SUB G1
April 2005
Introduction
Set up by three individuals Niki Smart, Jay Brett and Nick Mynott, SUB is a small company in southern California that caters to clients who want individual specialised vehicles. Their first vehicle, G1 a three wheeler is an evolution of work done by Niki Smart years earlier on the "One-up" that sat in London's' Millennium dome. G1 is a ground up build, demonstrating the company’s ability to produce, not just one, but a series of fully functioning, innovatively packaged vehicles that are road legal and that could be used in a day to day scenario as well as being pushed hard on a track.
The original One-up concept was 'An Engineering Aesthetic'. The project was about the design beauty that purely engineered forms posses from their focus on performance and efficiency. Smart looked a lot at castings and fabricated suspension parts as well as WW2 battleships and especially submarines. The idea was to be as minimal, without being a bike: one seat, three wheels and a small engine. His original used a 600cc Honda CBR located behind the driver. The resulting longer wheelbase (2.7m) made for a rear biased weight distribution. The track was 1.6m. While similar in concept, G1 makes use of a tight packaged V-twin to reduce the wheelbase to 2.3m (same 1.6m track) and to achieve a 50/50 weight distribution. The 50% on the rear wheel and 25% on each front creates a dynamic, stable platform.
A major aspect of the project was to design and build a vehicle with aesthetic appeal - a single seat, lightweight, high performance machine ideal for quick runs through canyons. The project was never about straight-line speed or acceleration. More important was to create a vehicle that handles predictably and controllably and is engaging and fun to drive, while keeping the project within a manageable budget and time frame.
So Why Three Wheels?
Even the sportiest of cars on the market seem unnecessarily big with much unused volume and weight. If you spend the vast sums of money that most exotic performance cars cost, the last thing that you want when pursuing the ultimate performance and efficiency is to put your friend next to you, destroying your power to weight ratio and upsetting the balance of the car. The idea of a single seater seems logical for the ultimate in performance, even for the road.
In the automotive world, the notion of using three wheels where four would do is often received with wonder and mistrust. It's usually employed as a sales pitch for vehicles that are generally odd or dubiously functional. The discussions for and against are largely based on issues of visual and dynamic stability, with the thinking that there is something missing (usually the forth wheel). The aim of this project was not only to build a vehicle that overcomes some of the stigmas of three wheeled vehicles, but to surpass them and to exploit their advantages in an exciting and desirable product.
Some points of the project philosophy:
* The cornerstone of the project was to balance the weight of the engine with the weight of the driver. The new package allows the vehicles to achieve a weight distribution of 25% on each front wheel and 50% on the rear.
* A low centre of gravity and minimal polar moment of inertia provide a stable but agile vehicle. Both recreational and sports driving will benefit from its responsiveness and nimbleness and it does not need power assisted steering or braking; so improving feel and reducing component complexity.
* Quick steering response is a by-product of reduced mass and low polar moment of inertia, not on the number of wheels or how they are configured. A typical three-wheeler is lighter and has approximately 30% less polar moment than a comparable four wheel design. The yaw response time is the time taken to reach steady-state cornering after a quick steering input. This is around 0.30 seconds for a softly sprung four-wheeler. Four wheel sports cars will respond in about half that time. For a well designed three-wheeler, it's as little as 0.10 seconds, which is a third less than a high-performance four wheel car's typical 0.15 seconds.
* A benefit of using three wheels is to qualify the vehicle as a motorcycle and not a car, provided that the gross weight falls under 1500lbs.
* Consequently the vehicle does not have to comply with the level of legislation that a car has to. This typically means registration and road taxation.
* As a motorcycle the vehicle can travel in the car pool lane on freeways, even with just one person.
By using a 1000cc-motorcycle engine, efficiency is ensured (40 to 50mpg); because of the light, compact engine and gearbox, and because the unit has been specifically designed to propel a small mass as opposed to the engine and drive train in a conventional car designed to propel an average mass of 3000lbs.
A major surprise is the use of motorcycle tires. This was to get the right tire contact patch area distribution as well as weight distribution, with minimum tire frontal area and rolling resistance. As the Morgan three wheeler demonstrated, you can attain high cornering speeds on narrow tires. While it was easy to find a rear tire with the required contact patch it was difficult to find front ones. However Avon builds a tire for the cruising market where they have widened the tire by splitting the conventional tire down the centre and added a spacer. Available in a choice of widths, the Avon’s have the desired contact patch and are designed and built for the weight of the vehicle. They have low rolling resistance and frontal area, to aid overall efficiency, and lend the vehicle a unique aesthetic quality.
The low centre of gravity makes life easy for the suspension. Long double wishbones at the front act through pushrods to inboard spring-shock units. At the rear, twin trailing arms act through a pushrod to a transverse mounted spring-shock unit. In such a light vehicle using rose joints throughout and needle bearings in the rockers minimizes suspension stiction. With a single tire at the rear, the front suspension system controls all of the roll. To minimize pitch under acceleration and braking, the front and rear geometry has a low, central, instantaneous pitch centre. This geometry also increases chain life by eliminating chain snatch.