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For obvious reasons, the steering system of a kart is rather
important. All too often the components connecting the steering
wheel to the front tyres - their condition, how they are fitted
together and their alignment - don't receive the amount of
attention they should. Apart from dangerous consequences of
component failure, poor front-end alignment also costs speed
down the straight AND through the corners, and can also lead to
excessive tyre wear.
Try this:
Inflate your tyres to race pressure. remove the chain (unless
it's a Rotax or Leopard - they've got a clutch). Put the kart on
a smooth concrete or asphalt surface, and install a driver. With
the steering straight, push it along. If all wheel bearings are
in good condition, the kart should easily roll forward, and keep
rolling some distance. Give it another push, but this time have
the driver hold a little bit of lock on the steering. Notice how
much more difficult it is to get the kart mobile, and how
quickly it comes to a stop? A number of factors contribute to
this, but it amply demonstrates the point that as soon as a tiny
bit of steering angle is introduced, the increase in rolling
resistance (drag) is dramatic. For this reason, a poorly aligned
chassis will be slow, and it doesn't take much work to get the
lost speed back.
To start with,
we need to acquaint you with some terms that are used in this
article. If a component has a proper name, we will use it.
STUB AXLE:
The stub axle is the pivoting member that includes the front
axle and steering arm. Two different stub axle configurations
are in common use today. If the pivot bearings are carried in
the stub axle (such as Tony Kart, Arrow, Monaco, CRG, etc), it
is called a 'male' stub axle. If the bearings are carried in the
chassis (eg Azzuro, Monza, earlier OCR and Swiss Hutless), it is
a female stub axle. There are point in favour of each design,
and we will discuss these later on.
STEERING
ARM:
The steering arm is the arm projecting rearwards from the stub
axle, to which the tie rods attach. These are usually angled inwards
in order to give an amount of Ackerman geometry.
PITMAN
ARM:
The pitman arm is the correct name for the lever, which
protrudes from the steering column, and to which are connected the
tie rods. The pitman arm may be a simple straight arm, a triangular
bracket or a combination of both. This 'belt and braces' approach
should tell you that even the kart designers are not fully convinced
which design is better.
TIE
RODS:
The tie rods are the adjustable links that connect the pitman
arm and the stub axles. They are usually either solid rod or tubular
aluminium.
KINGPIN:
The kingpin is the correct name for the bolt about which the
stub axle pivots.
The
angles and forces we will discuss are;
ACKERMAN:
Ackerman, in karting, is more an effect rather than true
Ackerman. the effect of Ackerman geometry is to cause the inside
wheel to turn more than the outside when the kart is steered. The
original intention of Ackerman when it was invented in the 1800s was
to allow the inside and outside wheels to turn around a common
centre, thus avoiding tyre scrub when turning. In karting, this is
still a factor, but the Ackerman effect of toeing out the wheels
progressively more as the steering is turned is used to accentuate
weight jacking, which we will discuss later on.
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