Axles are an essential component of all cars. Toll roads use this very loose definition of an axle: every pair of opposing wheels connected and the vehicle frame. Of course, there's much more to an axle than this, which we'll be covering in this post.
Your typical passenger car will have two axles, one for each pair of wheels. Certain types of vehicles will sometimes have more than two axles. Other kinds of motor vehicles might also use varying amounts of axles.
Continue reading to learn more about car axles and how they work in popular types of vehicles.
- What are Axles in a Car?
- How Does the Axle of a Car Work?
- How Many Axles Does a 4x4 Have?
- What is Considered a 3 Axle Vehicle?
- How Many Axles are on an 18-Wheeler?
- What is a Full-floater Rear End?
- What Does a Broken Axle Look Like?
What are Axles in a Car?
For a more proper definition, an axle is a rod that connects two wheels and turns the wheels when you're accelerating. When learning about your car, you'll also hear about bearings. These support the axle and sit inside the middle of the wheels.
The design of the axle keeps the wheels' position so that it can bear enormous amounts of weight.
Every axle differs depending on the type of car. Car experts say customized axles perform better at controlling speed and torque so long as it's properly maintained.
Cars can come with two-wheel-drive, four-wheel-drive, or all-wheel-drive.
How Does the Axle of a Car Work?
An axle's job is to make the connecting wheels move. It does this by transmitting torque to the wheels. This means enduring the forces of acceleration and braking while carrying the vehicle's weight. Your vehicle couldn't move without the axle.
The specific way an axle works depends on the type of axle you have. All cars have a split (or drive) axle, but some could have a dead axle as well.
Split Axles (Front-Wheel vs. Rear-Wheel Drive)
This is the more complex axle; it has a joint that connects to the driveshaft, which transfers motion to the drive axle. According to Veenstra's Garage, Front-wheel drive vehicles mix transmission power with the front axle. Rear-wheel drive vehicles have the drive axle turn from the back of the wheel.
Dead axles don't attach to the engine. Wheels connected to this type of axle only move when the vehicle moves. The primary purpose of dead axles is to help with carrying large loads and distributing their weight.
Signs it's Not Working Properly
Damage to any axle will prevent proper movement of the vehicle. It can get damaged by hitting steep potholes or by bad carrier bearings.
You'll likely need an axle repair if you hear or feel the following abnormalities:
- Bad vibrations after hitting a curb, bump, or pothole
- Grease leaking from the tire edge (note that this will cause damage in the long run, not the short run)
- Unusual loud clanking noises after putting your car into gear
- Vehicle won't move no matter how much you press on the accelerator
Later on, we'll talk about what a damaged axle looks like.
How Many Axles Does a 4x4 Have?
A 4x4 has two axles. But what do the 4's mean if it doesn't mean the number of axles? The first 4 represents the four-axle ends on both of the axles. The second 4 represents the wheel drive of the vehicle. The term "4x4" often gets mixed up with four-wheel-drive/4WD.
Both terms mean that four wheels get power transferred through the axles. The difference is that a vehicle with 4WD doesn't have to only have four wheels. Even all-wheel-drive/AWD could get confused with the previous terms.
People mix up these terms all the time because almost all consumer cars have four wheels. Therefore, there's no significant difference in features. It just has an advantage over 4x2s; 4x4s can handle off-road driving much smoother than 4x2s but are less fuel-efficient. The other difference is whether the driver has to activate 4WD (or AWD) or not.
What is Considered a 3 Axle Vehicle?
The most common vehicle with three axles are trucks with a medium-heavy weight capacity. Commercial coach buses and some full-size RVs (depending on the length) are also common examples.
3-axle vehicles have one axle connecting the two front wheels and two back axles connecting the other four. The extra axle is to help carry the weight of the cargo. One of the back axles will be powered from the engine, but sometimes both back axles will too.
Just a note for if you're towing a trailer on a toll road, all the axles count when calculating toll costs. That means the vehicles on your car, plus the axle(s) on your trailer, even if it isn't part of your vehicle.
How Many Axles are on an 18-Wheeler?
Here's a fact about axles that haven't been shared yet. An axle doesn't only connect one pair of wheels. Two pairs of wheels can attach to one axle. The proper term is "dual rear wheel." It just makes carrying cargo safer in case the main tire blows out while on the road.
We say this because, with the information already provided, it can seem like an 18-wheeler could have nine axles. However, they have five axles: one in the front, two in the middle where the trailer attaches to the truck, and two in the back of the trailer. The axles underneath the trailer have four wheels per axle.
Infrequently, you'll see a truck with more than 18 wheels. That's just because it's carrying super-heavy cargo, and the extra tires are for support.
What is a Full-floater Rear End?
The axles on the rear end of the vehicle handle more of the cargo weight, torque, and thrust. Depending on the make or model, your vehicle could have a full-floating or a semi-floating axle.
Full-floating axles are made for vehicles designed to handle extremely severe driving conditions or carrying heavy loads. These axles are quite heavy yet durable. The axle's housing supports the weight of the car. Its torque transmits through a separate weightless axle shaft.
It's much more common to see a vehicle with a semi-floating axle. These axles bear the weight, transfer torque, and weigh much less.
What Does a Broken Axle Look Like?
When you hear bad vibrations after a curb or a wobbly feeling at slow speeds, check underneath the vehicle. One way to visually tell your axle is damaged is by looking at the wheels. If it appears to wobble while in motion, the axle is bent. This could hinder the brakes' ability to function.
Another way to look is to examine the universal joints. A broken axle will have snapped around that area.
Depending on the build, your car could also rest lopsided. Although you can't see the axle, you can safely assume it's the problem if your car leans.
Is it Safe to Drive a Car With a Broken Axle?
Odds are you won't be doing any driving if an axle is broken; power can't transfer to the wheels without the axle. If it's only partially broken, it can still drive, but it's not safe at all. When it entirely breaks, control of the vehicle is lost. You risk crashing into something or another car.
If you feel that your axles are on the verge of braking, get your car towed to a mechanic to get it fixed. Do not try to ride it out until it completely breaks. It can break at any moment, putting you and others at high risk.