front end too light? Pics added

[davet]

Hey all,
Building this year's scout car. I may have cut body too light up front. Total body weight is .73 oz and the center is cut out. Wheelbase at 5 1/2". We'll have a sheet of 1/64" plywood on bottom and paper across the top for race day. We have 2 rows of 6 behind rear axle and another row of 6 up tight to the front of the axle. We can center 4 more cubes in front of the axle and only get .59 oz on DFW. This leaves me around .10 oz for tuning. I'd hate to have to put that 1/2 way to the front of the car to hit my target of .65 oz on DFW.
Is this low DFW weight an issue?

 

[txchemist]

Study the data from QT and the Governor race- some big clues are showing what is happening with light DFW.

 

[davet]

I did a search and couldn't find the info. I found QT's post on Governor's race but didn't see the DFW info.

Here is what I have. My boy is wanting an aircraft carrier so will this front design cause me front lift or drag?

 

[LightninBoy]

Is this low DFW weight an issue?

No. It's actually a bit too conservative IMO.

 

[HurriCrane Racing]

Much depends on the track you will be racing on. If it is smooth like the NPWDRL track, you will have no issues at all.
If the track joints match up poorly, the car could pop a wheelie. I think with that much riding on the DFW, you should be ok.
Good Luck!

 

[davet]

Is this low DFW weight an issue?

No. It's actually a bit too conservative IMO.

Oh man. I am so far behind you guys. I was nervous last yr running at .64 oz on the DFW. I actually thought of running the "ragged edge" this yr and trying .62 oz.

 

[davet]

I forgot to mention that with the .59 oz on the DFW we get a .667" COM as using the COM Visualizer site.

 

[B_Regal Racing]

I forgot to mention that with the .59 oz on the DFW we get a .667" COM as using the COM Visualizer site.

I do not know if it is right or wrong, but I stopped measuring COM and am just concentrating on the DFW weight only. There is a mathamatical relationship between the two (COM and DFW weight) for a given wheelbase. Since I typically do not change my wheelbase, I stopped paying attention to the COM. Any thoughts?

NOTE: I haven't won yet, so I could easily be doing what ever it is wrong.

 

[davet]

OK guys. I got the body weight down to .54 oz including the 3 braces and a piece of plywood for the bottom. After taking more wood off I found I had more flexibility in moving weight around. I can get it up to .65 oz on the DFW but we'll go for broke and try this.

Here's how it works out for .62 oz on the DFW and a COM of .698". 12 cubes in back, a single 1/8" cube between rear wheels, 6 ahead of axle then another 4 full size ahead of that. A piece of tungsten ahead of the cubes then another on the front axle. I still have a little room for fenders if we run them.

Anything jump out as a problem? No test track so we'll steer 4" in 4 feet.

 

[~JBD RACING~]

That's still too heavy for the front wheel...3 1/2-4 is a good starting point..

 

[B_Regal Racing]

That's still too heavy for the front wheel...3 1/2-4 is a good starting point..

After taking more wood off I found I had more flexibility in moving weight around. I can get it up to .65 oz on the DFW but we'll go for broke and try this.

I think this is mostly left to self-discovery, but I have found somewhere between .45oz to .55oz to be the preferred weight on the DFW, depending on what the car wants to be stable (for aluminum tracks). Not sure what others do.

 

[Peerless Racing]

I asked this Q during race season as I had very low weight on the DFW (0.3 oz.) the track was the determining factor for me. If the start gate is slamming you can watch the car jump sideways during the start. Once the slam was addressed the car did great. Additionally I added a small square of tungsten to get to 0.3 as it was 0.21 at first. Good luck.

 

[davet]

What kind of steer are you guys running on a BestTrack with low DFW weights like those? Last yr we had .65 on our DFW and the car was faster as we moved from 3 1/2-4" of steer. You guys must be running more steer or else we have way too much DFW weight or too much steer?

 

[ngyoung]

That part really takes testing. The general consensus is typically 4" over 4'. Any other tuning usually involves sendingthe car down a track at home or and event and making adjustments.

 

[rpenning1970]

I forgot to mention that with the .59 oz on the DFW we get a .667" COM as using the COM Visualizer site.

What and where is this visualizer site?

 

[davet]

I forget who but I believe it was a couple of members here that created it.

http://jsfiddle.net/minionsracing/UUnT5/embedded/result/

 

[Kinser Racing]

I believe it was Minions Racing (Ivin) that created it.

 

[rpenning1970]

Very interesting site, I plugged the numbers in for my daughters car which has gone the quickest i have ever seen any of our cars go which was a 3.15 on a 42' best track with all out of the box stuff, used prior year wheels with no reprep, original prep was DD4H wheel polish and axle polish and using red rocket, car set up was rear wheels 1.25 from rear, 5.125 wheelbase, DFW weight was .42 oz, left to right on rear was 2.54 oz and 2.09 oz (yes I know we were .05 oz over but did not catch until just before race, there scale did not pick it up), that gives a COM of .4262 which I understand is just insane. Going to figure out the other cars from last year and see what that tells me.

 

[davet]

What kind of steer did you have dialed in with that car? Any wobble?
I thought we were running on the edge last yr with 5 9/16" WB, .65 oz on DFW and COM of .725". You guys are really surprising me with these numbers.

I'm interested in what kind of numbers people are getting. It seems to me that the program can really help build more consistent cars and provide a way to clearly document how changes affect speed. Too bad this is my boy's last yr in scouts.

Is a longer wheelbase car more stable than a shorter one with the same DFW weight?

 

[rpenning1970]

My understanding is a longer wheelbase will always be more stable, I have to check steer, maybe I can do that tomorrow night. Daved what type of track did you runon and what times did you get? were you using bsa wheels and axle or aftermarket?