
So, you're finally ready to get started on transforming that pile of parts into a real street rod ? There are a few things to consider when setting up your front suspension, not only to make that buggy sprung beauty look right, but ride right and handle properly as well. We all know that hte bottom line is about looks, but what are looks worth if the whole thing does'nt work properly? A properly set up front suspension will not only make your rod ride and handle its best but will make it much safer and more comfortable on those long cruises that are the best part of our lifstyle.
WHAT IT IS
First, we need to lay a few terms on you. You can't tell a hairpin from a drag link without a program, so let's get the terminology straight from the beginning.
Axle:
The axle is a shaft or member on which a wheel or a set of wheels rotates. In
the case of front suspension, it's either shaped like an I-beam or is tubular
and rides perpendicular to the, framerails.
Batwing:
The batwing replaces the leading end of the wishbone where it mounts to the
axle and spring. Batwings are used when the wishbones are replaced with hairpin
radius rods or four-link rods. Some also incorporate a shock mount.
Beam axle:
A cast or forged axle whose basic cross-section resembles the letter I. This
shape allows for a certain amount of twist. This is helpful if one wheel travels
over a bump as the other stays flat, since it helps the suspension absorb bumps,
making the vehicle ride smoother.
Bumpsteer:
The tendancy of the axle to shift laterally in the frame of cars set up with
cross steering, such as a Vega box. Lateral movement of the axle, when combined
with the stationary steering box-to-spindle linkage, called the drag link, causes
the wheels to turn without steering input. This problem is corrected with the
use of a Panhard rod.
Camber:
The inward or outward tilt of the wheels as viewed from the front of the vehicle,
measured in degrees from vertical. Negative camber is when the top of the wheels
lean in, and positive camber is when they lean out. In solid-axle cars, the
camber is typically from +half to -half degree and is usually engineered into
the axle, and into the angle, the kingpin hole is machined into the kingpin
boss. Too much camber usually results in poor handling, as well as excessive
and uneven tire wear.
Caster:
The backward or forward tilt of the kingpin, measured in degrees from vertical.
A backward tilt at the top of the kingpin is known as positive caster, while
a forward tilt is called negative caster. Caster affects directional control
of the steering. Positive caster gives the vehicle a tendency to track straight
and also influences the steering wheel to return to a neutral, straight-ahead
position following a turn. A negative caster setting has the opposite effect;
steering becomes twitchy, increasing with vehicle speed, and it tends to wander
and swerve.
Coilover:
A shock with an integral coil spring. Coilovers allow the builder to omit the
transverse leaf spring and typically will ride better than the leaf spring.
Cross steenng:
The steering system originally found on the Model T, as well as later ('35-'48)
Ford vehicles. The steering box is connected to the righthand spindIe with a
drag link.
Drag link:
A bar that connects the pitman arm on the steering box with the steering arm
on the spindle.
Dropped axle:
An axle that has had its ends either heated and bent or is cast or forged in
such a way that the spindle mounting points, which are at each end, are raised
in relation to the suspension mounting points. Thus, it effectively lowers the
front of the vehicle a distance relative to the extent of the bend.
Four-link:
A four-link uses two separate bars per side, each with an individual mounting
point at both ends and will allow the front axle to move up and down while maintaining
its preset caster angle.
Hairpin ralius rod:
Hairpins replace the split wishbones in locating the front axle in the car.
Their trailing ends have one mounting point, similar to wishbones, but have
two mounting points at the front and must be used in conjunction with batwings.
The name comes from their shape, which resembles a hairpin.
Kingpin:
The pivot point for the spindle, which mounts to the end of the axle and is
the mounting point for the brakes and the wheel.
Panhard bar:
A bar that connects one end of the axle to the opposing framerail (right end
of the axle to the left rail). It stabilizes the front suspension laterally
and helps prevent bumpsteer.
Leaf spring:
A semi-elliptical spring made up of multiple elements, or leaves. The spring
rides perpendicular to the frame, with each of its ends attached to the forward
ends of the wishbone at the axle and its center secured to a crossmember within
the frame. This spring, made up of multiple components, tends to ride better
than a monoleaf. Its construction allows it to behave in a progressive manner,
as the spring is loaded during suspension travel. It's softer upon initial loading
and becomes stiffer as the spring compresses and loads its shorter leaves.
Monoleaf spring:
A semi-elliptical spring made up of one main leaf. This leaf is typically thicker
than the main leaf found in a multi-leaf spring.
Push-Pull steering:
Steering system typically found on Model A and Model B cars. The drag link attaches
to the lefthand spindle and pushes or pulls the spindle in a direction that
is parallel to the frame.
Reversed-eye spring:
A leaf spring whose outer mounting points, or eyes, have been turned in the
opposite direction to, allow a l-inch drop of the suspension with no discernable
change in the spring's loading characteristics.
Split wishbone:
The trailing end of the wishbone, where the two bars come together, is cut off,
thereby splitting the wishbone. The ends are then modified to accept a Heim
joint or a rod end. These new ends are then moved outward and are mounted to
brackets, which are typically bolted or welded to the framerails. The leading
ends are heated and bent just behind the axle so that they maintain their proper
alignment with the axle as well as with their new mounting points on the frame.
Split wishbones allow the front of the car to be lowered without the 'bones
interfering with the frame during suspnsion travel.
Toe:
The inward or outward angle of the ! wheels when viewed from above. Toe-out
is when the wheels point slightly away from each other, and toe-in is when they
point towards each other. Toe also affects handling and tire wear. Most hot
rods need between 1/8 and 3/16-inch toe-in, depending upon the tires used. Adjustment
is made at the tie rod ends.
Tube axle:
An axle constructed of tubular steel. This axle flexes much less than a beam
axle, and some builders recommend using a four-link suspension setup when equipping
a car with a tube axle.
Wishbone:
A large wishbone or Y -shaped component whose forward ends mount near the ends
of the axle and whose rearward end mounts under the car, usually to the torque
tube. The wishbone mounts the spring ends to the axle and locates the axle in
the car, keeping it perpendicular to the frame.
WHAT IT DOES
Each type of axle suspension setup exhibits different ride and handling characteristics,
each having its strong and weak points. While the stock beam axle with the factory
wishbone rode pretty well, we all know that pretty well doesn't cut it with
hot rodders. Aside from the need to get the cars closer to the ground, probably
the most obvious reason people started splitting wishbones was for engine and
transmission clearance. The stock 'bone was fine when running that old A four-slug
with a manual, but when time came for some zoom-in the form of V-8 power with
the occasional automatic-clearance problems emerged, and the immediate solution
was to split the wishbone. Split wishbones still work pretty well on cars with
beam axles and look "right" on a traditional low-tech car.
The next progression from split wishbones was the
hairpin radius rod. It allowed for clearance at its trailing end, since it was
designed to mount to the framerail. The advantages of using hairpins were that
they allowed for caster adjustment as well as having their forward mounting
points further away from each other. This made for a morestable front axle.
One drawback of hairpins is that, since they employ a single mounting point
at their fulcrum, they allow the caster to change as they move through their
range of motion during suspension travel. A beam axle allows for a certain amount
of twist as one wheel travels over a bump while the other stays flat. This works
well with hairpins, but many builders don't recommend using hairpins on tubular
axles. Since a tube axle is less forgiving
than a beam, and the axle is going to want to twist, there's a greater possibility of breaking some thing. This is not to say that hairpins and tube axles are enemies. They'll still work together - it's just that hairpins work better with beam axles, and four-Iinks work better with tube axles.
The development of the tube axle forced the development of the four-lInk system, which turned out to be a great advancement in street rod suspension. With separate fulcrum points for each bar, the four-Iink allows the axle to travel up and down in a parallel manner. This eliminates caster changes throughout suspension travel and results in a smoother, more predictable ride.
Coilovers were another big advancement for solid axle suspensions, as they allow much greater adjustability of spring rates over buggy springs. They tend to work much better with four-Iink suspensions as well. Being that a four-link allows the axle to travel in a straight line, there is much less of a chance that the collovers wIll bInd, even slightly, than with a hairpin or split wishbone setup, which cause the axle to travel in a slight arc.
WHAT IT MEANS
What this all boils down to takes us right back to square one. Looks. No matter
which suspension setup you think is best, you're most likely to use the one
that appeals to your own tastes. If you're building a traditional rod, you'll
probably lean towards hairpins and a beam axle, whereas if you're a high-tech
aficionado, you're more likely to go with a f.our-Iink/coilover setup. No matter
which style you choose, there is a proper way to put it all together. The bottom
line is to do it right, since there's nothing worse than having to do it twice.
RC