Derby Talk

My son's car made it to the district race today... We finished 2nd in the pack thanks to much of the forums advice and recommendations. My son is a Webelos II and has asked if we could build one final car for district. The track for district is 49ft vs the pack track at 35ft (both best track aluminum). All four wheels have to touch and only Standard BSA wheels/axles allowed.

Do you guys have any recommendations:

1. COG for this long of distance? 3/4", 1", other
2. Axles drilled in at angles or bend the nails in front, rear, both? If so recommended degree of angle.
3. Wheel base fully extended at 5 3/4" or different distance? Bring the fronts back from the fully extended wheel base?
4. Is there a worth while rail rider design for 4-wheels?

We won't race until probably early April and he would truly appreciate the feedback to maximize his odds.
Thanks in advance.

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I've never raced on that long a track so others are going to have better info.
I'd like to comment on the 4 wheels on the ground. It has been recommended to have Negative Camber and slight toe-OUT on the Non-Dominant front wheel. This is covered in the Search function. There is also a way to adjust the Non Dominant front wheel to not turn because it is just hanging on the axle. Our Inspector checks all wheels turn by putting one finger on the top of the car and pushing it. This lowers the Non Dominant front axle and raises one rear axle just enough to let all 4 wheels turn. When the weight of pushing down on the car is removed the car once again becomes a 3-wheeler.
I wish you the very best in your race.

Hi derbypain!

My thoughts about the cog for the two different track lengths are this.
On shorter tracks and aggressive cog is beneficial because the car only has to travel a short distance.
But for the longer tracks a less aggressive cog would be best..For making it a more stable running car for the longer distance it has to travel.

Plus speedster is on to something with his thought's for a 4 wheel touching car set up and how it might be inspected for a 4 wheels touching rule.
By the inspector rolling the car to see how the wheels move about on the axles is a different.. thing!
From how the car sets with a 4 wheels touching also!

Let's say we start of with 2.5 deg for the all the axles ..
backs cambered negative.( Top tilting in!) & zero toe.. so the rear wheels stay off the rail.
But the DFW (steering wheel!) will be cambered positive (top tilting out!)
and the non -dominant wheel will be cambered negative (top tilted in!)
this wheel should just lightly touch the track.. almost floating not resting on the axle.
The tricky part here is that you may have to take some bend out or add just a touch more after testing!

My thoughts for a 4 wheels touching rule is that .. the goal should be with all the wheels touching the car body that all 4 wheels touch the track.
but as the car go's down the track the dominant wheel makes contact with the track guide rail and then the wheel pushes out to the axle head.
The front of the car will then rise and lift the non-dominant wheel off the track to act as a 3 wheel car.

Plus you may find the car may need just a touch more steer to hold it to the rail as it slows down some what on the longer tracks to hold it to the rail.

But for your 4 wheels touching rule.. It would be best to ask for the ruling on how it will be inspected for!

whodathunkit wrote:Hi derbypain!

My thoughts about the cog for the two different track lengths are this.
On shorter tracks and aggressive cog is beneficial because the car only has to travel a short distance.
But for the longer tracks a less aggressive cog would be best..For making it a more stable running car for the longer distance it has to travel.

Plus speedster is on to something with his thought's for a 4 wheel touching car set up and how it might be inspected for a 4 wheels touching rule.
By the inspector rolling the car to see how the wheels move about on the axles is a different.. From how the car sets with a 4 wheels touching also!

Let's say we start of with 2.5 deg for the all the axles ..
backs cambered negative.( Top tilting in!) & zero toe.. so the rear wheels stay off the rail.
But the DFW (steering wheel!) will be cambered positive (top tilting out!)
and the non -dominant wheel will be cambered negative (top tilted in!)
this wheel should just lightly touch the track.. almost floating not resting on the axle.
The tricky part here is that you may have to take some bend out or add just a touch more after testing!

My thoughts for a 4 wheels touching rule is that .. the goal should be with all the wheels touching the car body that all 4 wheels touch the track.
but as the car go's down the track the dominant wheel makes contact with the track guide rail and then the wheel pushes out to the axle head.
The front of the car will then rise and lift the non-dominant wheel off the track to act as a 3 wheel car.

Plus you may find the car may need just a touch more steer to hold it to the rail as it slows down some what on the longer tracks to hold it to the rail.

But for your 4 wheels touching rule.. It would be best to ask for the ruling on how it will be inspected for!

Thanks to all the replies so far.. Getting some great feedback. Regarding the four wheel touching rule... Two years ago I was the district inspector for wheels/axles ...as part of my training they specifically had me role the car a few feet without putting pressure on top of the car to make sure there was not hidden three wheelers... Also the rules had this clause.. "A car must run on all four wheels. NO three wheel cars. (Note that a three wheel car includes a four wheel car with one wheel that does not consistently turn and bear the weight of the car. Such a car is not allowed)". If I can't do any type of three Wheeler is it best for my son the bend all axles (negative rear and positive front the same) and try to create a straight running car or is a rail rider still possible. This and the COG are my biggest concerns for a 49 foot track.

Also where can I find a test track to use in the Dallas/Ft. Worth area?

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Thanks for your reply on the 4 wheels touching
ruling and how it's inspected for.














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I would agree with the logic of easing off of the CoG a hair and aiming for stability down the straight section. That said, you definitely want to make sure you have enough steer to keep you stable out of the transition, since a zig-zag down the straight will eat your time as well. I wouldn't go full extended just for the sake of protecting the front wheels, but I definitely wouldn't go under a 5" wheelbase.

Sporty did a writeup on 4-wheel rail riding that might be helpful.

Vitamin K wrote:I would agree with the logic of easing off of the CoG a hair and aiming for stability down the straight section. That said, you definitely want to make sure you have enough steer to keep you stable out of the transition, since a zig-zag down the straight will eat your time as well. I wouldn't go full extended just for the sake of protecting the front wheels, but I definitely wouldn't go under a 5" wheelbase.

Sporty did a writeup on 4-wheel rail riding that might be helpful.

When you say a easing off on COG a hair do you feel 1" ahead of axles or 3/4" in front... I don't want to make any assumptions for him... I know with rail riding you can be more aggressive with COG but I wasn't quite sure where you would have normally started with COG to ease off a hair.... Thanks.. I know I will ask a lot of questions but this will be both his and my first jump into the more complicated builds. He is super excited about trying it out.

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derbypain wrote:

Vitamin K wrote:I would agree with the logic of easing off of the CoG a hair and aiming for stability down the straight section. That said, you definitely want to make sure you have enough steer to keep you stable out of the transition, since a zig-zag down the straight will eat your time as well. I wouldn't go full extended just for the sake of protecting the front wheels, but I definitely wouldn't go under a 5" wheelbase.

Sporty did a writeup on 4-wheel rail riding that might be helpful.

When you say a easing off on COG a hair do you feel 1" ahead of axles or 3/4" in front... I don't want to make any assumptions for him... I know with rail riding you can be more aggressive with COG but I wasn't quite sure where you would have normally started with COG to ease off a hair.... Thanks.. I know I will ask a lot of questions but this will be both his and my first jump into the more complicated builds. He is super excited about trying it out.

Good questions. I wish I could give you more concrete answers.

Just as a wild stab, I would say to consider a CoM of somewhere around 5/8" to 3/4" and working from there. If you had a track to test with, I'd say to tune the car so that you can be stable out of the transition with as little steer as possible.

OK great.. Our next dilemma is to find a test track to consistently use in the Dallas area. Other wise all these new methods could work against us.

Another question how or what tool do you guys use to rotate the axle/nails without ruining them. Whenever he pushed the nails in this year we need to rotate the front one and he had the hardest time. Needless to say one ruined nail and luckily a good back up nail saved the day. He started by pulling on the wheel and I reminded him that could mess up the wheel.

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derbypain wrote:OK great.. Our next dilemma is to find a test track to consistently use in the Dallas area. Other wise all these new methods could work against us.

Another question how or what tool do you guys use to rotate the axle/nails without ruining them. Whenever he pushed the nails in this year we need to rotate the front one and he had the hardest time. Needless to say one ruined nail and luckily a good back up nail saved the day. He started by pulling on the wheel and I reminded him that could mess up the wheel.

If your rules allow it, the "K-House" groove is your best friend there. Basically, it's a slot cut into the axle head to allow you to turn it with a screwdriver or knife tip.

Here's a DIY jig to assist you in cutting the groove.

Also, consider buying or making a gap gauge. Whenever you adjust the position of your axle, insert the gauge between wheel and body of car, and make sure your gap stays consistent.

BTW, even if you're using straight axles in the rears, a K-house groove can be useful, because twisting the axle as you insert or remove it can help it go in smoother.

Unfortunately.. The rules state "You may Not... Cut grooves or make dips in the axle"... You might could argue that I won't be affecting the axle by cutting a groove in the nail head but I may need to get a clarification on that.

The hardest thing I find is that once the nail is inserted at a credit card depth the nail head is very difficult to get a hold of with a tool (example needle nose pliers) without damaging.

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derbypain wrote:Unfortunately.. The rules state "You may Not... Cut grooves or make dips in the axle"... You might could argue that I won't be affecting the axle by cutting a groove in the nail head but I may need to get a clarification on that.

The hardest thing I find is that once the nail is inserted at a credit card depth the nail head is very difficult to get a hold of with a tool (example needle nose pliers) without damaging.

Those kinds of rules are typically meant to indicate along the running surface of the axle, but, I understand that you do not wish to give an unfriendly inspector a reason to disqualify your son's car!

When you talk to the race organizers, perhaps you can explain it's a "slot" not a "groove".

I just emailed the district coordinator and sent an image of the external "slot"... I agree with you that the rules were more for not affecting performance... This slot solely allows you to rotate the nail not change amount of surface area that touches the wheel.

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How can you precisely remove the 3 crimp marks without getting at least a slight "groove" in the shaft? I would just say that your son took the marks off and you don't have a lathe, if questioned about an axle groove. Hopefully they allow the K-House slot so you can give them a twist when it's time to take them out too. Until we wised up and found a way to make the slot, we would wrap blue painters tape around the end of a needlenose pliers and twist them that way. Unfortunately, this doesn't work well with a small wheel gap.

I'm also curious as to how they ensure 4 wheels touching. After cutting and sanding, dropping and drilling, I think it's more common that a body ends up with a slight warp creating a near 3-wheeler all by itself. Do they want you to bend an axle down to make sure even weight over all 4 wheels?

We ran on a 54' track at Council the last 3 yrs. We always kept the same steer as on the shorter tracks. We always went more aggressive on the COM as we progressed Pack to Districts to Council. We always ran .75" or less COM. We didn't test on a track. We tuned on our kitchen table, so I can't say if this is optimum or not. We ran extended wheelbase which may have helped keep her stable on the long flat.

When I get home from work I can get you our times on the 54' track if that would help in any way.

Good luck.

davet wrote:How can you precisely remove the 3 crimp marks without getting at least a slight "groove" in the shaft? I would just say that your son took the marks off and you don't have a lathe, if questioned about an axle groove. Hopefully they allow the K-House slot so you can give them a twist when it's time to take them out too. Until we wised up and found a way to make the slot, we would wrap blue painters tape around the end of a needlenose pliers and twist them that way. Unfortunately, this doesn't work well with a small wheel gap.

I'm also curious as to how they ensure 4 wheels touching. After cutting and sanding, dropping and drilling, I think it's more common that a body ends up with a slight warp creating a near 3-wheeler all by itself. Do they want you to bend an axle down to make sure even weight over all 4 wheels?

We ran on a 54' track at Council the last 3 yrs. We always kept the same steer as on the shorter tracks. We always went more aggressive on the COM as we progressed Pack to Districts to Council. We always ran .75" or less COM. We didn't test on a track. We tuned on our kitchen table, so I can't say if this is optimum or not. We ran extended wheelbase which may have helped keep her stable on the long flat.

When I get home from work I can get you our times on the 54' track if that would help in any way.

Good luck.

That would be great davet and thanks for the pointers on how you prepped yours ahead of time without a track...

I saw on the other topic you posted your time after sitting for a year on a 42 ft... All I can say is wow... A 2.91xx is awesome... I bet with those speeds you have dad's and inspectors going through the car going what did his son do to make it that fast. I had calculated an estimate for my son showing him that each one hundredth of a second difference between his car and the competition that it was about 1.4 inches of length... Your son's car must be blowing most of the competition out of the water as most I have been seeing are running 3.10s and higher.

If we were to get in the 2.9xxx range I would be extremely happy for my son. Congratulations on those times.

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