Honda NSF250R - First Look

Honda’s Moto3 contender is ready for action.

Honda NSF250R - First Look

Honda NSF250R

As the last surviving two-stroke world-championship class approaches its conclusion at the end of 2011, we get to take a peek into the future of the new four-stroke Moto3 class that will replace it in Grand Prix competition. Honda has already geared up for the class with its new NSF250R, developed in part by using the 1996 RS125R—the last “factory” Honda to compete in the 125 Grand Prix class—as its benchmark.

New rules dictate a maximum engine-bore size of 81mm with not more than four valves. Desmodromic and pneumatic valvetrains are not allowed, while the rev limit is restricted to a maximum of 14,000 rpm.

Moto3 Singles are intended to become the base unit for a modular racing-class system, with all three GP classes sharing the same 81mm bore. Next year’s 1000cc MotoGP bikes will be limited to four cylinders, but there will be no restrictions on valvetrain or rev limits. In 2013, we expect the Moto2 class to drop the current Honda CBR600RR-powered, single-make formula in favor of 500cc Twins with the same 81mm bore as in the other two classes.

Using the RS125R as a starting point created a challenging set of obstacles for Honda engineers to overcome. The biggest was maintaining the same level of overall vehicle compactness while shoehorning the much larger, 250cc four-stroke inside a twin-spar frame that has the same basic measurements as it did with the 125cc two-stroke. Engineers felt this was mandatory to make the transition from the 125s to Moto3 as easy as possible for the riders.

To squeeze that dohc engine into the frame, the engineers inclined its cylinder 15 degrees backward, and the head was rotated 180 degrees, placing the intake at the front and the exhaust at the rear, similar to the Yamaha YZ450F motocrosser. The muffler sits underneath the engine in an effort to concentrate mass closer to the bike’s center of gravity. The engine’s configuration also allowed the radiator to be tucked in close to the crankcase, helping the bike achieve its ultra-short, 48-inch wheelbase.

Despite regulations allowing a bigger bore, Honda chose bore and stroke dimensions of 78.0 x 52.2mm. A very short piston measures only 31.5mm tall and features crossed ribs around its pin supports for rigidity. A forged crankshaft turns on plain bearings with a forged, high-tensile-steel connecting rod also spinning on plain bearings. A single injector resides in a 50mm throttle body feeding a pair of 32.5mm titanium intake valves with twin 26mm exhaust valves getting rid of the used charge. Valves are set at a 21.5-degree included angle and are actuated by hollow camshafts via inverted cup tappets. No compression ratio figures have yet been released.

Honda claims 48 peak horsepower at 13,000 rpm, not fully exploiting the limits allowed by the rulebook, and 20.6 foot-pounds of peak torque at 10,500 rpm. Impressive figures for sure, especially considering the bike’s claimed 180-pound dry weight.

Seat height is set at a confidence-inspiring 28.7 inches. Rolling gear consists of 17-in. wheels front and rear in 2.50-in. and 3.50-in. widths, respectively. A single Nissin radial-mount four-piston caliper squeezes a 296mm disc up front. An inverted 35mm fork is set at 22.5 degrees. As always, Honda leaves it to the teams to choose spec of the remaining chassis components via the aftermarket or with in-house racing parts.

021 Honda NSF250R Rear wheel size

020 Honda NSF250R Rear disk brake

019 Honda NSF250R Frame layout

018 Honda NSF250R Figure CG swing arm

017 Honda NSF250R Rear suspension

016 Honda NSF250R Frontal projected area equivalent to RS125R

015 Honda NSF250R Fuel tank and air box

013 Honda NSF250R Newly designed frame body and swing arms

014 Honda NSF250R Fuel tank and air box

012 Honda NSF250R Engine

011 Honda NSF250R Cassette transmission

010 Honda NSF250R Cassette transmission

009 Honda NSF250R Camshaft

008 Honda NSF250R Cylinder

007 Honda NSF250R Piston connecting rod

006 Honda NSF250R Front disk brake

005 Honda NSF250R Front wheel size

004 Honda NSF250R Front suspension

003 Honda NSF250R

002 Honda NSF250R

001 Honda NSF250R