Lightweight Rules Shakeup | Isle of Man TT



Since its inception in 2012, the Isle of Man TT Lightweight race has grown in popularity for both riders and spectators, with some of the racing over the years closer and more exciting than any other TT class.

The very first 650cc Lightweight was won by the main instigator of the new class, Ryan Farquhar. Since that inaugural event Kawasaki twins went on to dominate: James Hiller won in 2013, followed by Dean Harrison and Ivan Linton in 2015 and 2016 respectively. Only recently has Kawasaki’s dominance been challenged by the Italian made Paton bikes, Michael Rutter taking the win in 2017 and Michael Dunlop in 2018 and ‘19. At the last Bennetts Lightweight race, Paton mounted Michael Dunlop broke the lap record (122.75mph) and held off Jamie Coward on the SB Tuning Kawasaki by less than two seconds.

But now we could be in for another shakeup as the Lightweight rules are about to change, allowing both Yamaha and Aprilia to compete for the first time. The new rules will permit twin-cylinder machines up to 700cc, which opens the door to both Yamaha’s MT-07 and the new Aprilia RS660. We wanted to pick our way through the rules and see who’s likely to gain and who may lose out. We’ll also chat to some of the key riders and teams in this class.

Back in 2012, when the class was re-created (the Lightweight class was until then for 250 two-stroke machines) the rules were simple enough: change almost anything you like, but not the frame, and away you go. The concept and the engineering challenges were loved by many with competitor and spectator intrigue surrounding the developments and paths each team and rider took. Over 60 bikes would be on the grid, every one of them with slightly different bodywork, suspension, brakes wheels… you couldn’t simply buy a race bike; you had to make and develop one of your own.

The realistic choice boiled down to two base bikes: Kawasaki’s then ER-6N, now the Z650, and Suzuki’s SV650. Both were designed to be everyday commuter bikes, easy to ride and novice friendly, so making them TT ready was like converting a shopping bike into a downhill racer.

Later, Italian outfit Paton joined the game, and if you had the budget their ‘base’ bike was already leagues ahead of the Kawasaki and Suzuki. Paton now produce a road replica of their TT winning lap record holder, the S1-R, for an eye-watering £42,000. The race bike, ready to go out of the box, will set you back €43,000 plus VAT.



Above (l-r): 2019 Isle of Man Lightweight TT top three: 3rd = Lee Johnston (Kawasaki),  1st = Michael Dunlop (Paton), 2nd = Jamie Coward (Kawasaki)



For 2021, the rules have changed to encourage manufacturers like Aprilia and Yamaha. However, their larger bikes will be governed, because machines over 651cc must use the throttle bodies and injectors found on the standard bike, with no modifications permitted other than the removal or fixing of the secondary butterfly.

The smaller, 651cc-and-under machines have no such restriction. Throttle bodies and injectors can be changed or bored out, and they can even use multiple injectors per cylinder. The smaller bikes will have a minimum weight of 150kg while the larger, over 651cc machines must weigh 160kg or more. Interestingly both capacities will have a rev limit of 11,000rpm. This will limit the tuning potential of the Aprilia as it already makes peak power at 10,500rpm, and will rev past 11,000rpm in standard form. The standard Kawasaki, meanwhile, peaks at just 8000rpm.

The remaining rules are virtually the same as before, which means you can change almost everything: wheels, suspension, subframe, pistons (same material, though), crank (but not lightened), cylinder head, exhaust, brakes, the list is endless. You can’t change the frame, must have a brake guard, rain light etc, but other than that it’s down to the team and budget.

Dave Hagen the Chief Technical Officer at the TT said, "The new regulations represent the latest evolution of this highly competitive class. In order to allow participation of a wider variety of manufactures I have, after consultation with both the TT promotors and competitor teams, drafted a new set of technical regulations. This will allow water cooled twin cylinder machines up to 700cc to compete. 

In drafting this new set of regulations and in order to accommodate the larger capacity, but as yet un-tested machines, I felt it was important to keep any overall changes to the existing regulations to a minimum. Having said that, there are some restrictions to machine weight and throttle bodies for the over 650 machines. 

In truth, we will not know how evenly matched these bikes will be until they have raced on the TT course for the first time. This change for 2021 should be very much viewed as a starting point. It is for this reason that I reserve the right to revisit these regulations for future events with a view to maintaining parity between the different capacity machines."


Aprilia RS660

Above: the new-for-2020 Aprilia RS660 becomes an attractive proposition considering the new rules



Aprilia RS660 – The sportiest bike in the category (if we disregard the expensive Paton) makes a quoted 100hp @10,500rpm at the crank with 49ftlb of torque at 8500rpm. Real world back wheel figures should be around 80-83bhp. Aprilia already provide a full Akrapovic race exhaust and ECU which allow the bike to rev higher, possibly over the new regulations limit of 11,000rpm. Estimated back wheel power, with a race exhaust and ECU, is 90-ish bhp.

That’s enough to make a competitive bike which should be reliable for less than £13,000 (£10,149 for the bike plus race parts). Weight wise at 169kg dry with road bodywork, it should be relatively easy to get the Aprilia down to 160kg by simply removing all the road gear. Tune the engine – porting, gas flow, increase the compression – and 100bhp could be achievable without changing the conrods and crank.  A specialist engine tuner with unlimited budget could push this further. The limit will be the restricted fuelling and rev limit. Once you’ve fitted race suspension, pads, bodywork and tyres, I’d estimate cost to be around £15-16k. The downside of the Aprilia RS660 is that it’s unproven in race trim. Will it last four hard laps around the TT? And it already makes peak power close to the rev limit.



Above: we took the MT-07 in road trim around the TT course back in 2016



Yamaha MT-07 – The Yamaha has always been and still is a fantastic road bike, and there’s so much pleasure to be had from the punchy 689cc parallel twin. In standard form it makes more torque than the Aprilia, and obviously more than the Suzuki and Kawasaki. Peak power is 74bhp at 9000rpm, which is a decent start, so there is still 2000rpm to play with. The Yamaha is also light at 182kg with fuel, which should equate to around 167kg-167kg dry. Aftermarket exhausts are already on the market with Akrapovic again producing a full race system that reduces weight by 3kg and adds 3bhp. Fit some aftermarket suspension, remove the standard road gear and replace it with some R6 bodywork, and you could have a lively, race bike with a solid power output of around 80bhp at the rear wheel. The bikes are already raced in America in the Twins Cup, which allows up to 800cc twins with varying weight limits and are competitive against the Suzukis. But although the standard bike produces more power than a Kawasaki or Suzuki, it’s going to take development to make it competitive at the TT, so is something of a trip into the unknown. However, racing specialist Crescent Racing have done an awesome job converting a Yamaha R3 into a race bike, so I’m sure they could do the same with an MT-07.



Above: Lee Johnston over Ballaugh Bridge in 2019 on the popular Kawasaki



Kawasaki Z650 – The new Z650 was introduced in 2017, replacing the ER-6N,  and was a massive overhaul of the Kawasaki. The Zed was considerably lighter and had a much-improved chassis, linkage and swing-arm. The engine was updated but it wasn’t a massive change from the ER-6N. Aside from the Paton, the Kawasaki has dominated the grids, and not just at the TT. In fact, most Lightweight-based road races look almost like a one-make series.

Specialist engine tuners are, as ever, pushing the boundaries, with power at the rear wheel close to 100bhp and just above. The level of engineering involved to transform a Z650 into a race bike capable of lapping the TT at over 121mph is truly impressive. The Kawasakis are race proven, and the rules allow you to run a lighter bike with tuneable fuelling. You can build a competitive bike for around £15,000, including a new bike, but the top bikes are 25k plus.



Above: outright lap record holder, Peter Hickman, on the 2019 Norton Superlight



Paton – The TT lap record holding S1-R is less than 651cc and will therefore be allowed to run at the lighter weight of 150kg and to have free reign to change its fuelling. Fast and light, they are essentially race bikes for the road, and have been unbeaten in the last three years at the TT. The downside is they are very expensive and only for the privileged few at 43,000 Euros plus VAT.

Suzuki SV650 – Another popular road bike that makes a good base for Lightweight racing. In standard form the V-twin makes more power and torque than the standard Kawasaki Z650. There are lots of aftermarket parts available and SVs are very widely used in mini-twin club racing where engine and chassis tuning is limited. However, as power increases towards to magic 100bhp mark, reliability becomes an issue, and at the TT nobody has yet made a Suzuki competitive at the top level.

Norton – In 2019 the Norton factory fielded the dream team and the Superlight showed promise, Peter Hickman eventually finishing 8th overall and lapping at over 120mph – not bad for a team in its first year on a underdeveloped bike. Peter still has the Norton and was planning on racing it in 2020. However, it’s unclear if the Norton will be eligible for the 2021 race and, if it is, whether Peter will ride it.


From a spectator’s point of view it’s going to be as exciting and as close racing as ever with more bikes and manufacturers involved. From the engineering side, I can’t wait to see the developments. A racing MT-07 is going to be fascinating and will be followed by the many thousands who own one, its been a best-seller in the UK. Aprilia’s RS660 should be fast with fewer changes necessary, but the initial outlay of   £10,149, as opposed to £6999 for the MT-07, may put some teams off. From a racer’s point a view, it’s a hard decision. Do you go with what you know with Kawasaki, or gamble with Aprilia or Yamaha? I’ve ridden all the bikes in contention and plan to go racing in 2021, but remain unsure which path to choose!


Ryan Farquhar (3 times TT winner and creator of the new Lightweight class – ‘I want to the class to be as competitive as it can be, with as many manufacturers as possible, like the Junior Supersport class or World SSP300, with KTM, Kawasaki, Honda and Yamaha all involved, but I’m a little disappointed by the new rules as the organisers have moved the goal posts without much consultation. The rules need to be more bike specific like the rules in Junior Supersport. Myself and others have put 8-10 years of development work into our bikes – not just the time but money also – and the new bigger bikes should have an advantage. They still have to be developed and turned into race bikes, but they should be capped, or the smaller bikes should be allowed to increase in capacity to make a level playing field.

Ian Lougher (10 times TT winner and Patton rider) – ‘I think the more the merrier. I’d love to see more bikes and manufacturers on the grid. I might be shooting myself in the foot with my Paton team, but we need more bikes on the grid. In American the MT-07 looks competitive, and it will be interesting to see what Aprilia does with their bike and the cost. We take a bit of flak for having an expensive bike, but you don’t have to do anything – it’s ready to race out of the box. When we first went racing we didn’t do any testing as the bike was too loud, we just turned up and went. Yes, it’s expensive but any top-level Lightweight will come in at upwards of £30k to £35k. Hopefully we can get going and have full grids in 2021.

PICS: Pacemaker Press