Originally Posted by
AdelaaR
Common man, it all depends on just how fast your brother is.
If your brother has 700c wheels with 48 teeth and rides at top speed on flat, you will never be able to keep up with him on a typical mountainbike set-up like 26" wheels with 42 teeth.
This is silly. Have you ever tried working out what sort of speed a 26" wheel with a typical 42 ring gear set-up equates too? About 26 miles an hour, with a decent spin rate. At least for a rider who has the power to maintain that speed against air resistance on a typical flat bar bike (which means no one.) If your top speed is limited by how fast you can spin the wheels with MTB gearing on the flat then you need to learn how to pedal correctly.
Once again, to the OP: just buy the bike you like. After test riding them, of course.