Wheelbase question for my cub scouts’ cars

[Hangtime]

I’ve stayed out of this discussion ‘cause I’m in no way a pro. But I’ll just mention this - another benefit of using a shorter wheelbase is that it is a little easier to get weight on that DFW.

 

[Mojo Racing]

Too much weight on the front, though, is a bad thing. So be careful with that.

 

[Hangtime]

I’m aiming for 15 - 20 g. Probably end up somewhere near the middle.

 

[CastleCrasher]

Prozach, That's possible certainly. Our district is 4 counties, but it's not like every kid from every pack of every county shows up. My son goes to karate with a kid who lives a town over, same grade, he beat us, got top 15. His dad is a CAT engineer and it's his 3rd boy lol. Then in our pack is the dad (pack scout master) and grandson of a pinewood derby legend, so that's been our competition.

 

[Brian Stanley]

So yeah, same here. Looking at my cars from this year (4 and 3/4 wheel base) vs my cars from last year (5 and 5/16" wheel base), I'm guessing (emphasis on guessing) that the wheels are getting moved back by a lot of the pros b/c, in addition to the fenders, it moves the COG back. My theory is, if you tune the car perfectly, that's going to be an advantage. More weight further back means more momentum. and speed. If you don't tune the car well, with that shorter wheel base, you might have some pretty serious wobbles though. Again, this is all a guess from someone that's far from an expert.

Last year, I had a much lighter car body, more tungsten cubes, and a COG that was pushed farther back than the year before. We put 10x more time and research into last year's car and expected a much better result. We won the pack race both years, but last years car was actually a little slower than the year before. Watching it go down the track, it's no mystery why. It was bouncing back and forth so hard, I was surprised that it didn't go flying off the track. It was a good track in good condition. Fortunately, it stayed on the track, but the experience was a valuable lesson. It's important to know your limitations. Depending on the skill level of the builder, at some point, less is more.

This year, we still don't have a decent tuning table. I'm just putting the 5kidsracing printout on a 5'table and rolling the cars on that. No matter how tight and flat we try to get that huge piece of paper, we're not getting consistent steer. I'm concerned the paper is still bubbling up just enough to alter the direction of the car. I'm looking for a piece of glass or something to put on top of it, but haven't found anything good yet. Our race is on 2/6, so we've got a little time to get it figured out.

It's not easy (at least for me) to get consistent results on a make-shift tuning board as it's hard to place the car down in the exact same spot/orientation each time. Also, if your results are inconsistent that can be a symptom of too small axles (too much polishing) or large wheels bores. I've got a good board now and you're welcome to come use it, I'll set the track up too this weekend if you want to do a few test runs.

 

[Prozach2]

It's not easy (at least for me) to get consistent results on a make-shift tuning board as it's hard to place the car down in the exact same spot/orientation each time. Also, if your results are inconsistent that can be a symptom of too small axles (too much polishing) or large wheels bores. I've got a good board now and you're welcome to come use it, I'll set the track up too this weekend if you want to do a few test runs.

We would love to take you up on that Brian! I'm going to do my best to get our cars finished Friday and Saturday. Assuming all goes as planned, can I send you a PM to set up a day and time? I'm waiting on some fenders to come in that I ordered from DD4H. Hope they come in tomorrow.

 

[CastleCrasher]

It's not easy (at least for me) to get consistent results on a make-shift tuning board as it's hard to place the car down in the exact same spot/orientation each time. Also, if your results are inconsistent that can be a symptom of too small axles (too much polishing) or large wheels bores. I've got a good board now and you're welcome to come use it, I'll set the track up too this weekend if you want to do a few test runs.

I also meant to reply to Prozach about results with steer measurement. And Brian it might help you too if you're in a pinch for a measurement. I only have a 35x13" piece of glass from one of my reptile cage doors. Tape a straight edge along the bottom corner edge and whatever edge the car steers away from and always stage the car against the 2 fences, push car, measure how far it turns away from the edge you taped to the NDF side. Use dowel rods, blank one pine blocks, carpenters square, etc. Somewhere there's a conversion chart or wizard for converting steer from one length to another, I think on Stan Pope's website. Example (not accurate conversion) input 3" over 30" and it equals 5" over 48". Since all I have available is that 35" glass that is perfectly flat, so the conversion is helpful when I'm trying to adjust to recommended setting I see here.

 

[Brian Stanley]

We would love to take you up on that Brian! I'm going to do my best to get our cars finished Friday and Saturday. Assuming all goes as planned, can I send you a PM to set up a day and time? I'm waiting on some fenders to come in that I ordered from DD4H. Hope they come in tomorrow.

Sounds good!

 

[CastleCrasher]

I thought about that too.

 

[Chris Stevenson]

I use a 4' piece of 3/4" oak plywood that I had left over from a cabinet build project a few years ago. I just drew a straight line down the middle and marked of my inch lines at the bottom. I use a 2X4 or 4X4 to lift one end. Put a moving blanket at the bottom for soft stops. Works great.

 

[CastleCrasher]

Another good point, launch method also needs to be consistent.