Radial tire
Encyclopedia
A radial tire is a particular design of automotive
Automobile
An automobile, autocar, motor car or car is a wheeled motor vehicle used for transporting passengers, which also carries its own engine or motor...
tire
Tire
A tire or tyre is a ring-shaped covering that fits around a wheel rim to protect it and enable better vehicle performance by providing a flexible cushion that absorbs shock while keeping the wheel in close contact with the ground...
(in British English
English language
English is a West Germanic language that arose in the Anglo-Saxon kingdoms of England and spread into what was to become south-east Scotland under the influence of the Anglian medieval kingdom of Northumbria...
, tyre). In this design, the cord plies are arranged at 90 degrees to the direction of travel, or radially (from the center of the tire).
History
A series of plies of cordRope
A rope is a length of fibres, twisted or braided together to improve strength for pulling and connecting. It has tensile strength but is too flexible to provide compressive strength...
reinforces a tire. Without this, a tire would be flexible and weak. The network of cords that gives the tire strength and shape is called the carcass. Since the 1960s, all common tires have a carcass of cords of polyester, steel, or other textile materials, inlaid with several layers of rubber.
In the past, the fabric was built up on a flat steel drum, with the cords at angles of about +60 and −60 degrees from the direction of travel, so they criss-crossed over each other. They were called cross-ply or bias ply tires. The plies were turned up around the steel wire beads and the combined tread/sidewall applied. The green (uncured) tire was loaded over a curing bladder and shaped into the mold. This shaping process caused the cords in the tire to assume an S shape from bead to bead. The angle under the tread stretched down to about 36 degrees. This was called the Crown Angle. In the sidewall region the angle was 45 degrees and in the bead it remained at 60 degrees. The low crown angle gave rigidity to support the tread and the high sidewall angle gave comfort.
By comparison, radial tires lay all of the cord plies at 90 degrees to the direction of travel (that is, across the tire from lip to lip). This design avoids having the plies rub against each other as the tire flexes, reducing the rolling friction of the tire. This allows vehicles with radial tires to achieve better fuel economy
Fuel economy in automobiles
Fuel usage in automobiles refers to the fuel efficiency relationship between distance traveled by an automobile and the amount of fuel consumed....
than vehicles with bias-ply tires. It also accounts for the slightly "low on air" (bulging) look that radial tire sidewalls have, especially when compared to bias-ply tires.
The first radial tire designs were patented in 1915 by Arthur W. Savage, a successful tire manufacturer and inventor in San Diego, CA. Savage's patents expired in 1949. The design was further developed and widely commercialized by Michelin
Michelin
Michelin is a tyre manufacturer based in Clermont-Ferrand in the Auvergne région of France. It is one of the two largest tyre manufacturers in the world along with Bridgestone. In addition to the Michelin brand, it also owns the BFGoodrich, Kleber, Riken, Kormoran and Uniroyal tyre brands...
in 1946, http://www.senat.fr/basile/visio.do?id=a/commission/fin/Fin991120.html&idtable=a/commission/fin/Fin991120.html#toc18. Because of its advantages, it has now become the standard design for essentially all automotive tires.
Construction
With only radial cords, a radial tire would not be sufficiently rigid at the contact with the ground. To add further stiffness, the entire tire is surrounded by additional belts that are oriented along the direction of travel. These belts can be made of steel (hence the term steel-belted radial), PolyesterPolyester
Polyester is a category of polymers which contain the ester functional group in their main chain. Although there are many polyesters, the term "polyester" as a specific material most commonly refers to polyethylene terephthalate...
, or Aramid
Aramid
Aramid fibers are a class of heat-resistant and strong synthetic fibers. They are used in aerospace and military applications, for ballistic rated body armor fabric and ballistic composites, in bicycle tires, and as an asbestos substitute. The name is a portmanteau of "aromatic polyamide"...
fibers such as Twaron
Twaron
Twaron is the brandname of Teijin Aramid for a para-aramid. It is a heat-resistant and strong synthetic fibre developed in the early 1970s by the Dutch company AKZO, division Enka, later Akzo Industrial Fibers. The research name of the para-aramid fibre was originally Fiber X, but it was soon...
and Kevlar
Kevlar
Kevlar is the registered trademark for a para-aramid synthetic fiber, related to other aramids such as Nomex and Technora. Developed at DuPont in 1965, this high strength material was first commercially used in the early 1970s as a replacement for steel in racing tires...
.
In this way, low radial tires separate the tire carcass into two separate systems:
- The radial cords in the sidewall allow it to act like a spring, giving flexibility and ride comfort.
- The rigid steel belts reinforce the tread region, giving high mileage and performance.
Each system can then be individually optimized for best performance.
Application
Radial tires have different characteristics of springiness from those of bias-ply tires, and a different degree of slip while steering. Motorists were not accustomed to the feel, hence the suspension systems of cars had to be modified. Ford Motor CompanyFord Motor Company
Ford Motor Company is an American multinational automaker based in Dearborn, Michigan, a suburb of Detroit. The automaker was founded by Henry Ford and incorporated on June 16, 1903. In addition to the Ford and Lincoln brands, Ford also owns a small stake in Mazda in Japan and Aston Martin in the UK...
engineer Jack Bajer experimented in the 1960s on a Ford Falcon, by giving it less tight steering, and adding both isolators to the drive shaft and bushings to the suspension, the latter being to absorb the thump of riding over asphalt expansion joints in a concrete roadway. Cars could now be made lighter because they would not have to make up for the deficiencies of bias-ply tires.
Radial tires have twice found application on bicycles, used on the 1980s Miyata touring bicycle; models 1000 and 610, and more recently in 2009 on the Maxxis Radiale.
Panaracer radial tires were also standard on the Jamis Gentry model bicycle in 1985.
Interestingly, the steel wires in radial tires become magnetic with use, and as they rotate a significant alternating magnetic field is created. It is quite measurable with an EMF meter close to the wheel well when the car is moving and is a spectrum of harmonic strengths from 10 to several hundred Hertz. https://prof.hti.bfh.ch/fileadmin/home/mik1/Magnfields_HPJ_revision.pdf