McRae 4x2
Driveline
Motorcycle engines are powerful, lightweight and compact. But motorcycle gearboxes are relatively fragile, being designed to feed power to the road surface via a small contact area. The tremendous torque reversals generated as off-road tyres crash back to the ground while racing cross country as sufficient are simply inadequate for standard transmissions.
The McRae solution was to utilise a CVT (Constantly Variable Transmission) where a big ‘rubber band’ takes power from the crankshaft to the differential via two expanding and contracting drive clutches. It sounds complex, but in principal it’s exactly the same as the Derailleur gear system on a mountain bike. The source was a snowmobile with a relatively torquey, 140hp 3-cylinder 1050cc, Japanese motor.
CVT
The CVT is key to using a compact motorcycle engine. It tolerates mud, water and dust, but fesh-fesh is problematic and slippage can occur. The solution – yet to be perfected in the finest of sand – is to create an over-pressure in the engine bay. This is achieved by sealing most of the bay, allowing a small exit for hot air to vent, while using fans to force in pressurised, filtered air.
The Kevlar-reinforced drive belts cost around £30 and can be replaced in minutes – a good deal cheaper that a traditional gearbox.
4x2 Tech Spec
Single-centre-seat with mid-mounted, dry-sumped, 3-cylinder 1050cc engine
Chassis: FIA homologated tube-frame
Overall width: 1820 m
Weight: 750 Kg (Dakar trim)
Power: 140hp / 132 Nm
Suspension: double wishbones; optional Reiger dampers
Electrics: bespoke, loom, ECU and dash by DC electronics
Driveline: Constantly Variable Transmission utilising reinforced Kevlar belt
Differential: Manually locking gear-driven Torsen differential, incorporating reverse gear by Quaife
Drive shafts: GKN M300 material
Top speed: 150 kph (limited for race regulations.)
Fuel capacity: 140 litres, 2 ATL fuel cells
Fuel system: Bosch
Engine management: DTA, including altitude correction
Air filter: K&N
Tires: ITP 9” Terra 10”Baja
Wheels: ITP T7 14” Bead lock
Steering: bespoke aluminium rack and pinion (1.7 turns lock to lock) with optional adjustable electric
McRae 4x2 Price: 70.000€
Motorcycle engines are powerful, lightweight and compact. But motorcycle gearboxes are relatively fragile, being designed to feed power to the road surface via a small contact area. The tremendous torque reversals generated as off-road tyres crash back to the ground while racing cross country as sufficient are simply inadequate for standard transmissions.
The McRae solution was to utilise a CVT (Constantly Variable Transmission) where a big ‘rubber band’ takes power from the crankshaft to the differential via two expanding and contracting drive clutches. It sounds complex, but in principal it’s exactly the same as the Derailleur gear system on a mountain bike. The source was a snowmobile with a relatively torquey, 140hp 3-cylinder 1050cc, Japanese motor.
CVT
The CVT is key to using a compact motorcycle engine. It tolerates mud, water and dust, but fesh-fesh is problematic and slippage can occur. The solution – yet to be perfected in the finest of sand – is to create an over-pressure in the engine bay. This is achieved by sealing most of the bay, allowing a small exit for hot air to vent, while using fans to force in pressurised, filtered air.
The Kevlar-reinforced drive belts cost around £30 and can be replaced in minutes – a good deal cheaper that a traditional gearbox.
4x2 Tech Spec
Single-centre-seat with mid-mounted, dry-sumped, 3-cylinder 1050cc engine
Chassis: FIA homologated tube-frame
Overall width: 1820 m
Weight: 750 Kg (Dakar trim)
Power: 140hp / 132 Nm
Suspension: double wishbones; optional Reiger dampers
Electrics: bespoke, loom, ECU and dash by DC electronics
Driveline: Constantly Variable Transmission utilising reinforced Kevlar belt
Differential: Manually locking gear-driven Torsen differential, incorporating reverse gear by Quaife
Drive shafts: GKN M300 material
Top speed: 150 kph (limited for race regulations.)
Fuel capacity: 140 litres, 2 ATL fuel cells
Fuel system: Bosch
Engine management: DTA, including altitude correction
Air filter: K&N
Tires: ITP 9” Terra 10”Baja
Wheels: ITP T7 14” Bead lock
Steering: bespoke aluminium rack and pinion (1.7 turns lock to lock) with optional adjustable electric
McRae 4x2 Price: 70.000€