Complex sentence: However the Speed 12 GTS did manage to compete in a few races in the FIA GT championship in the GT1 class, however sudden rule changes and the demise of the GT1 class suddenly rendered the Speed 12's existence, obsolete.
Split into simpler sentences: However the Speed 12 GTS did manage to compete in a few races in the FIA GT championship in the GT1 class. However sudden rule changes and the demise of the GT1 class suddenly rendered the Speed 12's existence, obsolete.