Two hundred and thirty horses per tonne, one wheel short of a full load, a helmet-clad Technical Editor, and a night out on the town is an interesting mix to say the least.

I'll be totally honest and confess three wheelers have never floated my boat. To be blunt, I'm bleedin’ terrified of the damn things, and I have a right to be. It's all my father’s fault. In his wisdom he decided to relive his youth and restore a Morgan three wheeler: a 1934 Matchless powered Super Sports to be precise, but that's of no consequence. The important thing to remember is it has three wheels, very thin ones at that. The only saving grace, I’m reliably informed, is it sports the superior configuration of two up front and one at the back. Turn the clock back fifteen years and imagine my 6 foot plus frame sitting alongside my father in the incredibly cramped cockpit for the very first time. Listening to the V twin bang away as the Wiltshire countryside swept past was, I must be honest, a pleasant experience in an odd sort of way. ‘Nostalgic’ is probably a more accurate description. Other road users were obviously distracted by the bright red machine hurtling towards them; more in bemusement than envy one would expect.

After a few miles my father came out with that unnerving remark, 'OK then, let's see what she can do!' Within seconds the stove-enamelled speedo needle was nudging an unbelievable 70 mph, and as we rounded a rather sharpish off-camber bend the rear wheel hit a manhole cover. The loss in traction was immediately apparent due to the rise in revs and more alarmingly the Morgan’s ass end traversing sideways across the asphalt! I’m not talking about an inch or two here. The damn thing slid so far, my left arm became acquainted with the hedgerow. A rather prickly one at that. My life flashed before me as my peripheral vision was occupied by my father frantically sawing on the 24 inch steering wheel to regain control. After gathering everything up (to his credit he did a bleedin’ good job of it) he glanced over with a wry smile and calmly said ….. “Now that's three wheeler motoring for you!” Suffice to say from that day on I have not been in a great hurry to passenger or pilot anything with less than four wheels.

With such memories you can imagine my reaction when I was given the opportunity to borrow a Grinnall Scorpion III for the weekend. To put it into context, the ‘III’ signifies the number of wheels. On the one hand I considered it would make an entertaining and informative read for you lot, but on the other, would I live to see my offsprings’ next birthday?

The research

Prior to the big weekend I decided to do a little research to try and allay my fears. Perusal of the manufacturer’s website is always a good place to begin and allows close scrutiny of specification and claimed capabilities.

On first inspection the Grinnall's footprint is alarmingly similar to the Super Sports: two wheels at the front and one at the rear. On further reading this is where the comparison abruptly ends - thank God! Externally the Scorpion's rear sits squarely on 8 inches of sticky Bridgestone Potenza rubber compared to the Mogy's 2 inch pre-war crossply affair, thus an improvement in traction! Under the skin the technology is light years ahead of the single tube structure of the thirties’ classic. Obviously this improves handling. Above all though, the twenty first century variant has some reassuring safety features such as twin roll bars and seatbelts, the latter of which my father regards as dangerous due to the possibility of being trapped in the case of a fire! You can now appreciate my somewhat unorthodox automotive upbringing.

OK, it’s all well and good reading the manufacturer’s claims but three wheels can’t be as stable or capable as four. Or can they?

Putting those demons to rest

The theory involved in chassis design and, more significantly, the choice of utilizing three or four wheels is extremely complex and here is definitely not the place for an in-depth lecture. However, to understand the logic behind the Grinnall’s design and, more importantly, explain its well-documented driving characteristics, a little classroom theory is necessary.

One or two wheels up front: what’s best?

There are obviously two predominant layouts for a three wheeled vehicle:
a) one wheel at the front, two at the rear - examples include the Reliant Robin and trikes (such as the Baron and Boom); and
b) two wheels at the front and one at the rear - examples include the
Blackjack Zero, CV3, Grinnall Scorpion III, JZR, Lomax, Malone ST F-1000, Morgan, Pembleton and Triking.

The obvious preference for ‘b’ is for some very sound engineering reasons. The single wheel upfront layout can suffer badly from oversteer which can be extremely disconcerting and alien to today’s front wheel drive society. Move the single wheel to the rear and the net result is a degree of understeer, arguably far more forgiving and familiar ground for most drivers.

The choice of layout also has a significant effect on a car’s stability during cornering if the driver is simultaneously braking or accelerating. Taking the Reliant Robin and trike brigade first, such designs can become destabilized extremely quickly if you haul on the anchors while negotiating a corner. Conversely, put power on too early while exiting an apex with a Scorpion and there is the possibility of suddenly losing lateral traction at the rear, resulting in a spin.

Comparing these two limitations, layout ‘b’ is considered to be the lesser of two evils. This is because braking forces can be considerably greater than those encountered during acceleration and, therefore, the front wheel layout limitations will be far more noticeable. As for destabilization during acceleration of our single rear wheel layout, this will be considerably less aggressive and is deemed far more controllable (and enjoyable!).

Are three wheelers susceptible to rolling over?

It is common sense to assume all three wheeled cars are more prone to rolling compared to the more traditional four wheel layout. This, in fact, is not necessarily true. What determines the tendency for a car to flip is the height of the centre of gravity and the width of the track (distance between the wheels on the same axle), not the number of wheels. There are many factors influencing a car’s stability, such as suspension and tyres, but for our comparison purposes this relationship can be represented by a very simple equation:

Rollover resistance = A / B

Where:
A = half the track
B = height of centre of gravity above the ground

As you can appreciate, the wider the wheels are apart and the closer the centre of gravity is to the road, the less likely the tendency to roll (increased rollover resistance).

Things are a little more complex in the case of a three wheeled vehicle with no rear track. In such situations an ‘effective’ track is calculated for our variable ‘A’ and is dependent on the fore and aft positions of the centre of gravity. In layman’s terms, the closer the centre of gravity to the two wheeled axle the higher the rollover resistance. This obviously makes the design of a three wheeler extremely challenging, but if executed correctly (as with the Scorpion) the end result can be far more stable than many four wheeled counterparts.

How well can a three wheeler corner?

Believe it or not, a well designed three wheeler can out-corner many conventional high specification sports cars! This is partly due to a term known as ‘yaw response’. Again in layman’s terms, this is how quickly a car can regain its composure after an input to the steering system. The lower this time value the more responsive a car will feel going into a corner. In relative terms a sports car will have a value around half that of a family production car. As for a well designed three wheeler, incredibly this can be almost half that again! This is thanks to the lower mass of three wheeler design (a mere 390 kgs in the case of the Scorpion) and a reduced polar moment of inertia. The end result should be a steering response not too dissimilar to a go-kart!

Technical summary

Well, there you go! A little dry theory, but it seems providing a three wheeler is designed with the necessary engineering prowess it can hold its own. I guess the only thing left is to see if all this theory is reflected in practice. Enter the Scorpion III.

Does practice match theory?

Finished in stunning yellow gel coat it is immediately apparent this Scorpion has been built to a high standard. Walking around the car, there is little to indicate the former owner’s hours of enjoyment behind the wheel. The modern styling definitely works and in my opinion is rather more appealing than a classic Morgan look-a-like. Probably the best view, for me, is the rear: the massive 8 inch tyre commands the scene as the stainless silencer lurks ominously to one side. On closer inspection you can identify the BMW driveshaft, but the rear billet alloy wheel is definitely not of bike origin. As with all Grinnalls, the BMW K-series touring motorbike is the willing donor vehicle and, in this case, the 8 valve 1,000 cc straight 4 unit is nestled amidships. Even though this is the least powerful of the engine family it still produces a respectable 200 bhp per tonne. More than enough to have some healthy fun!

Up front the oval wishbones are simply delectable and the tig welding is some of the best I have seen. The springs and dampers are nowhere to be seen as they are neatly mounted inboard. The installation therefore looks compact and purposeful and the drag coefficient is also reduced. If anything, the Scorpion III’s external presentation is sublimely uncluttered and purposeful, a perfect combination.

Moving to the interior the minimalist theme continues. No doors. No movable seats. Hardly a switch in sight. Even the handbrake is tucked under the dash. On first sight you wonder how a comfortable sitting position is feasible with just seat swabs attached to the sculpted rear bulkhead. However, the solution is simple. The pedals are mounted on an adjustable rack, with movement actuated by a simple pull of the lever.

Jumping into the cockpit takes a little agility, but the neatly profiled floor gives your left foot superb purchase while you swing your torso into position, a subtle indication of the obvious effort invested in the Grinnall’s design. Adjusting the pedals and adorning the ‘Luke’ harnesses (in that order) offers no challenges and at last I can sit back and survey the view. The lack of doors or sidescreens gives you a slight sense of vulnerability but the front view is intoxicating. The huge sculpted screen, devoid of wipers and demisting clutter, provides an amazing panoramic frontal view while offering sanctuary from the elements (and the odd bug or two) during flight. Sitting deep in the dash is the BMW instrument bezel complete with a prominent LCD gear selector indicator, an absolute ‘must have’ in any bike powered car to avoid the embarrassment of a box full of neutrals or repeated stalling at the lights. (This comes from painful personal experience.)

The miniature gear lever protrudes through the floor and connects to the BMW’s 5 speed sequential gearbox courtesy of a self-centering cable assembly. From neutral, indicated by a green light on the dash, I pull back for first, and then forward four times to climb the gears. It’s a simple process requiring only the slightest pressure on the clutch pedal.

Ignition

Adorning a borrowed Ayrton Senna replica helmet in an attempt to raise my self-confidence, I’m ready for the off. The starting procedure is simplicity itself. Ignition ‘on’ is achieved by turning a conventional key which also disengages the steering lock. Ensuring the box is in neutral I depress the stainless steel starter button mounted on the dash. The 1,000 cc engine responds instantaneously and settles into a 900 rpm idle. Even though my hearing is dulled by the helmet’s internal padding, the urgency of the distinctive BMW exhaust note raises my heart rate. Blipping the throttle winds her into a frenzy within milliseconds thanks to the near zero inertia of the German precision internals.

Piloting the Grinnall

Pushing the gear lever firmly forward is rewarded by a reassuring ‘clunk’ from the transmission. Glancing at the BMW instrument binnacle confirms the selection of first and my weekend of Scorpion ownership commences. Increasing the revs slightly and lifting the clutch rewards with an effortless take off, an astonishing feat when first piloting a bike powered car. This is probably thanks to the Grinnall’s lightness and impressive torque curve rather than my personal competence piloting such a projectile!

As I climb through the gears my senses are rewarded by the intoxicating whine of the BMW powerplant interrupted only by the slight hesitation between cog selections. It is only now I recall the sheer delight of a sequential box. At a flick of the wrist the digital display dances from 3 to 4 to 5 and then back down again as fast-approaching corners demand urgent retardation. No block shifts here, it’s just straight up and down. The brakes are firm and reassuringly powerful, thanks in main to the beefy 280 mm ventilated discs and Girling callipers up front. I struggle to see the need for the option of an AP racing brake upgrade.

With no obvious instability issues and confidence quickly growing, I decide to start pushing the Scorpion hard through the bends. The rewards are mind-blowing. Reaction to steering input is instantaneous, thanks not only to the two and a half turn racing rack but all the effort invested in the chassis and suspension design. With this in mind, I’m wary of applying power too early once exiting a corner, but it does not take long for my driving style to accommodate the idiosyncrasies of this little racer.

All in all the Grinnall is an absolute delight to pilot and I suddenly realise I’m grinning from ear to ear under my bright green and yellow skidlid. Sod the theory, this thing is just great fun! Gaining more and more confidence I decide to locate an isolated piece of tarmac - courtesy of the MOD - to see if that tail would actually break free if pushed to the limit; a rather foolish thought I know, but we all have to make sacrifices in the face of personal discovery. Winding the engine up to a 7000 rpm frenzy, I start performing an anti-clockwise circuit. As the revs climb, there is absolutely no sense of the rear braking away, it is literally glued to the tarmac. But suddenly - and I mean suddenly - the world is turned on its head! Well, not totally, but bleedin’ close. Unbeknown to myself, the dynamics of the design results in nearside wheel lift once on the limit, a most bizarre feeling I assure you, but one which was luckily and easily brought under control by a sudden stab of the steering wheel.

I’m amazed and inspired that such a small car can deliver so much excitement and driver feedback. Settling down a little I plan my route to the nearest city centre (Salisbury) to stimulate some public reaction. Parking the machine in the central market square, I retreat to a nearby bench to give my heart rate a chance to return to double figures and simply observe the reaction of passers by. “What the hell is that thing?” “My God, I bet that’s fun!” “That’s totally mad!” “It’s one of those kit car things, fancy a drive?” At this point I consider it worth intervening, as the hooded youths seem rather struck on the Scorpion in a possessive kind of way. As they see me quickly approaching one shouts “Respect man” and flicks his wrist in that youthful, Ali G manner. The group then retreats to a nearby wooden bench to finish consuming their cans of Fosters.

Adorning my helmet once more, I circle Salisbury’s one-way system trying to locate potential photo locations. Darkness is quickly approaching and a local nightclub seems the perfect backdrop. As you can see, the bouncers are more interested in the totty than the Scorpion. Obviously not your typical Kit-Car magazine readers!

The following day I use the Grinnall extensively and even show my father the capabilities of a twenty first century three wheeler. He is impressed to say the least, but I resist letting him behind the wheel ….. just in case. During my several hundred miles of ownership the car behaves impeccably, and even my wife thinks it looks ‘fun’, a compliment indeed. Most of the automotive machinery I park in our driveway is greeted by a rather different response.

If you are tempted, contact Grinnall Cars on 01299 822862 or visit the website at www.grinnallcars.com.