A radius rod is a suspension

Suspension (vehicle)

Suspension is the term given to the system of springs, shock absorbers and linkages that connects a vehicle to its wheels. Suspension systems serve a dual purpose — contributing to the car's roadholding/handling and braking for good active safety and driving pleasure, and keeping vehicle occupants...

 member intended to control wheel

Wheel

A wheel is a device that allows heavy objects to be moved easily through rotating on an axle through its center, facilitating movement or transportation while supporting a load, or performing labor in machines. Common examples found in transport applications. A wheel, together with an axle,...

 motion in the longitudinal (fore-aft) plane. The link is connected (with a rubber

Rubber

Natural rubber, also called India rubber or caoutchouc, is an elastomer that was originally derived from latex, a milky colloid produced by some plants. The plants would be ‘tapped’, that is, an incision made into the bark of the tree and the sticky, milk colored latex sap collected and refined...

 or solid bushing

Bushing (isolator)

A bushing or rubber bushing is a type of vibration isolator. It provides an interface between two parts, damping the energy transmitted through the bushing. A common application is in vehicle suspension systems, where a bushing made of rubber separates the faces of two metal objects while allowing...

) on one end to the wheel carrier or axle

Axle

An axle is a central shaft for a rotating wheel or gear. On wheeled vehicles, the axle may be fixed to the wheels, rotating with them, or fixed to its surroundings, with the wheels rotating around the axle. In the former case, bearings or bushings are provided at the mounting points where the axle...

, on the other to the chassis

Chassis

A chassis consists of an internal framework that supports a man-made object. It is analogous to an animal's skeleton. An example of a chassis is the underpart of a motor vehicle, consisting of the frame with the wheels and machinery.- Vehicles :In the case of vehicles, the term chassis means the...

 or unibody of the vehicle.

Radius rods typically are mounted ahead of the wheel. In that position they resist dive under braking

Brake

A brake is a mechanical device which inhibits motion. Its opposite component is a clutch. The rest of this article is dedicated to various types of vehicular brakes....

 forces and wheel hop under acceleration

Acceleration

In physics, acceleration is the rate of change of velocity with time. In one dimension, acceleration is the rate at which something speeds up or slows down. However, since velocity is a vector, acceleration describes the rate of change of both the magnitude and the direction of velocity. ...

.

Radius rods are customarily made of stamped

Machine press

A machine press, commonly shortened to press, is a machine tool that changes the shape of a workpiece.-Servomechanism:A servomechanism press, also known as a servo press or a electro press, is a press driven by an AC servo motor. The torque produced is converted to a linear force via a ball screw....

 steel

Steel

Steel is an alloy that consists mostly of iron and has a carbon content between 0.2% and 2.1% by weight, depending on the grade. Carbon is the most common alloying material for iron, but various other alloying elements are used, such as manganese, chromium, vanadium, and tungsten...

 or aluminum for lightness, as they are part of the vehicle's unsprung weight

Unsprung weight

In a ground vehicle with a suspension, the unsprung weight is the mass of the suspension, wheels or tracks , and other components directly connected to them, rather than supported by the suspension...

. Improvements in composite materials technology make possible plastic suspension links, although they are still uncommon.

Other suspension components can be made to act as radius rods under certain conditions. For example, the rear suspension of the original 1966 Oldsmobile Toronado

Oldsmobile Toronado

The original Toronado began as a design painting by Oldsmobile stylist David North in 1962. His design, dubbed the "Flame Red Car," was for a compact sports/personal car never intended for production...

 used shock absorber

Shock absorber

A shock absorber is a mechanical device designed to smooth out or damp shock impulse, and dissipate kinetic energy. It is a type of dashpot.-Nomenclature:...

s to connect the rear beam axle

Beam axle

A beam axle is a suspension system, also called a solid axle, in which one set of wheels is connected laterally by a single beam or shaft...

 to the frame; these shocks controlled longitudinal wheel movement, but their damping action prevented the forces of those movements from being felt by the passengers.

On a vehicle with longitudinal leaf spring

Leaf spring

Originally called laminated or carriage spring, a leaf spring is a simple form of spring, commonly used for the suspension in wheeled vehicles...

s, such as a Hotchkiss drive

Hotchkiss drive

The Hotchkiss drive is a system of power transmission. It was the dominant form of power transmission for front-engine, rear-wheel drive layout cars in the 20th century...

 suspension, the springs themselves provide some longitudinal wheel control. One or more torque arms may be added to provide supplementary wheel control, particularly for vehicles with strong torque

Torque

Torque, moment or moment of force , is the tendency of a force to rotate an object about an axis, fulcrum, or pivot. Just as a force is a push or a pull, a torque can be thought of as a twist....

 such as drag racers

Drag racing

Drag racing is a competition in which specially prepared automobiles or motorcycles compete two at a time to be the first to cross a set finish line, from a standing start, in a straight line, over a measured distance, most commonly a ¼-mile straight track....

. On some leaf spring-equipped vehicles, such as 1960s Chrysler Corporation cars, the springs are mounted so that a greater portion of the spring's length is forward of the wheels, improving wheel control on acceleration. A side effect of such positioning is that the shorter, aft portion of the springs may not be stiff enough to control wheel movement under braking forces, which can lead to pronounced wheel hop in hard stops.