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Mustang Solid Rear Axle VS Independent Rear Suspension

Created by Andrew Perry / 5 min read
Last Updated: 2/6/2025

Follow along below as we dive into the differences and features of the solid rear axle and the independent rear suspensions featured in your 1979-2025 Mustang!

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There are 2 main types of rear-end suspension setups available on the Mustang: the solid rear axle (SRA) or live axle and an independent rear suspension (IRS). From 1964 to 1978, the Ford Mustang came equipped with an SRA with leaf springs. In 1979 to 2014, Ford swapped over to an SRA using coil springs. However, in 1999 Ford released the Mustang Cobra model, introducing the independent rear suspension. All 1999-2004 Mustang SVT Cobra’s would come factory with IRS, as well as the S550 Mustang to current models from 2015+.

 

What is the physical difference between a solid rear axle and an independent rear suspension?

·   A solid rear axle setup also known as a live rear axle, is comprised of an axle tube housing that connects both rear wheels using full-length axles. This causes both wheels to move with one another.



·   On an independent rear suspension, the wheels are connected by axle shafts or half shafts. This system allows for each wheel to move freely from one another. IRS also uses lower control arms similar to the design of the front control arms. 

 


What does “IRS” stand for on a Mustang?

·   IRS stands for independent rear suspension.

 

What are the benefits of a solid rear axle?

·   Solid rear axle suspensions are lighter than IRS while still known for their durability. 

·   Solid axle setups are simpler systems in terms of fewer moving components, which allows for a smaller margin of error in terms of parts breaking.

·  Easier to build than IRS due to the simple and straightforward design.

· Great for straight-line racing. When paired with the right supporting mods, a live axle rear end can be almost as effective as an IRS.

 

What are the benefits of an independent rear suspension?

·   IRS suspension was designed with improved handling and overall better ride quality in addition to acceleration over solid axle suspension.

·   There is more controllability in each wheel when cornering versus an SRA. This includes a reduction in wheel hop as well.

·   Many aftermarket products and upgrades are offered to further improve or replace IRS components, such as stronger axle shafts, bushings, links, and arms.

·   Excellent for road course racing. With IRS, cornering and reduced body roll are major factors over an SRA suspension. 

 

Is independent rear suspension or solid rear axle better for drag racing?

·   The IRS system is great for many applications from racing at the drag strip to autocross. This independent suspension has showcased greatness in holding power while distributing it evenly between both wheels. The stability that IRS has through corners and bumps also carries through during acceleration, making it a great all-around setup.

·   Although the IRS is the latest and greatest technology when it comes to the Mustang, solid rear axle suspension is still commonly used in drag cars and is popular for swaps.
Thumbnail image of the author of this article, Andrew Perry.

About the Author

Andrew has been writing content for Late Model Restoration for over 2 years, producing over 50 articles. Over the years, Andrew has owned numerous Mustangs, including a 2007 V6, 2003 GT, 1967 GT, 1994 GT, 1995 GT, 2014 GT (2), 2000 V6 (V8 swapped), 2016 GT/PP, 1988 LX 5.0, and a 2009 GT/CS. Read more...