Arena Axes and Turn Delay
How many 'Arena Axes' there are defined determine how sharp you can turn. The default and classic number is four, which limits you to 90° turns. Server administrators define how many axes a game grid has. The more axes there are the less sharp your turns will be.
How fast you can turn depends upon the 'Turn Delay' setting. It puts a minimum length of time that must occur between turns. This handicaps how quickly you can turn.