The H&R RSS Mustang Coil Over Suspension Kit - First Class Stuff!

A good spring and shock package is critical to maximize performance, handling and grip. The trick is to come up with enough spring rate to support the chassis and enough shock rate to control motion – all without being so firm that the car skips across the bumps or bounces your fillings out.

Last year I tested the H&R Street Performance Coil Over suspension at Autobahn Road Course in Joliet, IL. I found it to be an excellent sporty street set-up that can even cross over to light-track use. For serious track day driving it was a little short on both spring rate and shock rate which is why I was very anxious to try H&R’s new RSS package.

With double adjustable front struts and a front spring rate of 630#, this looked to be within range for my CSR Mustangs (Club Sport Racer) specifications. The 515# springs concerned me until I discovered that they are “on the axle” springs. A little math and the motion ratio works out to the mid to high 400#’s, if the spring was on the shock, which is within my CSR specifications.

Opening the H&R RSS Coil Over box instills a feeling of confidence that you made a good purchasing decision. Everything is first class and looks top-end. Now looks can be deceiving, but in this case the quality proved out. As I was reading through the instructions, one thing I noticed was the front struts were adjustable and the rears shocks were nonadjustable.

If the rear shock valving is spot on this is not really a problem as most of the drama in getting a Mustang to handle is in the front. I have seen many a weekend warrior spend too much time adjusting on their shocks rather than focusing on honing their driving skills and ultimately adjusting themselves right into the fence. The same is true with the front struts but cleverly the H&R folks made the fronts double adjustable with one adjustment. Both bump and rebound are proportionally adjusted with one adjustment knob; not as precise as a true double adjustable but a big plus for the weekend warrior crowd.

In the Shop

Installation was a breeze. Everything is an OE replacement fit. The only change we made was on the front struts, we slotted the spindle mounting holes so we could adjust camber at the spindle rather than the top strut mount as some aftermarket “caster-camber” plates would suggest – see the side bar for info on my “Fixed Strut” strategy. In the back we also “pinned” the rear spring perch adjuster to the axle housing just to make it a bit easier to adjust rear spring/ride height Note: I have off-set bolt kits to adjust camber at the strut/spindle mount for those that don’t have the capability to slot the struts.

We installed the H&R RSS Coil Over kit on the CSR-69 (our current test mule – make that our current test “Stallion”). Along with prototype pieces from my new GT4 suspension system, the latest – Gen IV evolution of the renown AGS Systems. In my last test of the H&R Street Performance Coil Over suspension you may recall that I could feel the suspension giving up under really hard driving as the geometry went through the ranges during different driving events. This time I corrected the geometry both front and rear to what we’ll call AGS Gen IV specs for now, so we could get a really good read on how the RSS spring and shock package works.

We started at a ride height of around 26 ½” front and 26 ¾” rear (measured at the fender wells). From there we scaled the car and got the corner weights pretty close. This is where the fully adjustable spring perch feature of the RSS kit comes into its own. The ability to set ride height where you want it and adjust corner weights if you are so inclined, in my book is an invaluable attribute. As a side note - I also use the rear ride height adjustment to “dial-in” my rear side-view geometry i.e. squat for better off-corner bite – more on this in the GT4 suspension article.

I have a lot of experience with and really like the “Euro” style of shock valving (KONI, Bilstein, KW, etc.) so I made an educated guess of 3-clicks off full soft for the initial shock adjustment.

At the Track

We tested at Putman Park, in Green Castle, Indiana, a favorite for Indy race teams, drivers and me. The weather was absolutely perfect and the track was fast. I was not feeling up to snuff so I enlisted the services of a couple of my friends to perform testing duties – a very accomplished amateur racer Terry Lingner and an accomplished pro Mustang racer Paul Brown, who also happens to be my son.

Terry started in the CSR-69 in the morning as Paul was working with the Speedworks guys helping them develop and test their Miller Mustang Cup race cars. In the afternoon they switched cars but the results were the same. Both really liked the feel of the springs and shocks and especially with my full GT4 suspension system. The CSR-69/GT4 was instantly quick in a very quick group of cars. My initial guess on shock adjustment seemed to be where it needed to be and we never touch it again all day.

Where the H&R Street Performance kit was too soft on spring and shock rates for serious track, the H&R RSS Coil Over kit was not. In fact, it was a very good match for the full GT4 suspension package. There was enough spring rate to support the chassis and just the right amount of shock dampening to control motion – all without being too harsh or brutally stiff. What I liked was that you can click the shock adjustment down a bit and you have a package that is equally at home on the street for day-to-day driving albeit on the sporty side.

Another plus to the H&R RSS Coil Over kit I like is the availability of two optional spring packages – one about 10% softer, for day to day driving or the lighter V-6 Mustang and one about 14% stiffer which could be a big plus if you want to take a Shelby 500GT to the track with its massive front end weight.

Conclusion

All in all, I’m really pleased with the H&R RSS Coil Over kit for ’05+ Mustangs as it’s just what I was looking for –it looks good, fits good, and works really well. The H&R RSS Coil Over kit fulfills my stringent requirements for my new GT4 “Best in Class” AGS suspension system and will be the base shock/spring combo in my upcoming CSR-GT4, “Best in Class” Track Day Mustangs.