<VV> OFF TOPIC, but car related

[Kirk Eck]

Sorry for the off topic post but i need expert advice.
 I'm building, sorry that should read my son is
building a pinewood derby car (he really has done most
of  the work, he shaped it, sanded it and painted it)
I'm putting the wheels on, I have smoothed the nails
that the wheels turn on and have smoothed the wheels
themselves but my questions are, how much play should
there be between the car and the wheel? Just an FYI
the plastic wheels have a nail that goes through the
center and then they are nailed into the car. 
Obviously I don't want the wheels pressed against the
car body, but can there be to much space for the wheel
to move back and forth (I say yes but am not sure if
it is best to leave  it as tight as possible without
touching or give it a lot of room with the  hope the
wheel won't spin over and touch the body, does that
make sense?  Also should  I have  negative, neutral or
positive camber and should  it be on all four wheels
or just the front?

My son didn't want the car to look like a vair, darn
kids, but he did agree that  it should be a rear 
engine car, so all the weight is in the back!

Once again sorry for the off topic post but you guys
seem to know everything (or at least you pretend to!) 
I know for sure I will not be using Mobil 1 in  the
pinewood car : )

Kirk Eck