YouTube channel Tyre Reviews has posted an in-depth study of the effects different wheel/tire sizes have on the performance of a sports car. The team picked a Porsche 911 Carrera for the test, equipped with its own, purpose-designed Michelin Pilot Sport 4S NAO tires.
In its standard guise, the car uses 19-inch wheels on the front axle and 20-inch ones in the back. Paying extra nets you a set of wheels one inch larger. Michelin points out that different teams were working on front and rear tire sets, and that the specifications of each set were then improved individually based on its diameter.
As you can see, braking from 100 to 5 kilometers per hour (62 to 3 mph) on dry asphalt takes 33.18 meters (108.75 feet), while with the larger wheels, the brake path is shorter by a negligible 0.15 meters (one-half of a foot). Testing on wet road decelerating from 80 to 5 km/h (50 to 3 mph) returns 33.63 meters (110.33 feet) for the smaller and 33.67 meters (110.47 feet) for the larger tires. In other words, the difference is barely perceptible.
The test pilots also pointed out noticeable amounts of oversteer when driving the Carrera on the wet track with smaller wheels. Even so, they managed to complete the dry track in 71.53 seconds and the wet track in 97.55 seconds. Larger wheels are barely ahead with 70.43 and 96.83 seconds, respectively.