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Pedders eXtreme xA Coilover Kit (S197 2005-2014 Mustangs) First Impressions & Installation

If you've been following me, it's no secret by now that I recently got a sponsored set of Pedders eXtreme xA Coilovers to test, thanks to American Muscle. I have been wanting to do something about the stock suspension on my 2012 Boss 302 for a while but budget didn't allow. When the opportunity came knocking, I couldn't be happier. The kit includes coilovers only up front to replace the stock struts but maintains the separate "divorced" damper (shock/shock absorber) and spring setup in the back, a common solution for plenty of entry level/budget coil over options as well as more established brands like KW and Eibach until you get to their flagship or race kits. Even the Maximum Motorsport (MM) JRi coilover kit - a package that is far from a budget or mild street option - retains the divorced spring/damper mounting.

While a true coilover setup in the back would be better, it would be more expensive and at this price point, I think the money is better spent on the damper itself rather than a coilover design. Plus, the divorced spring/damper setup separates forces going through the spring vs the damper. The factory developed Boss 302S and Boss 302R cars used true coilovers in the back but tied the top of the rear damper/shock mount to the cage to reinforce the mounting point. Absent reinforcement and/or a thoroughly tested upper pad design with no failure, there is an increased risk of cracking or failure so its best avoided in my opinion in a budget option.


With that out of the way, let's get straight to the kit itself. In addition to the coilovers and springs and dampers/shocks in the back, it comes with shortened front sway bar end links and coilover spanners/wrenches for height adjustment. First off, let's start with specs:

Pedders xA front spring rate: 7 kg/mm - 392 lb/in.
Pedders xA rear spring rate: 5 kg/mm - 280 lb/in.

Compared to the stock Boss 302 spring rates:

Stock Boss 302 front spring rate: 2.6 kg/mm - 148 lb/in.
Stock Boss 302 rear spring rate: 3.3 kg/mm - 185 lb/in.

Given the same mounting setup in the back (i.e. separate spring/damper in stock mounting locations) and a solid axle, motion ratios are the same in the back. Front motion ratio would be slightly different due to the drop and possible camber (if you get the camber plates, more on that below), but at stock height and stock camber, it is also virtually unchanged. Given essentially unchanged ratios compared to stock, there is a very clear change to the stock handling balance with all else being the same. This is also true for S197 stock/base GT, Brembo/Track Pack GT, and Boss 302 Laguna Seca, all of which have different spring rates but still use numerically higher (stiffer) spring rates in the back than the fronts. 

The reversal in stiffness balance front-to-rear is the status quo for all mainstream S197 aftermarket lower springs, though, (i.e. Ford Performance, Steeda, Eibach, SR, H&R, and BMR) or coilover kits. The spring rates in this kit are significantly stiffer than the majority of lowering springs as you'd expect but they are on the softer side for a coilover setup which makes the rates a great match IMO for dual duty street/track setups without big aero.

My 2012 Boss 302 in 2019 (stock suspension) - T8 at Atlantic Motorsport Park - Kevin Doubleday©

Unfortunately, I don't have more specs to give you. I requested shock dyno results/graphs from Pedders but they said that was confidential. This is not unusual for shock/damper manufacturers to not share but it would have been nice to see before committing to the kit for moderate to heavy track use, especially if buying outright.


For a car that will see track time, the most important thing to know is that the S197 Pedders eXtreme xA coilover kit does NOT come with adjustable front coilover mounts. Pedders does offer S197 eXtreme XA camber plates but they are sold separately which are a must for a car seeing regular track time. Fortunately, whether you get just the coilovers or the camber plates, you don't have to worry about compatibility or fitment depending the S197 year and whether you have the early strut mounts (05-10) or newer (11-14). The non adjustable mount with the kit and the camber plate do away completely with the factory strut mount as you would with a coilover kit.

Aside from the camber plates, the package has plenty of adjustability built in. Height is adjustable from 1-3" both front and back compared to a standard GT according to Pedders. On a Boss 302 like mine, you can maintain stock height up front if you want, but you'll have a minimum drop of approx. 1" in the rear with the adjustable spring perches set to their max height. For a starting point to try to maintain stock geometry and clearance for my driveway, I left the rear at their max height (1" lower than stock) and dropped the front approx. 1/2". 

On a side note, if you have the stock driveshaft, you don't have to worry about pinion angles and potentially needing an adjustable rear upper control arm, but you would need at least an adjustable panhard bar to recentre the rear axle with a wide tire setup. However, I would strongly recommend a Fays2 Watts Link. You will never have to worry about adjusting a bar every time you make a small drop, it makes the car far more approachable and settled over bumps, and I have had mine for several years with countless track days and it shrugs off any sort of abuse you can throw at it with fantastic support, plus offering additional tuning by allowing you to move the rear roll centre.

The dampers are adjustable for both compression and rebound, although not separately. Pedders touts that they are monotube dampers which makes for good PR but whether they will hold up like a more premium twin-tube design such as Koni remains to be seen (make sure to follow for updates!). Both fronts and rears have 30 positions with nice distinct detents for each position and each position stiffens or softens compression and rebound at the same time.

Adjustability is also very easy and accessible for damper settings and ride height. A knob at the top of each damper/shock adjusts stiffness and you can access the front coilover height adjustment without affecting preload or taking it off the car, you just have to jack/lift the car, take the wheels off, and loosen the locking ring at the base of the threads, and screw the threaded damper/shock body into or out of the coilover sleeve to lower or raise the front. Likewise in the back, the adjustable spring perches are accessible just by jacking/lifting the rear end and taking the wheels off. Make sure to adjust the height of both the rear damper/shock as well as the spring perch since they are separate in the back.

The camber plates are unfortunately not as accessible. I had Maximum Motorsports (MM) Caster/Camber plates up until now on the stock struts and they (like plenty of other motorsport/track focused products) allow adjustment without dropping the struts, but the Pedders camber plates don't. The top of the strut tower conceals four nuts that lock the bottom plate the coilover mounts to to the top plate that mounts to the car/the strut tower. It's a simple universal design that Pedders (and others) uses across multiple platforms likely for cost and only customizes the shapes of the plates to suit the application/specific car.

As a result, this is more of a "set it and forget it" camber plate unless you feel like jacking your car up at the track, dropping the strut, and dialing more or less camber. I suspect that won't hurt them, though, since the camber plates are not marketed as a standalone upgrade and neither should they be. They are only compatible with the Pedders coilovers. On the bright side, they do have a good range of adjustability which I will talk about in the next post.


I decided to find an installation video and follow it. With the help of a good buddy of mine and his garage/lift, the install took about 2.5 hours (except for the rear dampers which would not have taken any longer but more on that in a sec).


I found more than one installation video on YouTube but unfortunately they all didn't detail a step in the rear damper installation. While the front coilover doesn't use any stock components aside from hardware/fasteners, the rear damper uses the factory rubber pad/mounts and I had two issues with that:

1. The damper rod for the Boss 302 is a larger diameter (thicker) than the GT. Since this kit is built around the GT dampers, the top washer/bushing assembly was too wide for the threaded end. I needed GT mounting bushings/nuts (stock Tokico rear damper/shock on the left with stock Boss 302 upper mount bushing and Pedders rear damper/shock on the right with stock Mustang GT upper bushing/nut assembly above). This is why we couldn't finish the installation the first time through. We wrapped it up with the Pedders coilovers and sway bar end links up front and Pedders springs and perches in the back. 

2. The Pedders washer on the damper side (i.e. where the bushing on the damper side mounts to the chassis) is very small. The rubber bushing itself would have a very small seating area as a result compared to factory dampers/shocks (above on the left) which have a large seat right into the body of the damper/shock. I didn't like the Pedders washer at all (below). 

For the rear damper install, I picked up a couple different parts; I bought genuine OEM upper bushing/washer assembly for a stock GT from our local Ford Dealer (two pictures up on the right hand side) so it could match the size of the threads on the Pedders rear damper/shock body. I also bought Monroe OEM equivalent dampers/shocks from a local parts store as a back up to make sure I had all mounting hardware/bushings just in case. I ended up using bits of both.

Each Monroe replacement damper/shock came with two round rubber bushings, two large washers, and a top mounting nut. I liked those larger washers much better than what came with the Pedders kit (pictured below is one of those rubber bushings and one washer on top of the Pedders washer for size comparison). 

I was going to use those round bushings that came with the aftermarket damper (above) which felt a bit stiffer than factory, but after mounting it I found the damper rod tilted towards the inside of the trunk. I ended up using the factory lower bushing that came with the car since they had a self centring boot (two pictures up) that ensured the damper/shock is centred in the chassis mounting hole for even distribution of loads to the chassis mounting point/pad (pictured below). I combined that with the large aftermarket washers (above picture) due to their thickness and far larger diameter, and took out the Pedders small washers. Finally, I used the Ford OEM GT upper bushing/washer assembly that I had picked up from the dealer (three pictures up).

On the bright side, the damper/shock bottom axle side mount uses a stiffer bushing in place of the factory rubber bushing. Assuming it articulates well enough to avoid any axle binding, it should be a good upgrade.

Swapping the rear shocks was simple which I did a few days later in my driveway once I had all the parts. You just undo the rear sway bar end links to rotate the sway bar out of the way, undo the upper and lower mounts for the dampers, and slide the damper out as you can see in the video. With that done, the car was finally ready for an alignment and corner balancing. Stay tuned for the next post very soon covering the track setup including alignment and corner weights, as well as review on the street and the track.

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