Drilling the DFW

[GravityX]

What is the typical drill height of the DFW? I've read many different suggestions here on the forum and it has made me wonder, does it even make a difference? With the DFW axle being bent for a positive cant when installed and then the degree of bend will effect how high it will raise the car. Higher, lower, same as the rear drill, many options, what is "right" (to use that word loosely)?

Am I just over thinking again or does not even have an effect?

 

[derby freak]

with the axle bent it lifts the front of the car some what and a lot of people don't like that so they will compensate for it by drilling the front set of holes higher in the body to drop the front end back down closer to even or below even. but as far as making a big difference i haven't tested it. i've saw fast cars with several different ways of drilling the holes. i've saw some fast cars where they didnt readjust the fence after removing the cant pin from the silver bullet and this will make the back of the car ride way low. i dont like that method myself i believe it would scoop too much air under the car. but, whatever you like i guess i like my cars to be a little lower in the front to push air over the car more and less under the car.

 

[ZZ Racing]

The height of the front of the car will change the toe on the rear, the higher the front gives you more toe out and lower gives you more toe in. It's not a lot of change but I have seen it make a change in times just by changing the elevation of the axle hole. Hope this helps.

 

[jator359]

So from your experience, which causes the least amount of drag, toe in or toe out in the rears?

The height of the front of the car will change the toe on the rear, the higher the front gives you more toe out and lower gives you more toe in. It's not a lot of change but I have seen it make a change in times just by changing the elevation of the axle hole. Hope this helps.

 

[Quicktimederby]

Every car is different. It depends on several other aspects. Bend of FDW axle, diameter of the FDW, wheel base and so on.

So from your experience, which causes the least amount of drag, toe in or toe out in the rears?

The height of the front of the car will change the toe on the rear, the higher the front gives you more toe out and lower gives you more toe in. It's not a lot of change but I have seen it make a change in times just by changing the elevation of the axle hole. Hope this helps.

 

[derby freak]

To find out what works the best for you just make small adjustments to this or that and keep building cars trying different things to see what works best for you. The guys that are on top of the leader board didn't get there overnight they did a lot of research and studying and this takes a lot of time. not days its more like years, you can get fast in a short period of time but when you get to a certain point the few tenths or the hundredth of a second you need to beat the best seems almost impossible and that is where it gets tough and takes a lot of research and also what separates the best from the rest.

 

[GravityX]

I keep plugging along and this is why I ask questions. I could be right in the middle of doing something related to these pinewood derby cars or not when these ideas or thoughts come about. I ask the question to see if I need to proceed with an idea or not. Usually if it is not so good of an idea the guys here on the forum will say that it isn't and I save some time.

I do a lot of R&D stuff, but the once a month testing is tough and it is usually trial by fire. I love the research that goes on with these cars and all the discussion that comes about in the forum. I pose questions when I see multiple solutions and weed them out. I'll keep going along as I have been. I'm having a blast with these little cars, who would have ever thought these cars could consume so much of your time.

 

[derby freak]

questions are good never stop asking most of the time though you will find that you will get several different answers to your question due to the fact people do things different each way may work well but you really need a track to see what way works best for you. just keep at it have patience and never stop learning dd4h has been in this for many years and I bet if you ask him he will tell you he is still learning new things. you're hitting 2.96's so you are doing well so keep it up you'll get there for sure if you do but i'm just warning you the toughest is probably yet to come the faster you get the less of a gain you will find and you will get to the point that you feel $20 is a cheap price to pay for a .002 gain.

 

[bracketracer]

I struggled with this question on the last car. Once I drew the shape of the car on the wood I could see my options were limited. I drilled the axle holes last on this car, after it was shaped and weighted to try for the most accurate alignment. The car was thin in the front so I couldn't drill too high. I lowered the rear axle holes instead (compared to how I had them before), to try to level the car. Can't go too far that way either with the angled holes or you'll be poking out the bottom!

 

[GravityX]

Looking forward to these coming days... My signature tells you where I'm going. A majority of my focus is in the SS class right now. I'm tossing together another SP car for Nationals so I'll have 2 in that class and 4 in SS.

.... but i'm just warning you the toughest is probably yet to come the faster you get the less of a gain you will find and you will get to the point that you feel $20 is a cheap price to pay for a .002 gain.

 

[GravityX]

OK, here is my rationale on this whole DFW drilling. I've seen some cars with some peculiar humps at the front of the cars and can only guesstimate these car are running relatively flat to the track. The hump is likely there to make room for the higher DFW drill location to tune out a raised nose. This makes a lot of sense. If the car is nosed up, the car can catch a lot of dirty air or otherwise, which may cause a loose or unstable car IMO.

Now, it's been mentioned that as the car is nosed upward, or down, if affects the toe at the rear of the car due to the canting of the axle drilling. My thinking tells me zero toe would be the fastest, therefore a flat/level car is desired. Any toe-in or -out may scrub speed. But does it create some instability if there is no toe? Likely a trade-off somewhere.

As I thought, the bend in the axle will certainly decide how much it will move the nose of the car up. Drill location will effect the amount of lift it brings to the car. Other items that I did not consider are the diameter of the wheel and the wheelbase, assuming the rear drill remains constant. This makes sense. So, various wheelbases change the location of the DFW drill if you want the car to remain flat. A longer wheelbase DFW drill wouldn't be as high as a shorter wheelbase DFW drill, with a same bend in the axle. So, wheelbase, axle bend and wheel diameter are the most common factors involved in determining how the car sits. Two factors can remain a constant: wheel diameter and axle bend. Wheelbase seems to be the most changed factor, at least in my builds. Now, I just need to start drilling some blocks for some R&D.

 

[ZZ Racing]

So from your experience, which causes the least amount of drag, toe in or toe out in the rears?

The height of the front of the car will change the toe on the rear, the higher the front gives you more toe out and lower gives you more toe in. It's not a lot of change but I have seen it make a change in times just by changing the elevation of the axle hole. Hope this helps.

I like to have just a touch of toe out but that's my preference. I just made a new car and I drilled the rears at 4 mm from the bottom and the front at 3.5 mm. This is a SP car and so far it's turning out to be a real fast car.

 

[5KidsRacing]

As I thought, the bend in the axle will certainly decide how much it will move the nose of the car up. Drill location will effect the amount of lift it brings to the car. Other items that I did not consider are the diameter of the wheel and the wheelbase, assuming the rear drill remains constant.

Length of hubs, rear wheel gaps, Teflon spacer thickness, amount of drift, wheels bead on/off on dfw...... more things that change how the car sits..... pwd... easy stuff.

 

[Quicktimederby]

I have done the hump in front on some of my cars, but it was solely for design purpose not frt axle height. My thinking in that design was to get the air off the majority of the body. Don't think it really works as to I have built some new ones with out it and they are just as fast if not faster.

OK, here is my rationale on this whole DFW drilling. I've seen some cars with some peculiar humps at the front of the cars and can only guesstimate these car are running relatively flat to the track. The hump is likely there to make room for the higher DFW drill location to tune out a raised nose. This makes a lot of sense. If the car is nosed up, the car can catch a lot of dirty air or otherwise, which may cause a loose or unstable car IMO.

 

[txchemist]

Here is how I let the Cubs figure it out. Most will say when they ride around in a car with a hand out the window, level has the least force against the hand- so we are attempting to make a level car. If a kid wants nose up or nose down, I let him try that also. Now I noticed only a very few kids can measure the correct height of the back and the front with a ruler. Here is a simple way that ALL kids can understand. On the track, or on a table top, put a stack of twelve dimes or so and slowly run the car into the stack to move the excess dimes off the top. Repeat with the smaller stack until you can just clear the stack. Do the same with backing the car into a stack. Now even the most math challenged kid can count the dimes and tell if his car is even, or nose up or nose down.

 

[OPARENNEN]

So from your experience, which causes the least amount of drag, toe in or toe out in the rears?

The height of the front of the car will change the toe on the rear, the higher the front gives you more toe out and lower gives you more toe in. It's not a lot of change but I have seen it make a change in times just by changing the elevation of the axle hole. Hope this helps.

I don't know if I understand some of this, but I say: No toe-in or out on the rears. Canting yes, but NO toe (in or out) on the rears. The purpose of the Silver Bullet is to be sure the rears are ABSOLUTELY parallel to the body, or if the body is curved, then TO THE TRACK.
Any deviation equals slow slow slower. IMHO

 

[GravityX]

I would agree that zero toe could equal more speed. This is why I ponder the idea of building a "level to the track" car. I'm looking for some additional speed in my next builds and hoping this can get me there. I've got new Cheetahs coming any day now to try with this build. I think my process can compete with the top dogs right now, but I continue to R&D new product looking for an extra .00xx sec. I need to measure current nose elevations and try to tune out the lift without altering too much.

Another thought that just came to mind, with a car nosed up could that have any effect on COM. I know COM is fixed as it's built into the car, but it moves in an arc when the car is nosed up or down. Or is it just too trivial to consider it as a factor? There I go thinking again.

 

[OPARENNEN]

I posted this question once and never got a response:

If the car's front is higher, thus allowing more air to enter beneath the the car, would that have a tendency to lighten the car without losing the forward momentum caused by the rear weighting. i.e. would lightening the car that way reduce the over all wheel friction picking up a 1000th or 2??? TXCHEMIST, DO YOU HAVE AN OPINION?

I would agree that zero toe could equal more speed. This is why I ponder the idea of building a "level to the track" car. I'm looking for some additional speed in my next builds and hoping this can get me there. I've got new Cheetahs coming any day now to try with this build. I think my process can compete with the top dogs right now, but I continue to R&D new product looking for an extra .00xx sec. I need to measure current nose elevations and try to tune out the lift without altering too much.

Another thought that just came to mind, with a car nosed up could that have any effect on COM. I know COM is fixed as it's built into the car, but it moves in an arc when the car is nosed up or down. Or is it just too trivial to consider it as a factor? There I go thinking again.

 

[txchemist]

Somehow I missed that question OPA

What I think is you have two different effects that combine for the result. If you raise the front of the car enough to get some air flow change, it might tend to push up on the front and make the front wheel look lighter and become more unstable, but the true weight of the car is not changed, The drag due to air friction can be increased and actually slow the car down. Now think about this- why is it that when you spin a wheel prepped for oil, you do NOT get a low friction time at all, 6-12 sec is not unusual where spinning a graphite wheel can hit 26 sec or longer. You need some weight on that oil wheel to drop the friction. Find a way to make that wheel super light, and the friction will increase dramatically.

If anything, if you could make the car nose push down a little more, it would drop the friction on an oil wheel. Now how about a car with back wheels oil, and make the com aggressive and the front wheel very light, so use a graphite wheel on the front?

 

[OPARENNEN]

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