Every car I ever built and weighted equal rears was at least .01 slower. Never going to do that again.
Tungsten Cube Placement
- Thread starter PushcartDerby
- Start date
Actually I put the weigh in and go. Don't think much about it. Build it from the back to the front.
Wow, I just built three new cars in the last couple weeks to have something in the May race...and adjusted weight to be equal on rears as discussed earlier. Dang, I could be .01 slower on all three cars. Ugh! Time for the X-acto knife to come out for major surgery??
Could this be due to sacrificing COM to get the wheel balance?
3 scales are needed IMO. You want to know what kind of weight is on the DFW, this will affect the amount of steer needed and how the car handles down the track. There is a sweet spot and it varies with each build. Play around with the weight distribution, listen to your car when it rolls down the tuning board. It'll tell you what it needs. Quiet is GOOD!
My plan is to try 12 cubes behind the axle then attach some kind of weight on the axle line. It may be wheel weights or plates. The remainder of weight will be ahead of the axle of course. With the additional weight on the axle line does it mean I have to put more weight further forward to keep the COM from being too aggressive? Is it better to do it this way or to just run the 12 cubes behind and 10-12 in front? If the COM is equal both ways what is the advantage to having added weight at the axle line such as with wheel weights?
It kind of depends on how light your car body ends up. For my bodies they all happen to end up leaving me with really short COM of less then 1/2" if I do 2 rows of 6 behind and in front of my axle line. I slid the front weights forward some to get right at 1/2". I remember DD4H mention only going with 2 rows of 5 in back and the rest in front of the axle. Since the wheel weights were introduced I think people are testing out different configurations.
davet said:
On both of my sons scout cars I can get 3 rows of 6 cubes behind the axel. Our rules state we have to use the stock wheelbase. Is that to much in the back?
Assuming we're talking about 1/4" tungsten cubes and a thin car, if you can get three rows back there, then your rear wheels are too far forward. Let me rephrase that, your rear wheels are further forward than the considered ideal. With three rows in back, that moves your COM 1/4 - 1/2" closer to the rear axle, which may very well allow the car to pop wheelies or force a lot of steer or both.
You only have to use the stock wheelbase, not the stock location. Put your rear wheels 5/8" from the rear of the car. Two rows of cubes behind the rears, and the rest of the weight right in front of the rear axles.
You only have to use the stock wheelbase, not the stock location. Put your rear wheels 5/8" from the rear of the car. Two rows of cubes behind the rears, and the rest of the weight right in front of the rear axles.
If you took a car body and weighted it with 12 cubes behind axle, wheel weights and as much weight just ahead of the front axle as possible then say a single cube further up to get a 3/4" COM, would that same body perform the same with 10 cubes behind axle, 12 just ahead of axle and no wheel weights? I'm just wondering if the same car body performs the same no matter how you place the weight as long as the COM is the same on each setup. Assuming all the weight is centered side to side in the car and not offset.
If so then I think that wheel weights or plates under the rear axle are only an advantage if the goal is to run a lower COM that isn't attainable by placing 12 cubes behind the axle.
OR, is there something else at work besides COM that makes added weight at the axle line advantageous?
If so then I think that wheel weights or plates under the rear axle are only an advantage if the goal is to run a lower COM that isn't attainable by placing 12 cubes behind the axle.
OR, is there something else at work besides COM that makes added weight at the axle line advantageous?
Wheels further back wins. If you have a 3/4" CoM, and the wheels are 5/8" from the end of your 7" car, the CoM is higher on the hill than if you had a 3/4" CoM and wheels at 2" from the end (or 1", or 1.5", etc.).
Also, and I don't know if this has been tested or not, but I believe that a denser CoM (all the weight together) will perform better than a car with the same CoM but with its weight spread out. So, the wheel weights help center the mass, which allows the car to rotate through the transition more easily. Furthermore, they drop the CoM toward the track, which also actually increases the height differential of the CoM (how far it drops).
Also, and I don't know if this has been tested or not, but I believe that a denser CoM (all the weight together) will perform better than a car with the same CoM but with its weight spread out. So, the wheel weights help center the mass, which allows the car to rotate through the transition more easily. Furthermore, they drop the CoM toward the track, which also actually increases the height differential of the CoM (how far it drops).
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