Want to know how it works? Fritz Grobe and Stephen Voltz of EepyBird have this to say on their website, www.eepybird.com:
After years of work, we've harnessed the explosive power of Coke and Mentos and achieved human propulsion! 54 bottles of Coke Zero and 324 Mentos mints combine to propel EepyBird into the annals of bizarre records. The Coke Zero & Mentos Rocket Car uses a piston mechanism: a six-foot long rod sits inside a six-foot long tube attached to each bottle of Coke Zero. When the Mentos drop into the soda, the pressure tries to push the rod out of the tube. With 54 rods all pushing at once, that gives us a lot of power. All that power is pushing against a solid wall that's attached to a sheet of plywood that runs under the rocket car itself - so the wall won't move, the rocket car will. We get one big push for six feet, and then it's all coasting from there.
I was fortunate enough to work with both Fritz and Stephen last year at Maker Faire here in San Francisco, and blowing things up with Mentos and Diet Coke is just as fun as it sounds!