Honda NR750 - Fast Bikes article, January 1992

UK magazine Fast Bikes devoted a large article and the cover of its January 1992 issue to the NR750. Below are extracts from the article:
No one motorcycle has captured the public imagination more over the last decade than the NR; nothing even approaches it, and there have been some exceptional motorcycles, each one hailed at the time as the ultimate. This is because, despite the undoubted radicalism of the technology, the excoticism of its incredible valve-train, the audaciousness of its oval pistons, the NR's attraction first and foremost is as an aesthetic and a stylistic work of art. It is an absolute, unmitigated masterpiece to be a classic, whether bike or car, a machine has to be positively beautiful from every angle.

The NR does not have a duff aspect. It is not some disjointed, abstracted vision of the future which pays no heed to stylistic continuity or history, nor a technological aberration of theory which can no longer see the wood for the trees; rather it's a brilliantly conceived and inspired revolution in motive physics pressed between the most exciting slopes and furrows of fibre (in this case, carbon fibre) ever conceived.

Previously Yamaha's 5 valves per cylinder and boring old round pistons represented the pinnacle of four-stroke engineering, but the NR's eight valves, twin conrods and oval pistons upstage this in terms of trick factor like Kevlar upstages denim as hip riding kit. In fact, the rest of the bike is relatively conventional in terms of design, other than the exotic materials used. Even the microprocessor controlled engine management with fuel injection is passé in the car world, although it is the most sophisticated to appear on a two wheeler. So it's that almost bizarre engine architecture on which all attention has been focussed.

The reasoning behind it actually includes one important parameter which is no longer applicable on the NR, at least as a road bike, which is that it must be restricted to a maximum of four cylinders. At the time of the NR500 Grand Pric racer's development (the progenitor of the 750) Honda's marketing proclaimed the overwhelming advantages of the four stroke over the two stroke, mainly because they weren't making any two strokes, and because Honda's historic Grand Prix successes with Hailwood, Redman and so on were all on four strokes. With their limited two stroked experience, they probably believed this themselves anyway.

The NR is an attempt to mimic the advantages of a V8, which they'd need to overcome the all-conquering four cylinder two strokes, while technically still fielding a V4 to comply with the regulations. The reasons for wanting to at least get close to being a V8 are compelling. Firstly, the greater number of cylingers for a given engine capacity, the greater surface area of piston. This piston area advantage translates as increased area to put valves into, enhancing further the power potential of an eight over a four because of improved breathing.

The NR's oval pistons mimic these eight cylinder characteristcs because they're each similar to two pistons glued together, providing the higher area but with only four pistons. A further advantage is gained over a V8 because the NR's piston circumference is 30% less than the equivalent two comparable round pistons, so that there's a useful reduction in friction between the piston and the bores - releasing even more power. Two conrods per piston are used, as they support the long piston more effectively than a single rod, which would require the piston itself to be very strong and so unacceptably large.

The combustion chamber itself is essentially a Cosworth-inspired narrow valve angle (27 degree) pentroof shape... only longer. A single plug would mean the flame front would not have reached its extremities by the time the exhaust valve opens, so two plugs are used (quite common even on conventional engines) to ensure that all the mixture is burnt usefully.

A central microprocessor is fed information from seven different sensors which the system then compares with an internal map before deciding on the ignition timing and injection volume and interval. A crank pulsar tells the control unit, the ECU, the exact position of the pistons and the engine speed; a PB sensor measures the intake manifold pressure to determine the injection volume; a cam pulars determines injection timing for each cylinder within the overall timing map (well trick); a throttle sensor measure not just throttle opening, but how quickly it's being opened (also well trick) to influence injection volume. Three more sensors measure coolant temperature, intake air temperature and ambient atmospheric pressure so the mass of air flowing into the engine ca be accurately gauged to ensure the right amount of fuel is mnixed with it - this means that even altitude changes (like wheelies...!) are catered for automatically.

These sensors and injection pump consume a lot of electrical power, which would mean an unacceptably large generator, so Honda uses a superlight neodynium-ferrite-boron rare earth magnet - obvious choice, really. This puts out about forty per cent more power than a common old iron one (like the RC30's) but again, must be a source of drag on the engine. Ditto the NR's traditional Honda high performance safety net of cam gear drive, although with few budgetary limitations these gears and holders could be machined to such precise tolerances, the disadvantages of added weight are all but negated.

Everything else about the NR is remarkably conventional; a twin-spar polished aluminium chassis pressing the motor in from both sides; remarkably conventional (if massive) 45mm Upside Down multi preload, compression and rebound adjustable front forks controlling the (slightly) unconventional (if a bit passé) sixteen inch front wheel; remarkably conventional rising-rate monoshock single-sided swing-arm guiding the 180 girth seventeen inch rear Michelin and remarkably conventional Nissin 4-pot front and rear discs hauling the 500lb plus motorcycle to a standstill.

There's been much talk from Honda about the uses of the NR. They've said that it's not a race bike, but a road bike. It has been designed, tuned and built for the road, rather than the track. However, the fact remains that it is derived from several NR racers, and thosebikes had fine racce engines. In truth, the two are nearer than Honda would have us think, as anyone who has wasted time and ground shifting an extra gear on exit from a corner would tell you. They both want the same things, the road rider and racer. Well, in theory at least.

It has a spread of power which easily rivals other smooth and linear performers such as the Triumph Trophy and Norton Rotary. High and widely spaced gears, however, mean the kind of immediate take-off offered by the former isn't readily available, but once the needle bounces above 2,500rpm you're there, in the power. After that, it's a clean sweep, right up until 8,000rpm. Then, with the muted, almost repressed wail of the exhaust resonting with controlled anger, the NR thrusts itself forward without equivocation. The credit for this midrange response must not go to any crichet pitch shaped piston or cylinder bore, but to simple old fuel injection providing immediate response in the upper regions. The power just keeps on coming. At 11,500rpm the toeque, some 50ft/lbs of it, just doesn't trail off.

The restricted 125ps is at your disposal from thereon and it's a tidal sea of power from everything from 8,000rpm through to the fifteen thou redline - an amazing spread of grunt coupled to an intoxicating punch of response. In fact it's so smooth Honda claim to have engineered in slight patches of vibration to keep the rider alert (though these are barely discernable except through the NR badged grips at 7,000).

Tall gearing means that at a constant 200kph the NR is barely turning five figures with five grand of usable power still to go and another 1,000rpm of overrev before the ignition limiter assures £38,000 doesn't become £15,000 through a moment of indiscretion. You can change gear anywhere between these two figures (10-15,000rpm, fools, not £38-15,000) and the NR surges forward again, much like a Turbo in the power, but not like a Turbo cutting in.

Aesthetically and ergonomically, it's a million miles away from the RC30. The old 750 looked too small for most people and felt it for many more. The NR is the virtual antithesis of this with a flexible, well-thought out perch. The footpegs feel highish at first, but the reach is just right. The bars are also on the high side, but the stretch between seat, bum and hands is spot-on from the first. Unlike the RC, there's also room to move about and shifting for a corner necessitates only the smallest of effort - well-placed tank knee slats help in this respect, giving the bike a balanced, chickable feel that belies its weight.

Steering is light, in the idiom of something like a GSXR750. Rake is a tightish 24 degrees thirty minutes, wheelbase 1433mm with an all-up weight of 222 kilos, or a dozen more than the heaviest big sports bike, the Suzuki GSXR1100R. That's a lot of motorcycle to pack into a small, compact shape, but it works. The highly-polished twin spar ally frame endows the NR with a low centre of gravity which is crucial considering the girth and weight it carries.

In tight and sweeping the turns the NR's front sixteen incher provides all the feedback you'll ever need - in graphic detail. The turn in and balance are sheer pleasure, but it gives nothing away on the straight either. Using Ricard's short 3.8km circuit meant that the full claim of 260kph couldn't be tested, but 245kph arrived pretty damn fast, with another 1,000rpm to come.

Weight alone, however, precludes the NR from steering like a middleweight, but the input and response are so accurate you don't want for any greater rapidity - that easily tapped power curve obliterates a multitude of sins when correcting a line.

The first gentle jolt of the NR's bars can tell you where the development has gone to better effect - the suspension. Thick (45mm) Upside Downers compress through 120mm of travel, and over the same distance for the rear. The set-up is relatively soft but movement from both ends is superbly controlled and it is, of course, a myth that suspension should be as hard as possible; on the contrary - it should be as soft as possible without prejudicing control. There is a feeling of sheer quality at work, and knocking the power off deep into a turn just encourages the NR to remind you of its mild and forgiving nature - you'd swear there was a good 30-40kg less at work. Late braking? The four-piston calipers acting on 310mm discs tempt you later and later on every lap.

With moderate input the bike flatters, making the pilot feel inestimably more capable than he really is, a shrewd move when you're selling something to the mega-rich of this World who though less likely to give the bike a damn good thrashing (they save that for their mistresses) still need a shot. They'll feel good about riding the NR at whatever velocity beacuse it behaves in the same way at 130mph as it does at 30mph; it's a perfect symbioses of smooth, subtle performance with market niche.

The engine screams for a wider application. If you want a stonking street single, imagine an oval piston one. If you want a smooth, predictable sports tourer, imagine an oval piston one. The world waits.

As it is, the NR is a bit of a sterile experience. What's the point in getting all lathered up about a bike that's simply out of reach? It's a wind up, really. It looks the sexiest thing you've ever seen. But really, though incredibly accomplished, it never really excites in the way a 'bad bike' should. It might look like the raunchiest ride you could ever imagine but in a disappointing way it fakes its orgasms. I 'spose you could say, the NR's a bit of a prick-tease.

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