Replacing the current 2-stroke, 125 cc machines currently used in the GP125 class, Honda developed the new “NSF250R” machine for entry riders to compete with, seizing the opportunity provided by the commencement of new 4-stroke, 250 cc Moto3 category, which starts in 2012.
With a mission of broadening the base for motorcycle motorsports cultivated by the RS125R, Honda aimed for a high-performance, lightweight, and compact racing machine that allows users to ride with the same sense of comfort as they did on the RS125R and this new machine inherits important elements from its predecessor, offering a good base to learn the basics in order to progress to the MotoGP class.
As a leader of the “NSF250R” development, on top of seeing the NSF250R expand the base for 2-wheel motorsports, as the RS125R did, and sharing dreams and excitement with our customers by revitalizing the Moto3 class, our greatest joy would be for the machine to serve as a springboard in creating future MotoGP champion riders. We really look forward to this new “NSF250R” being loved by more people around the world and helping them to realize their dreams in the world of motorsports, all the while being charmed by the machine.
Currently, the 2-stroke GP125 class is a gateway to success in road racing around the world, supporting young riders to experienced riders, and from local races to the MotoGP. The characteristic of the GP125-class machine is a body size allowing young entry riders to control the machine with relative ease.
The machine is very responsive and offers direct feel for the engine and contact with the frame, it is also equipped with a wide range of adjustable functions that boasts maximum machine performance. Honda believes these are important elements in helping riders reach the next level. Adopting the basic concept of inheriting these elements, the development objective for the NSF250R was to achieve the high performance and the easy handling of a 4-stroke engine, in a racing machine. In other words: lightweight, compact, high power and high efficiency.
The NSF250 engine was developed exclusively for road racing, to ensure superior quality and greater potential for commercial racing machine. With a development concept of “lightweight, compact, high output and efficiency,” numerous technological advances were introduced to create an engine befitting a racing machine.
The DOHC single-cylinder 249cc engine demonstrates a racing machine’s power delivery and response, with intake from front and exhaust to rear to improve air charging efficiency, and a cylinder tilted back 15 degrees to concentrate the engine’s mass, primarily to improve its stability. In order to deliver ample power into the high rpm range, the DOHC system incorporates titanium valves for both intake and exhaust (Honda patented). The new design also offers improved air charging efficiency along with ram-air intake, thanks to the straight intake port and throttle body with 50-mm diameter bore. In shaft layout, the balancer shaft is placed above the crankshaft to make the engine shorter and concentrate the mass.
Thinner lightweight piston (patent pending by Honda):
A thinner piston with an overall height of only 31.5 mm has been adopted, with a bore diameter of 78 mm. With improved combustion efficiency through a bulging shape side squish of the piston head, the engine inherits MotoGP technologies, such as two forged piston rings. On the back, higher rigidity for the two pin-boss connection ribs was achieved through Computer Aided Engineering or CAE analysis, allowing the engine to handle higher rpm and higher output.
Nut-less connecting rod:
A light nut-less type was chosen for the connecting rod. While a conventional connecting rod damps the big end with a nut and bolt, the nut-less connecting rod uses only a bolt to clamp the tapped hole cut directly into the rod. As a result, connecting rod weight is reduced, and the engine achieves increased revs and nimble responsiveness during powerful acceleration. Plain bearings are also adopted to handle higher output.
The NSF250R crankshaft realizes both high rigidity and precision required for a high-rpm, output racing engine, through a forged, integrated structure.
Plain bearings, which are effective for high output/low friction, smaller and more space savings than ball bearings, are used to realize a lighter and compact engine.
Reduced piston/cylinder friction for improved durability has been achieved by surface treating the cylinder with nickel silicon carbide (Ni-SiC) and an by using an offset cylinder shaft.
Titanium valves (Honda patented):
DOHC configuration, plus light and highly rigid titanium inlet and exhaust valves*1, allows the valves to function more precisely in the high rpm range. (*1. This is the first time titanium has been used for exhaust valves in a Honda mass-production mortorcycle.)
Sealed crankcase, dual-channel lubrication system:
Oil seal is set on each end of the crankshaft to seal the crankcase, and a dual-channel lubrication system is used, one on the crankshaft/piston side and the other on the transmission/clutch side. On the crankcase side, a force-feed system with trochoid pump is adopted, while an oil bath system used for 2-stroke engines is adopted for the transmission side.
Scavenging pump and reed valve:
To reduce friction, a scavenging pump is used to create negative pressure inside the crankcase. Through the use of a reed valve with optimized placement, pressure fluctuations inside the crankcase are constantly controlled, achieving friction reductions even during heavy loads on the engine (patent pending by Honda).
A cassette-type transmission is allows easy replacement of gear ratio for optimum performance at each racing circuit. The cassette-type design means that the gear cluster can be removed and replaced without removing the engine or disassembling the crankcase. And by making the close-ratio transmission of the RS125R available, the transmission provides convenience for RS125R users.
Fuel supply system:
Throttle body is equipped with IACV (Intake Air Control Valve). The IACV opening control and optimized intake air effectively control the engine-braking force of the 4-stroke single-cylinder engine, and provide the feeling of deceleration matching each rider’s preference. Air funnel precision has been enhanced through the adoption of a short aluminum intake funnel, which maximizes output characteristics and response.
Inheriting the RS125R’s compact frame, following technological advances were adopted to perfectly match the 250 cc, 4-stroke engine.
1) Cylinder engine tilted back, with intake from the front and exhaust to the rear
2) Throttle body inside the air box
3) Exhaust pipe in the reversed S (patent pending by Honda)
4) Midship muffler This Complete Built Up or CBU packaging allows mass concentration while achieving an inertial yaw moment on par with the RS125R.
At the same time, a high level of both maneuverability and stability were realized by optimizing weight distribution and the position of the center of gravity, for the excellent cornering performance required by lightweight class racing motorcycles.
The NSF250R’ frame is based on the RS125R’s proven unit. To optimize the rigidity in balance and torsion of a 4-stroke engine, frame specifications were determined from actual riding tests and CAE analysis.
For the front engine hanger and the main pipe section, optimum balance was achieved mainly by enhancing torsional rigidity. A newly configured swing-arm and frame body also resulted in a structure allowing smooth torsional characteristics. On the whole, stability during braking is improved, and a leeway and nimbleness during cornering exceeding those of the RS125R is ensured. The frame offers superb handling so that riders will not feel the weight increase of a 4-stroke engine, even when approaching corners.
As with MotoGP machines, the NSF250R’s throttle body is housed in the air box, and the air cleaner is placed between cylinder and radiator (patent pending by Honda). This layout allows a large 5-liter capacity air box, in the limited frame space while concentrating mass (oil catch tank capacity not included).
For air intake, a ram-air intake system is standard equipment. Air passing under the bottom bridge goes through the large air duct and is channeled straight to air box. This arrangement improves output by actively using the ram-air intake system. The oil catch tank is also cast-integrated into the bottom of the airbox, resulting in effective use of space and reduced weight.
As with the RS125R, front suspension is a 35-mm diameter inverted front fork. While the basic structure is the same as the RS125R, the front folk features an exclusive design including detailed settings high rigidity and stable performance to handle the increased vehicle weight and power output. The damping force adjustment function for compression and rebound is designed to meet the needs of a wide variety of riders, including beginners and those stepping up to this class.
Rear suspension features the same Pro-link suspension mechanism used for the RS125R. As the stroke increases, the cushion stroke rate grows, so the rider can easily feel the movement of the rear suspension and tyres gripping the road, allowing security when opening the throttle. Like the front suspension, basic configuration remains the same as the RS125R, except for revised damper characteristics to match changes in vehicle weight and output.
This swingarm is based on the RS125RW’s swing arms, lateral and torsional rigidity were reexamined, leading to an exclusive stamped structure in high-strength, lightweight 7000-series aluminum (also used in MotoGP) to strike a high-level balance with the frame. For the swing arms moves center of gravity forward to concentrate the mass.
ECU setting tool (HRC option, price to be determined):
As a means of attaining maximum machine performance, this tool is available for improved fuel injection and ignition timing setting. Following six features can be adjusted.
1) Fuel injection
2) Ignition timing
4) Auto shifter/ignition cut
5) Two different pattern data setting
6) Pit lane speed control (optional switch required)
Map mode selector switch:
Two patterns (optional): Whilst riding, the rider is able to experience the difference in settings more directly.
Pit lane speed-control switch (optional):
Switch for operating pit-lane speed set by ECU.