It goes by a number of names, among them Super Single and Super Mono, but in the road racing world, they’ve become an affordable way to get on the track without spending a small fortune on a full-blown Super Bike. But just like the Twins class that has become a favourite at events like the Isle of Man TT, what was once a class about being budget-friendly has turned into somewhat of an arms race. The winners are the spectators who get to see cheap road bikes transformed into absolute track monsters, and when Royal Enfield decided it would be a good way to get in on the action, there was only one man to turn to. Enter the legend that is Pepo Rosell, the man who has made turning road bikes into racers an absolute art form. And this is his latest creation, a Royal Enfield Guerrilla that is now ‘GRR 450 by XTR Pepo’, a single-cylinder, Super Mono, that made its debut at the recent Wheels and Waves festival.
The Super Single class has been dominated by a mix of dirt bikes from Japan transformed into fully faired road racers, and machines like the RC390 from KTM which have been produced from the factory to be easily transformed into budget bikes for racing. However, Royal Enfield is rightly proud of the water-cooled single-cylinder engine they have designed for use in platforms like the Himalayan and the Guerrilla, and they wanted to show it could easily stack up to its rivals. And so they sought out Pepo Rosell and commissioned him to build a bike that could more than prove the point.
The Spain-based builder might be known for his Radical Ducatis, but he’s always had a soft spot for the Super Single, so this build was right up his alley. To get started, Enfield sent him a 2024 Guerrilla 450 to serve as the base, but as is completely obvious from the photos, very little of the original bike remains. To kick things off, the only way to get an idea of what he was working with was for Pepo to strip the entire bike down so that he had just the bare frame in front of him. This has been modified to meet the design he drew up and to accept the modifications he had planned.
The first of which was to ditch the small factory swingarm and replace it with something that has a little more racing pedigree. And here Aprilia has done all of the necessary work, having crafted a beautiful aluminium arm for their RS660. A few changes were needed to make it work, and then with a custom mount, a Nitron adjustable rear shock has been added. The next task was to get the front end dialled in just as well, and the first step was to have a pair of custom triple clamps CNC machined from billet aluminium by S&P. Dropped through these is another Aprilia parts bin special, the fully adjustable forks from a Falco 1000.
Taking advantage of the lower legs has allowed Pepo to go to town with the Discacciati parts catalogue, adding their stunning fully floating rotors, beefy calipers and the whole system is powered by a PR 19 master cylinder up on the bars. To finish out the rolling chassis, keeping unsprung mass as low as possible was front of mind, so a set of lightweight forged alloy Dymags have been optioned with Continental tyres of Spain providing the 17in tyres. To ensure the rear end has all the best bits too, Pepo absolutely went to town, adding an NG rear rotor, JT and Talon sprokets for the 520 chain conversion. Before settling on Ducabike CNC rearsets with carbon heel guards, and adding a Brembo rear master and caliper.
The bodywork is always brilliant on an XTR build, but before it could take shape, Pepo had to build the architecture on which it sits. The front end features a completely custom fairing stay, while at the rear, the entire subframe is fabricated from scratch. The endurance bike look is his signature style, and Pepo worked with Futura 2000 and Alberto Caimi to come up with the exacting design. Then the drawings were sent to Crazy Bike, who have gone to town with the fibreglass, producing one brilliant piece after another. The fuel tank with the clear sides for level observation is the star of the show, and it brilliantly merges with the front fairing for the full racer look.
The belly pan helps to create the proper sport bike feel, but cleverly, an opening has been left at the front to funnel cool air over the semi-dry sump, helping to keep oil temperatures under control. There’s an ultra-modern front fender, while the rear hugger was made in-house by Pepo from carbon fibre.
To finish out the bodywork, the tail section is an absolute beauty, with unique lines and an ultra-aggressive looking cowl helping to set the whole bike off. As is often seen on an XTR build, Artenruta have taken care of the popping paint and graphics combo, while Pepo did the upholstery on the seat and sorted out the front and rear lighting.
At the heart of the bike is, of course, the 450cc, DOHC, single, which in stock form produces very similar numbers to the KTM RC390, which is a staple on tracks around the globe. But to add to the 40hp and 40nm of torque, Pepo fabricated a custom carbon fibre airbox, which ensures the engine is never out of breath. On the exhaust side of things, there is an X pipe which runs midway up the bike and sports a carbon fibre shield, and then the gases exit via a Spark/XTR muffler.
The GRR 450 by XTR Pepo now weighs just 131kg wet, and racing up the hill at Wheels and Waves it was clear that this absolutely is a true Super Single. Pepo Rosell pulls off perfection once again, and could we see Royal Enfield racing? We sure as hell hope so.
[ XTR Pepo | Photos by Carrascosa ]