Most blocks that come in pinewood kits don’t have straight holes cut for the axles. They’re all manner of crooked, so you’ll need to make your own holes using a miter saw or a drill press. You can also use a carpenter’s square and a hand saw to square up the holes, but it’s a lot more work and the results aren’t as good. When you put the axle holes in, make sure they’re a perfect 90-degree angle to the car’s body.
To install the wheels, use a steady pressure making sure you don’t bend the axle one way or another. The straightest holes in the world won’t help if your axles are bent.
The easiest way to test if your wheels are straight is to raise one end of your kitchen table slightly. Put a book under the legs of one end and you’ll have a little slope. Then place a ruler or other straight edge at the edge of the table and line up the car’s left wheels against the ruler. Let your car roll and see if it moves closer to the edge of the table or more toward the middle. Make sure you don’t let the car fall to the ground!
If your car pulls to one side, you need to check your alignment. Hold your car on its side with the two wheels hanging free. Take a ruler and gently lay it on the inside hub of the wheels. If one end of your wheel has a gap between the wheel and the ruler, you need to straighten that wheel.
To straighten the wheel, push on the wheel gently. You don’t need to push very hard. Make lots of small adjustments instead of a few big ones.
Retest and recheck the alignment after every adjustment.