Wizards of Ossa

The concept was radical – maybe too radical for some – with many basic design changes from what, for virtually 20 years, had become the accepted norm. 

 

Gas Gas, Sherco, Beta and even the four-stroke Honda RTL all followed a very similar concept, albeit with their own unique stamp applied.

 

The Ossa genuinely began with a totally blank sheet of paper. 

 

They intended to pioneer fuel injection on a two-stroke trials bike, seeing this as the future (the four-stroke RTL has always sported this feature) and the whole machine was effectively designed round the efi concept. 

 

This is why the cylinder barrel is radically inclined rearwards, so as to easily accept 

a straight inlet tract which the use of efi allows. 

 

This has the benefit of keeping the centre of gravity low – with injection, fuel is delivered under pressure so the fuel tank can be placed anywhere on the bike. 

 

Ossa took the radical step of mounting it as a main frame member, where the downtubes would normally be. 

 

The coolant radiator was then placed in behind, totally out of the muck – so no more clogged radiators. 

 

As well of being out of the muck it is also out of the airflow, so Ossa designed ducting to assist the electric fan in drawing clean, cooling air through. 

 

The air-filter is also tucked-in behind the fuel tank and mounted high-up, it is supremely well protected from mud and water ingress.

 

The all-new engine also features a cassette-style gearbox. 

 

This means you can remove the outer case and pull the whole six-speed cluster, including selector mechanism – forks and all – in a single unit. Importer Nigel Birkett reckons he can have the gear cluster in his hands inside 20 minutes.

 

With the inlet at the front, the exhaust port is underneath at the back of the near-horizontal barrel. In order to get sufficient length into the system to allow the two-stroke to give its best, the end result is a bit of an exercise in snake charming, with a lot going on in the expansion box. 

 

Because of this radical design, with the airbox, fuel and efi unit up front, there is absolutely nothing behind the footpeg area except for the exhaust. 

 

Remove the seat/ rear mudguard and all you see is the exhaust pipe. 

 

SPECIFICATIONS

2012 Model Ossa TR 280i Factory

ENGINE

Type: Liquid-cooled, single-cylinder, two-stroke with direct crankcase, reed-valve induction

Capacity: 272.2 cc

Bore x Stroke: 76 x 60 mm

Fuel Injection: Kokusan battery-less EFI system

Ignition: CDI Kokusan digital magnetic ywheel

Clutch: Hydraulic control

Gear box: 6-speed

Transmission: Primary through gears, secondary by chain

Engine lubrication: 2.5% Fuel/ oil pre-mix

CHASSIS

Type: CR-MO steel tube prole with pipe and cast aluminium bottom section

SUSPENSION

Front: Conventional Marzocchi 40 mm aluminium forks

Rear: Variable progression linkage system with TTX Ohlins mono-shock

BRAKES

Front: 185 mm diameter disk with four-piston calliper

Rear: 150 mm diameter disk with two-piston calliper

WHEELS

Front: 28 spoke rims with a 2.75 x 21” tyre

Rear: 28 spoke rims with a 4.00 x 18” tubeless tyre

ANCILLARIES

Engine protector: Made of Aluminium A7075

Kick-start: Cast aluminium

Gear/ brake pedal: Cast aluminium with retractable toe

DIMENSIONS

Wheelbase: 1,328 mm

Seat height: 655 mm

Fuel capacity: 3 litres

Dry weight: 67 kg

 

FOR FULL REPORT AND PICTURES SEE T+MX FEBRUARY 3