Home / Tech Tips: BMR S550 Rear Suspension Components

Tech Tips: BMR S550 Rear Suspension Components

Almost daily here at Lethal Performance we are asked what the best & most important components are to upgrade in the rear suspension for the 2015+ S550 Mustangs. What good is horsepower if you can't put it to the ground?

Jared & Christy took a trip over to BMR Suspension in Seffner, FL with our 2018 Mustang GT (aka Project Goldmember) to get the “Kelly Aiken” treatment. While there, we were able to pick Kelly's brain on the IRS and it's components. He has a surplus on knowledge on these cars from not only his own car (even planting GoPros underneath to monitor the suspension's activity) but also from the vast amount of fast cars using BMR Suspension, including 2 of the fastest IRS cars in the country. Check out the video & scroll down for tons of info!

We've created some awesome packages with all of the components recommended for you and your setup, from mild to wild. There is the Biscuits & Gravy package, the Bread & Butter package & lastly the Steak & Potatoes (with a side of NVH) package. Check all of the options out below to see which one is best for YOUR application.

Biscuits & Gravy Suspension Package (aka Level 1)

First, we brought you the "Bread & Butter" package, a collab between Lethal Performance & Kelly Aiken of BMR Suspension. While that kit has become hugely popular, it may be overboard for some of you who daily drive your car but still want to harness that power at the track. Or maybe you road race the car, hit HPDEs or just like to race it on the weekends. We worked with Kelly to put together the bare essentials, a starter package, for the 2015-up Mustang GT. These parts have seen 9 second runs & even 1.3 60's at the track. This is a GREAT place to start.

The "Biscuits & Gravy" package includes:

BK081 – Spherical Lower Control Arm Bearing

Designed to eliminate cradle deflection & wheelhop
“One of the most important & overlooked components” -Kelly Aiken
Factory bushings are molded from soft rubber & contain voids/air pockets, causing movement of the lower control arm during aggressive launching/driving. The solid spherical setup eliminates these voids, therefore eliminating the control arm movement.
Also keeps the wheels from moving forward due to bushing deflection at WOT
Click here for more info

TCA048 – Vertical Links

Light & strong, while still offering bushing compliance & no increased NVH
Limit range of cradle movement
Only vertical link on the market that has ability to grease/service the bushings ON the car
Click here for more info

CB010 - Cradle Bushing Lockout

Reduce Wheelhop, bushing deflection, and cradle movement
Built from 6061-T6 billet aluminum and stainless steel
Billet aluminum upper bushing lockout rings capture the inner bushing sleeve (front and rear) and the outer lip of the bushing cup on the cradle (front)
Lower bushing locating washers (front) capture the bottom portion of the bushings’ inner sleeves
Movement on any plane (fore/aft, lateral, and vertical) is nearly eliminated
Click here for more info

Click here for the "Biscuits & Gravy" package.

Bread & Butter Suspension Package (aka Level 2)

Based on his experience, we asked Kelly of BMR to pick out what he felt were the most beneficial components for these cars, the “Bread & Butter” as he calls it in the video (hence the name!). These chosen components will support cars going well into the 8s and those wanting to see low 1.2-1.4 60's.

The "Bread & Butter" package includes:

In an IRS car there are a couple of issues to address. The first issue is that the entire cradle assembly will move/rock. In our 2018 A10 car, Kelly was able to point out just how much movement there is in a factory setup. The factory cradle bushing has a small lip on the top which is a limiter. On our car, when we launched it at the track, this limiter was hitting the chassis, leaving a witness mark on the body from the cradle moving (see image).

CB005 – Cradle Bushing Lockout Kit

Designed to eliminate cradle bushing deflection & wheelhop
80%-90% reduction in fore/aft and lateral cradle bushing deflection
Comes with spacer rings to lock out the top of the cradle bushing so that it doesn't deflect at WOT
Comes with lower bushing mounts to eliminate lower bushing movement, keeping it from dipping down & causing the pinion to rise
Click here for more info

BK081 – Spherical Lower Control Arm Bearing

Designed to eliminate cradle deflection & wheelhop
“One of the most important & overlooked components” -Kelly Aiken
Factory bushings are molded from soft rubber & contain voids/air pockets, causing movement of the lower control arm during aggressive launching/driving. The solid spherical setup eliminates these voids, therefore eliminating the control arm movement.
Also keeps the wheels from moving forward due to bushing deflection at WOT
Click here for more info

Another issue to address on the IRS is the movement of the differential itself within the cradle. While looking under our car, Kelly was able to also show us the tell tale signs that our diff had moved from our track ventures. The first place to look are the front differential bushings. The factory bushings have small metal alignment nubs built in. On a factory car, these protrusions are barely visible (or not visible at all) however on our car, the passenger side was sticking way out and the driver's side only slightly out. This tells us that the diff moved enough to compromise the clamping force of the bolt & also stayed seated in a diagonal position.

Next, we looked at the rear differential bushings & bolts. It was clear here, also, that the diff had moved as the bolt on the passenger side was sitting much higher on the bushing than it was on the driver's side.

Want to sort that out? Here's what you need:

BK051 – Differential Bushing Lockout Kit

Designed to eliminate the voids in the stock differential bushing setup
Locks the differential movement so that breakage of driveline components is avoided
Click here for more info

If you're going to do the differential bushings, we HIGHLY suggest upgrading the hardware while you're in there. Not only are the bolts themselves stronger than the OEM pieces, but the kit also plays an integral role in limiting differential movement. In the rear bushing, the stock bolt has a ton of play in it as it is a smaller diameter than it's location. This causes the diff to be able to move, as shown by the bolt being off center in our car, which in turn changes pinion angle, causing vibration & driveline parts carnage (like us breaking our driver's side axle on Project Goldmember). This play in the bolt also leads to the bushing & cradle actually slicing/cutting the bolt when the car is loaded up & launched. No bueno! Then there is the front bushing setup, which is a threaded design from factory. Because the bushing sheer strength is relying on the threaded part of the bolt, it is much weaker than if it were to rely on the shank (or solid) part of the bolt. These are all helped with the hardware upgrade kit.

LP-550179 – Extreme Differential Bushing Hardware Upgrade Kit

Designed as an upgraded version of BMR's RH017 Hardware Upgrade Kit
Upgrades both the front & rear differential bushing bolts to stronger pieces
Sleeve placed in rear diff bushing eliminates void from factory
Front bushing threads are drilled out & bolt is replaced, with bushing sheer on solid part of bolt and a nut in the rear, which is roughly 70% stronger
Click here for more info
For those that don't wish to drill out the front bushing, you can use BMR part no. RH017, found here, which supplies just a stronger bolt replacement

Continuing on, the following components will allow more fine tuning of the rear suspension:

TR005 – Double Adjustable Rear Toe Rods

Stock stamped steel pieces equipped with eccentric bolt slip & pivot under load, changing the alignment of the rear wheels
BMR pieces keep geometry better during suspension arc due to offset spherical bushing
Come with lockout plates for the mounting point to eliminate the eccentric bolt from factory that turns
Allow for a wide range of adjustment
Click here for more info

TCA048 – Vertical Links

Light & strong, while still offering bushing compliance & no increased NVH
Limit range of cradle movement
Only vertical link on the market that has ability to grease/service the bushings ON the car
Click here for more info

Click here for the "Bread & Butter" Suspension Package.

Steak & Potatoes (with a side of NVH) Suspension Package (aka Level 3)

The "Steak & Potatoes" suspension package is catered to those who are hardcore about racing their car at the track. The S&P package is essentially the Bread & Butter package on steroids. It is a total IRS solution that solidly mounts the subframe and differential to the chassis.

Not only does the package add springs & a few other components on top of the Bread & Butter package, but some of the pieces are replaced with their stronger, more solid counterparts. For example, the solid IRS subframe bushings (BK048) are used in lieu of the cradle bushing lockout kit. The solid differential bushings (BK050) are used in place of the more street friendly differential bushing lockouts & hardware upgrade kit (the bushings are now solid & will not put damaging loads onto the fasteners that tend to break in the factory setup so the need for the stronger hardware is eliminated). Also, the rear lower control arm bearing (BK055) is a stronger, more solid piece than the spherical bearing (BK081) included in the Bread & Butter package.

This aggressive setup will surely get your car launching & 60-footing with some of the fastest cars on the track. In fact, these are the very same parts that are on the ONLY two S550 IRS cars to currently go 1.1X sixty foot times.

PLEASE NOTE: With these solid components you will experience an increase in NVH and a rougher ride on the street.

The "Steak & Potatoes with a side of NVH" package includes:

SP089 Front Springs

Designed for the street/performance enthusiast
Lifetime warranty against sag
Linear spring rate offers plenty of support, keeping the body flat and level in the corners, while remaining soft enough for a comfortable ride on any road
Click here for more info

SP088 Rear Springs (or SPH767 for MagneRide equipped cars)

Designed for the drag race crowd who want to the ultimate in straight-line acceleration
Feature a fine-tuned spring rate (800 lb/in rear) to give you great handling and a smooth ride
Linear spring rate offers plenty of support, while remaining soft enough for great weight transfer
Lifetime warranty against sag
Click here for more info

BK055 Rear Lower Control Arm Bearings

Eliminate bushing deflection, transferring power instead of absorbing it
Drastically decreases lower control arm movement by solidly linking the rear portion of the lower control arm to the cradle, eliminating the factory rubber bushing "voids"
Reduces wheelhop and increases handling
Click here for more info

BK048 Solid IRS Subframe Bushings

Eliminates rear cradle movement
Increases the rigidity and stability of the chassis to provide maximum control and consistency
Minimizes differential movement by replacing the soft rubber stock bushings with solid two-piece Delrin bushings
Click here for more info

BK050 Solid Diff Bushings

Eliminate differential movement and pinion rise over the factory rubber bushings
Replaces the soft rubber OE bushings with four solid two-piece aluminum bushings
Click here for more info

TR005 Adjustable Toe Links

Stock stamped steel pieces equipped with eccentric bolt slip & pivot under load, changing the alignment of the rear wheels
BMR pieces keep geometry better during suspension arc due to offset spherical bushing
Come with lockout plates for the mounting point to eliminate the eccentric bolt from factory that turns
Allow for a wide range of adjustment
Click here for more info

UTCA064 Camber Links

Greasable, solid Delrin bushings add a solid, more responsive feel over the stock rubber bushings
Internally fluted, which allows grease to evenly coat the inner sleeve; the flutes also direct grease to the outer edge of the bushing, keeping the thrust surface lubricated
Work best for drag racers who have lowered ride heights and are looking for ZERO camber
Designed longer than factory length to correct suspension geometry on lowered S550s
Greatly reduces bushing deflection
Click here for more info

TCA045 Vertical Links

Eliminates vertical link flex, giving you much improved repeatability on the street, starting line, or in the corners
Solidly link the spindle to the lower control arm, eliminate deflection and wheel alignment changes
Click here for more info

Ford Performance M-5A460-M Knuckle Toe Bearings

Replaces the rubber Toe Link Bushing in the rear knuckle with a production style bearing
Removes suspension compliance with minimal impact to ride quality
Improves handling, especially in power down situations
Click here for more info

Optional Add-Ons:
VIK-B358AM Vi-King shocks (recommended for drag race use)
Koni Adjustable Front Struts (recommended for cars with 1000+rwhp)

Kelly & BMR Suspension have been badass enough to even supply shock & alignment settings when using their complete setup! Click here to check it out.

Click here for the "Steak & Potatoes (with a side of NVH)" Suspension Package.

There are many more suspension components that BMR Suspension offers and that you, the customer, can upgrade but these are the basics & will definitely help to get you to where you want to be on the track. Give us a shout with any questions at 877-2-LETHAL or by email at support@lethalperformance.com.