How many axles are in a car? What even are axles on a car, and what type of axles are there? Here’s a complete guide.
Have you ever wondered how many axles a car has? Well, the answer’s pretty simple. A road-going passenger vehicle almost always has two axles.
These axles are what connect the front wheels together and the rear wheels together.
Although it might sound like a simple question, there’s much to consider about axles. For instance, what counts as an axle? This has changed slightly over the years as technology has advanced.
So, yes, a car almost always has two axles.
This guide will explain all the intricacies you need to know to understand how they work.
Table of ContentsShow
What Are Axles On A Car?
An axle is a shaft fixed to the center of a rotating wheel. The wheel can either spin with the axle or around it.
Traditionally, an axle is a simple rod connecting two wheels. Think of the models you might have made in elementary school using LEGO or Erector/Meccano. These axles were used on old-fashioned cart or horse-and-carriage applications.
The shaft shafts sit in the axle housing. This protects it and helps to bear the vehicle’s weight.
The same principle applies to cars, but there are now many different axle types. A significant disadvantage of the original format is that each wheel is impacted by what’s happening on the other side.
All manufacturers design their cars with independent driven wheels and suspension. This maximizes car control, making driving safer.
In FWD vehicles, the front axle is live, while in RWD vehicles, the rear axle is live.
Here are a few terms you might come across in this article and when discussing the number of axles a car has.
- Front axle – an axle connecting the two front wheels.
- Rear axle – an axle connecting the two rear wheels.
- Stub axle – used for the front wheels (for steering).
- Live (or “driven”) axle – a live axle turns with the wheels, transferring power to them.
- Dead (or “non-driven”) axle – does not transfer power to the wheels – it simply connects them to the car.
- CV axle/driveshaft – “Constant Velocity”, by far the most popular kind of live axle. There are two CV shafts per live axle (confusingly).
- Differential – a “diff” isn’t directly part of the axle shaft. Still, it does connect across the same two wheels, allowing them to rotate at different speeds when necessary.
The following should make sense, then:
- In a front-wheel-drive car, the front axle is live while the rear is dead.
- Likewise, in a rear-wheel-drive vehicle, the front axle is dead, and the rear is live.
Four-wheel-drive models have two live axles (at the front and back), although the transfer case can make one of them – usually the front – dead.
All-wheel-drive usually utilizes a front-wheel-drive setup most of the time. When needed, the rear axle can become live, delivering temporary power. It then returns to its dead state.
What Are Live And Dead Axles?
All axles are either “live” or “dead”. Whether it’s the front, rear, or neither depends on the powertrain. Front-wheel-drive, rear-wheel-drive, all-wheel-drive, and four-wheel-drive all make a difference, of course.
- Live axles transfer power straight from the transmission into the front wheels, forming part of the drivetrain.
- Dead axles are found on the front of rear-wheel-drive cars and vice versa. They’re simply responsible for holding the wheels on the car, distributing the car’s weight, steering (in a RWD setup), and keeping vehicular control. As such, they aren’t part of the drivetrain.
What Are Floating Axles?
Car axles usually come in “floating” variations. You’ll usually find a semi-floating or three-quarter floating rear axle in road cars. However, some larger trucks and racecars might have fully-floating models.
- Semi-floating axles are essentially one unit. The shaft connects to the flange onto which you place your rotor and wheel. Inside the axle housing, bearings connect it to the shaft.
- Three-quarter floating axles are a sort of happy medium. A wheel hub is bolted onto the outside of the axle housing, like in a fully-floating model. However, it’s rigidly attached, keeping the whole system tighter.
- Fully-floating models are when the axle shaft connects to a separate wheel hub. It’ll have between 31 and 40 splines on its end to intersect with the hub. The wheel is then placed on the hub, itself bolted onto the outside of the axle housing.
What’s The Difference Between Types Of Floating Axles?
Full-floating axles are best for heavy vehicles, off-roading, and racing. They allow the car to absorb and control much more force (including general weight), meaning the flange/wheel hub doesn’t contort.
In extreme situations (such as those in cross-country journeys and track days), the flanges on semi-floating axles can warp, leading to a temporary loss of brakes. Not so good!
- In technical terms, a semi-floating axle has to handle the car’s weight, forces from the side (cornering), and driving torque.
- In three-quarter axle setups, the vehicle’s weight is borne by the axle housing. This means the shaft only has to deal with torque and side loads.
- Fully-floating axles only need to handle driving torque.
As such, fully-floating axles are the strongest and most efficient at transferring power to the wheels. They’re also the most expensive to build, so you’ll usually only see them on sports cars, off-roaders, and trucks.
What Is A CV Axle?
A Constant Velocity axle is responsible for driving the wheels in the driven axle(s). CV axles are most commonly known as driveshafts.
They allow rotational torque force to be transferred at angles. Each driveshaft has two CV joints to transfer the power from the transmission to the wheel.
Although it still counts as one axle, there are actually two driveshafts to each wheel across it. They meet at the transmission. One drives the right wheel, the other the left.
The most common problem with CV joints is the rubber boot splitting or tearing. When this happens they leak grease, and grit and debris enter. If this happens, you’ll need a new boot to prevent the CV joint from eventually seizing.
What Are Stub Axles?
Stub axles are connected to the front, and rear axles, and wheels are fitted directly onto them.
At the front, to allow for steering, the stub axle is hinged to the steering knuckle, with a kingpin forming the pivot point. In turn, the kingpin is mounted on bushes on the end of the stub axle.
Ball bearings are included in the wheel bearing to prevent wear while turning.
On the car’s dead axle, stub axles simply attach the wheels to the vehicle to distribute the weight. Two stub axles allow for independent suspension.
There are four types of stub axle:
- Elliot stub axle
- Reverse Elliot stub axle
- Lamoine stub axle
- Reverse Lamoine stub axle
There’s no need to understand these different stub axles in any great detail for now.
How Many Axles Does My Car Have?
Almost every car in the world comes with four wheels spread across two axles. The only exceptions are highly modified vehicles.
Remember, the axle is (in simple terms) the rod that connects a pair of wheels across (transversely) the car – that is, across one “axis”.
Some commercial pickup trucks and many semis come with four or even six wheels per axle. They better distribute the vehicle’s weight and increase grip. However, there’s still only one axle connecting them all.
Look at one side of your vehicle. How many sets of wheels can you see? Almost certainly, two. That’s how many axles you have.
How Many Axles On A Car: Conclusion
A modern front-wheel-drive car will have two axles: one at the front and one at the rear. However, yes, they’re technically made up of four half-axles.
The live axle will always have two half-axle driveshafts taking power from the transmission to the wheels. The dead axle (if there is one) will have two stub axles to allow for independent suspension.
It’s not worth getting bogged down on the technicalities, although it is good to know. So far as everyone is concerned, we can continue to refer to cars as having two axles. Simple.
Notice any clunking sounds coming from the wheel area of your car or see significant steering/tire wear issues? The axle might be the problem.
Take your car straight to a mechanic, driving slowly. Diagnosing and fixing the problem now might save you lots of money in the near future!