The TT class using machines similar to Superbikes but with severely limited modifications is Superstock TT.
Superstock TT motorcycles are production-based machines derived from road-going superbikes. The class is designed to keep the bikes closer to showroom specification than the heavily developed machines used in the Superbike TT, so engine, chassis and aerodynamic changes are much more restricted.
The class normally uses large-capacity four-stroke motorcycles, including four-cylinder machines from over 600cc to 1,000cc, three-cylinder machines up to 1,000cc and two-cylinder machines up to 1,200cc. Superstock bikes also compete on treaded road tyres rather than the slick tyres associated with many closed-circuit racing categories.
Superstock TT began in 2005, replacing the 1,000cc and 600cc Production TT classes. It is sometimes confused with the Senior TT, but Senior is a race title that can accept eligible Superbike, Supersport and Superstock machinery; Superstock is the specific production-based class.