Introduction
The story of the RC31 is an interesting tale, analogous in some respects to the Shelby cobra. Paradoxically it is considered a generic tool of the motorcycle courior and a modern classic with race pedigree and unique caché. It was designed by Toshiaki Kishi, levereged from the RC30 project, it was the second Honda motorcycle with Pro-Arm rear suspension. The NT650's main visual distinction is it's frame and swingarm. The dual spar aluminum frame and single sided swingarm (licensed from ELF) were pretty high tech in 1988. The mildly tuned motor is descended from the VT500 and has been seen in several other models, in one guise or another. The RC31 was ahead of its time in many regards and has since grown to cult status in North America, despite modest sales there. The RC31 was one of the first modern Naked bikes, released several years before the Ducati Monster and Suzuki SV650.
The designer
Toshiaki also designed the Super Blackbird, 1988 CBR1000, 750 Africa Twin, Hornet 900, 2002 VFR800, Z50R, RC45, and a lot more. He is considered one of Honda's greatest designers and is still active in the motorcycle design arena.
Models
NT650 Hawk U.S. (2200 units), Europe (600 units)
The Hawk GT was introduced in 1988 and produced through 1991. In 1988 the bike was sold in the colors Metallic Tempest Gray and Candy Flair Blue. For the remainder of the bikes production run it was only sold in red.
Current owners are passionate about their bikes, however in 1988, the RC31's aluminum chassis was relatively expensive. The retail price differential between the Hawk and the CBR600 was less than $1000. This resulted in very slow sales for the naked bike. By the mid-90's the U.S. market had caught up with the design and left over models were being snapped up.
NT650 Bros (Product one) 4100 units & NT400 Bros (Product two) 13937 units
The Japanese Bros was more successful with over 18,000 units sold, the majority of which (71%) were the 400cc sleaved down variant, known as product two. This was due to a prohibitive tax on vehicles exceeding this displacement. The Japanese government wanted to discourage mass ownership of motorcars due to the Island's population density. The Bros is distinct from the Hawk in two respects, it has a close ratio gearbox and the trim has more chrome & aluminum.
In the late 90's most domestic RC31's found their way to Europe via the grey market, there was strong particularly demand for the Bros in Ireland. The country's VRT tax system favoured older vehicles. Motorcycle couriors and commuters purchased both product one & two, for their reliability, broad power band, flickability, robust design, ease of maintenance and the availability of replacement components via the breakers yard.
NTV600 Revere
Excluding the 600 Hawks that were imported into germany, the Revere was the only NT650 derivative available in Europe. It is distinguished from Hawk and Bros by the following characteristics, the heavy steel frame, power sapping shaft-drive, larger 5 gal gas tank, longer rear end, and 600cc motor. This model had no sporting potential but was successful in a touring role. An interesting modification is to graft the Revere petrol tank to the Hawk to double it's endurance range.
Two Brothers Racing
The story of the RC31 would terminate here without the intervention of three year old North American road race team TBR, comprised of brothers Kevin and Craig Erion with their tuners Mike Velasco and Dan Kyle. In 1989 TBR selected the NT650 Hawk GT as their racing platform.
“Nobody had raced the Hawk,” said Erion. “We missed the first two races of the season developing the bike and, to the total surprise of all, we entered and won the remaining five races, taking the 1989 GP2 class championship.” In 1990, TBR moved up to campaign in the open-class Pro Twins GP1 series, finishing 3rd overall for the season. “We took that bike from 39 rear-wheel horsepower in stock trim to over 70 horsepower (probably 85hp) in race trim,” said Erion. “We were competitive and we began to get noticed.”
In 1991, TBR traveled to Japan to compete in the All Twins Battle and they caught the attention of HRC Director Mr. Oguma, who invited them to visit Honda R&D to meet the NT650’s designers and discuss ways to increase power. “A designer at Honda R&D, Mr. Hasumi, became interested in our work,” said Erion. “His team was designing the CBR600F2 for ‘91, and Honda wanted to field an F2 race team.” For 1991, TBR had a Honda contract to race the F2 in Supersport and the RC30 in Superbike, thus beginning a relationship with Honda that would flower and bear fruit for many years to come. While TBR had moved on from the RC31 platform, other teams had followed suit and were tasting victory with the "RaceHawk".
T.B.R. RC31 Race specification.
The basic concept ot the RC31 race engine was Velasco's, based upon his years of work at Honda Racing. The heads were ported by a respected Canadian, Rick Tomacic, and according to Erion, flow better than factory VFR heads. The RC31's heads were fitted with 1mm oversize Del West titanium valves, which weigh only 60 percent as much as steel valves. Light titaniurn valves continue to follow a cam contour long after steel valves would have floated. Velasco selected a Megacycle cam, based on what had worked in VT500 Ascots. Three-milimeter-oversize Wiseco domed pistons (82mm) were installed, increasing the displacement to 700cc with a compression ratio of 12:1. Con rods were cut from titanium billet by Crowers "really big, and 60 to 70 grams lighter than stock," says Erion.
The downdraft intake system was topped by two 39mm racing CV carburators taken from an RC30 race kit. Ignition came from a Honda RS750 dirt-tracker, providing 36 degrees advance by about 3000 rpm for optimum performance with higher compression. The new ignition system extended the rev limit to 12,000 RPM and eliminated the requirement for a battery. The Exhaust system dimentions were copied straight from the RS750. Kerker fabricated the two-into-one exhaust pipe in stainless, feeding an RS-style canister and muffler section.
Engine longevity was increased by the installation of an RC30 radiator and another sourced from a VFR750. Coolant from the bottom radiator was pumped to both cylinders in parallel, eliminating the issue of rear cylinder overheat experienced with O.E.M. sequential routing.
A complete road-race front end was lent by Honda, taken from a ex-Joey Dunlop Isle of Man TT1 bike. Twin 323mm disk brakes, machined-from-solid calipers with Nisin pads, delivered more than double the original stopping power. A Fox shock controled the rear suspension. The 17-inch rims were 3.5/4.5-inch, shod with bias-ply front/radail rear mchelin 250 GP slicks.
RC31: Characteristics of a superlative race platform.
Light weight.
The NT650's lighter weight (308 lbs + fuel, in race spec) translates to less inertia and momentum, hence it can brake later, turn quicker and maintain higher cornering speeds.
Rigid frame.
The rigid frame resists flexing and twisting. This torsional rigidity maintains alignment of the front and rear wheels, which translates to conering stability and consistent handling.
Engine Layout.
The compact 52 degree engine configuration, locates the engine mass close to the RC31's centre of gravity, this mass centralisation minimises rotational momentum, the tendency for an object to continue to move in its original direction of travel.
Short wheelbase.
As a motorcycle turns, the steering axis is pulled to the side, and the rest of the frame will pivot on the rear wheel's contact patch. The longer the wheelbase, the less the frame will turn with a given sideways movement of the steering axis. Thus, a short wheelbase tends to turn quicker, while a long wheelbase requires the front wheel to turn further, to produce the same effect on the motorcycle's frame.
V-twin inate traction control.
A v-twin's power delivery differs from 4 cylinder engines, the power pulses are further apart. This brief pause gives the rear tyre a chance to recover traction. The upshot of this is, the rider can get on the power earlier with less risk of a highside.
A flat torque curve.
Such torque characteristics are ideal for an inexperienced racer, for it gives good acceleration as long as the engine is in more or less the right gear. There is no "sweet spot" on which the rider must keep the tach needle hovering by ceasless and precise shifting.
SuperHawk prototypes
Let's advance to 1995, Honda's RC45 (750cc V4) has been relegated to second fiddle by the all conquering Ducati 916 (916cc V2). Large displacement v-twin sportbikes have become the only means of ataining BSB and WSB glory, given the championship regulations of the period.
Honda's first big bore v-twin prototype was a collection of parts-bin spares, built by Honda's U.S. research and development team. The American-built prototype used an 1100cc motor from Honda's VT1100 custom bike, fitted in a frame from a Hawk. It used standard wheels, with a modified front end and was fitted with a sports fairing.
Tagged the FireHawk, it was ridden extensively by Honda test riders and members of the public who had voiced interest in buying a Japanese V-twin sportbike. Renowned tuners, Two Brothers Racing were invited to test and comment on the top-secret project. The test results were favourable and were sent to Japan along with a video lobbying for the bike to be built.
Honda Japan's R&D team then built their own V-twin called the VR980. It used a Bros 650 frame, a 750cc Africa Twin engine, bored and stroked to 980cc. The brakes, forks, swingarm, rear shock and wheels were taken from a FireBlade and the half fairing came from an Africa Twin. It was tested successfully at Honda's Tochigi test track in Japan. It has been rumoured that the VR980 went head to head with a Ducati 916 at Tochigi and won. While this is uncorroberated, it seems plausible, considering what Honda's strategic objectives were.
SuperHawk not so super
Honda launched it's first 1000cc v-twin sportbike in 1997. Christened the Superhawk, it was devoid of allmost all of the characteristics of it's predecessor. In fact it was suspeciously similiar to the Suzuki TL1000S, both had trelis frames and 90 degree v-twin configurations. They arrived in the same year and targeted the same sport touring segment. An all out battle for market share was scheduled to commence, when Honda received a windfall, the TL's rear rotary damper was defective and caused twitchy handling. A product recall was issued and the TL was forever (unfairly) cast as the "tank slapping widdow maker". The TL left the stage in 2001. The main flaws with Superhawk were that the frame flexed excessively, the use of the engine as a stressed member to support the swingarm led to fractured crankcases.
Why was the VR980 not put into production?
Tooling already scrapped.
U.S. prefered sport tourers rather than all out racers.
Europe - a premium bike that's really a courior bike with a bigger engine?
Honda would surrender the spare parts cash cow.
SV650 the spiritual successor
Our story now comes full circle with the SV650, Suzuki's TL project, mortaly wounded by savage reviews, never came to fruition. Suzuki regrouped and evaluated opportunities to draw a return from the TL's development costs. Introduced to the RC31 via the showdown with it's successor, the "superhawk", Suzuki appreciated the market potential of the NT650 design.
Suzuki had noticed that the RC31 was satisifing a diverse range of niche market segments with a single design base, entry level, commuter, courior, female rider, experienced rider, customization enthusiast, club racer and professional racer. In 1999 they drew upon their TL design experience to produce a facsimile of the NT650 and named it the SV650. It received rave reviews from the motorcycle press and enjoyed strong global sales, helped by the higher price differential to the CBR600 of $2300.
While Suzuki has incorperated a decade of technical advancement into the SV650, the SV and NT are conceptually identical. This shared ethos can be distilled to one word, fun, arguably more fun than any race replica. Superbikes offer adrenaline pumping velocity with a twist of the throttle but if we are honest the true fun of motorcyling is sub 90MPH on a twisting backroad.
Sources
Wikipedia
Toshiaki Kishi Biography / Stuart Ballard / Motorcycle design.com
Bros serial number range
TBR biography
Bird of Prey by Kevin Cameron
Winning by Nick Ienatsch
VR980 article/MCN (Brittish) / David Schnur / U.S. Hawklist
The story of the RC31 is an interesting tale, analogous in some respects to the Shelby cobra. Paradoxically it is considered a generic tool of the motorcycle courior and a modern classic with race pedigree and unique caché. It was designed by Toshiaki Kishi, levereged from the RC30 project, it was the second Honda motorcycle with Pro-Arm rear suspension. The NT650's main visual distinction is it's frame and swingarm. The dual spar aluminum frame and single sided swingarm (licensed from ELF) were pretty high tech in 1988. The mildly tuned motor is descended from the VT500 and has been seen in several other models, in one guise or another. The RC31 was ahead of its time in many regards and has since grown to cult status in North America, despite modest sales there. The RC31 was one of the first modern Naked bikes, released several years before the Ducati Monster and Suzuki SV650.
The designer
Toshiaki also designed the Super Blackbird, 1988 CBR1000, 750 Africa Twin, Hornet 900, 2002 VFR800, Z50R, RC45, and a lot more. He is considered one of Honda's greatest designers and is still active in the motorcycle design arena.
Models
NT650 Hawk U.S. (2200 units), Europe (600 units)
The Hawk GT was introduced in 1988 and produced through 1991. In 1988 the bike was sold in the colors Metallic Tempest Gray and Candy Flair Blue. For the remainder of the bikes production run it was only sold in red.
Current owners are passionate about their bikes, however in 1988, the RC31's aluminum chassis was relatively expensive. The retail price differential between the Hawk and the CBR600 was less than $1000. This resulted in very slow sales for the naked bike. By the mid-90's the U.S. market had caught up with the design and left over models were being snapped up.
NT650 Bros (Product one) 4100 units & NT400 Bros (Product two) 13937 units
The Japanese Bros was more successful with over 18,000 units sold, the majority of which (71%) were the 400cc sleaved down variant, known as product two. This was due to a prohibitive tax on vehicles exceeding this displacement. The Japanese government wanted to discourage mass ownership of motorcars due to the Island's population density. The Bros is distinct from the Hawk in two respects, it has a close ratio gearbox and the trim has more chrome & aluminum.
In the late 90's most domestic RC31's found their way to Europe via the grey market, there was strong particularly demand for the Bros in Ireland. The country's VRT tax system favoured older vehicles. Motorcycle couriors and commuters purchased both product one & two, for their reliability, broad power band, flickability, robust design, ease of maintenance and the availability of replacement components via the breakers yard.
NTV600 Revere
Excluding the 600 Hawks that were imported into germany, the Revere was the only NT650 derivative available in Europe. It is distinguished from Hawk and Bros by the following characteristics, the heavy steel frame, power sapping shaft-drive, larger 5 gal gas tank, longer rear end, and 600cc motor. This model had no sporting potential but was successful in a touring role. An interesting modification is to graft the Revere petrol tank to the Hawk to double it's endurance range.
Two Brothers Racing
The story of the RC31 would terminate here without the intervention of three year old North American road race team TBR, comprised of brothers Kevin and Craig Erion with their tuners Mike Velasco and Dan Kyle. In 1989 TBR selected the NT650 Hawk GT as their racing platform.
“Nobody had raced the Hawk,” said Erion. “We missed the first two races of the season developing the bike and, to the total surprise of all, we entered and won the remaining five races, taking the 1989 GP2 class championship.” In 1990, TBR moved up to campaign in the open-class Pro Twins GP1 series, finishing 3rd overall for the season. “We took that bike from 39 rear-wheel horsepower in stock trim to over 70 horsepower (probably 85hp) in race trim,” said Erion. “We were competitive and we began to get noticed.”
In 1991, TBR traveled to Japan to compete in the All Twins Battle and they caught the attention of HRC Director Mr. Oguma, who invited them to visit Honda R&D to meet the NT650’s designers and discuss ways to increase power. “A designer at Honda R&D, Mr. Hasumi, became interested in our work,” said Erion. “His team was designing the CBR600F2 for ‘91, and Honda wanted to field an F2 race team.” For 1991, TBR had a Honda contract to race the F2 in Supersport and the RC30 in Superbike, thus beginning a relationship with Honda that would flower and bear fruit for many years to come. While TBR had moved on from the RC31 platform, other teams had followed suit and were tasting victory with the "RaceHawk".
T.B.R. RC31 Race specification.
The basic concept ot the RC31 race engine was Velasco's, based upon his years of work at Honda Racing. The heads were ported by a respected Canadian, Rick Tomacic, and according to Erion, flow better than factory VFR heads. The RC31's heads were fitted with 1mm oversize Del West titanium valves, which weigh only 60 percent as much as steel valves. Light titaniurn valves continue to follow a cam contour long after steel valves would have floated. Velasco selected a Megacycle cam, based on what had worked in VT500 Ascots. Three-milimeter-oversize Wiseco domed pistons (82mm) were installed, increasing the displacement to 700cc with a compression ratio of 12:1. Con rods were cut from titanium billet by Crowers "really big, and 60 to 70 grams lighter than stock," says Erion.
The downdraft intake system was topped by two 39mm racing CV carburators taken from an RC30 race kit. Ignition came from a Honda RS750 dirt-tracker, providing 36 degrees advance by about 3000 rpm for optimum performance with higher compression. The new ignition system extended the rev limit to 12,000 RPM and eliminated the requirement for a battery. The Exhaust system dimentions were copied straight from the RS750. Kerker fabricated the two-into-one exhaust pipe in stainless, feeding an RS-style canister and muffler section.
Engine longevity was increased by the installation of an RC30 radiator and another sourced from a VFR750. Coolant from the bottom radiator was pumped to both cylinders in parallel, eliminating the issue of rear cylinder overheat experienced with O.E.M. sequential routing.
A complete road-race front end was lent by Honda, taken from a ex-Joey Dunlop Isle of Man TT1 bike. Twin 323mm disk brakes, machined-from-solid calipers with Nisin pads, delivered more than double the original stopping power. A Fox shock controled the rear suspension. The 17-inch rims were 3.5/4.5-inch, shod with bias-ply front/radail rear mchelin 250 GP slicks.
RC31: Characteristics of a superlative race platform.
Light weight.
The NT650's lighter weight (308 lbs + fuel, in race spec) translates to less inertia and momentum, hence it can brake later, turn quicker and maintain higher cornering speeds.
Rigid frame.
The rigid frame resists flexing and twisting. This torsional rigidity maintains alignment of the front and rear wheels, which translates to conering stability and consistent handling.
Engine Layout.
The compact 52 degree engine configuration, locates the engine mass close to the RC31's centre of gravity, this mass centralisation minimises rotational momentum, the tendency for an object to continue to move in its original direction of travel.
Short wheelbase.
As a motorcycle turns, the steering axis is pulled to the side, and the rest of the frame will pivot on the rear wheel's contact patch. The longer the wheelbase, the less the frame will turn with a given sideways movement of the steering axis. Thus, a short wheelbase tends to turn quicker, while a long wheelbase requires the front wheel to turn further, to produce the same effect on the motorcycle's frame.
V-twin inate traction control.
A v-twin's power delivery differs from 4 cylinder engines, the power pulses are further apart. This brief pause gives the rear tyre a chance to recover traction. The upshot of this is, the rider can get on the power earlier with less risk of a highside.
A flat torque curve.
Such torque characteristics are ideal for an inexperienced racer, for it gives good acceleration as long as the engine is in more or less the right gear. There is no "sweet spot" on which the rider must keep the tach needle hovering by ceasless and precise shifting.
SuperHawk prototypes
Let's advance to 1995, Honda's RC45 (750cc V4) has been relegated to second fiddle by the all conquering Ducati 916 (916cc V2). Large displacement v-twin sportbikes have become the only means of ataining BSB and WSB glory, given the championship regulations of the period.
Honda's first big bore v-twin prototype was a collection of parts-bin spares, built by Honda's U.S. research and development team. The American-built prototype used an 1100cc motor from Honda's VT1100 custom bike, fitted in a frame from a Hawk. It used standard wheels, with a modified front end and was fitted with a sports fairing.
Tagged the FireHawk, it was ridden extensively by Honda test riders and members of the public who had voiced interest in buying a Japanese V-twin sportbike. Renowned tuners, Two Brothers Racing were invited to test and comment on the top-secret project. The test results were favourable and were sent to Japan along with a video lobbying for the bike to be built.
Honda Japan's R&D team then built their own V-twin called the VR980. It used a Bros 650 frame, a 750cc Africa Twin engine, bored and stroked to 980cc. The brakes, forks, swingarm, rear shock and wheels were taken from a FireBlade and the half fairing came from an Africa Twin. It was tested successfully at Honda's Tochigi test track in Japan. It has been rumoured that the VR980 went head to head with a Ducati 916 at Tochigi and won. While this is uncorroberated, it seems plausible, considering what Honda's strategic objectives were.
SuperHawk not so super
Honda launched it's first 1000cc v-twin sportbike in 1997. Christened the Superhawk, it was devoid of allmost all of the characteristics of it's predecessor. In fact it was suspeciously similiar to the Suzuki TL1000S, both had trelis frames and 90 degree v-twin configurations. They arrived in the same year and targeted the same sport touring segment. An all out battle for market share was scheduled to commence, when Honda received a windfall, the TL's rear rotary damper was defective and caused twitchy handling. A product recall was issued and the TL was forever (unfairly) cast as the "tank slapping widdow maker". The TL left the stage in 2001. The main flaws with Superhawk were that the frame flexed excessively, the use of the engine as a stressed member to support the swingarm led to fractured crankcases.
Why was the VR980 not put into production?
Tooling already scrapped.
U.S. prefered sport tourers rather than all out racers.
Europe - a premium bike that's really a courior bike with a bigger engine?
Honda would surrender the spare parts cash cow.
SV650 the spiritual successor
Our story now comes full circle with the SV650, Suzuki's TL project, mortaly wounded by savage reviews, never came to fruition. Suzuki regrouped and evaluated opportunities to draw a return from the TL's development costs. Introduced to the RC31 via the showdown with it's successor, the "superhawk", Suzuki appreciated the market potential of the NT650 design.
Suzuki had noticed that the RC31 was satisifing a diverse range of niche market segments with a single design base, entry level, commuter, courior, female rider, experienced rider, customization enthusiast, club racer and professional racer. In 1999 they drew upon their TL design experience to produce a facsimile of the NT650 and named it the SV650. It received rave reviews from the motorcycle press and enjoyed strong global sales, helped by the higher price differential to the CBR600 of $2300.
While Suzuki has incorperated a decade of technical advancement into the SV650, the SV and NT are conceptually identical. This shared ethos can be distilled to one word, fun, arguably more fun than any race replica. Superbikes offer adrenaline pumping velocity with a twist of the throttle but if we are honest the true fun of motorcyling is sub 90MPH on a twisting backroad.
Sources
Wikipedia
Toshiaki Kishi Biography / Stuart Ballard / Motorcycle design.com
Bros serial number range
TBR biography
Bird of Prey by Kevin Cameron
Winning by Nick Ienatsch
VR980 article/MCN (Brittish) / David Schnur / U.S. Hawklist
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