Different Types of Chassis (Cont'l)

Glass-Fiber body
To many sports cars specialists, glass-fiber is a perfect
material. It is lighter than steel and aluminium, easy to be
shaped and rust-proof. Moreover, the most important is that it
is cheap to be produced in small quantity - it needs only
simple tooling and a pair of hands. There are a few
drawbacks, though: 1) Higher tolerence in dimensions leads
to bigger assembly gaps can be seen. This is usually
percieved as lower visual quality compare with steel
monocoque. 2) Image problem. Many people don't like "plastic cars".

Glass-fiber has become a must for British sports car specialists because it is the only way to make small
quantity of cars economically. In 1957, Lotus pioneered Glass-Fiber Monocoque chassis in Elite (see
picture). The whole mechanical stressed structure was made of glass-fiber, which had the advantage of
lightweight and rigidity like today's carbon-fiber monocoque. Engine, transmission and suspensions were
bolted onto the glass-fiber body. As a result, the whole car weighed as light as 660 kg.

However, this radical attempt caused too many problems to Colin Chapman. Since the connecting points
between the glass-fiber body and suspensions / engine required very small tolerances, which was difficult
for glass-fiber, Lotus actually scrapped many out-of-specification body. Others had to be corrected with
intensive care. As a result, every Elite was built in loss. Since then, no any other car tried this idea again.

Today, no matter Lotus, TVR, Marcos, GM's Corvette / Camaro / Firebird, Venturi and more, employ glass-
fiber in non-stressed upper body. In other words, they just act as a beautiful enclosure and provide
aerodynamic efficiency. The stressed chassises are usually backbone, tubular space-frame, aluminium
space-frame or even monocoque.

Advantage: Lightweight. Cheap to be produced in small quantity. Rust-proof.

Disadvantage: Lower visual quality. Unable to act as stressed member.

Who use it ? Lotus, TVR, Marcos, Corvette, Camaro, Firebird ...

Carbon-Fiber Monocoque
Carbon Fiber is the most sophisticated material using in aircrafts, spaceships and racing cars because of
its superior rigidity-to-weight ratio. In the early 80s, FIA established Group B racing category, which
allowed the use of virtually any technology available as long as a minimum of 200 road cars are made. As
a result, road cars featuring Carbon-Fiber body panels started to appear, such as Ferrari 288GTO and
Porsche 959.

There are several Carbon-fibers commonly used in motor industry. Kevlar, which was developed by Du
Pont, offers the highest rigidity-to-weight ratio among them. Because of this, US army's helmets are made
of Kevlar. Kevlar can also be found in the body panels of many exotic cars, although most of them
simultaneously use other kinds of carbon-fiber in even larger amount.

Production process
Carbon-fiber panels are made by growing carbon-fiber sheets (something look like textile) in either side of
an aluminium foil. The foil, which defines the shape of the panel, is sticked with several layers of carbon
fiber sheets impregnated with resin, then cooked in a big oven for 3 hours at 120°C and 90 psi pressure.
After that, the carbon fiber layers will be melted and form a uniformal, rigid body panel.

Carbon-Fiber Panels VS Carbon-Fiber Monocoque Chassis

Porsche 959, employed carbon-fiber

in body panels only, is obviously ....

.... inferior to McLaren F1's carbon-

fiber monocoque. This structure not
only supports the engine / drivetrain
and suspensions, it also serves as
a very rigid survival cell.

Exotic car makers like to tell you their cars employ carbon-fiber in construction. This sounds very
advanced, but you must ask one more question - where is the carbon-fiber used ? Body panels or Chassis
?

Most so-called "supercars" use carbon-fiber in body panels only, such as Porsche 959, Ferrari 288GTO,
Ferrari F40 and even lately, the Porsche 911 GT1. Since body panels do nothing to provide mechanical
strength, the use of carbon fiber over aluminium can barely save weight. The stress member remains to be
the chassis, which is usually in heavier and weaker steel tubular frame.

What really sophisticated is carbon-fiber monocoque chassis, which had only ever appeared in McLaren
F1, Bugatti EB110SS (not EB110GT) and Ferrari F50. It provides superior rigidity yet optimise weight. No
other chassis could be better.

Carbon Fiber Monocoque made its debut in 1981 with McLaren's MP4/1 Formula One racing car, designed
by John Barnard. No wonder McLaren F1 is the first road car to feature it.

Car Body Chassis

Ferrari 288GTO (1985) carbon fiber panels steel tubular space frame
Porsche 959 (1987) carbon fiber panels steel monocoque
Ferrari F40 (1988) carbon fiber panels + doors steel tubular space frame
McLaren F1 (1993) carbon fiber panels carbon fiber monocoque
Ferrari F50 (1996) carbon fiber panels + doors carbon fiber monocoque
Lamborghini Diablo SV mostly aluminium panels, with
steel tubular space frame
(1998) carbon fiber bonnet + engine lid
Lamborghini Diablo GT mostly carbon fiber panels +
steel tubular space frame
(1999) aluminium doors

Engine act as stressed member - Ferrari F50

Unlike McLaren F1, Ferrari F50's rear

suspensions are directly bonded to
the engine / gearbox assembly. This
means the engine becomes the
stressed member which supports the
load from rear axle. Then, the whole
engine / gearbox / rear suspensions
structure is bonded into the carbon
fiber chassis through light alloy. This
is a first for a road car.

Advantage: lighter still.

Disadvantage: engine's vibration

directly transfers to the body and
cockpit.

In 1963, a revolutionary chassis structure appeared in Formula One, that is, the championship-winning
Lotus 25. Once again, that was innovated by Colin Chapman. Chapman used the engine / gearbox as
mounting points for rear suspensions in order to reduce the width of his car as well as to reduce weight. In
particular, reduced width led to lower aerodynamic drag. Of course, the engine / chassis must be made
stiffer to cope with the additional stressed from rear axle. Today, F1 cars still use this basic structure.

Characteristics of carbon-fiber monocoque:

Advantage: The lightest and stiffest chassis.

Disadvantage: By far the most expensive.

Who use it ? McLaren F1, Bugatti EB110SS, Ferrari F50.

Aluminium Space Frame

Audi ASF
Audi A8 is the first mass production car featuring Aluminium Space Frame chassis. Developed in
conjunction with US aluminium maker Alcoa, ASF is intended to replace conventional steel monocoque
mainly for the benefit of lightness. Audi claimed A8's ASF is 40% lighter yet 40% stiffer than contemporary
steel monocoque. This enable the 4WD-equipped A8 to be lighter than BMW 740i.
 ASF consists of extruded aluminum sections, vacuum die cast
components and aluminum sheets of different thicknesses.
They all are made of high-strength aluminium alloy. At the
highly stressed corners and joints, extruded sections are
connected by complex aluminum die casting (nodes). Besides,
new fastening methods were developed to join the body parts
together. It's quite complex and production cost is far higher
than steel monocoque.

The Audi A2 employed the second generation of ASF technology, which involves larger but fewer frames,
hence fewer nodes and requires fewer welding. Laser welding is also extensively used in the bonding. All
these helped reducing the production cost to the extent that the cheap A2 can afford it.

Advantage: Lighter than steel monocoque. As space efficient as it.

Disadvantage: Still expensive for mass production

Who use it ? Audi

Lotus Elise

Elise's revolutionary chassis is made of

extruded aluminium sections joined by glue and
rivets. New technology can make the extruded
parts curvy, as seen in the side members. This
allow large part to be made in single piece, thus
save bonding and weight.

To Lotus and other low-volume sports car makers, Audi's ASF technology is actually infeasible because it
requires big pressing machines. But there is an alternative: extruding. Extrusion dies are very cheap, yet
they can make extruded aluminium in any thickness. The question is: how to bond the extruded parts
together to form a rigid chassis ?

Renault Sport Spider bonds them by spot welding, while Lotus Elise uses glue and rivet to do so.
Comparing their specification and you will know how superior the Elise is:

Renault Sport Spider Lotus Elise

Weight of chassis 80 kg 65 kg
Torsional stiffness 10,000 Nm/degree 11,000 Nm/degree
Thickness of extrusion 3 mm 1.5 mm

Lotus's technology was originated by its supplier, Hydro Aluminium of Denmark. Hydro discovered that
aluminium extrusion can be bonded by epoxy resin (glue) if it is adequately prepared by a special chemical
in the bonding surface. Surprisingly, glue can bond the sections together strongly and reliably. Most
important, the aluminium extruded sections can be made much thinner than traditional welding technique.
Why ? because welded joints are weak, so the thickness of material should be increased throughout a
member just to make a joint strong enough. Therefore Elise's chassis could be lighter yet stiffer.
 Glue can be clearly seen during
production.

Unquestionably, Lotus Elise's aluminium chassis is a revolution. I expect to see more British specialty
cars to go this way.

Advantage: Cheap for low-volume production. Offers the highest rigidity-to-weight ratio
besides carbon fiber monocoque.

Disadvantage: Not very space efficient; High door sill.

Who use it ? Lotus Elise, forthcoming Lotus M250, Opel Speedster

Copyright© 1998-2000 by Mark Wan

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