These days, when a car company has a hot new model to introduce, it stretches the process over numerous press events in order to maximize the coverage. This week, Ford, which has us all drooling to learn more about its upcoming Shelby GT350 and GT350R told us a great deal about the hot new models’ chassis.
Brakes
For example, the GT350 and the even racier GT350R will come with a very powerful and sophisticated braking system. The front rotors are 15.5 inches in diameter, while the rears measure 14.9 inches; both are cross-drilled with carefully chamfered holes to minimize the chances of cracking.
To save weight, these rotors employ aluminum hat sections. Moreover, the rotors float on a circle of pins that connect them to the aluminum mounting hats. Floating rotors are free to expand radially as they get hot and are less likely to distort.
The rotors are manufactured by first casting and partially machining. Then the pins are inserted into radial holes in the rotors. The aluminum hat sections are cast around the pins. Finally, they receive their final machining to make sure that all of the surfaces are totally concentric.
The calipers themselves are made by Brembo—there are one-piece, six-piston units in front and one-piece four-piston pieces in the rear. These calipers are unique to the GT350 with their own piston sizes and are radially mounted in the front, which means that their mounting bolts screw into the uprights parallel to the brake rotor rather than perpendicular to it. This radial mounting is more rigid than the conventional method and results in less pad kickback during hard usage, making for more consistent braking. It also reduces heat transfer from the rotor to the hub, which helps wheel-bearing life. To minimize fade, dedicated brake ducts front and rear feed air to the ventilated rotors.
Suspension
Those radially mounted front calipers attach to new aluminum uprights that have different suspension pickup points than the standard Mustang; this is to accommodate the wider wheels and tires. Standard Mustangs have front wheels between 7.5 and 9.0 inches wide, while the GT350 gets 10.5-inch-wide front wheels and 11.0-inchers out back. Going further, the R model uses 11.0-inch-wide wheels up front and 11.5s at the rear. (Both cars feature 19-inch wheel diameters all around.) The additional wheel width means that the kingpin axis needed to be located farther outward and thus required moving the pickup points of the two lower suspension links farther apart. The new upright is also lighter than the one on lesser Mustangs.
Of course, the rest of the suspension was also upgraded for greater precision. For example, the inner pivot on the front suspension’s lateral link, which is the one most important in transferring cornering forces to the chassis, uses a solid ball joint in place of a compliant bushing.
The springs and shocks were totally recalibrated for both GT350 versions. The R model gets the third-generation MagneRide suspension, the first Ford application for this technology, which uses magnetorheological fluid to almost instantaneously change shock fluid viscosity and thus can update damping forces every 7 milliseconds. Eric Zinkoski, GT350 suspension tech specialist, says that the system delivers the expected track-capable handling on the GT350R, while also providing a surprisingly comfortable ride on the road.
Another detail change is the winding of the rear springs. Normally, these springs are wound in the same direction, which introduces a slightly uneven spring performance between the inboard and outboard springs during cornering. On the GT350, these springs are wound in opposite directions to eliminate this small problem. This change required new rear lower control arms, however, and they also received other detail changes that improved their stiffness while reducing their weight.
Tires and Wheels
Most of these changes were made in order to make the best use of the GT350 larger and sticker tires. On the standard GT350, the tires are Michelin Pilot Super Sports designed to meet the specifications laid down by Ford Performance engineers. The fronts are 295/35s, while the rears are 305/35s. The R model gets super-sticky Michelin Pilot Sport Cup 2 tires, sized 305/30 and 315/30. The Cup tires are basically street-legal race rubber.
The R’s wheels, as you may already know, are made from carbon-fiber, which reduces their weight by around 13 pounds per wheel—or about 50 pounds total—over the aluminum wheels on the standard GT350. These CF wheels have passed all of the standard Ford durability tests for curb impacts and they are painted to eliminate the ultraviolet light degradation that can affect carbon-fiber composites. In fact, Adam Wirth, GT350 supervisor for suspension, tires, and wheels, says that the CF wheels don’t propagate cracks as readily as aluminum wheels do and thus are actually more tolerant of minor impacts. Unfortunately, the thick paint completely covers the intricate carbon-fiber weave which is one of the appealing properties of this material.
The center sections of these wheels, where the lug nuts attach them to the uprights, are made from aluminum, and the inner rims of the front wheels are plasma coated with a ceramic layer to insulate them from the heat of the hot brake rotors during track driving. It’s the same ceramic coating that was used for the 2011 Shelby GT500 cylinder surfaces, although the coating is unfinished and feels relatively coarse in this wheel application.
Aero and Cooling
The GT350 has extensive aerodynamic changes, including an all-new front end. The goal is to reduce lift and even achieve positive downforce while producing sufficient cooling flow to keep the GT350 temperatures under control during the toughest conditions.
The R model gets dedicated air-to-oil coolers for the engine, transmission, and differential. The first two are in the outer corners of the front fascia and exhaust into the front wheel wells. Those wells also have vents on their rear side, which exhaust to the vents in the front fender, both promoting air flow and reducing lift. The differential cooler sits behind the rear axle, above the diffuser. It’s fed by a pair of NACA ducts on the GT350’s underside.
This cooling became necessary when Ford decided to perform a durability test for the GT350R that consisted of a 24-hour run at a race track where the lap times were kept within three percent of the car’s flat-out max. The only things that could be replaced during the 24-hour run were brake pads, tires, and fuel. Any other failures and it was back to the drawing board.
Zinkoski says that he and his team have tested the car at 15 different tracks, including the Nürburgring, within the past 12 months alone. He promises that we will be satisfied by the car’s performance on the track and even more impressed by its usability on the street. We are eager to verify his claims.
This entry passed through the Full-Text RSS service - if this is your content and you're reading it on someone else's site, please read the FAQ at http://ift.tt/jcXqJW.
from Car and Driver Blog http://ift.tt/1AITaz7
via IFTTT
0 comments:
Post a Comment