NEED ADVICE AND HELP

[tomaszk]

I'm new to pinewood derby.I never heard about till this year when we signed in our son to the local Pack. is very cool. We both like going to meetings every week. But let's get back to my issue. There was coming derby and we had to build our car. We got starter kit. I had no knowledge about this, so I started watch some videos and read articles online to get info. I bought some supplies like weights some tools and we build our vehicle. I build two of them and choose the faster one for race. Our local rules do not allow to modify axles means cannot bend them only polishing. Also wheels and wood blocks we can use only official BSA wheels and blocks with ready cuts for axles. The axles coming in the kit are not so great as you know guys they need a lot of work to make them smooth. I decided to buy something better and ordered Viper grooved stainless steel axles.After assembly I did some tests and found something bad.  CAR IS NOT ROLLING STRAIGHT. My question is : What to do to make car rolling straight with straight axles??? I couldn't find answer my self. So we used car for derby. We won in the Pack but finals where not lucky. In one race got vibrations which slowed him down badly. After finals I spoke to experienced people and someone tell me there is some trick. ANYONE KNOW WHAT TO DO ? PLEASE HELP ! Thanks.