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IRS vs Live Axle: Is There a Superior Choice for Your Muscle Car Project?

Car enthusiasts have a tendency to be fanatics not just for their preferred brand or model, but also for specific types of automotive engineering.

Rear-drive, mid-engined, turbocharged, naturally aspirated, automatic transmission or manual. We all have our favorites.

S197 Mustang Rear Axle

Suspension design might not be argued about quite as much, but even that has its distinct factions and the most obvious example is the live axle vs independent rear suspension debate, particularly when it comes to American performance cars.

2020 Shelby GT500 on Nitto NT555 RII DOt drag radials

For decades (with the exception of the Corvette) nearly all rear-drive American performance cars used rear live axle setups. And it was only in the last 10 or 20 years that IRS has basically made the solid axle extinct.

But is the live axle as archaic and inferior as its made out to be? Can the old-tech live axle actually be better than IRS? That depends on who you talk to.

S550 Mustang with Nitto NT555 RII

Using 2005+ present Ford Mustang as our demo model we thought we’d take a birds eye view and look at some of the pros and cons for each setup.

Solid Axle: Pros

Despite the fact that it’s been phased out from all modern American performance cars, a classic dialed-in solid axle can still work extremely well.

First off it's simpler. There are less moving parts involved with getting your car’s power to the ground—and the weight of all necessary components is generally lighter than an independent rear suspension as well.

Shelby GT500 Mustang on Nitto NT555 G2

Need to replace your rear end? There are endless options available, from dirt cheap junkyard replacements to fully-assembled ready-to-install upgraded units from a variety of aftermarket manufacturers.

Form a performance standpoint, a live axle is still a very effective solution, and there’s a reason why a lot of drag racers prefer a solid axle over an IRS setup. It’s easier to get power down at launch especially when running large, sticky tires like a Nitto NT555 RII street legal drag radial.

S197 Mustang GT Burnout

Generally, a live axle should also be more durable for drag racing, with less likelihood of breaking axles/joints in high power applications. This is true even when using a road course tire like a Nitto NT01.

And speaking of road racing and track days, a live axle can still perform extremely well when set up right. And since you’ll typically be driving on a smooth race track the extra flexibility of IRS isn’t needed as much. Just look at how well Ford dialed-in the live axle setup on the 2012-2013 Mustang Boss 302.

Mustang Boss 302 Rear Suspension

Solid Axle: Cons

On the other hand, there’s a reason the Mustang ditched its live axle after the 2014 model year. And the biggest reason for that is simply a lack of refinement.

S197 Mustang Suspension

In hard performance applications, it might not matter as much, but refinement is a big deal for most drivers. And a live axle is generally going to be less comfortable and less predictable.

S197 Mustang Burnout

And while raw handling figures might not be impacted at much, a solid axle car is generally going to take more driver effort to be smooth and consistent while cornering. For better or worse, a live axle is going feel a lot less “modern.”

Independent Rear Suspension: Pros

Naturally, an independent rear suspension excels in areas where a solid axle doesn’t. Comfort is a big positive, and with the rear wheels reacting to the road independently of each other, it’s much easier to soak up bumps.

2015 Mustang GT and EcoBoost

Most of these benefits will be noticed during everyday driving, with a more comfortable ride and more predictable handling.

S550 Ford Mustang Rear Suspension

There are benefits to this in spirited driving as well, especially if you aren’t on a glass smooth surface. For example, an S550 Mustang with IRS is less likely to get upset over uneven pavement than S197 with a live axle.

Independent Rear Suspension: Cons

Despite being the default choice for the modern Mustang (as well as the Camaro and Dodge Challenger) IRS isn’t always perfect.

S550 Mustang EcoBoost Red

Launching a high horsepower, rear-drive car with IRS can be challenging—especially when wheelhop rears its ugly head. It’s basically a side effect of each wheel being able to move up and down apart from each other and is a bane of IRS drag racers everywhere.

S550 Mustang GT Drag Racing

There’s also the added weight and complexity of an IRS setup, and this one of the reasons the S550 Mustang weighs more than the S197 it replaced.

Thankfully, there are aftermarket upgrades you can get which can improve IRS performance under hard acceleration. Steeda’s “Stop the Hop” kit is one of these, and it’s greatly improved our S550 Mustang GT project car.

S550 Mustang Steeda Stop The Hop Kit

The Verdict?

If your car is a daily driver or something you enjoy on public roads often, you’ll probably appreciate the refinement that independent rear suspension brings.

S550 Mustang GT on Nitto NT55 G2

If your car is a weekend toy or track project, you’ll probably be fine (or maybe even better off) with a solid axle, especially one with supporting aftermarket suspension upgrades.

S197 Mustang Boss 302 Rear Suspension

And fortunately, there are enough upgrades for both types that either setup should be able to work well for your uses.

S550 Mustang GT on Nitto NT555 G2

As with many debates in the car world, there’s really no definitive right or wrong answer for this question. And that’s a good thing.

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