What Is Axle?- Definition, Uses | Types of Axles

An axle is a rod or shaft that rotates the wheels and supports the weight of your vehicle. Axles are essential components of any vehicle and come in three main types: front, rear, and stub. Let’s break down the types of axles and look at how to choose the right axle ratio for your vehicle.

What is an 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 the vehicle, with the wheels rotating around the axle. In the former case, bearings or bushings are provided at the mounting points where the axle is supported.

In the latter case, a bearing or bushing sits inside a central hole in the wheel to allow the wheel or gear to rotate around the axle. Sometimes, especially on bicycles, the latter type of axle is referred to as a spindle.

What does an axle do?

A car axle is the mechanical link between your transmission and your wheels. Essentially, car axles are part of the system that takes the engine’s power to turn the wheels and propel the car. They generally work the same whether a manual or automatic transmission car.

In front-wheel drive vehicles, people refer to the shaft connecting the rear wheels as a “dead axle” because it doesn’t provide power to those wheels. The shaft allows the rear wheels to turn while powering the front wheels.

In a rear-wheel drive car, the front wheels are connected by a dead axle instead. “Most axles on front-wheel drive and all-wheel drive cars today are ‘CV’ or ‘constant velocity’ axles,” says Jaime Boucher, an ASE-certified master technician and the shop foreman at Cantin Chevrolet in Laconia, NH.

These are sometimes called “half axles” or “half shafts” because each wheel has a dedicated axle shaft instead of one shaft that connects both wheels.

Factors That Decide the Type of Axle in a Car

Several factors determine which type of axle a vehicle needs. For example, the technical requirements and the force generated play a major role in the decision on the type of axis.

Some vehicles have pre-built axles in standard formats. Others have bespoke axles that meet the needs and specifications of the car. Custom axles are best for cars as they allow more individual control over the wheels. These axles can fine-tune the speed and torque of the wheels.

Types of Axles

Axles come in three standard types:

1. Rear axle: This axle is responsible for the power supply to the drive wheels. It comes in two halves, called half-waves, which are connected by the differential. In most cases, the rear axles are under tension, meaning that they rotate with the vehicle’s wheels.
2. Front axle: This axle is located in the front of the vehicle and is responsible for assisting in steering and processing bumps on uneven road surfaces. They consist of four main parts: the beam, the swivel pin, the tie rod and the stub axle. The front axles must be as robust as possible. That is why they are usually made of carbon steel or nickel steel.
3. Stub Axle: Stub axles are attached to the vehicle’s front wheels, with kingpins connecting these axles to the front axle.

Types of Rear Axles

Not all rear axles are the same, as the support and mounting methods there are three types of rear axles:

1. Semi-floating axle: This rear axle connects the wheel to the flange on the outside of the axle shaft and holds it securely. One bearing supports the axle shaft and the other is in the axle housing. Since it has two bearings, a semi-floating axle must be larger than the other options to produce the same torque. Semi-floating axles are used for automobiles, SUVs, and medium-sized trucks, Pickups with half a ton and low power.
2. Full-floating axle: As the name suggests, thanks to two bearings, this type of axle effectively floats in place and maintains its position. It only transmits the drive torque. Fully floating axles are best for larger vehicles, e.g. heavy trucks. Some medium-sized trucks with larger towing capacity or those with all-wheel drive can also benefit from fully floating axles.
3. Three-quarter floating axis: It is more complex than the semi-floating axle and also more reliable. It helps in maintain wheel alignment and handles side thrust and driving torque.

Types of Front Axles

There are vehicles that have two main types of front axles.:

1. Dead Front Axle: These axles stay in place and don’t rotate with the wheels. Most dead front axles and differentials have housings that prevent them from coming into contact with water or dirt.
2. Live Front Axle: Unlike dead front axles, live front axles deliver driving power from the gearbox to the front wheels.

Types of Stub Axle

As The Engineers Post explains, there are four types of stub axle:

1. Elliot: This type uses a kingpin, a yoke, and a cotter to connect to the front axle.
2. Reverse Elliot: This type has the opposite arrangement of a standard Elliot stub axle.
3. Lamoine: This stub axle type has an L-shaped spindle instead of a yoke-type hinge.
4. Reverse Lamoine: It has the opposite layout of a standard Lamoine stub axle.

How Many Axles Does a Car Have?

The number of axles in a car depends on the type of vehicle. In most cases, cars have two axles to turn the wheels. Larger vehicles that carry more passengers and have more wheels can have more axles.

It’s easy to identify the number of axles your car or other vehicle has. Just look at your car from the side and then count the pairs of tires. Most cars have a total of four tires or two sets of tires, one in the front and one in the rear. Two sets of tires correspond to two axles.

• 2-axle vehicle with 2 axles. Examples are bicycles, motorcycles, ordinary cars, light trucks, medium-duty trucks (like Chevy Silverado 3500, Ford F-350 and Dodge Ram 3500 as examples with “duallies”), and even some class 8 trucks (package delivery companies that run double trailers, and triples where legal, between terminals tend to use two-axle tractors).
• 3-axle vehicle with 3 axles. straight trucks with a pair of rear axles to carry the extra weight coming from the cargo, a Greyhound bus, some full-size RVs, and majority of tractor units for semi-trailers. 3-axle combination vehicles with small utility trailers also covered. (Examples would be the Ford Focus and Honda CRV). A car like a stretch limousine having three sets of tires also has three axles.
• 4-axle vehicles with 4 axles. Examples are Tri-drive highway tractors that are often used for oversize loads, dump trucks with lift axles, concrete mixers with two steer axles and two drive axles. A 4-axle combination vehicle could also be standard highway tractors with single-axle trailers, 2-axle shunt trucks moving standard 2-axle dry vans around in a trucking company’s yard or at a distribution center, or a pickup that has a 2-axle travel trailer.
• Big freight trucks have 5 axles in total. 3 located on the truck and the other 2 on the trailer. An 8-wheeler also has 5 axles, one located in the front, 2 in the middle located at the location where the trailer is attached to the truck and then 2 at the back of the trailer. The axles found underneath the trailer got four wheels per axle. There are vehicles with even more axles but they are specialized vehicles designed to haul the gigantic and long loads.

How to Know When Your Axle Is in Disrepair

Because axles are essential to your car’s operation, it’s important to keep them working properly. if you see one of the following signs, you can tell that your axle is in disrepair:

• You hear a loud clunk when you put your car into gear.
• You feel vibrations when you operate your car.
• Your vehicle won’t move forward or backward even though it’s running.

Why Should You Inspect Your Axles?

Regular axle inspection is an important part of car maintenance because spotting trouble early on can help you avoid expensive repairs in the future. The cost of axle repair can increase drastically if you have to replace any of the axles.

What To Look for When Inspecting

Most car mechanics will inspect your axles whenever you bring in your car – but you can also conduct an inspection yourself. You won’t need any tools to do it, but you will need to get underneath your vehicle.

Depending on how low your car is, you might need something to lift it up off the ground. You can use carjacks or vehicle ramps to do this.

Visual Inspection

The easiest part of the inspection is taking a close look at the boot, which is responsible for keeping joints lubricated and preventing dirt and water from getting in. They explain that the boot has ribs in it to allow it to flex and move with the vehicle.

Check for holes, splits, or grease that is leaking. Next, you should inspect the shaft for any nicks, dings, or dents, as well as if there are signs that anything is rubbing on it.

You also need to check the clamps that connect the boots to the shaft to ensure there are no leaks.

Driving Inspection

You can also take a test drive to determine if there is anything wrong with your axles. If you notice any of the following signs, your axle might be in disrepair:

• When you put your car into gear, there is a loud “clunk” sound.
• Your car vibrates when you operate it.
• There is a clicking or popping noise when you turn your car.
• Your car is running, but it won’t move forward or backward.

Top 6 Signs of a Damaged or Broken Car Axle

When a car axle breaks, either abruptly (like hitting a curb) or due to frequent overuse (like driving with too much payload), you’ll usually know there’s a problem because the tires simply won’t spin. However, there are some signs and symptoms of axle damage that might indicate a broken axle—and a visit to an axle repair shop is on the horizon.

#1. Car Won’t Budge.

The most obvious sign of a broken axle is when your car tires won’t rotate. The car will turn on fine. Its engine will sound happy as a clam when you rev it. There aren’t any electrical issues—no dashboard warning lights, no weird clicking sounds. It. Just. Won’t. Move.

Why does this occur? It’s usually the result of a bent axle joint that’s finally snapped like a Slim Jim. You’ll need a tow truck to haul it to a repair shop near you for an inspection and axle damage repair.

#2. Vehicle Strains.

Car axles are fairly resilient, but when they’re under pressure, you’ll feel it in the gas pedal. When an axle is bent or damaged, your vehicle might begin to strain. You’ll put it into gear and notice right away that power isn’t getting transferred to the wheels (i.e., it’s slow to get going).

A straining vehicle doesn’t necessarily mean that you have a bad car axle, however. This should accompany some other signs of axle damage (below).

#3. “Sputtering” Noises.

Along with straining to move, the vehicle may also make sputtering, bumping or clunking sounds. This is because the axle is not able to transfer adequate power to the wheels.

These bad axle sounds will be audible when the car begins to move as well as when turning the wheels.

#4. Wheel Wobbling & Vibrations.

Underinflated tires, unaligned wheels and loose lug nuts can also make your vehicle vibrate. But if you notice any other signs of axle damage, don’t disregard it! Your car is incredibly dangerous to drive once you begin noticing vibrations caused by a damaged axle or other suspension problems.

#5. Brake Pad Misalignment.

You’ll notice some braking issues once your bent axle starts going bad. The brake pads will begin to shift and become misaligned with the wheels and rotors, and once that happens, you may notice the vehicle skids or slips to a stop. Over time, the brakes will eventually cease to function at all.

#6. Leaking.

The brake seal on an AWD or 4WD vehicle’s driveshaft may shift and begin to leak small amounts of oil. This will be noticeable when looking at the brake drum.

Axle CV joints can also leak grease, which is not as detectable. However, once this happens, the joints will collect dirt dry out, and deteriorate quickly.

How to Choose the Right Axle Ratio for Your Pickup Truck

In addition to unique torque, engine, and transmission specifications, many trucks also have custom axle ratios. An axle ratio like 3.55: 1 means that the driveshaft will turn 3.55 times every time the wheel turns once.

In most cases, a standard final drive ratio works well for most drivers who are not expecting large loads. However, if you are pulling heavy trailers or want to pull large loads, you may want the highest final drive ratio possible.

Are Car Axles Covered by Insurance?

If your car axle is damaged or broken as a result of an accident or hazard, it may be covered by your car insurance (depending on your specific policy). Damage from wear and tear or aging is not covered by car insurance.

It is possible to buy warranty coverage for major components, such as the engine and transmission, but this is separate from insurance and subject to its own set of rules and restrictions.

FAQs.