Why Muscle Car Guys Love the Live Rear Axle so Much

When the newest generation Ford Mustang was revealed to be housing an Independent Rear Suspension (IRS) for production, there were some mixed reactions. For the Road Racing/Autocrossing Mustang fans, the reaction was, “YESSSSS!!!“, for the traditional Mustang fans it was, “NOOOOOOOO!!!!“, and for Europeans it was “About time you cavemen.“

But why were so many people upset with the addition of an IRS? After all, isn’t an IRS better? Well, that’s a matter of perspective really. My goal here today is to explain some of the benefits of a live axle and why muscle car guys in particular love them.

What Are the Benefits of a Live Axle Rear?

A live axle rear is a very simple rear diff and rear suspension setup. It’s basically just a horizontal tube, with axles that connect the outside brakes/wheels to the inner differential, which then connects to the drive shaft. Poof. That’s all there is. You can then add various suspension components to connect it, like lower control arms, sway bar links, spring/shock perches and mounts, etc. In essence, because of its simplistic design, the live axle has the following advantages over an IRS (in general):

(1.) Less Complexity: This simple design means the live axle is easy to make durable and has lower manufacturing costs. Upgrading and replacing components is also cheaper and easier to do. Not only that, but there is less overall weight, which is better for performance.

(2.) Great Option for Powerful RWD cars: Affordability isn’t the only reason live axles tend to make it into muscle cars. With the exception of the GM 7.5” 10-Bolt rear end, most live axles made can handle some abuse and put the power down. Muscle cars have big torquey engines, and thus need a strong and stable diff/suspension setup to transmit that torque to the wheels. In addition, wheel hop and “squirrely” behavior caused by spinning the tires in a RWD car is a BAD thing. A live axle’s inherent design makes it perfect for putting the power down efficiently and accelerating in a straight line, which is why a comparable car with a live axle will have better acceleration times, along with less weight.

Comparing an IRS to a Live Axle, and how to Improve the Live Axle.

The Ford Mustang has flirted with an IRS in the past, however. It was a staple part of the 1999-2004 SVT Cobra design. The benefits of this IRS setup were improved ride comfort (something the Mustang was begging for) and better handling. To put it simply, a live axle’s main failure is that with ride quality. Live axles do not like bumps or angles in the road. When manufacturers put in an IRS, this is usually the reason why, since customers demand comfortable cars. An IRS can move each wheel independently and has less unsprung mass (in a live axle, the whole assembly is the unsprung mass), meaning it can absorb bumps and go around angled roads (corners) with much greater ease. Thus, handling can be improved since now the wheels can move with the road and glide over bumps. The differential also never moves and remains centralized.

However, as I said before not everything is hunky-dory with the IRS. That independent wheel movement and extra weight can have negative impacts on performance in powerful RWD cars unless upgraded properly. In fact, the SVT Cobra’s IRS was heavily criticized by owners, with some even swapping the IRS out for a live axle because of wheel hop, traction issues, and trouble going in a straight line. Here’s a video to show what I’m talking about:

And this is precisely why muscle car guys prefer the live axle. Now as I’ll explain later, modern IRS systems have vastly improved, which is why they’re great in the new Mustang and Camaro, but back to live axles.

So What About Handling?

Live Axles are often criticized for their lack of ride comfort and worse handling, and they certainly deserve some of that criticism. Luckily the aftermarket has given us numerous solutions that make a Live Axle come very close in performance and comfort to an IRS. Some basic upgrades include:

(1.) Traction adders: Torque arms, Sway bars, lower control arms, shocks/springs and relocation brackets. Look at the red components on my Camaro’s live axle to see these.
-A torque arm is the crowd favorite of live axle guys because it’s a suspension arm literally designed to push the whole axle down into the ground, which gives better traction, less brake dive, and proper setting for pinion angle. IRS cars have found these torque arms to be beneficial too, in order to improve traction.
-Relocation brackets and LCA’s have the same goal as the torque arm, to help keep the whole live axle down on the ground stiffened up. Relocation brackets are mainly used on lowered cars.
-Sway bars: A sway bar helps keep the live axle stable through the corners and off the line in a drag race.
-Shocks/Springs: Stiffer Shocks and springs help keep the axle planted to the ground and absorb energy from bumps better, but be careful. Too stiff and performance might be negatively impacted.

(2.) Panhard bar and Watts Link: As said before, in an IRS the differential doesn’t move and is kept central, which highly desired for good handling and comfort. Well unfortunately in a live axle we can’t keep the diff from moving, but we can keep it centralized. That’s what the panhard bar and Watts Link accomplish.
-Most live axle rears just use panhard bars due to lower cost and less complexity, since it’s just a bar that connects one side of the live axle to the other side of the car’s frame. This helps keep the rear from moving laterally, but it isn’t perfect. Think of the panhard like the radius line on a circle. As you increase the angle of that set radius, the point on the circumference moves just ever so slightly horizontally. This the disadvantage of a panhard, it creates a small arc within the roll center of the differential, and thus the car has different handling characteristics depending on the direction you turn it. The longer the rear end (and thus the panhard), however, the less noticeable this effect is.
-A Watts link, on the other hand, is like two small panhards connected to a center bar that rotates on the center of the diff. It keeps the diff almost perfectly center, and in terms of handling and comfort is about as close to an IRS as a live axle can get. Here’s how they look:

Fear Not Live Axle Fans, as IRS Systems Have Vastly Improved!

While the IRS still has some negatives that muscle car guys aren’t huge fans of, the good news is both Ford and Chevy have been working hard to make them better and better. The new GT’s IRS uses many aluminum parts to keep weight low, and GM’s new Alpha platform IRS setup in the 6th-gen Camaro has proven that it can not only handle straight line duty, but can even keep up with near race cars like the BMW M4 GTS on the track!

So if you’re someone with a non-current muscle car, you live axle isn’t as bad as everyone online says it is, it has its own distinct advantages. With proper modifications your live axle can keep up with its IRS counterparts in terms of handling and comfort.
Let’s not get too discouraged with these new generation muscle cars with IRS setups though, as they have shown you can have your cake and eat it too.