These are some great tips posted by W Racing on another forum:
Derby time is aproaching so here are some tips for 2012. Hopefully others will pitch in with their favorite tips.
Properly drilled holes are the foundation of a fast car. Use the Silver Bullet.
READ and understand the rules of the race.
Ask the race officials if you have questions... (Get answers in writting if possible)
Determine the following:
Can I:
Drill holes or do I need to use slots (Holes are better, use The Block to drill them.)
If I can drill holes can I extend the wheel base (Extended faster)
Can I use any axles or only BSA axles (Most races will require BSA axles). [no advertising for this vendor] axles are the fastest available if your rules allow them...
Can I taper the heads of the axles? This is a rule that some folks will cheat on by tapering 1-2 degrees. Not enforcable and not a good rule... However if you have the rule make sure your axles heads are not tapered.... (rare rule fortunately)
Can I raise a front wheel (3 wheels touching) recomended
ADVANCED QUESTIONS:
Can I cant rear wheels?
Can I railride (Run the rail ;D).
Maybe too advanced. Just ask if it is allowed. You can make a fast car without these.... However faster car if you can do them...
TIPS:
ALIGNMENT IS KEY TO WINNING:
If you can drill axle holes. Drill them perfect. This is the foundation of the car. and the foundation of your alignment.
The Silver Bullet allows you to drill perfect holes...
EXCESS WOOD: Cars with excess wood make it harder to get the COM right. Cars in the 0.6 - 1.2 ounce range work best. Good to have 3.5 ounces of concentrated weight if you can get it. (Lighter cars will work as well... However it is not necessary and BSA cars often run with brutal stop sections so the cars need to be a bit robust)
CAR NOSE:
You should have a 1/2 flat area on the center front of your car for the starting pin and for the finish line.
If you can extend the wheel base do so...
Rear axle back as far as possible 5/8. Front axle 7/8 back to protect against rough BSA stop sections.
If you can not extend the wheel base can you chop the rear 1/4 inch of the block off and glue to the front? Ask the race folks...
Folks sweat over COM...
Not as important as alignment. If this is your first car start at 3/4"
Build a test car to get the COM correct. Weight should be all in one place near the rear axle...
Most people make the mistake of chasing a certain COM and adding weight all over the car. Dont do this...
Once you get a working design prototype car with correct COM. Start making the real car...
If money allows use Tungsten Disc or tungsten cubes.
Place the weight near or around the rear axle.
FOR BSA races be careful to not cut the axles on your car unless the race officials allow it. Even then keep the tips of the axles as proof.
Allow 3 weeks to build car if possible.
Father / son takes more time to mesh schedules. Paint two weeks before race if possible...
Skip paint on bottom of car to save time...
Prep an extra wheel and axle or two for a crash on race day...
Use [no advertising for this vendor] graphite and polish kit. Oil DVD if allowed.
If you railride (Run the rail ;D) Have fun. Post questions. No one will know who you are