Thought I would share the proceedures I follow to tune up the cars. 

Remove rear tires
Remove magnet
CA glue eyelets on front axle
Remove front tires and Tyre True front wheels
Remount front tires and Tyre True tires
Tape motor into chassis
Tyre True rear wheels
Install and Tyre True IG7005 silicone tires
Hot glue rear axle bushings
Oil motor and rear axle bushings
Grease gears
Add ¼ ounce weight to front of car
Oil front axle
Assemble car

"Tyre True" is a reference to this piece of equipment:
http://www.area3slots.com.au/index.html

I was reluctant to pay so much for something, but this has been the single most important slot car product I have bought besides the track.  It makes all the cars run smooth and true.  It is amazing how well a car will run when it's wheels are round.  There are other similar product available, so this is not your only choice.  I recommend you try one.  You will not regret it.

I also like to replace the braids with Slot.it braid.  The Slot.it stuff is thinner and softer so the guide won't be held up out of the slot.  The Cartrix guide is a shallow one for Scalextric Classic and SCX track so it does not sit as deep in the slot as say a Slot.it or NSR guide will.