Pack race - asking for advice

[Extreme]

Hi All

My son is having a pack race, they are racing on a 32 ft wooden track. There is a rail in the center (not sure of the racing terms for it). My question is, what would be more important for you to race with. Aerodynamic car or a car that has alot of weighted added?

We built 2 cars, one car weights more and the other car is more aerodynamic. Here are the set ups for the cars.

1st car - 3/8 thick, polish axles, pro ultra lite tires, being aggressive with the com at 3/4. Total weight being added to the car is 4 oz, Rear weight of the car is 3 3/4 oz.

2nd car - 1/4 thick, groove axles, Bsa pro stock wheels. Aggressive with the com at 3/4. Total weight added to the car 3 3/8 oz .. 3 oz of weight in the rear.

What car would you use?

Thanks in advance
Brian

[tkp]

Choice A- especially with the ultra lites and more added weight.

You have more added weight in one central area at 3/4 cog- therefore, you should have the ability have a quicker car due to gravity acting on the increased weight alone. And again, the lighter wheels will help you off the start no question.

However, sometimes the way the car just comes together, alignment etc, ...sometimes can surprise you so I wouldn't rule out the potential that car 2 may actually take car 1 on the Track if all things aren't equal. Meaning- lubrication, axle, wheel prep, alignment, rail riding ability etc...

But- on paper and if all things are equal....Car A technically should be quicker.

Aerodynamics has a very small affect- assuming that you don't have big feathers hanging off the car that is! And being the fact that one car is 3/8 and the other is 1/4 -not that significant.

At the end of the day, both configurations should produce pretty quick cars for a Pack race.


I'll let others chime in, but I would think that with lighter ultra lite tires and more weight, these are the two biggest contributing factors that I see as the difference between your 2 cars and the advantage for car 1.

[Extreme]

I just got car # 2 - Rear to 3 1/2 oz. wonder if I should just take the pro ultra lite tires out of car # 1 and put them on car # 2 so I can add more weight to the car. Pondering

[tkp]

So how much total weight have you added to car #2 then at this point?
I'm assuming cog is still 3/4?

If you have added at least 3.75 to 4.0 of weight in each car, again, chances are you have two very good cars- (considering as mentioned previously, that you will have great wheels, axles, alignments, etc, etc)

I would see how they run at Pack then adjust for Districts if needed.....just my two cents!

However, there are many more folks on this site that may recommend to bleed it for as much speed as possible and say go for it....

[Extreme]

TKP
First I want to say thank you for replying to my post. Car 2, up to 3 1/2 oz for the rear so far. I have read in some of the post about taking wood off the car so you can add more weight. Where would be the best place to remove the wood from?
When you wrote alignment, Rail riding ability etc... Rail riding, I just dont understand it, when would you want to rail ride? Does it depend on the track?
This pinewood derby building is addictive, lately been spending hrs of reading info and messing around with a car design that I would like to try out for myself at the pack race for the fathers race. Down to it, son has 2 cars and I am working on one for myself.

Thanks again TKP

Brian

[roosclan]

Feb 1, 2009 9:32:27 GMT -6 Extreme said:

TKP
First I want to say thank you for replying to my post. Car 2, up to 3 1/2 oz for the rear so far. I have read in some of the post about taking wood off the car so you can add more weight. Where would be the best place to remove the wood from?

The front would be the best place. You basically want 4oz. on the rear axles and 1oz. on the front. If you can hollow out anything in the front of the car, that would be the place to do it.

When you wrote alignment, Rail riding ability etc... Rail riding, I just dont understand it, when would you want to rail ride? Does it depend on the track?

If your track is smooth, then rail riding is the way to go.
Basically:

• raise one of the front wheels just enough to keep it off the track.
  
• cant the axles a bit so that the wheels won't rub on the body of the car
  
• steer the front dominant wheel (FDW for short) so that the car drifts toward the raised wheel about 2" over 4-8'. This will cause the car to ride the center guide rail down the track instead of bouncing back and forth, robbing your car of speed.
  

[Extreme]

roosclan
Thanks for your reply. Pack track is wooden 32 ft and districts is a speed track. I read what you wrote about raising one front tire. Rules state all 4 tires must touch the track.
From behind the front axle toward the rear axle, there is 2 3/4" that has not been touched. If I take out some wood in that area, dont I have to add more weight to the front as well?

[roosclan]

Feb 1, 2009 13:47:36 GMT -6 Extreme said:

roosclan
Thanks for your reply. Pack track is wooden 32 ft and districts is a speed track. I read what you wrote about raising one front tire. Rules state all 4 tires must touch the track.

That is very unfortunate! See if you can make the wheel bore slightly larger and place the axle just a hair higher so that the wheel still touches, but barely touches the axle. It might help a bit.

From behind the front axle toward the rear axle, there is 2 3/4" that has not been touched. If I take out some wood in that area, dont I have to add more weight to the front as well?

So there's no room in front of the front axle to remove wood? Are you using an extended wheelbase? What about hollowing out the underside of the nose in front of the front axle?

You generally don't want to add weight to the front unless you have less than 1oz. on the front wheels (stability issue). You can hollow out between the front and rear axles and still add weight just before the rear axles to keep the proper front/rear weight ratio.

Is there any way you can post a pic of your car so we can see what you're dealing with?

[ProQuest]

I have to say that Roosclan's recommendation to enlarge the bore of the non-dominant wheel and place the axle hole slightly higher is brilliant!!! Roosclan, correct me if I am mistaken, but the idea in that technique would be to have the non-dominant wheel touching the track, but to render the axle on that side non-weight bearing. The placement of the axle hole will be a tough operation, but the dividends could be substantial if you do it well.

I've never competed in a race that required all 4 wheels to touch, but if I ever do, I will definitely adopt that speed strategy.

Just want to give credit where its due.

ProQuest

P.s. On further reflection, I'm not sure you would even have to raise the axle. You might accomplish your purpose simply by reaming the bore by a considerable amount. Just a thought.

[Extreme]

roosclan, ProQuest

I posted a photo so you can see what I am working with. The rules for the BSA is 4 wheels must touch track, standard wheel base. Sorry took a while to post pic. I had to find out how to post the photo first.

[roosclan]

Feb 1, 2009 23:32:38 GMT -6 ProQuest said:

I have to say that Roosclan's recommendation to enlarge the bore of the non-dominant wheel and place the axle hole slightly higher is brilliant!!! Roosclan, correct me if I am mistaken, but the idea in that technique would be to have the non-dominant wheel touching the track, but to render the axle on that side non-weight bearing. The placement of the axle hole will be a tough operation, but the dividends could be substantial if you do it well.

I've never competed in a race that required all 4 wheels to touch, but if I ever do, I will definitely adopt that speed strategy.

Just want to give credit where its due.

ProQuest

Thanks, but I can't take credit for it since I read it on one of the 3 PWD forums I go to. I just can't remember which one and who originally came up with the idea. I just modified it a bit (I think) by raising the axle slightly. It wouldn't be by much.

P.s. On further reflection, I'm not sure you would even have to raise the axle. You might accomplish your purpose simply by reaming the bore by a considerable amount. Just a thought.

My idea is to have the wheel touch the top of the axle, otherwise you have a wheel that's floating around with nothing to keep it stable, which might create a ton of wobble in that wheel. At least with the axle and wheel touching in one spot, there might be more stability for the wheel. We can run 3 wheels, so I've never tried it.

[roosclan]

Feb 2, 2009 21:27:16 GMT -6 Extreme said:

roosclan, ProQuest

I posted a photo so you can see what I am working with. The rules for the BSA is 4 wheels must touch track, standard wheel base. Sorry took a while to post pic. I had to find out how to post the photo first.

Wow, there is sooooo much wood that can be removed! I don't have any photoshopping software, otherwise I'd edit your pic for a mock up of some possibilities.

1st thought:
hollow out the entire underside from the 3 holes back to your weight pocket (make it one BIG weight pocket)

2nd thought:
do what we've done with my Bear's car and make a big hole in the middle and cover it with 1/64" plywood so there is a smooth surface to paint on.


I wouldn't recommend making the hole extend between the front axles like we did. I'm actually a bit concerned about strength, but we're also using carbon fiber slats along the inside of the side rails, possibly a short piece between the front axles sitting flush with the bottom, and plywood covering the entire top and bottom.

[Extreme]

roosclan
You have a pm

[Derby Monkey]

I race low profile cars at 1/4 thick. I have come up with several different designs in order to remove as much wood as possible. I have thinned some down too much because I have broken several bodies.

This car is just about right. With tungsten, I can get the COG at 3/4" or less.

[Talk-n-Derby]

Feb 2, 2009 21:27:16 GMT -6 Extreme said:

roosclan, ProQuest

I posted a photo so you can see what I am working with. The rules for the BSA is 4 wheels must touch track, standard wheel base. Sorry took a while to post pic. I had to find out how to post the photo first.

I might suggest, if you can finish routering out the bottom of that car, you could lose alot more wood weight, which would then allow you to add more dense weight exactly where you want it to be. After adding in all of your weight, you could cover the bottom of the car with some clear packing tape, so as to give some extra aerodynamics to the car, without much weight. The tape's smooth surface will allow your car to pass air without having it catch in your cavity, thus creating drag/friction.