BSA Ariel 3


Make Model

BSA Ariel 3




Single cylinder, 2-stroke


50 cc  / 3.0 cub in.
Cooling System Ari colled with fan
Compression Ratio 7:1
Carburetor Encarwi S8
Mixture 24:1


Bosch flywheel magneto
Starting Pedal

Max Power

1.3 kW / 1.7 hp @ 5500 rpm
Clutch Plate type automatic


Final Drive Belt
Frame Steel pressing with torsion bars connecting the rear hinging unit

Front Suspension

Single sided tubular fork, suspension provided by rubber in compression

Front Brakes


Rear Brakes

One drum
Wheels 3 x 12 in., interchangeable
Front Rim Pressed steel
Rear Rim Pressed steel

Front Tyre

2 x 12 in

Rear Tyres

2 x 12 in

Fuel Capacity 

2.8 L / 6 US pints

The Ariel-3 was launched with a fanfare from the BSA management, and round condemnation from the motor cycling press, around June 1970. Those who thought that Ariel-3 meant an Ariel version of the Triumph Trident had their hopes cruelly dashed. It was a three-wheeled moped (I had one hell of a job trying to persuade DVLC to issue me a V5 for a three-wheeled moped, and despite sending numerous photos they still insisted that their computer could only recognise two-wheeled moped) with automatic transmission and a novel hingeing system whereby the front could be leant like a conventional two-wheeler, while the back part, containing the engine & transmission unit, sat squarely on the road on its pair of wheels. All wheels were 12 inch diameter and took the same 12 × 2 tyres as the Raleigh Wisp moped. All wheels were interchangeable and a spare could be had as an extra. These pressed steel wheels were fastened to the hubs by three studs, making wheel changing in case of a puncture far easier than with any other moped I can think of.

The engine was a 50cc fan cooled single cylinder two-stroke made by the Dutch Anker concern, fitted with a plate type automatic clutch driving a pulley for a toothed belt which transferred drive via a reduction ratio, to the nearside rear wheel, the reduction being achieved by a final drive chain and sprocket. One unfortunate point about the set up is that it seems that the Anker engine does not seem to have been designed for being fan cooled in an enclosed space, so the cooling fan was fitted outboard of the engine drive pulley and only turned when drive was being transmitted (ie: the vehicle was moving), so heavy traffic work could cause a degree of overheating. The fan was pressed onto its boss and this also tended to work loose, resulting in a lot of rattling but not a lot of cooling. This happened to mine, but it was easily cured with a couple of tack welds. The other end of the crankshaft was fitted with a Bosch flywheel magneto incorporating lighting coils to power the 15 Watt headlight and 6 Watt rear light. Much the same as any other flywheel magneto in design, it did its job reliably and never gave me problems at all. They never provided a rear brake light though, which I feel was a ridiculous omission at such a late date and a stupid way to save a few pence at the expense of safety.

The engine unit in all, was quite a robust motor, giving l.7bhp at 5,500 rpm from its iron barrel 7:1 compression ratio cylinder. Carburation was by an Encarwi S8 feeding the engine via a reed valve situated in the base of the crankcase. Fitted on its curved inlet manifold, the carb' hung out towards the back of the engine cover and in extremely cold weather tended to suffer icing of the jets until the unit got warmed up, when the heat from the close proximity silencer kept it warm enough. The silencer itself was a squarish box across the rear of the unit, discharging at low level, horizontally to the near side (or directly over pedestrians feet and ankles if you happened to be sitting at the kerbside). The engine ran on a two-stroke mix of 24:1 and the six pint fuel tank was situated to the front and above the engine unit at the front of the box covering the whole rear unit, with the fuel filler protruding through the top of the cover. This box cover was mainly a steel pressing, but fitted with white plastic side pieces which formed the outsides to the rear mudguards, the inners being part of the engine bay. An optional extra basket could be had for fitting to the top of the engine cover, but as I quickly found, anything carried in it which was not indestructible, soon suffered terminal damage due to the severe banging and crashing of the rear unit (all unsprung weight) on all but the smoothest of surfaces.

The main chassis/frame unit of the Ariel-3 was a rather neat steel pressing, enclosing both the pedalling gear and the torsion bars connecting the rear hinging unit. It also held the cables to the throttle, choke and rear brake all neatly out of the way. Access to the adjustment and servicing points within this box section was via a small round screw fixed plate at the front on either side and along the top section above the pedals, where a plastic grooved foot strip covered the access slot. Correct adjustment to the two torsion rods within this box was essential for the safe steering of the vehicle.

With a conventional (rigid) tricycle, steering, as for a sidecar outfit, is by turning the handlebars either left or right. However, the Ariel-3 is meant to be ridden by leaning on bends, as for a conventional moped and for this type of riding, turning the bars as well is an unnatural act. Yet, because the Ariel-3 is a tricycle, albeit with the rear part hinged, leaning over on its own is not enough to initiate cornering by itself and it has to be steered as well, and this is done by steering the rear wheels to push the vehicle into a turn. The two torsion rods are adjusted up so that as the front leans further over, the rear wheels steer a tighter turn and provided that the adjustment is correct this all happens smoothly and gives the same results as would be expected with a normal bike. However, with the rods out of adjustment what happens is that when the rider first starts to lean nothing seems to happen and they continue straight on. Panic then sets in and the rider leans further, at which point the slack in the rods gets taken up and the Ariel-3, seemingly with a mind of its own, shoots into the bend far sharper than the rider intended. I feel that it is from Ariel-3s in this state that most of the "dangerous" reports come from. Set up right with the hinging mechanism in good order, there was no real problem and certainly I never worried on that score. Although there was always a feel of initial resistance to banking, more sensed than anything, which although not noticeable if the rider was positive about cornering, might worry someone who approached a corner with trepidation.

At the front end, the front wheel was carried on a single sided tubular fork leg, using trailing link suspension provided by rubber in compression. Front and rear brakes were small drum brakes (on only one of the rear wheels) and although not exceptional, were up to general moped standards of the day. The front mudguard was a plastic moulding, as was the front apron type legshields which formed a mounting for the AC horn and a flat surface for a horizontally mounted forward facing number plate.

The headlight was a single filament (non dipping) unit and the handlebar controls were the cheaply made cycle type, all of which instantly gave "poor quality" impression at first glance. A pity really for quite a lot of the bike was well made, including the very comfortable Denfeld saddle which was far better than those on most mopeds of the day. The whole presentation was typical of the BSA management of the day's approach in building down to a price in such a way that they ruined any chance of the thing being accepted as a serious vehicle rather than an overgrown toy. The plastic front mudguard, legshields and engine compartment side panels were white in all cases but, as far as I am aware (not having seen any other colours) the metal pressings were available in either bright blue, orange or a lightish olive green (mine was blue) and an Ariel-3 motif was in white block letters on a black background on each side of the front legshields together with a stylised version on each of the rear engine compartment side covers.

The Ariel-3 had to be pedalled to start the engine, like many mopeds of the day with that type of automatic clutch. The decompressor which was linked to the twistgrip was used at this stage by rolling the twistgrip back past the tickover/neutral point against spring pressure, this also being the way the engine was stopped. The rider then pedalled away and as soon as the drive took up and spun the engine the twistgrip was opened, the left thumb operated choke lever was pressed and all being well the engine would fire straight away. The choke could then be released almost immediately. Speed was then controlled by the twistgrip and the front and rear brakes, fitted to the right and left handlebars respectively. It was as easy as that. The vehicle could be pedalled as an unpowered cycle, as the moped laws of the day insisted it should, but I wouldn't recommend the practice unless one was fond of masochistic exercises, the engine being disconnected by opening the engine bonnet and sliding the sprung loaded driving sleeve, which is splined to the shaft, away from the driving pulley, so taking the connecting dogs out of engagement - much like some older lawnmowers. Rotating it through ninety degrees while out of engagement, locks it in position - and the reverse of course re-connects the drive.

This new vehicle was intended to be mainly sold in Britain, a country where vast numbers of people are almost paranoid in their worries about what the neighbours (or their assumed peer group) will think of them. People who would rather suffer in some way rather than take a sensible solution which, in their eyes, would cause them to lose face, or dignity, in the eyes of their friends. In such a climate, even the traditional moped has always found it rather hard going in the sales charts, compared with countries like Holland, Belgium, France and Italy. Britain was not the country to launch such an unconventional vehicle and expect large sales. The top management at BSA have often been accused of making the most appaling decisions and it is not difficult to see why. Most were not motor cyclists, some didn't even like bikes, while others were apparently even ashamed to be involved in selling motor cycles. Yet they were quite happy to make big decisions on what they thought motor cyclists and other "ordinary" (unlike themselves) people should accept as transport. Most of these rash decisions could easily have been avoided if the simple move had been taken of removing all directors company cars at development time and letting the directors be the initial market research on their own products instead. Three months travelling into and out of their expensive driveways each day by Ariel-3 would have focussed their minds wonderfully on what "ordinary people" might feel when contemplating a purchase. The company in its own right might still have been with us today.

In summary, the Ariel-3 was not such a badly constructed bike, except for the stupid cheapness already mentioned. As a design exercise it worked quite well and was quite ingenious. However, it was only a partial solution to a mainly imagined problem. It did not, because of its banked front, provide the total stability of a tricycle which someone with a fear of balancing needed. Neither did it provide the precise handling or the ease of management (ie: pushing and lifting it around) of a conventional moped. It was also more complicated and needed precise setting up of the torsion rods. Yet even a company like the mighty Honda was tempted to flirt with the idea (perhaps [heir directors also no longer ride motor cycles) and produced the Stream. Looking quite smart, expensive, comfortable and much more the complete vehicle and less like a toy than the Ariel-3, it also was launched with a lot of self acclaim and again failed to sell.

However, it was much better presented than the Ariel, although, ironically, it was not as engineeringly correct as the Ariel-3 with its rear wheel steering assistance. The market though, for a flexible tricycle, just doesn't seem to exist, and while the public might be interested in technical innovation, when it comes to parting with their money they have other priorities. As for me, the following winter I switched to using my sidecar outfit during the worst of the weather and parted with the Ariel-3 at the end of 1982. Like most others, I enjoyed it as an interesting diversion, but not a lot else. Were I looking for a new form of transport but was a bit worried about a moped only having two wheels, I doubt that the Ariel-3 would have tempted me either.

Article by: Cohn Atkinson