Mustang GT350/GT350R: Steering, suspension, brakes

By Christopher A. Sawyer
The Virtual Driver

(May 16, 2015) Unlike the original, the new GT350 is not an afterthought created to give Ford’s new Pony Car the street cred to go with its looks. It was part of the 2015 Mustang program from its inception, which gave engineers the opportunity to build in those items that would make this transition easier, rather than add them on at great expense later.

Thus, the new GT350 does not require that major changes be made to the Mustang’s structure, and  those that have been made were be done with minimal rework.

From the A-pillars forward, the GT350’s bodywork is unique, and features wide aluminum fenders with integrated heat extraction vents, and a new hood, grille and front fascia. The leading edge of the hood is more than an inch lower, and rises to encompass a central hot air exit that exhausts over a more rounded power dome. A carbon fiber grille opening reinforcement panel is used, and it cuts weight by 24% compared to the regular Mustang’s stamped steel part. It also eliminated the need for a finishing cover, and this reduces weight by a further 1.9 lb.

The grille and front fascia control airflow for the radiator, front brakes and standard transmission and oil coolers. Also, the outer slots in the front fascia feed ducts that create an air curtain around the front wheels in order to reduce turbulence, and provide a low pressure zone into which the exits molded into the front fenders can dump their air.

Continuing up front, the first thing you notice are the wheels and tires. The base GT350 wears 295/35R-19 Michelin Pilot Super Sport tires on 10.5-in. alloy rims. Ford engineers worked with Michelin to create tires with a GT350-specific sidewall construction, tread face and compound. Move up to the GT350R, however, and the alloy wheels are replace with carbon composite rims that feature a ceramic coating on the inner rim that is applied using a plasma arc.

Though Ford wouldn’t comment, I believe these wheels are supplied by Australia’s Carbon Revolution, and seriously reduce unsprung weight at each corner; approximately 50 lb. total compared to the standard GT350. Custom Michelin Pilot Sport Cup 2 tires with shallower tread replace the Super Sport tires on the GT350R.

The front suspension gained aluminum knuckles, new and more widely spaced lower pickup points, and a reduction in the virtual kingpin offset. Together this combination reduces steering effort while improving both steering response and feel. On the other hand, the geometry of the independent rear suspension remains basically the same as that on stock Mustangs. However, during testing drivers noticed a difference in at-limit behavior when turning right or left.

The culprit, they discovered, were the rear springs. In most cases, the springs are the same side-to-side, that is, they are wound in the same direction and are interchangeable. Under most circumstances, this has little to no noticeable effect on feel or response. In the case of the GT350 and GT350R, however, the engineers discovered a difference in the way the car responded in right and left corners, and traced the imbalance to the rear springs. Both rear springs are now wound toward the car’s centerline, which equalizes forces but required a new left-hand lower control arm and spring pocket. In addition, the rear tires have been increased to 305/30R-19s on 11-in. rims.

In a first for Ford, magnetorheological dampers are used at each corner, and can respond within seven milliseconds. I had my first experience with this technology in 1987, when Monroe offered a test drive in a Ford Thunderbird fitted with these devices. The transformation was eye-opening, and was built on response curves, etc. created by Lotus and TRW in the early days of active suspension systems. At the time, however, it wasn’t possible to produce iron filings in a sufficiently standardized shape, or a hydraulic fluid that — when combined with the iron — would not thicken or freeze at extremely low temperatures.

Also, response times were limited by the electronics of the day. Over the years, these problems have been eradicated, and MR shocks have made their way into various Acura, Audi, Ferrari, GM, and Range Rover vehicles. Now they are standard on the GT350, but their high cost (“Many times that of a standard hydraulic damper system,” according to GT350 vehicle dynamics supervisor Brent Clark.) has kept them out of most new vehicle programs. However, the need for the GT350 to be capable and comfortable on both street and track, coupled with the fact that the 2013 Camaro ZL1 already adopted this system, pushed Ford to follow suit.

Though approximately 10 lb. heavier than a non-MR system, the difference in ride, feel and performance is worth the weight increase. The GT350 has a ride height sensor at each corner, and feeds this information as well as steering wheel angle, yaw rate, wheel position, damper temperature, vehicle position, etc. to the suspension controller. And while Ford did not follow BMW in rigidly mounting the rear suspension subframe to the body, it did go for what it terms “rigid bushings” to eliminate as much high-g compliance as possible without ruining the car's on-road ride. In addition, it claims the slight “waddle” exhibited by the standard Mustang over rough surfaces has been eliminated by the shift to MR dampers.

Even more interesting are the brakes that were co-developed by Ford and Brembo. At the center of the new design is a two-piece cross-drilled iron rotor with an aluminum hat. Though heavier than a carbon composite rotor, Ford claims this design is as fade resistant and less expensive. The cast-iron rotors feature brass-coated steel pins on their inside circumference.

This assembly is placed in a mold, and the aluminum hat section is cast in-place, capturing the steel pins. A space between the rotor and hat allows for the dissimilar materials to expand independently of each other without transferring large amounts of heat energy to the hubs. The front rotors are massive 394 mm (15.51 in.) units, while the rears are slightly smaller at 380 mm (14.96 in.).

Six-piston mono block calipers are used in front, with four-piston units in the rear. Because the rear calipers are fixed, the rear brakes feature a drum-in-hat design where a drum parking brake is fitted to the rear of the hat.

The Virtual Driver