Longer track

[Brian Clark]

Question for you guys. In your set up what changes would you make if your racing on a 63 foot track vs.a 42 foot track?
Thanks!

[Brian Clark]

I'm guessing you would use a little more steer to keep it on the rail, but what do I know I'm a newbie.

[whodathunkit]

Hi Brian, And .

Some of the set up changes I'd try for the longer tracks would be to change up the COG.
And maybe take a chance running it someware around 1.5".
But that's just me!

heres a topic about tips for a 56" foot track: hopefuly it will help you out.
http://www.derbytalk.com/viewtopic.php? ... cks#p73321

Sporty, Stan, or FS,
may all have different takes on the placement of the COG for the longer tracks
hopefuly one of them will chime in.

Whoda.

[Stan Pope]

I think that Whoda is on the right track.

My logic is that on the longer track you will be coasting farther. This means that friction losses, including those from DFW Toe-in are more important. To me this suggests that moving the CM forward a bit from what is optimum for a short track on order to get by with less toe-in is probably in order. How much? Can't tell you.

[FatSebastian]

I'm guessing you would use a little more steer...

Most people do not have a lot of experience racing on very long tracks (including me), so precise expert recommendations are harder to discover. Nevertheless, I agree with Stan that you will likely want less steer-in on a longer track. In addition to Stan's reasoning to decrease friction, a longer distance offers more exposure to potential track defects which could upset a strongly steered car.

Whether one needs to further alter the weight distribution really depends on how aggressive the CoM is in the first place relative to the kind of track. As Whoda suggests, my feeling is that most experienced Scout-built cars tend to play that aspect somewhat conservatively.

[Stan Pope]

... a longer distance offers more exposure to potential track defects which could upset a strongly steered car.

I don't follow the logic of this statement. Here is why: I understand that the purpose of increased toe-in is to overcome track defects.

By moving the CM a bit forward from its optimum short track location, the weight on the DFW increases and allows less toe-in to accomplish the same control. Less toe-in means less sliding distance for the DFW, more than offsetting (I think) the added weight on the DFW.

One thing is for sure... few folks will have a test-bed for proving our thoughts!

[Brian Clark]

Thanks for the help guys.

[FatSebastian]

I understand that the purpose of increased toe-in is to overcome track defects.

Newton's third law implies that greater force will cause a greater reaction. My supposition is that there may be types of more severe defects (perhaps a mis-aligned joint?) to which a strongly steered car could adversely react simply because of the increased application of sideways force.

[Stan Pope]

I understand that the purpose of increased toe-in is to overcome track defects.

Newton's third law implies that greater force will cause a greater reaction. My supposition is that there may be types of more severe defects (perhaps a mis-aligned joint?) to which a strongly steered car could adversely react simply because of the increased application of sideways force.

Thank you! That makes sense, but is inconsistent with my experience. On 28' test track tests (with questionable joints) our times for rather extreme CM locations (1/2 oz on DFW) improved with increased toe-in. We did not go to extremes with the toe-in, trusting that the event track(s) would be better aligned. (Mostly that has been true.)

[Speedster]

Is everyone assuming this is a 63' "Best" track with a 7' hill and the rest flat? What if this is a 63' track with a 14' hill and the rest flat, or perhaps there are 2 stop sections and the flat isn't really that long. It would be interesting to know what the track looks like when constructed, the actual flat distance the car must travel to the timer, and what all the rules are covering the construction of the car. Should this car be built with a 5" wheelbase and 4 matching fenders? It will be interesting to learn about the car that wins this race.

[Stan Pope]

Is everyone assuming this is a 63' "Best" track with a 7' hill and the rest flat?

No, I'm thinking usual approx. 4' high start line with extra sections added ahead of the finish line. Is there a 7' option? Or just usual sections added in ramp?

It would be interesting to know what the track looks like when constructed, the actual flat distance the car must travel to the timer, and what all the rules are covering the construction of the car. Should this car be built with a 5" wheelbase and 4 matching fenders? It will be interesting to learn about the car that wins this race.

Indeed!

[Brian Clark]

Yes they added 3 sections in front of the timer, same height as regular.

[Stan Pope]

This might be useful:

If your wheelbase is 5-3/4", moving the CM from 5/8" to 7/8" forward of the rear axle changes the DFW weight from 0.54 oz to 0.76 oz.
If your wheelbase is 4-5/8", moving the CM from 5/8" to 7/8" forward of the rear axle changes the DFW weight from 0.68 oz to 0.95 oz.

Note that moving the DFW back 1-1/8" toward the rear wheels increased the DFW weight, allowing either more extreme CM location OR reduced DFW Toe-in! Which you would choose might depend on track length.

[FatSebastian]

That makes sense, but is inconsistent with my experience.

Experience trumps supposition. It also probably helps to employ positive camber on the DFW, rather than negative...

[Stan Pope]

... It also probably helps to employ positive camber on the DFW, rather than negative...

Yes!!! Excellent reminder! That reduces the sliding distance markedly, and, therefore, the energy loss during the coast, since the Work = Force * Distance!