This odd-looking creation could be the start of something massive – it's the first prototype of an entirely new design of leaning four-wheeled bike which not only offers a massive increase in safety but, should it reach production, will be legal for anyone holding a car driving licence to use without taking an extra test – all while keeping the cheap road tax, good fuel economy and exemption from congestion charging that goes hand in hand with bike ownership.

This odd-looking creation could be the start of something massive – it's the first prototype of an entirely new design of leaning four-wheeled bike which not only offers a massive increase in safety but, should it reach production, will be legal for anyone holding a car driving licence to use without taking an extra test – all while keeping the cheap road tax, good fuel economy and exemption from congestion charging that goes hand in hand with bike ownership. Following on from our first glimpse of the 4MC, Ben Purvis takes a closer look at the development of this remarkable machine and talks to inventor Nick Shotter about the 20-year obsession that led to its creation.

Think about it for a minute. In the UK alone, there are around 30 million car licence holders, compared to two million with bike licences. If just 0.0001 percent of those drivers – one in 10,000 – decided to buy such a vehicle in one year, it would instantly become the country's best-selling bike. That's a big pot of gold at the end of this particular rainbow and with that perspective inventor Nick Shotter's obsession the concept, which has seen him give up everything in pursuit of getting this prototype running, seems rather less crazy.

What is it?

Neither a bike nor a car, the 4MC is currently only a prototype designed to prove the concept of Shotter's leaning suspension ideas. However, should something reach production using the same ideas it would be classed as a tricycle according to European legislation– a long-ignored category that sits somewhere in between the two. But with controls like a bike, similar width to a two-wheeler and the ability to lean around corners, to all intents and purposes it's a motorcycle in all but name. But since it falls into the virtually forgotten B1 licence category – which is automatically granted to anyone passing their car driving test in Europe – it's a bike that can be ridden by virtually anyone.

What's so clever about it?

While Piaggio's MP3 has now started to get us used to the idea of a leaning trike, Shotter's concept holds several key advantages thanks to the unique suspension design that's the subject of his patents.

Compared to the MP3, there are two key differences. First is the number of wheels. Despite being narrower than an MP3, the addition of another back wheel adds a massive amount of extra stability. Shotter says: “Imagine you have a triangle linking the three wheels. Halfway along the bike's length, where the center of gravity is, the two lines linking the front and rear wheels are only half as far apart as they are at the front wheels. The center of gravity only needs to move outside these lines for the bike to fall over.”

With four wheels, those imaginary lines are parallel, and just as wide where the bike's center of gravity is as they are at the front, giving greater stability. Shotter said: “I've even tried locking my bike at full lean in one direction, and then riding in a circle the other way, so I'm leaning out of the direction of travel. It feels weird, but it didn't fall over.”

The other key advantage of Shotter's prototype is its low center of gravity. By using leading arms at the front and trailing arms at the back, compared to the Piaggio set up which is like two conventional scooter monoforks attached above the front wheels to a pair of tilting beams, Shotter's machine has all its suspension mounted as low down as possible, keeping the center of gravity very low. Again, that means it can lean further before tipping over. Horizontally-mounted shocks, with the front spring above then engine and the rear below on the prototype, are each attached to a “balance beam” - a transverse linkage that is connected to a wheel at either end via a pushrod. The beam allows each wheel to move independently, while sharing its spring with the other wheel on the other side of the bike.

Cleverly, each wheel has its own damper, but they are interlinked. In normal use, the operate independently, but at the flick of a switch valves re-route the damping oil to connect each pair of dampers. The result is when one damper compresses, the oil above the piston inside is routed to the area below the piston on the damper opposite, forcing it to move in the same direction. This basically locks the two wheels together, so the bike can no longer tilt. As well as being far lighter than the Piaggio solution to this problem, which uses a brake on the tilting axis to prevent leaning, Shotter reckons he will even be able to add a form of stability control to his design, using a fast moving valve, like that in an ABS brake system, to quickly alternate between the free-moving and locked damper positions when sensors register a slide that is leading to the bike tilting too fast.

Yet more advantages come from the 4MC's trailing/leading arm suspension thanks to its geometry. As it tilts, the track actually becomes wider, increasing stability and also incorporating an added safety measure, as even if the suspension isn't locked, at a standstill the tires would need to move away from each other to allow the bike to tip over. The arm set-up also means that as the bike leans, the wheelbase becomes shorter, with the suspension on one side dropping and the other rising, improving the cornering while maintaining straight line stability.

Even in the event of a puncture, the bike is designed to remain safe and stable, the steering geometry designed so, say, the left front tire blows, its extra drag will make the wheel try to turn to the right, canceling out the tendency for the whole machine to dive off in the direction of the blown tire. In tests with a deflated tire, the machine still tracks straight and can be steered normally.

While the extra wheels offer a grip and stability advantage compared to conventional bikes, the leaning ability means it actually uses that grip better than a car can manage. When a normal four-wheeler corner, the weight is transferred to the two outside wheels thanks to centrifugal force. But by leaning, the 4MC keeps the pressure even on all four wheels in corners as well as on straights, using the maximum potential grip of all the tyres at all times. The same applies on cambers and over bumps, again times where a non-leaning four-wheeler's centre of gravity will be moved away from the middle.

The Prototype

There's one thing Shotter is quite clear about: whatever form the 4MC reaches production, it won't look much like the prototype.

Designed around a Yamaha YP 400 engine and transmission, the prototype has been developed to include endless levels of adjustment, so the geometry of the suspension can be tweaked and altered. On a production version, this wouldn't be necessary. And nor would the frame. Shotter envisions a bike with a purpose-made engine that doubles as the main chassis part, with the leading and trailing arm suspension simply bolted directly to it . “Using the Yamaha engine meant I had to build a frame,” he said, “So this prototype is much heavier and longer that it really needs to be. Built around its own engine, the bike could be 70kg lighter at around 200kg for a 400cc, or as little as 160kg for a 125cc, as well as being six to eight inches shorter. But all I am intending to do is prove my suspension ideas work, and for that, this prototype does the job.”

To demonstrate how much could be stripped off the bike in production form, Shotter has painted all the parts that wouldn't be there on a production machine in blue.

The Tesseract connection

During the 4MC's development Yamaha has been quickest to offer help and support with the project – supplying the prototype's YP400 engine at “a very special price” and, according to Shotter, showing the most interest of all the manufacturers he has so far approached.

Intriguingly, while Yamaha has not made an approach to actually buy the design, its Tesseract concept bike – a leaning four-wheeled superbike revealed at the Tokyo show in October 2007 – uses a remarkably similar design, complete with leading and trailing arm suspension with similar linkages to Shotter's machine. And it came long after Shotter's designs were revealed to the company.

According to Shotter, attempts by Yamaha to patent the Tesseract's suspension system have been knocked back by the European Patent Office because they are too similar to the patents he has already filed. And since the Tesseract was shown, rumors from Yamaha suggest the firm is now working on a scooter-style machine with leaning four-wheeled suspension.

The rivals...

Shotter's belief that a tilting machine available to car drivers will be a huge hit should be proved one way or another this year with the introduction of Piaggio's MP3 LT.

Although in appearance identical to the stock MP3, the new LT features one key difference; its front wheels are a couple of inches further apart. And that extra width means it's no longer registered as a motorcycle, with the need for a suitable licence, but as a quadricycle that can be ridden using a car licence, regardless of engine size and with no need for a CBT or L-plates.

And rather than being a problem for Shotter, the MP3 LT could be just the thing he needs to get his project off the ground. If it's a success – and with 30,000 normal MP3s already sold and the LT reaching a far bigger audience there's no reason to expect it to be anything else – other bike makers are likely to sit up and take notice. And in the rush to get a competitor on the market, what could be better than buying the rights to a design that's already been done.

Even if manufacturers try to go it alone and design their own takes on the idea, they are likely to struggle when it comes to designing a leaning system that's effective and different enough to Shotter's design to avoid having to pay royalties on his patents.

How the 4MC was made

“Why don't they do it like that?” It's a question we've all asked before; the sudden moment of clarity that gives you an insight into how some everyday item could be improved. For most of us it's an idle, passing thought. We assume our idea has already been thought of and dismissed by others far more qualified. But for Nick Shotter just such a moment has turned into a 20-year labour of love in the pursuit of turning his concept into a marketable reality.

The moment came when Shotter, an engineer, was working as a bike courier in London to earn some extra cash. A small off back in 1989 saw him out of action with a broken hand, and got him thinking – how could he keep the traffic beating ability of a bike but massively cut the risk?

“It was when I was stuck in traffic driving a van and motorcycle couriers were going past me,” he said, “It dawned on me again how great bikes are through traffic, and got me thinking about how to make bikes safer.”

And long before the MP3 was even a twinkle in Piaggio's corporate eye he came to the conclusion that more wheels meant more safety, and a narrow, leaning machine with more than two wheels would be the ideal solution. Little did he know then that the idea would lead to him working full time for eight and a half years on creating his 4mc and prototype, with no income and just the hope that eventually a major firm would have the same vision and be prepared to pay handsomely for the rights to use the ideas he's developed.

“It started as a hobby, really,” he said, “My first thoughts were about how to get more rubber on the road, and I quickly realised the whole thing had to lean, so the answer was to have four thin wheels.

“For the first eleven years I didn't tell a soul. I was working at home, spending every spare moment on it, and when I won a Government Smart Award in 2000 I went full time on it. I thoroughly researched the patents on the subject, and there were none like this. Patents are crucial, because at the end of the day, that's what I'll be selling.

“There's been no pay coming back at all during that time. Eight and a half years. That's the equivalent of around £224,000 in lost wages alone, and on top of that we put in another £87,000 from me and my family, and around £81,000 has come from others, including the £36,000 Smart award and even £10,000 from a guy who just wanted to help. That's £392,000 it's cost so far, coming from me, my family and investors.

“When I got married five years ago we looked at our finances and realized that either the project had to go or the mortgage had to go. And even if we'd sold the house we'd still have had to find money to rent somewhere else, so that wouldn't have helped. So I started looking for cheap accommodation, so we could let our house out rather than abandon the project. My wife was all for it, saying 'if you don't do it, and then someone else does, you will always regret not doing it.'”

“So we looked at the alternatives, and found out about house-sitting. We found a couple who wanted to go to the Bahamas for two and a half years, and we took over their house. That meant we could let our house, and put the money into the project instead, . Then there's the workshop I used, where the owner said that rather than charging me an hourly rate, he would accrue the hours, and I could pay him when I make money by selling the intellectual property in the designs. I spent nearly 4000 hours in that workshop.”

The effort that's gone into the prototype is simple staggering. The front wheels alone accounted for some 300 hours of work, machining them from solid blocks of alloy to accommodate the bike's rim-mounted disc brakes. Shotter even made the front brake discs and calipers himself.

Now, more than twenty years on from the original spark, the prototype of his machine has finally been completed and undergone its first tests, and as the only man to have ridden it so far, Shotter is finally convinced that he's been right all along – the prototype offering more stability than even an MP3 can muster while remaining as narrow as a conventional bike.

For more information, see: 4MC.

Ben Purvis

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