Sideways on a tilting 4-wheeler: the next generation of fun machines
By Loz Blain
May 7, 2009
If the fun we had aboard Piaggio's MP3 is any indication, motorcycles with more than two wheels have a big future ahead of them. The additional stability and traction you get from a tilting three-wheeler is quite an eye-opener, and they're still exceptionally fun to ride. If you want to take the concept one step further, though, an extra wheel at the back as well can actually make the entire bike narrower while delivering the sort of stability that can let you safely powerslide and drift all four wheels on an oily skidpan. Remember Yamaha's wild and wonderful Tesseract concept from 2007? The company is keen to get one into production, but as it turns out, Yamaha has run into trouble with patents held by an ex-courier and motorcycle safety advocate from the UK who has been working on a road-ready tilting 4-wheeler for more than 20 years.
Nick Shotter was a London motorcycle courier - and therefore, it's fair to suggest, a complete nutter. The task of forcing a motorcycle through London's choking traffic, racing the clock in the cold, wet UK winter is only attractive to hoons and lunatics, and those who do it for any length of time know that accidents and injuries are very difficult to avoid.
It was an accident that got Shotter thinking about how motorcycles could be made safer, while still being narrow enough to lane-split through traffic. In 1989 he started the design process for his "4MC" tilting 4-wheeler project.
His design finalized, he began shopping the concept around to all the major manufacturers in 2002 - and has spent the last five years building up the home-made, rideable prototype you see in the photos and videos here.
A triangle base platform like that featured on the Piaggio MP3 can deliver amazing rider feel and huge front-end stability up to 40-degree lean angles, by which point you're leaving a fair bit of nice Italian paint on the ground and giggling like a schoolgirl. But if the center of gravity goes outside the triangle described by the wheelbase at a standstill, the MP3 simpy falls over - as many new riders who forget to put their feet down at the lights have been discovering.
The extra fourth wheel on the 4MC prototype gives a much broader balance range for the bike's center of gravity - so it's happy to sit at full lean at a standstill OR when being belted around a tight corner.
As the lean angle increases, the wheels move slightly further apart, increasing stability when you really need it - and this works as a backup system when you park the bike and leave it on an angle - the tires grip and prevent the bike from tilting any further.
Steering is handled by a pair of upwardly looping front suspension arms, which allow a nice tight turning circle. Like a bike, you'll countersteer the 4MC into corners - and the combination of leaning into the corners while having the stability and grip of 4 wheels means that the 4MC will use its grip much more effectively than a car can. A sporty tilting 4-wheeler could end up being exceptionally fast in the twisty stuff.
Shotter has built in a clever hydraulic anti-tilt system to keep the 4MC relevant to city use as well. At slow speeds, the rider can engage the anti-tilt system to let them creep along at very slow speeds, fully balanced and without needing to put a foot down.
When the system is engaged, the suspension dampers in the right and left arms at each end of the bike are connected through an oil valve, forcing the left and right arms to move together.
Despite the additional wheels, the 4MC is exceptionally narrow, with a width of 58cm, or 66cm if you count the handlebars. Honda's CB600 Hornet, for comparison, is 74.5cm wide. Admittedly, the 4MC doesn't yet have mirrors, but it should be absolutely fine for lane-splitting and traffic-busting.
The tilt lock's obviously also useful when parking - no side stands here. Just pull the park brake lever, which locks the brakes and the suspension at whatever angle the bike's already sitting at.
The 4MC Prototype
Shotter has put over 4 years and a bucketload of effort into the prototype shown in the photos and video here. Built purely as a proof of concept, it doesn't carry road gear like lights, fairings, mudguards and indicators.
The prototype 4MC is designed to demonstrate of the tilting 4-wheeler platform and as such it does an excellent job, as the video below will attest. It uses a Yamaha YP400 engine - but ideally the 4MC will be developed around a purpose-built engine. Shotter has had to build a heavy custom frame around the prototype, but in a production setting he believes the engine should be designed such that the leading and trailing suspension arms bolt directly to the motor, so the frame can be ditched altogether.
With a custom-designed engine, the production version could weigh as little as 160-200kg dry, depending on engine size.
The prototype's fuel tank has been placed between the two rear wheels to make the operation of the front wheels, suspension and steering arms more visible. In a production setting, the tank would be relocated up front.
The prototype also allows a wide range of suspension and chassis adjustments which would be unnecessary on most production models.
But Will It Sell?
The 4MC is a highly non-traditional motorcycle concept, and as such, it'll have serious difficulties breaking into the conservative motorcycle market. Having said that, the Piaggio MP3 and Gilera Fuoco are making considerable headway for such a radical idea. The simple fact is that even the most hardened biker, after five minutes in the saddle, can't deny how much fun they are to ride.
The 4MC will be equally hilarious on the road, but even more stable, and potentially more performance-oriented - a mixture that, as a confirmed hooligan, I find very attractive. Take a look at the oiled skidpan test video below and tell me you wouldn't love to fang a 1000cc version of that puppy to and from work on a wet day.
Yamaha announced its Tesseract concept in late 2007, but it has stalled before reaching production, because its design was so close to Shotter's that the company will have to license Shotter's intellectual property if it wants to go into production. The man's clearly onto something that could be a ridiculous amount of fun. Here's hoping Yamaha or one of the other majors manages to run with it and get a performance version to market.
More about the system and the prototype at the 4MC website.