On a Pinewood Derby Scout car, the grooves for the axles are not
centered. Is it best to have the wheels more toward the back or the
front of the block of wood. Also, what is the best way to smooth the
wheels and axles for maximum speed?

johndmn...

Thanks for your question.  When I read the subject of your question, I
was immediatately transported back to my time as a scout and the year
I placed 2nd in the District races.  Funny thing was, all I did was
paint the car as my father was out in back, melting down lead, sand
papering the axles and doing everything else.  Of course, I did get
the glory :)

There are several things you can do to improve the speed of your
Pinewood Derby Car.  Here are some hints that are directly related to
the axles and the wheels:

Reducing Wheel Drag 

-Before you start to carve the car, fill in the axle slots provided in
the kit with epoxy. Put the car on its side in a vertical drill press
with the top against the fence. Drill perfectly aligned axle holes
(slightly undersized) for the two rear wheels and ONE front wheel. Put
a thin (.02-.04) shim between the top of the car and the fence. Drill
the second front wheel. When the car is assembled, it will run
straight and true (less drag from side to side) on three wheels with
the four l serving only to keep the car in the lane but with much less
drag since it isn't rubbing on the track.

-Minimize the wheel/axle contact area. Each end of the wheel hub rubs
against something, the outer edge against the nail, and the inner edge
against the car body. If the hub is slightly hollowed out (concave)
there will be less surface area rubbing and less friction. The hollow
will also serve as a graphite well.
Minimize the wheel/track contact area.

-A usual recommendation is to buff the wheel smooth. A better
recommendation is to buff the wheel to enhance its running on a thin
edge. This will reduce the drag if the wheel is at all out of perfect
alignment.
Make the wheel lubricate itself. Using right-handed and left-handed
taps of the appropriate size, tap the axle hole in each wheel from
both sides (one side with the LH tap, one side with the RH tap) 2/3rds
of the way through so that when the wheel is rolling forward the
graphite flows toward the middle. This not only keeps the graphite in
place, but changes the contact friction between the wheel hub and the
axle from a sleeve bearing to an edge bearing.

-Have only three wheels touching the track. Raise a front one
slightly. There is less friction with 3 wheels rolling than 4.

Reducing Axle Drag 

-Put each axle part way into a hand drill. Polish the head and area
where the wheel hub rubs with toothbrush and toothpaste or silver
polish (the paste kind).

-If you have access to a buffing wheel mounted on a bench motor, use
can apply jewelers rouge on the buffing wheel and chuck the axle in a
drill motor and apply to the buffing wheel. Dremel also makes a cotton
buffing wheel that could be used. Jewelers rouge is a commercial
polishing compound.

-File down the edges of the chisel point on the axle This should be
obvious but perhaps is not. If you try to insert the stock Scout axles
in the wheel without filing the edges, it may score the inside hub of
the wheel. This is not desirable.

As for where to put the wheels, use the groove closest to the end of
the block of wood as the rear axle. I read some examples of winning
cars stating that the rear-axle placement was about a half an inch
from the rear of the car and the front axles 6 to 6.4 inches from the
rear of the card.

I hope the above information allows you and your son to create a
winning car.  Below, I have placed a collection of links where you can
find additional information on building a winning car.  If you need
any additional clarification, please let me know prior to rating my
answer.  Thanks again for your question and good luck at the races!!!

Regards,

-THV

References and Additional Information:

How do you make fast cars?
http://www.supertimer.com/pinewood/FasterCars.html

Pinewood Derby Hints
http://www.winderby.com/h-hints.html

The Ultimate Pinewood Derby Site
http://members.aol.com/randywoo/pine/design.htm

Pinewood Derby Car Design
http://members.aol.com/standcmr/pwdesign.html

DESIGNING YOUR PINEWOOD CAR TIPS FROM THE MASTERS !
http://www.geocities.com/%7Epack215/pwd-design.html

How To Improve A Pinewood Derby Racing Car
http://members.aol.com/StanDCmr/scfair.html

Very fast and helpful response.