Accurate testing on a shorter track?

Discussions on buying, building or rehabbing a race track. Topics like plans, materials, tools, construction, finishing, commercially available tracks, and so on.
User avatar
Vitamin K
Master Pine Head
Master Pine Head
Posts: 980
Joined: Sat Apr 20, 2013 7:26 pm
Location: Montgomery County, MD
Contact:

Accurate testing on a shorter track?

Post by Vitamin K » Fri Oct 18, 2013 12:36 pm

Okay, so I need so input from people who are smarter than myself. I'd like to build a test track to tune cars on, but finding appropriate straightaways isn't a trivial task indoors.

I suppose I could set it up to be used outdoors, but since the ground isn't flat, I'd have to build some kind of levelling mechanism for the track.

The other option would be to go with a shorter track...say...20 feet instead of 30. My question for the physics and math gurus is...can a 20 foot track be constructed that would give the same performance as a 30-40 footer? That is, can I effectively scale the track down, but still get the same results? That is, if car A always beats car B on the 30 footer, would it do the same for the 20 footer?

My suspicion is that while a shorter track might give reasonable results, the modified distance (and, consequently, speed) would cause some factors to be emphasized over others. I also imagine that the center of mass might have a different effect.

Any thoughts?



User avatar
birddog
Master Pine Head
Master Pine Head
Posts: 307
Joined: Thu Apr 26, 2012 12:40 pm
Location: Denver, CO

Re: Accurate testing on a shorter track?

Post by birddog » Fri Oct 18, 2013 2:26 pm

Ideally, you want to replicate the track you actually race on to get the best predictor of how your car will run during the real race. That includes track length, but length may not be the most significant factor if you are testing on a track with outside rails and you are running on a track with inside rails. Matching "track type" may be more important in some cases.

I have experience testing on a 35' test track and racing on a 42' race track. The results of testing scaled well to the real track with those lengths.

With shorter lengths, you may not see how your car runs "on the flats". Wobbles can sometimes happen there and you need enough track to be able to catch and fix those.

I only setup our track about 1 week before race day and we have to be careful during that one week as the track does get in the way of living in our house, but it can be done.

Hope that helps,

Birddog



User avatar
FatSebastian
Pine Head Legend
Pine Head Legend
Posts: 2646
Joined: Wed Jun 17, 2009 2:49 pm
Location: Boogerton, PA

Re: Accurate testing on a shorter track?

Post by FatSebastian » Fri Oct 18, 2013 4:26 pm

Vitamin K wrote:can I effectively scale the track down, but still get the same results? [...] the modified distance (and, consequently, speed)
You will probably want a track height that is close to the height upon which you will be competing. The car does slow down a bit in the flat, but speed across the flat is mainly governed by the height of the starting peg relative to the flat.



Speedster
Pine Head Legend
Pine Head Legend
Posts: 1334
Joined: Sat Feb 18, 2012 2:48 pm
Location: Toledo, Ohio

Re: Accurate testing on a shorter track?

Post by Speedster » Sat Oct 19, 2013 7:31 am

Good answers from birddog and FS. Set the timer the distance your car will run on the Pack or District track. Record the time. Then move the timer to the 20' mark and record the time. It would be nice if you have a winning car or are able to acquire one to see how it performs at the two distances. I have lots of questions but I would go way Off Topic. email me.
Cheers
Bill



User avatar
Vitamin K
Master Pine Head
Master Pine Head
Posts: 980
Joined: Sat Apr 20, 2013 7:26 pm
Location: Montgomery County, MD
Contact:

Re: Accurate testing on a shorter track?

Post by Vitamin K » Sat Oct 19, 2013 7:55 pm

The thing of it is, I've seen winning cars that are a little behind at the bottom of the slope, but pull ahead as they make their way down the flat straightaway. Is this not common? My worry is that a shortened track won't accurately gauge the "coasting" performance of the car. :thinking:
FatSebastian wrote:
Vitamin K wrote:can I effectively scale the track down, but still get the same results? [...] the modified distance (and, consequently, speed)
You will probably want a track height that is close to the height upon which you will be competing. The car does slow down a bit in the flat, but speed across the flat is mainly governed by the height of the starting peg relative to the flat.



Speedster
Pine Head Legend
Pine Head Legend
Posts: 1334
Joined: Sat Feb 18, 2012 2:48 pm
Location: Toledo, Ohio

Re: Accurate testing on a shorter track?

Post by Speedster » Sat Oct 19, 2013 9:52 pm

I think it is not SUPER common but it does happen. I suspect it is axle and bore prep. Obviously, having a track like the one you will be racing on is the best. However, probably doing something is better then doing nothing.
Best of Luck.



User avatar
Stan Pope
Pine Head Legend
Pine Head Legend
Posts: 6888
Joined: Sat Jul 05, 2003 7:01 pm
Location: Morton, Illinois
Contact:

Re: Accurate testing on a shorter track?

Post by Stan Pope » Sat Oct 19, 2013 11:33 pm

Vitamin K wrote:The thing of it is, I've seen winning cars that are a little behind at the bottom of the slope, but pull ahead as they make their way down the flat straightaway. Is this not common? My worry is that a shortened track won't accurately gauge the "coasting" performance of the car. :thinking:
Consider the array of causes of the "come from behind" performance:
1. lower bore/axle friction, rolling friction and edge friction
2. lower wheel run-out
3. better rear axle alignment
4. lower rail-guiding friction

You can assess improvements in the first three with short-track testing.
The last you may have difficulty assessing because of the trade-offs involved. The trade-offs include CM vs DFW Toe-in (more extreme CM may require more Toe-in) and optimum DFW Toe-in for the competition track.

You don't really need a track to assess the first three, but it is easier to see the results, and a lot easier for your youngster to see them. :)


Stan
"If it's not for the boys, it's for the birds!"

TXDerbyDad
Master Pine Head
Master Pine Head
Posts: 185
Joined: Wed Dec 12, 2012 4:04 pm
Location: Dallas, TX

Re: Accurate testing on a shorter track?

Post by TXDerbyDad » Sun Oct 20, 2013 11:57 pm

Stan Pope wrote:
Vitamin K wrote:The thing of it is, I've seen winning cars that are a little behind at the bottom of the slope, but pull ahead as they make their way down the flat straightaway. Is this not common? My worry is that a shortened track won't accurately gauge the "coasting" performance of the car. :thinking:
Consider the array of causes of the "come from behind" performance:
1. lower bore/axle friction, rolling friction and edge friction
2. lower wheel run-out
3. better rear axle alignment
4. lower rail-guiding friction

You can assess improvements in the first three with short-track testing.
The last you may have difficulty assessing because of the trade-offs involved. The trade-offs include CM vs DFW Toe-in (more extreme CM may require more Toe-in) and optimum DFW Toe-in for the competition track.

You don't really need a track to assess the first three, but it is easier to see the results, and a lot easier for your youngster to see them. :)
My understanding as an amateur physicist is that, all things being equal, the car with the weight distributed farther behind for the ideal center of gravity would be acted upon longer by gravity and appear to "speed up" on the flat compared to cars with suboptimal weight placement, say front or middle of the car. I see this every year at our Pack races for those who don't listen to the part about optimal weight placement. :wall:

Again, that's with all things being equal, which is realistically impossible to measure with multiple cars, but it seems that you're not even addressing weight distribution on your list.



User avatar
Stan Pope
Pine Head Legend
Pine Head Legend
Posts: 6888
Joined: Sat Jul 05, 2003 7:01 pm
Location: Morton, Illinois
Contact:

Re: Accurate testing on a shorter track?

Post by Stan Pope » Mon Oct 21, 2013 1:17 am

TXDerbyDad wrote:... but it seems that you're not even addressing weight distribution on your list.
I did not include CM Loc explicitly since it is a "slope issue", not a "flat issue".

I did include CM Loc as a part of the 4th item. The reason is that I recall top racers commenting that they use less aggressive CM Loc on longer tracks. I believe that their reasoning is that more aggressive CM Loc's dictate more aggressive DFW Toe-in. More aggressive DFW Toe-in increases DFW Friction losses whose penalty is greater on longer flats.

Experiments with my grandsons (and their dad) seem to support that view, although all of the testing was on a 4-section Freedom track. The testing involved a small (1/4 oz.) trim weight that we could move around on the car and then adjust the DFW toe-in to max performance. With most of the cars tested, there was a point at which moving the trim weight farther back prevented us from reaching comparable performance. Our conclusion was that there is an optimum CM Loc for each track dependent on the length of the flat and the smoothness of the track.

If you feel it is a "come from behind issue" then by all means, include it in your list!


Stan
"If it's not for the boys, it's for the birds!"

User avatar
FatSebastian
Pine Head Legend
Pine Head Legend
Posts: 2646
Joined: Wed Jun 17, 2009 2:49 pm
Location: Boogerton, PA

Re: Accurate testing on a shorter track?

Post by FatSebastian » Mon Oct 21, 2013 10:53 am

Vitamin K wrote:My worry is that a shortened track won't accurately gauge the "coasting" performance of the car.
There are several excellent aspects that have been discussed already, which makes me wonder if I am confused as to what you seek to accomplish with a test track.

I perceive your question as whether you should build a shorter test track indoors, or a longer test track outdoors with the added complication of a leveling system. I would go with the shorter indoor track (with the correct height), simply because of the nuisance associated with using a track outside which requires you to set up / take down every day (dew, weather, temperature changes, sunlight, etc.) and the extra expense and storage of having a longer, heavier, more complicated track.

One can conjure mild disadvantages against having a shorter test track if a longer track is used officially, based on physics arguments. But a test track is for "testing" and with that comes experimental uncertainty. Presumably, your test track will not be the official track for competition, so whatever is optimal for your track does not guarantee optimality in the racing environment regardless, even if you go to great pains to emulate the official track as much as possible. The condition of a guide rail in the flat can play a major role in how much speed is lost in the flat (particularly with rail-riding), and the longer the "coast" the greater the probability that the car will encounter rail defects. There are many aspects over which you have no control. But -- your team will build a better car with a shorter test track than a longer one that you cannot use because it is too much hassle.



Speedster
Pine Head Legend
Pine Head Legend
Posts: 1334
Joined: Sat Feb 18, 2012 2:48 pm
Location: Toledo, Ohio

Re: Accurate testing on a shorter track?

Post by Speedster » Mon Oct 21, 2013 12:31 pm

I thought he wanted to build a track where he could reach a certain elapsed time so he could win on the aluminum track he races on at District. He has taken 1st place at his pack his 1st year of racing. If he can get some elapsed times at his District, or the winning car, he can figure out how much faster he has to go. As an example, I have compiled a record of the times fast cars record 30' on Lane #1 of my wood, circular arc track. Thank you Sporty and Noskills. I know the elapsed time our car turned on my wood track and it took 1st place at the Pack level. I know the elapsed time our car turned on each of the 4 lanes of a 35' Best track at District because they scored with Elapsed time. The 8 fastest cars were moved to a Freedom track where points scoring was used so I don't have an elapsed time. However, our car dominated on the Freedom track so we were happy about that. I tested a car on my track belonging to a friend of mine competing in a different grade group and told him he should make it to the final track. He took 1st place at our Pack and District. Even though it would be nice, you don't really need the exact track you will be racing on. If you have a quality one lane track, a quality timer, and can get information, your test track will give you a huge advantage. You will have a certain elapsed time you will want to reach and when making adjustments you'll know if you're going faster or slower.



User avatar
FatSebastian
Pine Head Legend
Pine Head Legend
Posts: 2646
Joined: Wed Jun 17, 2009 2:49 pm
Location: Boogerton, PA

Re: Accurate testing on a shorter track?

Post by FatSebastian » Mon Oct 21, 2013 1:02 pm

Speedster wrote:...you don't really need the exact track you will be racing on. If you have a quality one lane track, a quality timer, and can get information, your test track will give you a huge advantage.
Exactly.

From the original question, it was not clear to me if Vitamin K would be using a timer.



Speedster
Pine Head Legend
Pine Head Legend
Posts: 1334
Joined: Sat Feb 18, 2012 2:48 pm
Location: Toledo, Ohio

Re: Accurate testing on a shorter track?

Post by Speedster » Mon Oct 21, 2013 2:46 pm

You're right, FS. I apologize.
He actually stated to me he would like to outfit his Pack's track with a timer. I then assumed too much. I can't see what help it would be to run a car down a track without a timer. I suppose if you have a quality 2 lane track and build multiple cars you could run the fastest one.



Rukkian
Master Pine Head
Master Pine Head
Posts: 199
Joined: Wed Jan 20, 2010 1:59 pm
Location: West Des Mones, IA

Re: Accurate testing on a shorter track?

Post by Rukkian » Mon Oct 21, 2013 2:53 pm

To go cheap, we built a quick 2 lane, 24' track at home. No timer or anything, it was approximately $22 and a few hours labor. It is useful, as we take last years cars, make sure they look good, then use them as a baseline. While we may not be able to get millisecond changes, we have been able to do some quick tuning to get the kids' cars faster than without testing.

I know that using a timer would be more accurate, but any test track allows for some tuning to make it faster. If we have a more competitive area, and wanted to spend the money, we could definately ramp it up some.



User avatar
FatSebastian
Pine Head Legend
Pine Head Legend
Posts: 2646
Joined: Wed Jun 17, 2009 2:49 pm
Location: Boogerton, PA

Re: Accurate testing on a shorter track?

Post by FatSebastian » Mon Oct 21, 2013 3:14 pm

Rukkian wrote:It is useful... While we may not be able to get millisecond changes, we have been able to do some quick tuning to get the kids' cars faster than without testing.
Yes, thank you; this is part of my own confusion with the original question. One can discuss the performance differences from testing on a 20' flat v. a 30' flat, etc., but it was not obvious to me whether K's testing environment is going to be sensitive to them. (Comparable track height seemed relevant regardless.)



Post Reply