Semi-trailer truck and its Wheels and tires

Semi-truck also known as semi-trailer (or semi-trailer, eighteen-wheeler,big rig,tractor-trailer or,by synecdoche, semi-trailer) is a combination of a tractor and one or more semi-trailers used to carry goods.The semi-trailer is attached to the tractor with a hitch called a fifth wheel.

Types of trailers 

There are many types of semi-trailers in use, designed to haul a wide range of products.

• Box or dry van

• Bus

• Auto movers

• Intermodal chassis

• Dry goods

• Dump

• Tablet

• Hopper bottom

• Short man

• Refrigerator

• Refrigerator

• Tanker

Coupling and uncoupling

Cargo trailers are easily attached and released with a kingpin hook to a horseshoe-shaped quick release hitch called a fifth wheel or turntable hitch on the rear of the traction engine.A truck trailer cannot move on its own because it only has wheels on the rear end: it needs a front axle provided by the traction engine to carry half the load's weight.When braking hard at high speeds, the vehicle has a tendency to fold at the pivot point between the towing vehicle and trailer.This type of truck accident is known as a "trailer swing," although it's also often described as a "jackknife." A jackknife is a situation where the hitch swings relative to the trailer and vice versa.

Wheels and tires

While twin wheels are most common, the use of two wider single tires (known as super singles) on each axle is becoming more popular on bulk carriers and other weight-sensitive operators.The use of super single tires has grown in popularity as efforts to reduce greenhouse gas emissions intensify.This configuration has several advantages.The first of these is Super Singles to reduce fuel consumption. In 1999, tests on an oval track showed a fuel saving of 10% with Super Monorail.These savings are achieved because less energy is wasted on tire sidewalls that flex less.Second, lighter overall tire weight allows the truck to carry more cargo. A third advantage is that fewer brake units are packaged in a single wheel, allowing for faster cooling and less brake fade.

One of the main disadvantages of super singles is that they are not currently as widely available as standard tires.Also, if one tire is flat or damaged, there is no other tire on the same hub to maintain the dynamic stability of the vehicle as dual wheels do. With two wheels, the remaining tire may be overloaded, but usually allows the vehicle to be stopped safely or driven to the repair shop.

In Europe, superbikes became popular when the permissible weight of semi-trailers was increased from 38 to 40 tons.In this reform, the trailer industry replaced two 10-ton (22,000-lb) axles with dual wheels and three 8-ton (18,000-lb) axles with wide-based single wheels.The significantly lighter axle weight of the SuperSingle must be taken into account when comparing the road wear of single and dual wheels.Most super singles sold in Europe have a width of 385 mm (15.2 in).The legal load limit for standard 385 tires is 4,500 kg (9,900 lb).(Note that expensive, specially reinforced 385 tires approved for 5,000 kg (11,000 lb) do exist.They have very little market share, except for mounting on steering axles).