Newbie tuning question

[RobSwift]

New member to the forum, and can’t say enough about how glad I am to have found this place. My oldest son just started Cub Scouts and I’ve been helping him build his first Pinewood Derby car. Thanks to all the helpful info I’ve found here we’ve gotten off to a good start, and had some success at a practice / tuning session his pack held last Monday. The official Derby is being held this Monday night and I want to make some tweaks based on what happened in practice, and am hoping you guys can help me.

Our pack rules require the axle slots to be used, and to use the axles and wheels from BSA kit. So, we’ve put together a rail rider with canted axles on the rears and DFW (I will get a SB Pro next year). Everything is canted at 2 degrees (negative on rear and positive on DFW). The NDFW is mounted tight to the body and doesn’t touch ground. The COM is 0.8 – 1 inch and we went to the practice with the drift about 1.5 or 2 inches over 48.

Our pack uses an aluminum BestTrack, and during practice, the car screamed out of the gates and beat every car it faced on all three runs. But, I noticed the rear wiggling on the straights (especially bad the first run) and want to correct that. After the practice, I looked closer, and noticed the rear wasn't aligned right. The D side rear wheel did not move to the axle when the car rolled forward, and only did that when the car rolled backwards. I tweaked that alignment and it works fine now. I also found the gap was slightly bigger on that same rear wheel and corrected that too. After making those corrections I tested the drift and found the car was now going about 6 or 7 inches over 48. I tweaked the DFW so that it now drifts about 4 inches over 48.

My question is, should I shoot for drift closer to 3 or 2 inches since the original setup I ran during practice was drifting about 1.5 or 2, but I later found that the rear was not aligned and gaps were not consistent? Will using 4 inches of drift be too aggressive since my COM is almost 1 inch?

I wish I could do more practice runs to be sure, but unfortunately I don’t have track access until the Derby.

 

[Mojo Racing]

on a cub track, you are safer with a 4" steer over 48"
other cars will be wiggling, and you want your car to be stable, not on the edge. Their wiggles will cause your son's car to wiggle if you are too close to the edge.

 

[GravityX]

If the DFW axle turned and caused the steer to change you may want to secure the axle down with one of two techniques, either put a drop of water in the axle hole to allow the wood to swell and tighten its grip on the axle. Or use some Elmer's glue, or some other wood glue, in the axle hole. Use a toothpick to apply a small amount on the hole. Either of these methods will allow you enough time to adjust steer. Allow things to dry and set up before rolling down the track again, this should hold the DFW axle in place and hold steer.

 

[RobSwift]

Thanks again to everyone that helped me with tuning advice. We had the derby last night, and I went with 4” of oversteer, and used Elmer’s glue once everything was set. The car was much faster than at practice, and seemed more stable. The rear still wiggled a slight bit on the straights, and I think the culprit may have been BSA axles I over aggressively filed / polished till they were too small.

At the derby my boy’s car won his den and placed 2nd overall in his pack. That was a bit bittersweet because he posted the 3 fastest runs of the night, 2 of which came in the last 2 heats of the pack finals (which included smoking the champion). The only stumble occurred in the 2nd heat of the pack finals where his car was a half-length ahead on the straight and was between two wigglers that caused his car to wiggle too. His car slowed notably at the end of the straight, and he came in 3rd on that. It was our only off performance of the night.

Needless to say I have a lot to learn, but thankfully I’ll have lots of opportunity since next year my youngest will be a Lion cub, and my oldest will only be a Tiger. This forum has been a fantastic source of information, and I’m already dreaming up new car ideas. I’m feeling the bug, and am planning to get some more pine blocks and start experimenting with new car designs this weekend!