Weight distribution on Long wheel base car vs shorter wheel base

[FDM]

We usually race a long wheel base car for our pinewood derbies, however we wanted to try a shorter (5 inch) wheel base car, esp since all the pros seem to race that setup. When we tested this car on our wooden test track we ended up being slower than the longer wheel base, which is counter intuitive since a shorter should be faster. Both cars are running the same wheels (we switch them out) and same steer (~3-4 inch over 4 feet), and the same weight setup, ~2.05 ounch behind the wheels the rest in front, slightly biased towards DFW. The longer wheel base frame weights about 11.2 grams and the shorter about 10 grams. So the shorter wheel base car has some extra putty to get it to the same weight. I know a lot depends on how straight you drill the axle holes (both drilled with the same jig, which I know isn't a guarantee for same results) so maybe the longer wheel base car has better alignment. My question is, is their a different optimum weight setup for a shorter vs longer wheel base car, should we put more weight behind the rear axle with one the wheel bases or should the same weight setup give similar results? Or is their something else we are missing? We will play around with it a little but I thought maybe the experts can chime in and point me in the right direction.

 

[TRE]

Put 12 cubes behind the rears and the rest in front with any wheel base..your drill is probaly better in the faster car

 

[FDM]

Thanks for the reply, I will change the setup slightly then, since I have some heavier tungsten behind the axle and change it out for 12 straight cubes (try to get it close to 2 ounce) and put the rest of the heavier stuff I have in front of the axle. How important the drill job is maybe our car from last year which with only 10 cubes behind the rear axles still managed to be faster than any car we build so far and got in the top 10 of NYC race last year (not that means much to most league racers). I start to understand why everyone here is so meticulous about checking how true their rear axle drill jobs are.

 

[TRE]

Rear drill and wheels are where most of the speed is at

 

[Skywalker Racing]

Are you able to get very consistent runs with the same car on that test track? Just wondering if the track itself is to blame. And how much difference are we talking?

 

[FDM]

These runs were relative consistent for a wooded track maybe 0.01 variation. The shorter wheel base is about 0.015 - 0.020 slower. So not by that much, but its a 32 foot track, so on the longer 42 track the difference should be bigger.

 

[Jimmy & his 2 Kids]

If I may... when it comes to winning or loosing... that’s plenty much difference.

 

[bracketracer]

Even if the car is on graphite, a .01 variance is pretty big wooden track or not? It's going to be tough to fine tune a car if it can't run consistent numbers. Is the track in that poor shape?