Here's the answer to the million dollar question.  What do I suggest?  First I say check you rules......  Then use the following advice.

So my choice:  Physics car body 3-wheel racer.  Lead Weight. 3k bent axles (3x 2.5, 1x 1.5), pliers, Wheel Polish kit or service, Derby Dust graphite.  You will have to choose what wheels you want to play by, but they will determine speed of car second to tuning the axles correctly


Pinewood Derby Tuning is the Key

So you are going to need to focus mainly on tuning or adjusting your axles.  You want your car to go down the track as straight as it can without going side to side.  Easiest way to do this is 3 wheels touching and make it ride along the center strip.  So you purposely make it track to the high side.  Takes time.  Not technical, Not complicated, just time.  The correct tool-- axle pliers.  This $25 purchase is the difference between a headache and a breeze.  what you will need is 4x bent axles so that you can do this:  for 4 wheels I always suggest 3x2.5 1x1.5 angles

If you have to do 4 wheel tuning....

Pinewood Derby Speed Axles

polish level.... 
3k for graphite with break-in 
100K for oil or graphite with just dust and spin.  You are substituting the lube for a higher polish metal.  
Bent axles will be fastest (rail riding) however each axle needs to be adjusted (tuned) so that it steers the car down the track and not side to side.  Each axle will have to be adjusted:  Watch the tuning video above...substitute treadmill for tuning board if needed.  Bent axles for the wheel to ride in one spot and also change the amount of tread presented to track.  Ice skates vs rollerblades just the inner part of wheel will touch. (red wheel). 
Picture
Picture originally published on Derbytalk.com forum

Pinewood Derby Speed Wheels

Wheels

Lighter the better. Lighter wheels will require use of tuning pliers however to remove axles/wheels.  
Polish the bores.  Either you or me.  Its pretty simple.
Flawless bores will eliminate any abnormal rotation in relation to wheel spinning around axles.  

Weight reduced wheels start around 1.7 grams. Have all the lettering.  Charlie Bravo or Black Op's will be those weights. Charlie Bravo has factory outer tread.  Black Op's will have lathed outer tread.
Derby Worx makes a 1.5 and 1 gram wheel, but a little more noticeable machining done to them.   Lighter is always better! They are all very fast wheels.  Choose what will meet your pack's rules.

Pinewood Derby Graphite Lube

Graphite on graphite has a lower coefficient of friction than steel on plastic.  Our theory is build layers of lube on layers of lube.  Then you have graphite on graphite peeling off each race.  Break In / Lube building process
 


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