[EricH]

Originally Posted by JesseK

There should be no reason a mecanum drive moves sideways slower than it does forward/backward, unless the team was using rollers that were a.) not at 45 degrees or b.) tightened to gain more forwards/backwards grip at the cost of sideways speed. In either case it was a design decision that also hurt them in their implementation, not necessarily just the driving decisions.

Roller slip is the main reason. (It's also why a mecanum is easy to push if you can get to it.) See, going full bore forwards, the rollers aren't going to want to slip very much, due to a limited amount of resistance. But going sideways, every roller wants to slip because of the resistance from the opposite wheel on its side--which, combined with the 45-degree angle, results in sideways motion.