The SUB G1 - 135hp 1000cc V-twin three-wheeler
March 18, 2006 For those who have looked enviously at three wheeled prototypes such as the Volkswagen’s GX3, Heikki Naulapaa's Aprilia Magnet, Tommy Forsgren's Hermes, Elisha Wetherhorn's Rider, Mercedes-Benz Life-Jet , Peugeot’s 20CUP, Toyota’s I-Swing, Dimitrios Scoutas' Skipee and the Phiaro Eternity, here’s one you can buy and use on the road. Powered by 1000cc of liquid-cooled DOHC, eight-valve, V-twin Suzuki motorcycle engine producing 135hp (98.6 kW) and 105 Nm of torque driving through a six-speed sequential gearbox, the SUB G1 three-wheeler weighs just 330kg, giving it Formula car power-to-weight, handling and aerodynamics. Set up by ex-GM automotive designers Niki Smart, Jay Brett and Nick Mynott, SUB is a small company in southern California that caters to clients who want individual specialised vehicles. Initial production preparations for the SUB G1 are underway and will be limited to a maximum of 25 units, with a minimum of 15 to start production. Cost of each vehicle will be US$80,000 with a US$25,000 security deposit.
So far, three SUB G1s have been built, with two in Southern California and the third located in dry storage in England. “The project spawned from wanting to build something for ourselves that we could keep, use and showcase the range of our abilities,” says SUB’s Jay Brett. “That was simply said, and the project took nearly three years to complete the first three vehicles, where as we had intended to take only a year and a half.
“The two that are in California are fully licensed and streetable as motorcycles. They have covered nearly 5,000 miles and make heads turn big and small, young and old, male and female. Buoyed by the level of public enquiry, we are now testing the waters for a very limited production and possibly a revised second version.
“The SUB's are very quick and highly responsive. The steering has a 1:1, lock to lock, ratio. This is very effective for canyon roads and track testing. We intend to experiment with different ratios to reduce the super quick steering input responses. The vehicles are then registered as “special construction motorcycles”.
“The vehicle feels big, as you get accustomed to the cockpit. There is quite a bit of noise, as you are sitting alongside the engine. Driving on the road you are smaller than most cars and much lower to the ground. You feel like a racecar driver as it has Superbike-like quickness and formula car handling. There is an awareness you also must have of your surroundings, much like a motorcyclist, in that you have to predict and judge your environment, other cars and trucks, road surface conditions, as well as distracted onlookers. It all combines to create an unbelievably fun, unique, and visceral experience.”
The first vehicle, the SUB G1 is an evolution of work done by Niki Smart years several years ago entitled 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.
Building the prototypes
Each individual brought a complementary skill set to the project. Smart is a designer, and fabricator whose résumé includes work on the Aston Martin Vantage concept and the ultra-light weight Ariel Atom sports car. Brett's background of Industrial design and his ten-year involvement in film and automotive concept vehicle construction lends the project his expertise in fabrication and program management. Mynott, a digital modeller, has an extensive background in automotive, product design and engineering and has worked on the construction of 6 concept and race vehicles within the last 4 years. The combination produced the expertise in design, modelling and build required for the project, the overlapping skills creating an effective team.
Advanced 3D surfacing software was used to model the entire car from the ground up. From initial suspension geometry in wire frame to the completed wishbones uprights and wheel arches, all modelled and animated through its full range of motion. The computer enabled the team to design, refine and simplify each component, reduce costs and simplify assembly all before committing to production. In it's element as a tool for building and checking interference, fit and assembly the computer was used to speed production, reduce errors and produce a higher quality at a reduced costs to the team. Throughout the build phase, modifications were updated in data and the physical models continually checked against the digital model to ensure tolerances were met.
Co-ordinate geometry machines and white light scans ensured that all the space available was utilized to best effect, giving a finished product that is tightly packaged, of minimum weight and has a formula feel. Once surfaced and highlighted, the body tools were CNC cut to produce highly accurate low cost re-usable moulds. A complete cross section of tooling from plaster, foam and clay to composite epoxy and even rapid prototype parts were used. Composite parts were oven cured before being finished and painted. Great importance was given to materials and finishes, from the powder coated two piece custom made forged wheels to the black phosphate finish of the steel bolts that hold the aluminium alloy uprights together. Everything was given the same degree of consideration and importance to ensure a coherent high quality finish. The result is three fully functioning road legal custom built vehicles that were delivered on time, on budget and to a very high quality. Vehicles that have s ince driven over 1000 miles each with only suspension and spring rates needed to be dialled in.
What's it like to drive?
The three cars are each individually fitted to the customers with custom seats and floor mounted pedals positioned to cater to their range in size; from 6 foot 8inches tall, to 5 foot 10 inches. The car uses a modified motorcycle wiring loom and the gauge pack is carried through as well, with everything functioning including the fuel level meter. The indicators and lights are positioned around the gauge pack within easy fingertip reach without having to take our hands off the wheel. Each car is fitted with a four point anti-submarining harness and uses a cut off Momo steering wheel for better gauge visibility. The cockpit walls are high giving the formula car feel while rear visibility is good due to the positioning of the mirrors. The gear stick is mounted close to the steering wheel on the firewall that separates the driver from the engine which maintains the 6 speed sequential box form the TL1000R.
The steering is quick with one complete turn for lock to lock. The brakes are strong and progressive giving good feedback. Driving on the road you are smaller than most cars and much lower to the ground. You feel like a race car driver because it has super bike-like speed and formula car handling. The ability to see the wheels further enhances the formula feel of the vehicle with the ability to place the wheels right on the curbs through corners. It all combines to create an unbelievably fun and unique experience.