Benefits of ultralight / ladder bodies

[e/o]

First time posting. Thanks to everyone here for tons of great information!

I am curious if there are benefits of a very light car body / ladder bodies independent of COG.

My sons' pack and district rules both require that I use the original slots/wheelbase. Without an extended wheelbase (and assuming I don't move a slice of the car from the back to the front, which I think my den would consider to violate the "spirit" of the rules), I already have a lot of space behind the rear axle, and can get a car's COG down as low as .5" simply by cutting a very narrow wedge.

Are there additional reasons to create an ultralight car body, cut additional weight pockets, make a ladder body, etc. if I do not need to do so to get the COG further back? My initial thought is that there's no upside, and but wonder if I am missing an additional advantage.

 

[M Tull]

I asked a similar question a few years ago ... I think the answers are still relevant. http://pinewoodderbyonline.com/threads/lite-body-advantages-for-standard-wheel-base.5316/
Crash Enburn and others gave great responses ... and some funny ones.

 

[e/o]

Thanks for pointing me to that thread. I confess I'm still a bit confused as to whether there is a benefit separate from COG, but the thread has a lot of other useful discussion.

 

[TRE]

The lighter the body the more weight you can get in the back

 

[DuckOfAllTrades]

Thanks for pointing me to that thread. I confess I'm still a bit confused as to whether there is a benefit separate from COG, but the thread has a lot of other useful discussion.

Just my two cents, and NOT an expert, but besides COG, I would say the only other benefit would be low profile, aerodynamics and the fact that it makes moving the weight around easy. I think you'd be able to try a number of configurations with a ladder body/light weight body. It allows you to place the weight where you want it, to distribute it to the wheels the way you want to. Other than that, I'd just say it looks really cool. Mainly I'd guess it's the aerodynamics that would matter at a pro level.

 

[e/o]

That's fair. If we had access to a test track, we'd definitely make a ladder body so we could more easily play around with weight placement combinations. I guess a ladder body might also let us get a little closer to balancing the weight left to right; right now we go with "not TOO unbalanced laterally."

 

[DuckOfAllTrades]

That's fair. If we had access to a test track, we'd definitely make a ladder body so we could more easily play around with weight placement combinations. I guess a ladder body might also let us get a little closer to balancing the weight left to right; right now we go with "not TOO unbalanced laterally."

I feel you on the weight placement! I've never had the way to measure how much weight is on each wheel, it's a guessing game. I usually go with drill the holes centered of the car, melt the lead and pour it in method. I have sometimes played around with placement by drilling out some of the lead, and adding it in at other places, but have never seen any uptick in speed. I think at the scout level, it really doesn't matter, so I just worry about COG. If I DO need a bit of weight at the front of the car to balance my COG, I usually place it on the side of the Front Dominant Wheel. Not sure if that's right or not, but makes sense to me so that's what I do. We have to have four touching, and so I float one front wheel. If I add weight to it, it's just brining more force down on a wheel that I want touching as little as possible.

 

[Mojo Racing]

Okay... My $0.02.

I have helped a bunch of cub scouts work on cars, and they all run ladder bodies. Mainly because of the low profile and the ability to put weight where we want to. It has worked great for all of them.

Now... Ultralight? Be careful with that. Remember, a 7-10 year old boy or girl is going to be handling this car, or worse, a cubmaster who "knows everything about pinewood derby". I know league racers who will trash a body if it is more than 7 grams. Cub scout cars should have a little bit more beef to them to handle the abuse from the inspector who "tosses" the car into a box or basket after inspection, or a boy who likes to run and forgets he has a car in his hand, or for the cubmaster who drops a car onto a staging gate.

If you car body weighs between 10-13 grams, don't sweat it too much. You will be happy later when your car has that "shewww" moment.

 

[DuckOfAllTrades]

Now... Ultralight? Be careful with that. Remember, a 7-10 year old boy or girl is going to be handling this car, or worse, a cubmaster who "knows everything about pinewood derby".

Oh my! This is a good point. In my troop, there is ALWAYS at lest 4-5 little guys rolling there cars around on the ground, and pushing them as hard as they can and letting go, sometimes crashing them together, sometimes into a wall. This would be an accident waiting to happen!

 

[e/o]

So based on the advice in this thread (and a few others), I practiced cutting some ladder bodies. Once I got one I thought was pretty solid I assembled the car, putting 2 oz behind the rear axle and the rest just in front, with weight skewed towards the FDW side.

When I weighed it, the back wheels were balanced and I had 10 grams on the DFW.

Out of curiosity, I put the pieces of wood I'd removed from between the ladder rungs back in and removed a proportional amount of weight from the back. This version of the car is still balanced left-right but has 16 grams on the DFW.

Under these circumstances, does it make sense to stick with the plank body and not the ladder body for scout races? It is not clear to me that I should go 16 grams even if I can, and obviously the plank is a sturdier build. Am I being too conservative?

 

[txchemist]

The average time at the typical Pack gets worse each year. No need to increase your margin of victory from 3 car lengths to 4. Cheap plank with good design is just fine. I make & sell two ultra lights and a plank. Plank with stock wheels & axles(made in china) on this body set 11 year track record last month and won by so much, Cheater Cheater! was heard.
The stop section was bad, and any ladder car would have been toast. This was from a crew charging $100 to run the derby- so sturdy is good for Cubs. Put a skin on it and it looks fine.

 

[FDM]

I totally second the comments about building a sturdy car for scouts. We normally 'overbuild' our ladder cars, because on the track we use (best track 42') the stop section is not very good or too short and any fast car will slam into the end barrier resulting on the car lifting up from it's back wheels. We we normally build a ladder body and then put a 1/64 ply cover from top to end, sanding down the part that doesn't cover the weight pockets to reduce some weight. Also we put 2-3 balsa ribs in the middle/front section of the car. We normally end up with bodies weighing about 10-14 gram including top vinyl cover (which weighs about 1-2 grams). I think a few gram more or less is less important than a good drill. We build a body beginning this year that weighs 10 gram with cover and all, however it was not as fast as another car which had a body of about 14 grams (same wheels and axles). Also for a scouts it's easier to build a car body with more wood left on it than going really thin on the sides which will break much easier. Last year my son build a ladder car but we opted to 10 cube weights behind the axle instead of the usual 12 just so it would be easier to cut for him. He still won Pack, district and finished top 10 in NYC.

 

[Ohly]

Oh my! This is a good point. In my troop, there is ALWAYS at lest 4-5 little guys rolling there cars around on the ground, and pushing them as hard as they can and letting go, sometimes crashing them together, sometimes into a wall. This would be an accident waiting to happen!

This happens every year at our Pack Race. Scouts love to smash the cars together and see the results, normally a crying father in the corner.... My fix for this problem was to let my son build a "Tank" Car that is almost a simple block with 10 oz of weights in it and Tungsten bumper. As to not be the crying father with a broken ladder car...

 

[e/o]

Thanks. Think I'm leaning towards trying to sell my scout on the plank. Our stop section is awful.

My scout has come in second in the Pack to the same kid both his Tiger and Wolf years. The kid who beat him won districts, and is crossing over, so honestly, my scout could probably redo his car from this year exactly as is and still win next year. Would rather continue to make speed improvements, but will feel pretty silly if he's leading by .15 when his car splits in half.

 

[Jimmy & his 2 Kids]

If you car body weighs between 10-13 grams, don't sweat it too much. You will be happy later when your car has that "shewww" moment.

So true... reading this I had to share our shewww moment from last years Awana GP. This video is my daughters first run. This is where we see that one stop section is not enough to stop a fast car. My daughter about crapped herself. Fortunately a little CA and it was fine but it was a heart stopper for a second there...

 

[txchemist]

I have seen District races where many cars went over just like that. I had brought a pillow, but they would not let me put it on the stop section, so I put it down below and caught my grandsons car OK. I then picked up my pillow and a bunch of parents all wanted it put back in case their car went over- so I left it there.

 

[Jimmy & his 2 Kids]

I have seen District races where many cars went over just like that. I had brought a pillow, but they would not let me put it on the stop section, so I put it down below and caught my grandsons car OK. I then picked up my pillow and a bunch of parents all wanted it put back in case their car went over- so I left it there.

Good thing is they immediately recognized the issue and put bean bags on each lane. We still waited at the finish line to safely stop each car when our 3 cars ran... just in case. I am bummed that I forgot to push them to get a second stop section. This years race just so happens to be tomorrow. Reminds me I have to find some bean bags tonight in case they don't have any.

 

[Pinewood Outlaw]

Time to buy a extra stop section. We also use a sticky lent roller and clean the stop section rubber off between races as graphite buildup is the main culprit of scout cars sliding all the way to the end. After 3 years of racing we going to replace our original rubber because of a few cuts in it and the pores in the rubber seem to be worn smooth.

 

[Reecedad]

when we went to our district race and I saw there was only one stop section I mentioned my concern to those in charge. They allowed me to catch My sons car before it went off the end.

 

[dan9592]

What I do to prevent this on one stop section race tracks is days before race I put a small spot of paint on bottom of car in the back and put a little sand in the wet paint and let dry or you can put a small piece of grip tape on bottom. It hard on the stop sections but better than destroying a car or cars. That’s the great thing about Midamerica races they have long stop sections so this is not needed.