Weight Placement

[derbydadgeek]

Thanks to everyone that has posted all their tips on this forum over the years. My son and I have spent hours reading and learning about what it takes to make a fast car for his first district race in a couple of weeks. Body is built with a 3* rear cant and as light as we could build. Wheels and axels will be prepped using all the tips given by the top racers on this forum. The one area where we are struggling is weight placement. Since we don't have a test track, we don't know where to place the cubes for the best performance. I know that every car is different but, if one were to have a well drilled car on a smooth track, which of the following two configurations would you choose?



Really appreciate your help!

 

[TRE]

that info is top secret

 

[derbydadgeek]

Afraid of that...makes sense why I haven't seen it posted. Don't want to step on any toes here so I'm happy to withdraw my question and take my best guess.

 

[TRE]

If you have a good drill go with the one on the left..maybe move 1 more cub to the dominant side

 

[derbydadgeek]

The drill job seems to be pretty good - migration is even and rolls straight in both directions. I'll take your advice and move one over just to be safe. Thanks for your help!

 

[TRE]

gltu

 

[derbydadgeek]

Thanks....we're hooked!

 

[Kinser Racing]

Niether

 

[derbydadgeek]

Thanks Kinser. Was wondering if even weight on the rears was more important than weight farther back. Guess it is somewhere in between that can only be found out by running it. Gut tells me to run a triangle towards the DFW - like TRE said.

 

[LostAussie]

Confused by your numbers. I would have thought the right placement would have greater difference in weight between the 2 rears than the left placement but your numbers show that there is a greater difference on the left placement.

 

[derbydadgeek]

I was a little surprised myself - thought there would be more on the dominant rear with the one on the right. Weight was measured with DFW on a block the height of my scales and each rear was on a separate scale, and then flipped for DFW weight. Since they all add up to the total weight I assumed they are right. I'm a little worried that we are too aggressive with a standard wheelbase. We built a second car that has 10 behind the rear with a COM closer to 5/8 - It may be safer to run that one. Decisions....

 

[HurriCrane Racing]

I'm with Kinser. Let the car tell you where it wants the weight.
A lot will depend on the quality of the drill. Keep in mind what kind of track you will be racing on. Rough with jacked up joints or smooth like the league track...

 

[Vitamin K]

Confused by your numbers. I would have thought the right placement would have greater difference in weight between the 2 rears than the left placement but your numbers show that there is a greater difference on the left placement.

That much is simple enough to address. When you raise a wheel, all of the weight on the side with the raised wheel gets carried by rear wheel on that side. On the other side, the weight is split between the rear wheel and the dominant front-wheel. Thus, biasing weight towards the DFW side brings the weight on the rears closer to even.

 

[LostAussie]

That much is simple enough to address. When you raise a wheel, all of the weight on the side with the raised wheel gets carried by rear wheel on that side. On the other side, the weight is split between the rear wheel and the dominant front-wheel. Thus, biasing weight towards the DFW side brings the weight on the rears closer to even.

Thanks. Makes sense.

Have only ever looked at back to front com not side to side. Is there a recommended place for side to side com?

 

[Vitamin K]

Thanks. Makes sense.

Have only ever looked at back to front com not side to side. Is there a recommended place for side to side com?

Like Tre said, you're getting into protected info. This is stuff that the fast guys have figured out after lots of trial and error and are not vocal about. I am still mostly clueless.

I will say that a lot of fast racers no longer really think in terms of "Center of Mass" in the sense of balance in front of the rear axle, but rather look at the weight on all three touching wheels, and have their own preferences for what they shoot for.

 

[LostAussie]

Like Tre said, you're getting into protected info. This is stuff that the fast guys have figured out after lots of trial and error and are not vocal about. I am still mostly clueless.

I will say that a lot of fast racers no longer really think in terms of "Center of Mass" in the sense of balance in front of the rear axle, but rather look at the weight on all three touching wheels, and have their own preferences for what they shoot for.

Thanks. Found an old thread with some interesting info in it along with a good tool from minion racer any gravityx.

Need to get me a track so I can do some of my own testing.

 

[BulldogRacing]

Ask the guy who is setting up the track if you can race your 2 cars to see which one you want to enter. Do a quick run befor the race and you'll have your answer. 2 cars are better then one.

 

[derbydadgeek]

Like the way you think Bulldog!

 

[derbydadgeek]

Like Tre said, you're getting into protected info. This is stuff that the fast guys have figured out after lots of trial and error and are not vocal about. I am still mostly clueless.

I will say that a lot of fast racers no longer really think in terms of "Center of Mass" in the sense of balance in front of the rear axle, but rather look at the weight on all three touching wheels, and have their own preferences for what they shoot for.

Thanks - think I'm starting to get it. Does this logic make sense? The goal would be to have even weight on the rear wheels while the car is running. As the car is running down the track the DFW will press against the rail causing weight to shift from the non dominant side to the dominant side. This means you would want less weight on the DRW than the NDRW when the car is static. Amount of steer, or pressure against the rail, would determine the differential.

 

[Vitamin K]

Thanks - think I'm starting to get it. Does this logic make sense? The goal would be to have even weight on the rear wheels while the car is running. As the car is running down the track the DFW will press against the rail causing weight to shift from the non dominant side to the dominant side. This means you would want less weight on the DRW than the NDRW when the car is static. Amount of steer, or pressure against the rail, would determine the differential.

Just thinking for me personally, I think that trying to figure out what happens when the car touches the rail is a little too much in the regions of unknowns. I think I would shoot for getting a balanced COM for the width of the car as a starting point and then try experimental tuning from there.

But I haven't really unlocked much speed on my own, so that's just speculation.