How does a Tire Size affect Your Speed?

Transmission Speed~
Despite popular beliefs, speed is not measured by the number of tire rotations a car makes while moving. Speedometer readings are based on the speed of the gears in a car's transmission. When a car is built, it is stocked with wheels that rotate in accordance with the speed of the transmission, resulting in accurate speedometer readings.
Changes in Tire Size
When factory-calibrated tires are replaced with larger tires and rims, a car's transmission will continue to run at the same speed. Larger wheels will make fewer rotations than smaller tires. This means, as the transmission continues to clock a specific speed, larger tires will actually cause the car to move more slowly than the speedometer reads. Depending on the increase in tire size, a car will usually travel about 5 to 15 percent slower. The opposite effect is realized when smaller tires are installed.
Calculating Actual Speed
It is important to know exactly how fast a car is moving to ensure speeding laws are not broken. To ensure this is always known when traveling, the following formula allows drivers who ride on larger or smaller ties know how fast they are actually moving at all times:
New tire size (diameter) x speedometer reading / stock tire size = actual speed

My 17" Pegasus rims Whereas, as factory produced for Myvi is 14"
Do Your Math!