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| This page explains the terminology used for front end
setup in a sandcar. The science of steering geometry for a
sandrail is no different than for a street car, but the numbers are
different. Of course sandcars have more suspension travel, and
they use different tires, but the terminology and theories used to make
a car handle well is the same. The importance to have a sandrail setup
correctly is just as helpful as it is for a street car, maybe more so,
simply because the tire traction available in the sand is less than
car on blacktop. If a sandrail isn't setup correctly you will
suffer from ill handling characteristics that prevent the car from
turning as well as it could otherwise if setup correctly.
Here we are going to explain the terminologies for
front end adjustment and measurement, but we will not tell you how to
setup your car because that changes for each wheelbase and wheel track
width. The manufacturer of your chassis is responsible for
understanding the science of front end setup and fabricate the car's
front end to work best in the sand. Although you have some ability to
change some of the front end attributes, it is limited in some areas.
Opinions on front end setup vary greatly from one
builder to another, hence some cars handle better than others, based on
their front end steering geometry, how correct it is, wheel base, and
the weight distribution of the car. If you have ever driven in
multiple sandcars you know how different they can steer. Some car
builders don't even make their own suspensions, they buy them from
another fabricator and slap them on a frame. In these cases the
steering geometry specific to that frame can be poor unless carefully
engineered.
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Here's an example of the affect that ACKERMAN has on
the front wheels. This affect, or Ackerman, is
built into your front front end to independently manipulate the turning angles of each wheel
at slightly different angles.
When going straight each wheel should have a slight toe-in, as shown in
the second picture below. But when turning either direction, you'll see the inside tire
must turn with a sharper angle than the outside tire. This is
because when turning the car the inside tire naturally needs to make a smaller
circle than the outside tire. The difference in angle between the
two tires increases gradually the sharper the turn you make. All
automobiles for the street has Ackerman engineered into the front end to
maximize tire life. In a sandrail it's important to have Ackerman
built in to maximize the grip with the sand so the tires don't work
against each other. If the tires work against each other you
dramatically reduce the traction of the wheels and they will always be
skidding in turns, so to speak. |
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This is an example of Toe-In. This is important
so your car tracks properly. At neutral ride height the tire's
should be slightly toed in. Opinions differ on this but 1/8" to
1/4" toe in is generally what most run in the sand. If you have
toe-out you will notice the car will wander on flat ground and possibly
hunt for a track, resulting in a squirrely feel.
The effect of bump steer happens when the suspension
goes up and down. With bad front end engineering you will see bump
steer mess things up. The toe-in can radically change as the
wheels travel up and down. Ideally as
the suspension goes from full droop to full compression the toe-in
alignment will not change much. Total elimination of bump steer is
very tough do, but too much is bad. |
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Tire camber is the angle of the tires in relation to
the ground when viewed from the FRONT of the car. Generally
speaking most folks run no negative camber or positive camber at neutral
ride height. Some manufacturers build in some negative camber as
the suspension goes up (camber gain), and this doesn't hurt anything usually, but it's
bad to have positive camber at any point. |
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The caster setup in your front end affects the
ability of your car to go straight and track easy at high speeds without jerking the
wheel out of your hands. Caster angle can be important if your sandcar doesn't have power steering.
Too little caster and you'll have a
tough time holding on and going straight through the bumps.
Caster also affects the camber of the tires when
turning, giving the affect like the tire is "leaning" into the turn.
Too much caster can have bad effect though. The more you increase
camber the less sharp the tires turn for the given distance your
steering rack moves the tires. No caster will result in a squirrely
feeling car at high speeds and provide no camber change in turns (a bad
thing).
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