The aluminum twin-spar frame would eventually become a core technology for Honda.
The NV0B frame comprises thick aluminum square pipes measuring 40 mm x 100 mm. Two lines run along the surface of the pipe, indicating that there are ribs inside. Early aluminum frames with two ribs inside, including the one used on this machine, had a "cross pipe" connecting the girders that extended to the left and right behind the steering head to increase torsional rigidity. (Photo/Shinobu Matsukawa)
The NV0B's "conventional body layout" core was the twin-spar extruded aluminum frame with two ribs inside. When you cut the square pipes in half, you can see the cross-section with two reinforcing plates built into them.
Honda first used this frame configuration on the 1985 GP250 Works road racer RS250RW, coded as NV1A. Although the machine was officially named RS250RW, it was the first-generation NSR250, and the development engineers recognized it. It was completed at the end of August 1984, before the development of the NV0B started. Testing staff confirmed good performance, so Honda used it for the NV0B.
HRC chassis design engineer Takashi Kudo, the creator of this innovation, said, "When using aluminum, which is weaker against stress concentration than steel, it is difficult to achieve rigidity even by combining thin square pipes, so it makes sense to use square pipes with a large cross-section. However, if you enlarge the cross-section without doing anything, you cannot ensure the possibility of deformation increases and then the calculated rigidity. Therefore, ribs are inserted into the square pipe to support the cross-section so it does not collapse."
The engine is suspended from the twin-spar aluminum frame, a familiar feature of HRC road racers in the late 1980s. Even after nearly 40 years since its manufacture, its beauty has not been lost. The previous NV0A used a pull-type clutch with the release on the outside of the basket, but this NV0B uses a push-type clutch. The width has increased due to the three-shaft engine, so the primary purpose of the change was to slim down the clutch mechanism. (Photo/Shinobu Matsukawa)
The previous NV0A chassis was also a twin-spar type, but it was a press frame made by welding press-formed parts together. If appropriately designed, it was possible to obtain high rigidity, which you could control by changing the thickness of the plate material in different parts. However, the amount of work involved in producing it was huge, and it was difficult to correct distortion due to a fall or to modify it while it was in use. On the other hand, frames made of extruded aluminum, which you could manufacture mechanically, were much easier to produce, correct, and modify than pressed frames. They had the advantage of ensuring high rigidity while maintaining a certain level of lightness.
After they established the technology for the twin-spar frame made of extruded aluminum with two ribs inside on the RS250RW [NV1A], they used it on the NSR500 [NV0B] and the RVF750 [NW1A], three HRC works road racers introduced in the 1985 season. The cross-sectional dimensions of the aluminum square pipes were 40 mm x 80 mm for the GP250 racer NV1A, 40 mm x 100 mm for the GP500 racer NV0B, and 40 mm x 90 mm for the TT-F1 racer NW1A. The cross-section size, aspect ratio, and number of ribs would change in response to later changes in how they thought about frames.
Furthermore, the chassis of HRC road racers that followed in the late 1980s had an aluminum frame with one or two ribs inside, except the 1988 RCB400, which tried out a monocoque frame. This technology was also widely used for street bike chassis and became essential when discussing Honda sports bikes from the late 1980s to the 1990s.
The first bike to use aluminum frames with two ribs was the 1985 GP250 works racer, the NV1A. Due to HRC's marketing strategy, the bike was named "RS250RW," which means a works-spec model of a commercially available racer, but in reality, it was the first NSR250. The development code for the 1986 GP250 works racer, the first to use the name "NSR250" as an official model, was "NV1B". (Photo/Jiro Ishida)
The NW1A was the first bike to use the name "RVF750." It also used aluminum frames with two ribs inside and was equipped with a 4-stroke V4 engine based on the VF750F. The same bike, with Wayne Gardner and Masaki Tokuno riding on it, won the 1985 Suzuka 8-Hour Endurance Road Race and the Endurance World Championship title by Gerard Coudray and Patrick Igoa that same year. (Photo/Shinobu Matsukawa)
Honda also used aluminum frames with two ribs on the NW1A; the first TT-F1 works racer "RVF750" model. This year, the same bike made its debut at the 24 Hours of Le Mans motorcycle race, held on April 28-29 as a standalone event outside of the Endurance World Championship series. However, both of the bikes that competed retired due to frame damage. The area between the gusset on the underside of the frame around the head pipe and the bracket attached to the engine hanger broke due to stress concentration.
The frame is made in the same way as the NV0B and NV1A, and both bikes were already racing in the World Grand Prix that had already begun. Fortunately, there were no problems at the South African GP, which had already finished, but HRC quickly reinforced the frame before the upcoming Spanish GP, and nothing happened.
