Gati or nadai or 'pace' assumes that the talam is the same speed. It is the time between the aksharam (beats?) that varies to give the gait or pace. While the chathusram and tisram show the difference, the 5, 7 and 9 have extended the akshram. (Also it is not 'chaturasram') A very necessary topic today with many singers abusing the system, but more research needs to go into this piece.