The code, still rough though.

Arduino Hamster Wheel

const int inPin = 7;   // pushbutton connected to digital pin 7
//const int cmPerClick = 51; // cm
const float inchesPerClick = 20.1; // inches

int val = 0;     // variable to store the read value

float totalDistance = 0; // total distance in inches
int lastTime = 0;
float difference = 0;
int time = 0;
boolean clickRead = false;
float rps = 0;
float runningSpeed = 0;
String output = "";
float numberOfSeconds = 0;

void setup()
{
  Serial.begin(9600);
  pinMode(inPin, INPUT);      // sets the digital pin 7 as input
}

void loop()
{
  val = digitalRead(inPin);   // read the input pin
  time = millis();
  if (val == HIGH && clickRead == false)
  {
    difference = time - lastTime;
    numberOfSeconds = difference / 1000.0;
    rps = 1.0 / numberOfSeconds;
    runningSpeed = 3 * rps * 6.28;
    //runningSpeedMiles = runningSpeed / 63360;
    totalDistance += inchesPerClick;
//    output = String(String(runningSpeed) + " Inches/Sec (" + String(totalDistance) + " inches traveled)");
//    Serial.println(output);
    Serial.print(runningSpeed);
    Serial.print(" Inches/Sec (");
    Serial.print(totalDistance);
    Serial.print(")\n");
    clickRead = true;
    lastTime = time;
  }
  else if (val == LOW && clickRead == true)
  {
    clickRead = false;
  }
  
}