Supersport? Superstock? Superbike? Supertwin?

Explaining the different types of solos raced at the Isle of Man TT Races

There are five different classes of bike at the 2024 Isle of Man TT Races: Superbike, Supersport, Superstock, Supertwin and Sidecar, and each has two TTs over race week.

Setting aside the sidecars, which are a unique proposition in themselves (although if you want some pub ammo, they are bespoke racing sidecars powered by tuned 600cc motorcycle engines) we have four different solo classes featuring bikes which look quite similar to the uninitiated.

So if this all seems a bit bewildering, we’ve come up with this quick guide to help you sound like a racing god the next time you’re sitting trackside with your mates.

Superstock

Let’s start with Superstock, if only because it’s the easiest to understand and the most relatable to road riders.

These bikes start life as 1000cc sports bikes we can buy and ride on the road, bikes like the BMW S 1000 RR, Honda CBR1000RR Fireblade and Kawasaki ZX-10R to name but three. The ‘stock’ comes from the fact that they must be run in near standard trim, with only a few racing modifications allowed for safety and rider preference.

The engine needs to maintain the standard internals and can’t be tuned up, although teams are allowed to fit a lightweight race exhaust system. Lights and mirrors are removed, along with the numberplate and associated paraphernalia.

Stuff like handlebars and footpegs can be changed, there’s no performance benefit there but they are more durable and appropriate for racing purposes, and the bodywork is also replaced – although this has to follow the shape of the standard ‘homologated’ bikes.

Bigger windscreens can be fitted though, to make the bikes more aerodynamic for the high speeds found at the TT. Like all TT bikes, the fuel tank also needs to be enlarged in order to be able to carry enough petrol to complete the two laps needed between pit stops.

Suspension can be upgraded by changing the rear shock absorber and the fork internals, likewise brakes can be upgraded but must retain the standard calipers.

Superstock bikes can be identified by the red number plates. They make over 200bhp and in many cases are as fast as full blown Superbikes.

FUN FACT: Peter Hickman goes into TT2024 having set the fast ever lap time of the course on a Superstock specification machine. He averaged a staggering 136.358mph on a ‘stock’ BMW M 1000 RR on his way to victory in last year’s second Superstock TT.

Superbike

Now we’ve mentioned it, what the heck makes a Superbike so super?

These are the crème de la crème of TT race bikes but like the Superstockers they start out as standard production bikes.

The rules allow for much more modifications and tuning. The engine can be tuned, with around 240bhp possible, the electronics more adjustable and the chassis upgraded. Standard suspension and brakes can be replaced in their entirity by full racing units of the team’s choice, while the swingarm can be replaced with a bespoke item and the frame modified through bracing, which allows the riders to fine tune the feel of the chassis.

It's not a complete free for all though. There are still rules as to what you can and can’t do (you can’t run an engine bigger than 1000cc or fit a turbocharger, for example) and you have to run the same homologated bodywork as in Superstock. These bikes can be very expensive to build and run though, easily going into six figures for a top spec machine, and they are considered more difficult to ride than a ‘stocker’, which is why the times are very similar between the two categories.

FUN FACT: Such is the speed of a superstock machine, and as a cost saving measure, most privateer riders use one (superstock) bike for both the Superbike and Superstock classes. True Superbikes are only eligible for the Superbike and Senior TTs and can be identified by their black numbers on white backgrounds.

Supersport

This is a really interesting class, with new rules in recent years opening it out to a number of new motorcycles.

Introduced in the late 1980s, historically this class was for screaming 600cc four-cylinder machines which had highly tuned engines and chassis regulations similar to the Superstock category we mentioned earlier. As well as the fours, 675cc triples (like the Triumph Daytona 675) and 750cc twins (which hadn’t been utilised since the old Ducati 749 some 20 years ago) were also allowed, but with less and less of these kind of bikes being sold, the rules have been changed to allow different bikes in regardless of capacity.

Now bikes like the 959cc Ducati Panigale V2 and Triumph Street Triple 765RS (fitted with a fairing) can compete, with clever electronics being fitted to balance the performance of the various machines – keeping the power in line with the best of the 600cc machines. The result is a motorcycle which produces in excess of 140bhp and gives a lap average of 130mph in the right hands. It’s so interesting we did a full story about it here.

Because Supersport bikes have a wide range of engine configurations and capacities, the aural experience of these TTs are more diverse than most, with booming twins sounding very different to the shrill 600s and bassy triples. Visually, they can be identified by their blue numbers on white backgrounds.

FUN FACT: The ‘next-generation’ rules also allow the Suzuki GSX-R750 into the class, even though the design dates back to 2011.

Supertwin

Our favourite category (did we mention Entire Cover sponsors one of the two Supertwin TTs?) these little bikes are all about massive corner speed and clever engineering.

As the name suggests, Supertwin bikes have two cylinder engines. They start out as production bikes like the Kawasaki Z650, Yamaha R7 and Aprilia RS 660, but the rules are the most liberal of all the solo classes at the TT, so they are heavily modified. These bikes can be identified by their green number plates and their distinctive deep exhaust note.

Engines are tuned up, with the best bikes making around 100bhp – quite a hike from the 70-ish of a standard bike – and the chassis are given a good make over too. Things like brakes, wheels and suspension can be changed and bodywork can be swapped for more aerodynamic items to give more speed, with many teams fitting fairings from Moto2 or 250GP race bikes.

Frames are braced to make them stronger and there’s probably more work going into a good Supertwin than any other category of bike. The retro styled Paton S1R has been the most successful bike in recent years, and uses a Kawasaki 650 engine.

The best riders can lap the 37.73-mile course at an average of over 120mph but teams have to balance outright performance with the need for reliability. The Supertwin TTs traditionally have the highest number of retirements through mechanical failures of any class, as riders squeeze every last bit of performance out of their machines.

FUN FACT: This class was previously called the Lightweight TT, with a 650cc engine capacity. The rules were changed for 2022, to allow bikes with a slightly larger capacity to compete (namely Aprilia and Yamaha). The Supertwin name was adopted at this time.