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This article was first published in 2008.
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When the NSU RO 80 was released in 1967, the
car was greeted with universal acclaim.
It immediately won Car of the Year awards, and
road tests in Europe, the US and Australia were glowing in their praise. Here
was a car with not only a brand new design of rotary engine, but also a stylish
and elegant body that had an aerodynamic drag figure superior to nearly
everything. Add to that front-wheel drive, four wheel disc brakes, class-leading
power steering and a well-developed suspension. And all from a company, NSU,
previously known only for motorcycles and small rear-engine cars!
The Ro 80 was a tour de force – but it sent NSU
broke.
So how did one of the most advanced and
welcomed cars ever made prove such a disaster? It’s a fascinating technical
story.
Let’s start with the engine.
Twin Rotor Wankel
Mounted longitudinally at the very front of the
car, the twin rotor Wankel used peripheral intake and exhaust ports and
displaced 1 litre (497.5cc x 2). While one of the very first production cars in
the world to use a rotary engine, the Wankel was certainly not an unknown design
to NSU: at the time of release of the Ro 80, the company had built 3000 small
rotary outboards and 2500 single rotor NSU Spider cars.
The Ro 80 engine used aluminium alloy rotor
housings and a 9:1 compression ratio. The rotor tip seals were cast iron and the
wearing surface of the rotor housings was a nickel and silicon carbide coating
that was electrically deposited. Two spark plugs per chamber were fitted (in
later engines this was reduced to one plug per chamber) and the two plugs were
fired simultaneously. Ignition on early engines was by traditional coil; this
was upgraded to electronic ignition on later cars.
Carburetion was by a twin-choke Solex, the unusual
aspect being the use of one very small choke (18mm) and very large choke (32mm).
These chokes fed long intake runners that merged only at the inlet ports. The
exhausts of each rotor were kept completely separate.
Power was listed at 113hp at 5500 rpm and peak
torque 117 ft-lb at a high 4500 rpm. The peripheral porting helped give a
strong top-end but low-rpm torque was poor – this graph is an interesting
comparison of the Ro 80’s power and torque outputs compared with the
contemporary Rover 2000TC, itself not a scintillating engine. As can be seen,
the 2 litre Rover has about a third more torque at lower revs.
The Wankel was said to weigh only two-thirds that
of a reciprocating engine developing the same peak power, and furthermore, NSU
said the cost of producing the engine would be reduced to well below that of a
conventional engine – the target was 60 per cent of the cost of a six cylinder
of equivalent power.
At the time of first release, NSU engineers were
said to have overcome the development problems of the rotary: chatter marks on
the epitrochoidal surface, apex seal wear and high oil consumption. The car’s
warranty was two years or 24,000 miles – far better than the then prevailing
average.
Road testers and owners universally commented on
the engine’s smoothness and ability to rev. Later, they also commented on the
incredibly short time the engines lived...
Transmisison
Bolted to the back of the rotary was an
interesting transmission. Similar to the Sportmatic design used in some Porsches
of the time, the Fichtel and Sachs semi-automatic used a vacuum servo-controlled
clutch, a torque converter and a 3-speed all-synchro transmission. Incorporated
in the gear lever knob was a micro-switch that triggered the clutch.
In normal town use the gearbox could be left in
second gear, being driven as a full automatic. However, for better performance,
the gearbox was changed conventionally.
This semi-auto trans was the only transmission
available; it was fitted after NSU engineers experienced snatching in the
driveline on throttle lifts. (Remember that peripheral porting of the rotary!)
The presence of the torque converter overcame this problem.
Some drivers loved the transmission, while others
hated it. It appears that the system had to be finely adjusted if jerkiness –
especially on down-changes – and noise were to be avoided. In any case,
off-the-line acceleration was always leisurely.
Drive was to the front wheels - the whole engine
and transmission being mounted ahead of the axle line.
Just the refined and sophisticated driveline would
have made the Ro 80 a startlingly innovative car, but there was far more.
Suspension
The front suspension was not groundbreaking in the
mould of the contemporary Citroen hydro-pneumatic systems, and the hydraulic
Hydrolastic system fitted to some Austin models, but it was still
extraordinarily well developed.
Front suspension used MacPherson struts, something
then still relatively rare on a front-wheel drive car. The front coils were
offset from the axis of the strut to reduce stiction and side-loadings, and the
front wheels had no less than 7.4 inches of travel. An anti-roll bar was used –
another then unusual aspect of the design was that the anti-roll bar did not
help located the wheels; instead a lower triangulated wishbone was used. (Like
many aspects of the Ro 80, this is something we now take for granted in most
MacPherson strut designs.)
Rear suspension took more than a passing glance at
BMW and Mercedes Benz practice and used semi-trailing arms (angled at only 10
degrees) and mounted on a sub-frame. Like the front suspension, spring and
dampers were concentric. No rear anti-roll bar was fitted, something that
certainly raises modern eyebrows. Rear wheel travel was an astonishing 10
inches.
Road testers and owners alike commented on the
extraordinarily comfortable ride, one that had little pitch. Initial tests were
also glowing in their praise of the car’s handling, it being said to have only a
touch of understeer. However, later tests – perhaps within the context of
improving front-wheel drives – talked about a lot of body roll and understeer
that could not be throttle-controlled. The tail, for example, stayed resolutely
planted, no matter what was done with the accelerator pedal or steering!
Tyres were to modern eyes tiny – just 175 width on
14 inch rims (alloy on later cars). The specified tyres were, however, very high
performance – Michelin XAS radials.
Steering
The ZF steering used a geared rack and pinion
system, aided as standard by a hydraulic ram. Steering feel was said to be
excellent at all speeds, however, as time passed and power steering became more
common, the 3.75 turns lock to lock attracted some criticism.
Very unusually for the time, the steering column
did not extend past the front bulkhead, improving safety in the event of a
front-end crash. In contrast, most cars then had steering columns that extended
well forward; the steering wheel being pushed into the driver as the front
crumpled.
Steering
Geometry?
One
of the most interesting aspects of the steering is one that is not actually
identified in accounts of the car – the amount of scrub radius provided by the
front steering geometry.
By
all accounts, the Ro 80 was wonderfully stable in poor conditions, something
often associated in the contemporary road tests with the front-wheel drive
chassis. However, looking at the drawings of the Ro 80, it appears that very
little scrub radius was used – and in fact, depending on where the exact pivot
axis is drawn, it could even be negative rather than the then-universal
positive.
Negative
scrub radius steering has the ability to self-correct when one wheel encounters
more resistance than another, and since the descriptions in the road tests again
and again describe the uncanny ability of the car to stay straight, we wonder if
the Ro 80 wasn’t in fact the first car to use this steering geometry...
At
minimum, it certainly had very little positive scrub radius.
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Brakes
Even in the braking system the Ro 80 was unusual
for the time.
Front discs were large and mounted inboard either
side of the gearbox. Rear brakes were also disc and incorporated separate drums
for the handbrake. The braking system used a tandem master cylinder with two
independent circuits – one circuit operating all four wheels and the other, just
the front wheels through the second pair of cylinders on the twin pot brakes.
The rear brakes used a load-sensitive proportioning valve.
Body
The body shape of the Ro 80 was quite startling. A
low nose, high boot, concealed rain gutters and lack of ornamental chrome gave
rise to plenty of comments that the body was shaped by engineers, not stylists!
(The Ro 80 doesn’t look startling today because most of the styling cues were
picked up in the later Audi 100, a car that set the aerodynamic sedan styling
agenda for the next 20 years.)
The claimed drag coefficient was 0.355, a figure
then at least 25 per cent better than achieved by a typical car of the same
class. Wind tunnel wool tuft testing shows amazingly good flow, especially in
the reattachment on the boot-lid. (This author has never seen any evidence than
any other three-box cars of the era achieved attached flow on the final third of
the car. Typically, any wool tuft pics are careful not to show this area!)
The low drag co-efficient (and relatively small
frontal area – the car was quite low) were responsible for the ability of the Ro
80 to run to 117 mph on only 113hp (that’s 188 km/h on only 84kW!).
Interestingly, a US magazine measured aerodynamic
lift at 100 mph (160 km/h) at a massive 150 lbs (68kg) front and 140 lbs (64kg)
rear. At least the lift was largely the same front and rear...
The car had a mass of about 1300kg.
On the Road
The Ro 80 had a range of competitors; in most
European markets it was compared with cars like the Rover 3.5, Jaguar XJ6 and
Mercedes 280SE. Interestingly, in acceleration to 100 km/h, maximum speed, fuel
economy and the standing quarter mile, it was largely inferior to these
cars. In fact, only in fuel economy did it comprehensively beat the thirsty
XJ6.
Another car that the Ro 80 was compared to was the
Citroen ID20. Against the Citroen it had similar performance but had much poorer
fuel economy. However, the NSU handled better.
A 1968 road test best summaries the strengths and
weaknesses: Wankel engine smooth and quiet; performance good, economy poor;
very quiet at speed and handling outstanding; well made, roomy and very
comfortable.
What Went Wrong?
Initially the demand for the Ro 80 was so high
that there was a waiting list. Owners raved about the cars, particularly their
ability to travel long distance in silent stability. Fuel economy, especially
away from city confines, was within the ballpark of other cars of the same
performance and if that performance was a bit sluggish off the line, well the mooted
triple rotor Ro 80 would soon fix that.
And then, all at once, the whole thing came
crashing down.
Simply, the innovative rotary engine proved to
have a fearsomely short life. Engines worked perfectly for, in some cases, just
days. Few cars did more than 50,000 kilometres on the original engine. The standing joke
was that if you were driving a Ro 80 and saw another, you’d not wave but instead
hold up the number of fingers that corresponded to how many engines you’d gone
through...
The eccentric shaft was upgraded with massively
increased lubrication, tip seals were modified, an over-rev dashboard buzzer
added, the ignition system and number of spark plugs changed – but still engines
failed. And not only did they fail catastrophically, but owners also complained
about oil-fouled plugs and difficult starting. One enthusiast driver recounted
that he became adept at changing plugs, removing carburettor jets and blowing
through them, resetting the clutch servo and adjusting idle speed! And even
then, that car’s engine died at just over 30,000km...
At least maintenance oil costs were reduced – the
engines used so much oil that the factory decided to drop oil changes, instead
using a ‘total loss’ approach. To be fair, oil was always intended to be
injected into the combustion chambers, but the mind boggles at the thought of an
oil consumption so high the complete sump contents were changed frequently
enough to never need draining...
When engines failed NSU replaced them at a nominal
charge (and often free), but the costs of doing so sent the company into a
downwards spiral that was arrested only when it was taken over by
Audi/Volkswagen.
Conclusion
The Ro 80 remains one of the few really brave cars
launched by any car company in the world. (Arguably, it took until 1998 for
Toyota to match the scale of innovation with the Prius.)
Designed from the ground-up for the new-age rotary
engine, the Ro 80 incorporated the very best clean-sheet design aspects that
could be then integrated into a safe and stylish car. Compared with its German
prestige competitors, it was daring; perhaps only the French Citroen went even
further. Perhaps not inconsequentially, Citroen was also working on a rotary
powered car – it also proved a failure.
However, the NSU engineers’ work was not in vain:
many innovations of the Ro 80 were to become mainstream over the next two
decades – but the rotary engine was not one of them.
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