Project Budget 400WHP S197 Mustang Track Car: Part 7 – Springs, Shocks and Bars

S197 Mustang rear suspensionNext up are the rear springs and shocks.  The S197 Mustang rear suspension consists of an axle-mounted inboard spring, and a further outboard shock, which has more control and precision than an inboard mounted shock.

S197 Mustang stock spring and bumpstopWe removed the rear swaybar and shock to get to the rear spring.

S197 Mustang rear shock Steeda Pro-Action vs stockWith the rear shocks removed, we can see the new Steeda Pro Action Shocks (bottom) are also the same length as the factory shocks (top).

S197 Mustang rear spring removedNext, we removed the factory rear spring.

S197 Mustang Stock Axle BumpstopThe axle-mounted bump stop is the limiting factor of the rear suspension travel.  The new Steeda Sport springs will lower the rear ride height (and rear travel) by 1.25”.  This will cause us to hit the bump stops sooner and harder on the street, as well as potentially under normal accelerating conditions.  This will significantly hurt rear grip and ride quality.

S197 Mustang bumpstop removedWe unbolted the axle-mounted bumpstop in anticipation for a proper rear bumpstop that I am developing and will be out very shortly (stay tuned!).

Quick Reference:

Page 1 – Front OEM Spring/Shock Removal
Page 2 – Front Steeda Spring/Shock Install
Page 3 – Rear OEM Spring/Shock Removal
Page 4 – Rear Steeda Spring/Shock Install, Steeda Swaybars
Page 5 – Front Swaybar and Radiator Support Brace Removal
Page 6 – Front Steeda Swaybar and Radiator Support Brace Install, Rear Swaybar
Page 7 – Rear Steeda Swaybar Install
Page 8 – Street Review, Bumpsteer Kit, New Steeda Suspension Package



  2. Billy Johnson articles are the best. I have had tons of miatas and now I want something with some actual hp and a lot better as a cruiser. I like this bodystyle the best out of the 2005+ Mustangs and following Billy’s blueprint sounds like it would be an amazing street car.

  3. What about just leaving the rear bar off? Or is that only suggested if you are running a Watts Link? Great article, glad to see the S197 the attention it deserves!

    1. It depends on the rest of the suspension setup. As I mentioned in the previous article, most Watts Links raise the rear roll center too much, increasing roll resistance and weight transfer (hurting rear grip). Because of this, removing a rear swaybar is a common solution to the problem of having a high rear roll center. Running too stiff of a rear spring in a WL or PHB rear setup often leads to a loss of rear grip, where removing the rear bar would also be a solution. There are many different ways to make a car turn a fast lap. Some have more strengths than weaknesses but various setups can be made to perform similarly over 1 lap. At Roush, we won a ton of races with a rear swaybar and a panhard bar. This project is focused on how to make a great handling car that doesn’t beat you up on the street for as little money as possible, and we are achieving that. Ditching the rear bar off our setup would not make our car handle better, and this rear bar may not make a car with a Watts Link handle better. That’s part of the development process, which takes testing.

  4. Really enjoying this build!

    What size is the stock sway rear sway bar? Is it viable to use the stock bar in lieu of the 7/8″ Steeda bar?

    1. This is the same size as the stock 05-10 GT rear bar and smaller than the 11-14 rear bar. To make a car have a balanced handling characteristic, the entire suspension system from the springs, shocks, swaybars, tires, differential, and geometry all need to work together. In general, people tend to put too large of rear swaybars on their S197 Mustangs; taking grip away from the rear in attempt to make the car more balanced, rather than working on ADDING grip to the front to make it balanced.

    1. A shorter shock body would have no effect since the suspension travel is limited by the factory AXLE-mounted bumpstop.

  5. Thank you for the write up, looking forward to purchasing that Steeda package when it comes back in stock next month! As for wheels, are those the S550 PP wheels (255/275 if I remember correctly)? Will you be moving to a square setup with this build, or sticking staggered? Thanks again!

  6. Billy,

    I’m curious on when you think we can see an update on the rear bump stop discussed in Page 6: “We unbolted the axle-mounted bumpstop in anticipation for a proper rear bumpstop that I am developing and will be out very shortly (stay tuned!).”

      1. I’m curious on when you think we can see an update on the rear bump stop discussed in Page 6: “We unbolted the axle-mounted bumpstop in anticipation for a proper rear bumpstop that I am developing and will be out very shortly (stay tuned!).”

        Any word on this?

  7. Hi there, I was wondering if you think buying BMR K-member and a BMR A-Arm support brace (since they seem to go hand to hand with each other) is a good choice? Do you have much experience using those parts and how it collaborates with other suspension parts? It seem like a good choice considering you are shaving weight at the front despite spending a couple more hundred dollars.
    And one more question, what are your thoughts on a rear shock tower brace? Is that also worth a buy?

  8. Just bought a 2014 GT and this documentation of your design and build is outstanding. Not likely to track it, but I do want to have a more serious road car. Looking at cutting some costs, following your suspension plan, would changing the
    Steeda heavy duty mounting plates to the Ford Performance Racing mountain plates
    Steeda lower control arms with Steeda X11 ball joints
    Provide good feel and control?


    1. Billy, After reading through the comments in section 6, I found a similar question and your reasonings for Steeda LCA added to the build. Sound thought process. Thanks again for this excellent article series.

  9. Hi Billy, a question regarding the springs. My 2014 GT has had the Ford Performance K springs lowering 1.5″ all the way around. Will this work well with your recommendations every where else on the suspension?

    1. I’m not sure what the K spring rates are vs Steeda. I would imagine they aren’t too far apart and most of the other parts of the build should work great with them.

  10. “I urged Steeda to offer this setup as a handling suspension package because of how well balanced and grip-oriented it is. They actually did it and created the Steeda Mustang Sport Handling Package (555-2356).”

    You should clarify that it’s listed for 2011-2014. Guess early S197 owners are just out of luck.

  11. Billy,

    I’ve been replicating this build as closely as possible over the past few months. So far, I’ve done the engine upgrades, tuning, and just recently installed all of the suspension and handling upgrades as suggested. I’m scheduled to get the Eaton LSD installed tomorrow. With the changes made so far, the car has obviously been lowered and handles much better. I can’t wait to see how it performs with the Eaton LSD. I am running into a minor issue since making the changes and that is hood flutter over 80 mph. I’m curious if you ran into this problem during your build and/or if you have suggestions on how to address it. As always, great stuff and really enjoying the process so far. Thanks.

    1. Did you finish the build? How closely did you follow the build? How does it perform? I am looking to replicate this build. Thanks

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