Rodding Roundtable
Rodding Terms - Chassis Related

  • 8" Ford - Similar to the 9" rearend but with a smaller ring gear. Not as strong as the 9" but capable of holding moderate horsepower. It is called this because of the ring gear diameter.
  • 9" Ford - A much sought after rear end used in many Ford cars and trucks from the early 60's to the mid 80's. It is called this because of the ring gear diameter.
  • Ackermann Steering - A double-pivoting steering system where the outer ends of the steering arms are bent slightly inward so that when the vehicle is making a turn, the inside wheel will turn more sharply than the outer wheel. This is done to compensate for the greater distance the outside wheel must travel.
  • Ackermann Angle - The toe-out or toe-in of a vehicle with Ackermann steering when the wheels are positioned straight ahead.
  • Beam Axle - Solid straight axle usually suspended by two parallel or one transverse leaf spring(s).
  • Brake Bias - balance of braking force between the front and rear brakes.
  • Bump Steer - When an uneven road surface causes a vehicle to steer or lose directional stability, this is called "bump steer." At the front, bump steer is associated with the tie-rod and linkage-arm relationship. It is caused by the method of locating the rear suspension, the type of rear suspension, and the geometry of the various linkages. In race cars, bump steer is designed out of the suspension so that the handling is as precise as possible. In most cars it is present to some degree. In fact, it can be useful to allow engineers to design a small amount of understeer or oversteer into the chassis.
  • Caliper - The apparatus on disc brakes which hold the disc pads and straddles the disc. When actuated the pads press against the disc to stop or slow the vehicle.
  • Carson Top - A chopped, padded non-folding top used on custom roasters and convertibles and originally invented by Glen Houser at the Carson Top Shop in Los Angeles.
  • Camber Angle - The inward or outward angle which a front-wheel spindle makes with a vertical line, as viewed by either the front or the rear of the vehicle. Positive camber results when the top of the tire tilts out further than its bottom. The adjustment of this setting affects both tire wear and vehicle handling.
  • Caster Angle - The forward or backward tilt of the steering axis as viewed from the side. If the point of load is ahead of the point of contact, the caster angle is positive. The caster angle tends to keep wheels in a straight line. Proper caster adjustment improves both tire wear and fuel economy.
  • Center of Gravity - Point where the weight of a vehicle appears to be concentrated and if suspended at that point would balance front and rear.
  • Coil Spring - The most common type of spring on modern cars, where a coil of tempered metal takes the compression loads as the wheels move.
  • Crossmember - A cross tube that connects one frame rail to the other. Also used to mount other components like the front & rear end, and motor & transmission.
  • Differential - The gear assembly connected between the driving wheels (or front and rear axle in case of 4WD or AWD) that permits the wheels to turn at different speeds.
  • Drum Brakes - Contain two brake shoes inside a drum.
  • Disc Brakes - A brake where a kidney-shaped brake pad, lined with asbestos or other heat resistant material is pressed against a disc attached to the wheel to stop the car.
  • Decked - Removal of the trim and lock mechanism from the decklid of a car
  • Ex-Gasser - Hot Rod, usually a Willys, Austin, or Anglia, that was originally modified for a drag racing and later returned to street use.
  • Four Bar - A suspension design that replaces a wishbone with 4 locating rods, two on each side.
  • Frenched - Welding and molding headlight or taillight bezels to the fenders, making them an extension of the fender and creating a tunnel effect.
  • Gear Ratio - The number of revolutions a driving (pinion) gear requires to turn a driven (ring) gear through one complete revolution. For a pair of gears, the ratio is found by dividing the number of teeth on the driven gear by the number of teeth on the driving pinion gear.
  • Hotchkiss Drive - The method of connecting the transmission output shaft to the differential pinion by using open driveshafts. The driving force of the rear wheels is transmitted to the frame through the rear springs or through link arms connecting the rear axle housing to of the vehicle. Combines both steering axis and camber angles.
  • Hotchkiss Suspension - A live-axle rear suspension in which leaf springs handle both the axle's springing and its location. See hotchkiss drive.
  • Independent Front Suspension(IFS) - A suspension design that allows the front wheels to move independent of one another.
  • Independent Rear Suspension(IRS) - A suspension design that allows the rear wheels to move independent of one another. Usually from a Corvette or Jaguar.
  • Kingpin - A hardened steel pin that is passed through the steering knuckle and axle end. The steering knuckle pivots about the kingpin. A vertical or inclined shaft about which a steered wheel pivots. In newer cars the kingpin has been replaced by ball joints.
  • Kingpin Axis - The centerline of the ball joints in a front suspension system. Also called "swivel axis"
  • Kingpin Inclination(KPI) - The angle made of the kingpin axis to the perpendicular as viewed from the front. An alignment adjustment where the tops of the kingpins are tipped inward toward each other. This places the center line of the steering axis nearer the center line of the tire-road contact area. Thus when the vehicle comes out of a turn, the steering wheel returns to the straight-ahead position. Also called "steering axis inclination" or "swivel-axis inclination"
  • Kingpin Offset - A geometric parameter which is "positive" if the kingpin axis intersects the wheel plane at or below ground level, or is "negative" if the point of intersection is above ground level. Also called "scrub radius"
  • Locking Differential - Applies power to both drive wheels at all times regardless of which one has better traction. This special differential reacts when one wheel (or axle in the case of 4WD) starts slipping by firmly locking up the gears to prevent that slippage.
  • Limited Slip Differential - A mechanism that limits the speed and torque differences between the two wheels on an axle (or front and rear axles in the case of 4WD/AWD). Limited slip ensures that some power is always applied to each of the wheels, even when one is on a slippery surface. This is the essential element to avoid getting a vehicle stuck in snow or mud.
  • Master Cylinder - Holds the brake fluid for a disc brake system.
  • Manual Transmission - A system where the driver selects the proper amount of power and torque linking the power of the engine to the wheels. Involves a stick shift and is normally available in 4, 5 or 6 forward gears and 1 reverse.
  • Nosed - Removal of the chrome trim from the hood.
  • Orphan - Term used to describe cars that were built by companies no longer in existence. Examples are Nash, Hudaon, Packard, Plymouth, AMC, Studebaker.
  • Odd Rod - Basically a hot rod built from an orphan car or otherwise unusual automobile.
  • Oversteer - the tendency of an automobile to steer into a sharper turn than the driver intends sometimes with a thrusting of the rear (fishtailing) to the outside.
  • Perimeter Frame - Sometimes called a Space Frame. Steel frame making up the chassis of a car or truck. The engine, transmission, body panels and interior are all attached to the frame. Most cars today do not use a frame but are instead made with unibody construction.
  • Power To Weight Ratio - This is the relationship between horsepower and the weight of the car. The greater the horsepower is in relation to the weight of the car, the faster the car will go and the faster it will accelerate.
  • Proportioning Valve - A valve which can be used to adjust front to rear brake bias.
  • Pinion - A gear with a small number of teeth designed to mesh with a larger geared wheel or a rack. Used in rack and pinion steering and the differential ring and pinion.
  • Power Steering - Steering that has been designed to make the wheel move more easily than in a manual steering system. Hydraulic power assists the process utilizing hydraulic fluid. The fluid increases pressure in the power steering pump and aids in the movement of the steering mechanism. This fluid, called power steering fluid, is what is replaced at regular intervals to keep steering soft and comfortable. Variable assist power steering systems (sometimes called Speed Sensitive Steering) stiffen at high speeds for better control and soften at lower speeds to make operations, like parallel parking, easier to accomplish.
  • Quick Change - A rear axle design that allows for a gear change without a disassembly of the rearend.
  • Rack And Pinion Steering - Steering system technology that allows for more responsive handling and is found mostly in newer cars. The steering shaft has a small gear at its bottom. It meshes with a toothed bar connected to the steering linkage that controls the two front wheels.
  • Scallops - Precisely rendered geometric patterns painted on a car as an accent.
  • Scrub Line - An imaginary line used to measure the degree of ground clearance a car will have. The line is determined by measuring the height of the tire sidewalls, front & rear, and then rains the car up that distance before plotting the scrub line.
  • Shaved - Removal of side trim and/or door handles.
  • Split Wishbones - In order to clear most modern V-8 engines the wish bone is split into 2 seperate rods that are attached to the side of the frame.
  • Springs - Work in conjunction with shock absorbers or gas/oil; springs extend or compress to cushion road irregularities.
  • Stabilizer Bar - A metal bar, usually in a rough U-shape, which links wheels on opposite sides of the car. It tends to keep the wheel motion similar for each side, thus it reduces the roll or sway of a car. As a result, it is frequently also called a roll bar or sway bar. Almost always installed on the front suspension, but many touring or performance cars use rear stabilizer bars also.
  • Tail Dragger - A custom that sits lower in the rear than in the front.
  • Torsional Rigidity - Sometimes called chassis stiffness. It relates to how rigid the chassis is in twisting. Imagine a sport utility vehicle that needs to climb over rocks. Those without long suspension movements sometimes have lower torsional rigidity to allow the chassis to respond to uneven ground. A passenger car, on the other hand, should have high torsional rigidity in order to give the car a smooth ride, less vibration and better handling. Sports and performance cars are usually the stiffest in order to minimize any flex except for that offered by the springs and shocks to obtain consistent handling.
  • Toe In - The amount by which the front of a front wheel points inward or outward. A slight amount of toe in is usually specified to keep the front wheels running parallel on the road by offsetting other forces that tend to spread the wheels apart.
  • Trailing Arm - A rear suspension element consisting of a lengthwise member that pivots from the body at its forward end and has a wheel hub rigidly attached to its trailing end.
  • Understeer - Front-end plowing or diving.
  • Underslung Frame - A frame design of the pre-war era whose characteristic feature is that the frame members run below the axles.
  • Ventilated Brakes - Brakes with numerous small holes drilled into the brake disc, facilitating cooling.
  • Wishbones - Refers to the stock early Ford triangular radius rod setup which kept buggy sprung front axle straight. The left and right ends of the wishbone are attached to the axle with a third attaching point that has a ball pivot on it.
  • Z'ed - When a frame is cut, usually in front of the rear wheels, and a section is welded in to raise the axle so large tires can be used at stock body heights, racers say their car has been z'ed [pronounced ZEED, not ZED], referring to the new appearance of the frame.

What's New
Email Services
Message Boards