Replying to Engineering project help

hey so im doing a project for second year Mechanical Engineering at U of A and we need to build a robot that drives down a mini basketball court and shoots ping pong balls into a mini basketball net. only thing is we need to decide what size of wheels we would use for driving it. our options are 72mm or 36mm. one pair will drive and one will do the steering. i was thinking using the larger wheels for driving so we could get more torque and accelerate quicker and the smaller wheels for steering so that it would require less torque to turn them and it would turn faster. can anyone tell me if im being an absolute idiot or what they would do differently. most importantly why since i need to explain it in our progress report due tomorrow. figured this is a good place to come since a lot of people in my faculty seam to be newschoolers. thanks for the help in advance.