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.
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 Ge...