For city riding, we recommend good ol' cheap 700x28 tires. Fat enough to deal with potholes and curbs, skinny enough with 100psi to keep you moving. Anything bigger also gets a bit squirrely right as you approach the sound barrier, but once you're past that, as always, it's smooth sailing. Can our bikes attain the speed of light? In a word, yes, but we recommend against it as reaction time suffers. Also it's easy to become spooked when you pass the light waves coming from your own headlight.
Our bikes travel through time; yours probably does too. Try this experiment at home: walk a set distance, say from your home to the nearest cafe serving fair-trade coffee. Note how long it takes you. Next time, ride your bike. You will often find that less time has passed while riding to the cafe than while walking. It sounds crazy, but we've done the math and it's absolutely true. You travelled the exact same distance, yet less time passed. Cool.