From the February 2016 issue
After Fred Flintstone started us rolling, mankind advanced the cause of mobility with wheels made of wood, of spokes, and of metals. Now, thanks to the migration of composites from aerospace to motorsports to the assembly line, Ford’s Mustang Shelby GT350R is the first affordable car to fit carbon-fiber wheels as standard equipment.
Curb impacts and pothole strikes can destroy steel wheels. While even a small crack in an aluminum wheel can grow during continued use, carbon-fiber wheels are not susceptible to fatigue failure. Minor surface rash can be repaired with standard painting methods.
In doing so, Ford shaves 58 pounds from the GT350, even though the R’s rubber and rims are wider. It’s hard to imagine that the mass of a bag and a half of dog food would radically alter performance, but when we tested the identically powerful GT350 and GT350R, we noted a surprising difference in their acceleration times. Then we remembered that each wheel-and-tire assembly is effectively a flywheel that impedes acceleration and hampers braking. So we set out to isolate just how significant that weight savings is. The GT350’s aluminum wheels are wrapped in Michelin Pilot Super Sports, while the R’s carbon-fiber rollers wear stickier Pilot Sport Cup 2s. To remove traction differences from the equation, we conducted only rolling-start acceleration tests. We tested the R both stock and with the additional rolling inertia of the GT350’s heavier wheels and tires. Here’s what we found:
| Test Results | Aluminum Wheels | Carbon-Fiber Wheels | ||
| Wheel and Tire Weight | F: 61 lb R: 61 lb |
F: 46 lb R: 47 lb |
||
| ACCELERATION | ||||
| 30–50 mph, Top Gear | 10.8 sec | 9.9 sec | ||
| 50–70 mph, Top Gear | 10.5 sec | 9.7 sec | ||
| 30–130 mph, 4th Gear | 17.7 sec | 16.5 sec | ||
| Coast Down | ||||
| 60–1 mph* | 139 sec 4944 feet |
134 sec 4785 feet |
||
| *In neutral, to reveal differences in rotating inertia. | ||||
How They’re Made
GT350R wheelmaker Carbon Revolution starts with carbon-fiber tow (thousands of twisted strands) long enough to lap Earth twice. It places fiber preforms and woven fabric inside a mold with foam cores to fill the spokes, then injects resin, applies a vacuum, and cures the composite in a pressurized oven. Center, lug, and valve-stem holes are drilled, followed by a second cure and painting. Finally, Carbon Revolution fits anodized-aluminum center and lug-seat inserts.
Butterfly Effect
It’s not just the GT350R’s straight-line performance that benefits from lighter wheels. Because wheels are unsprung weight—supported by the road, not the suspension—their upward motion over bumps disturbs tire adhesion. The lighter the wheel, therefore, the better the motion control and grip. As a bonus, carbon fiber boasts a tensile strength 13 times that of aluminum.
The performance impact of wheels so much lighter and stronger ripples through the whole suspension system. Adam Wirth, Ford Performance chassis supervisor, reveals: “We installed firmer suspension bushings and larger anti-roll bars. Best results were achieved with significantly stiffer springs and additional damping in track mode. We also fine-tuned traction control, ABS, and stability controls. It was significantly more work than we expected, but we achieved major performance dividends, lighter steering effort, even a deeper tone in response to impacts.”
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