Location of Tungsten Cylinders

[huntersdad]

I am using Tungsten Cylinders this year. My goal is to get the COM to about 3/4". I thought that I would place 3 cylinders behind the rear axle and three about 1/2" in front of the rear axle. I am running a low profile car with an extended wheelbase. Does this weight placement sound about right or is this too much weight behind the rear axles? Any ideas about proper weight placement when using Tungsten Cylinders?

[rpcarpe]

Welcome!
To get a COM of 3/4", I usually follow the meaurements given in David Meade's Speed Secrets book. Three rows/tubes of weight with the rows at 3/8", 7/8" and 1 3/8" in from the back of the car. Rear axle slot drilled at 5/8" from the rear of the car.

You can experiment by sliding the weights into the holes, gently press in your axles and wheels and test your COM. By changing the placement of tungsten & lead, I've gotten very aggressive COM of 1/2-3/4".

Hope this helps.

[tkp]

Previous post is very precise and play with that. Our approach every year is pretty much same deal- we typically use a dremmel to cut out a cavity JUST in front of the rear axle. We typically use 4 (.5 oz) cylinders of tungsten JUST in front of the rear axle- all in a row. This weight totals 2 oz. Then, just in front of that row and touching the other weights- toward the front of the car- we add another cylinder if our car is light enough. So now we have 1 single cylinder just in front of the row of 4 that backs up to the rear axle- make sense?

We usually place this one sideways/horizontal, which is opposite the other 4 which are vertical in order to fit in.

So now the total weight directly in front of the real slots are 2.5 oz. The back 4 are vertical and 1 is horizontal to keep weight back as far as possible.

Lastly, we then put the rest of the weight behind the rear axle- ie the other 3 cylinders- 1.5 oz. We again use a dremmel to drill a cavity and put these directly in the cavity that is near the rear end/edge of the car. We typically place these vertical- but horizontal would work as well.

So with 2.5 oz just in front of the rear axle and another 1.5 just in front of the rear of the car- that, almost every year, puts us right at 3/4 to 7/8 worse case. We also leave a little room in the rear cavity for race day weight adding.

Last point- our body of our cars usually weighs about .5 oz so were able to add at least 3.5-4.0 oz every year. Not sure on your car body weight, but this would change your weight config a bit.

[jsg]

There are so many variables depending on body design. I would open up cavities within an 1/8" of the sides behind the axle and about the same dimensions in front of the rear axle. Then I use tape to hold them in place. Check the COM. Leave a little to epoxy the cavities full when done.

[andylester]

Check out the weight placement on this car.

www.derbymonkeygarage.com/products/Skid_Marx_Pinewood_Derby_Car_Kit-251-6.html

It is a stock BSA wheelbase, but this one works well and is pretty fast. I would think with an extended wheelbase, put them a bit closer to the rear and you should be fine.