We just had our council race last night and it was terrible. My son's car and his best friends car, which I helped build. Completely tanked. They ran worse than the pack race. Both cars where basically the same. I did everything to the letter all of the tips I picked up from here. I should have left them alone. But we wanted to be faster. So after the pack race I purchased the black ice polishing kit. Did both sets of wheels. I tightened up the wheel gaps. The lifted wheel I had tight to the car body. I had around 4 to 5 inches of steer in 4 feet. It made the cars worse. I really don't know what I did wrong. I feel bad for the boys. They where so disappointed. I have year to get it right.
Welcome to my world ....

I have been where you are at and it is not a pleasant place to be. However ...this is a real important time to teach the boys what life is about. You can cave and give in to the bad feelings or you can choose to move forward and teach them a valuable life lesson. I am an optimist so I think you will move forward!
Now for the analytical part of my brain. Did the cars really tank? Did they race on the same track. Was it set up the same? What were the times? Did they have any of the same competition? Was the competition just that much better? How did the cars act? All of these questions can help you determine was there something actually wrong or were there new variables that caused you to believe you went the wrong direction when in fact, you may need to step up your game. My guess is that the answer is probably some of both (speaking from experience).
Take a collective breath and think about these questions. Then take another and think about what you want to teach the boys. Then get busy and start to figure out how much of what you believe is true (the cars tanked) and how much of it is that the variables changed and the competition was better?
Just so you know, I may be back here in a month with the same sort of issue as we are making lots of changes before my son's last district race. We have never won the pack race, but have been second. I am hoping that we can get a handle on all of the changes for the district race. We are keeping a positive attitude and troubleshooting each step of the build together as issues arise.
Remember for the boys ...if you did your best then you did what you were supposed to do. Also, next year your "best" will be at a new level because of what you continued to learn!
Keep your head up as the boys are watching what you do!!!!
Also, if you do discover some mistakes, make sure to discuss them with the boys. Then make plans on how you will do it better next time. This will keep them involved and learning not only about Pinewood Derby, but also about how to handle life when it doesn't go exactly as planned.