack v2.16.0.0' to take part in UKGTR season 16 races. The new skins are included in the 'skins pack GT2 v2.16.0.0'. You do not need the skins to join the races but, the cars look a bit odd without them.
There are no changes to the physics but, you still need the physics pack. You will also have to reinstall the sound pack after updating to season 16 physics if you want the add on cars to use the correct sound files.