When transitioning into
the 2015 S550 Mustang, Ford was faced a chance to truly change the
driving experience of the car. The Mustang that was incredibly straightforward with its solid rear axle
design was no more - in its place came the first independent rear suspension Mustang since the 2004
Cobra. Independent rear suspension is a major advancement for the best-selling coupe in the world.
Independent rear suspension, while common on many performance coupes both inside and out of the United
States, had not been available on the Mustang until the S550 generation outside of just the 1999-2004
Cobra. The return of independent rear suspension meant reworking handling upgrades for the Mustang since most
companies had worked heavily on the solid rear axle setup found in the Mustang in years past. With every
generation running on a solid rear axle dating back to the original in 1964, the welcome change did come
with some complications but was met with overall excitement. With modern technology in the suspension
including the MagneRide system, independent rear suspension is much more stable but does it change the
personality of the Mustang?
Solid Rear Axle
Benefits Of SRA
Independent Rear Suspension
Benefits Of IRS
Uses & Applications
From the beginning, the Mustang has run on a solid rear axle across the rear of the car. This is the
simplest setup for connecting the rear together for suspension and in a rear-wheel-drive car, it is also
an effective way of putting a lot of power down for not much money. A solid rear axle or solid axle
suspension consists of the suspension pieces sitting on the solid rear axle that connects the back
wheels under the car. It is a very basic and easy to engineer setup which explains its use in many
vehicles such as the Mustang until 2015 and the Wrangler as well as racing cars found in NASCAR. This
type of suspension is cheap and effective in straight lines and when trying to kick the tail out on a
car since it is predictable to control. Many cars used to run with a solid rear axle including most muscle cars, the Crown Victoria, and other
front-heavy cars. In cars like the Mustang, the solid rear end helps with weight distribution and in
many cases can perform equally as well when set up properly. This setup is very simple in relation to
different rear suspension options and truly fits the old adage of “if it ain’t broke, don’t fix it”.
While it is old technology, the Solid Rear Axle setup is proven to work well. When a driver is aware of
the shortcomings found in Solid Rear Axle cars, they can in most cases correct their driving enough to
not only keep pace with cars on IRS but in some cases beat them as well. Cars equipped with solid rear
axles do benefit from some weight savings because of their setup. Solid rear axles are lighter weight
than independent suspension because they lack the engineering required to keep both wheels separately
stable. A solid rear end saves weight by not needing the overengineered suspension equipment in the
back.
Another major benefit of SRA over IRS comes in the form of durability. While it may be old technology,
SRA is still around because it is highly durable and can take a serious beating without needing to
repair it. The simple construction lets it handle abuse in the Mustang associated with racing, hard
launches, and aggressive cornering as well as in off-road vehicles by providing better power application
and suspension tuning. With the Bronco Raptor, Ford even brought back the solid rear axle because it is
more durable While muscle cars have held onto their solid rear axles for years, moving towards independent rear
suspension was a logical step towards advancing the Mustang name. Independent rear suspension made its
first appearance on the Mustang in 1999 on the Cobra and as a result these cars drove much better than
the normal GT models at the time. Independent Rear Suspension allows each wheel to adjust separately
from the other, keeping it more stable over bumps, sharp corners, and acceleration. As a result, these
cars have better road manners over bumps and potholes in day-to-day driving. Many European and Japanese cars feature Independent Rear Suspension setups since their performance
vehicles were designed for sharp turns both on and off of pavement. These cars are able to handle easier
on winding terrain as the rear wheels do
not shift as one unit, rather they adjust separately from each other. On terrain that may differ around
bends, IRS can adjust more quickly and adapt to the new level of elevation. While SRA is incredibly usable in many settings, IRS definitely has its place in the performance world.
The performance found in IRS suspension focuses on handling and ride quality whereas SRA focuses on
straight-line performance and durability. As it has been stated, IRS keeps the rear of the car more
controlled around corners as it can adjust more than SRA can. The separate suspension per wheel can
function independently as a result of its setup. This keeps a car more properly planted on the road
around corners and over rougher patches of pavement. In a Magneride-assisted
car, this suspension acts
in conjunction with the magnetic fluid inside it to give the smoothest ride possible. Outside of ride quality, IRS when tuned properly can handle road courses or canyon and mountain roads
with ease. It takes less to adjust in IRS cars than with SRA cars since they already work independently
of each other. SRA cars need to be fully dialed in in most cases to handle at the same level as an IRS
car. While they may feel more predictable, IRS cars still will handle better, even if it feels less
predictable behind the wheel. IRS also has more adjustability regarding upgrades since each individual
aspect of the suspension can be modified. A lot of the uses and applications of these rear setups can be used interchangeably, but they do have
their strengths and weaknesses against each other. These suspension options can be used in the same
settings, but they will display their strengths and weaknesses when directly tested against each other.
As stated, the old-school solid rear axle setup is incredibly durable and great to use for smooth tracks
and for drag racing in stock form, and when modified can compete nearly as well around a track as a car
fitted with independent rear suspension. A solid rear axle is a great starting point for building up
handling. They are more predictable and communicative than independent suspension is since it is one
large connected rear axle. It is more useful to have a solid rear axle if you want to learn to control
your Mustang before tracking it. Independent suspension is a great advancement over the solid rear axle in many ways. For the experienced
driver, an independent suspension setup will help them dominate on the racetrack. With the ease of
driving over rougher or uneven terrain common in this setup, IRS is better at taking sharper turns and
handling faster movements than a solid rear axle could. While it is a more complex setup for suspension
and has more than can be a problem over time, it is more capable when in the hands of a well-trained
driver. While IRS is designed to improve handling, they do have major applications on the drag strip. While these
setups are more well suited for cornering, we at Steeda have proved how quickly these cars can go down
the drag strip with our Silver Bullet drag car. These cars require more rear-end bracing to perform as
quickly but they are able to evenly distribute their power between the rear wheels. The S550 Mustang has
proven itself to be an absolute monster on the drag strip, partially due to the lightning-quick 10R80
transmission, but the independent rear suspension is a great way of evenly putting the power down. With
a well-upgraded suspension and our Stop
The Hop drag kit, these cars can tackle the drag strip perfectly, outrunning many more powerful
cars.
Best Mustang Motors Ever Track Specials: 2021 Mach 1 vs. 2012-2013 Boss 302 Does My Mustang Have MagneRide?Solid Rear Axle vs. Independent Rear Suspension
Solid Rear Axle
Benefits Of SRA
Independent Rear Suspension
Benefits Of IRS
Uses & Application
Steeda's
Silver Bullet Mustang drag car equipped with full
Steeda drag racing components for IRS
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