Stock wheelbase...best to shift axles back?

[Vitamin K]

So, our rules dictate a wheelbase of no more than 4.5 inches. Pretty close to stock wheelbase on a typical BSA block.

However, I realize that this leaves us free to, if desired, shift the axles back a bit (We could do the same with the stock slots by cutting off some wood from the back and gluing it to the front).

So we'd have something like:

Code: Select all

-(O)--------(O)-------

instead of:

---(O)--------(O)-----

(Ascii-art not to scale.)

So, my questions are:

1) Is there a benefit to shifting the wheels further to the rear (while keeping the wheelbase intact)?

2) If we do, or do not shift the wheel locations, how would those considerations affect our final choices for setting our center-of-mass? Would there be any effect?

[sporty]

The farther back. Gives s slight increase of speed over stock. Wheels are further back. Weight location can be further back also.

[FatSebastian]

1) Is there a benefit to shifting the wheels further to the rear (while keeping the wheelbase intact)?

Generally this configuration also allows for slightly more pressure / weight to be applied to the DFW, since the DFW is closer to the rear (when the mass is concentrated). This potentially improves steering, and thus, stability.

[ngyoung]

This may help, it depicts 1/4" cubes in the weight pocket. This isn't at 4.5" WB but just set your axle line at 5/8 from the back and go from there. I usually shade everything a hair away from the end to make sure the back weights don't end up sticking out the back.

[Noskills]

Search under the term extended front end or EFE. There are some posts on it. We won districts last year with an extended front end stock wheelbase car. Put 2 rows of 5 behind the axel as suggested by Sporty and the rest in front. I think I have photos on DT of that car. Search under "Stampy" the cars name.
Noskills

[Speedster]

Noskills, it would be interesting to learn what would happen if you could run that car down a Best track and then cut a 1/4", or whatever the amount would be, off the front and run it down again. If the front is a piece of thin wood the weight shouldn't make any difference. Would it be faster, slower, or not make any difference? I understand what Physics says but I wonder what the Best track would say.
Sporty recently stated he had success with 1 1/2oz behind the rear axle slot on a stock wheelbase car. Two rows of 5 cubes weighs 1.690 oz. Nine cubes weighs 1.520 oz. Would the car be faster with 9 cubes in the rear as oppose to 10? If the 10th cube is moved in front of the rear axle slot, what would happen? If the car is retuned would it be faster or slower? I have absolutely no idea.

[Noskills]

Speedster,

Alas all questions that must go unanswered due to lack of track, time and car build specifically to allow the moving of weighs around. I think in general to get back to the question at hand, most agree that the extended front end is the way to go when stock wheel base is required.

Noskills

[Vitamin K]

This is an interesting question. The maximum length of the car is 7", but since the wheelbase is locked at ~4.375", is there any benefit to extending the nose out, once I've shifted the axles as far back as they'll go? I don't believe there's any minimum length to contend with. If we were able to run an extended wheelbase, the chassis length gives us benefit, since we need it for the wheelbase, but if our wheelbase is locked, what benefit do I get from running a 7" chassis?

Here's an example of what I've been playing with for my daughter's car. Was originally my son's design, but he decided he didn't like it, but my daughter did, so...



Just wondering which one would perform best.

Noskills, it would be interesting to learn what would happen if you could run that car down a Best track and then cut a 1/4", or whatever the amount would be, off the front and run it down again. If the front is a piece of thin wood the weight shouldn't make any difference. Would it be faster, slower, or not make any difference? I understand what Physics says but I wonder what the Best track would say.
Sporty recently stated he had success with 1 1/2oz behind the rear axle slot on a stock wheelbase car. Two rows of 5 cubes weighs 1.690 oz. Nine cubes weighs 1.520 oz. Would the car be faster with 9 cubes in the rear as oppose to 10? If the 10th cube is moved in front of the rear axle slot, what would happen? If the car is retuned would it be faster or slower? I have absolutely no idea.

[Vitamin K]

Hmm, of course, to reply to my own post, having a longer car means that your weight starts higher on the track, thus giving a greater potential energy, no?

[MaxV]

Exactly, you shifted the wheelbase back to get the balance point further back (relative to the starting pin). But if you shorten the car, you are shifting the balance point forward (relative to the starting pin).

[ngyoung]

Yeah. Do NOT shorten the car. You want your back end to be as far from the starting pin as possible. Just for perspective look at some of the top adult league car winners, a majority of them are close to standard wheel base with the back axles at 5/8" from the back. Some may push it to 5" but anything beyond that you can't really get a good front fender on.

The main benefit to extended wheel base is for making it easier to have a stable car. A stable EWB car is not inherently any faster then a stable SWB car when both have the same rear axle location.

[Speedster]

Noskills, I wrote that to try to get you to do some testing. I suppose that could be considered teasing. When I was doing all the testing this past summer I could not get a significant change with the shifted wheelbase. It would be interesting to see what would happen with a Best track. spring start, and run 8 or 10 times. My track is very smooth but I don't pretend it is as good as any of the aluminum tracks.
Maybe we can get Max V to run the test.
Bill

[Noskills]

Here is the stock wheelbase we did well with last year:
http://www.derbytalk.com/viewtopic.php?f=19&t=7677

Now that I get to write the rules for district the stock wheel base requirement is being lifted. As ngyoung suggested I am making a 5 in wheelbase car with front and rear fenders. My kids will have 5 in wheelbases without fenders. Photos coming of mine (the sooner I get mine out of the way the sooner I can help the kids)

Noskills

[pwrd by tungsten]

For top speed the rear wheel must be as far back as the rules allow. This is key to a fast car.

[davidwilkie]

This may help, it depicts 1/4" cubes in the weight pocket. This isn't at 4.5" WB but just set your axle line at 5/8 from the back and go from there. I usually shade everything a hair away from the end to make sure the back weights don't end up sticking out the back.

Is there a reason you have more weight on the right side? Are you trying to put more weight on the right rear wheel?

We always center our weight. Should we put more to the DFW side or something?