strange handling chassis

[stevphens]

Just completed a brass inline retro chassis (IRRA rules) which corners in a strange way. When I try to loosen it up to make it faster, it goes from too tight to very loose. Tried adjusting the guide and front wheel height. Also rear tire traction. I can get it close, but even though it is very fast when tight, I can't make it neutral (optimum). It always goes from too tight to very loose. It weighs 109 grams with running gear. Does anyone know if removing some weight would help? If so, from what part of the chassis? Or is there something else I can do to find that fine line?
Thanks!

[dominator]

Need some more info:
If you can post a pic that would be awesome to see a new build and so we can help you more.

What size wire did you use for the main rails?
What kind of tires are you using on the front and rear?
What kind of track and gearing are you using?
What thickness and type/style of body are you using?
109 grams is a great starting weight so that is probably not the immediate problem.

[stevphens]

Main rails are single (each side) .062 piano wire. Wings are .032 brass.
Front tires are .750 diameter, .225 wide, large magnesium hubs, uncoated sponge rubber, independent rotation.
Rear tires are JK treated, medium hub, .820 diameter, .810 wide on 1/8 rear axle. I've tried other harder tires, but it's looser and slower.
Gearing is 8/29 (IRP angle pinion, Parma crown).
Track is a flat 90' hill climb, light spray glue.
Body is a red fox Ferrari GT, .007 (I think)
Cut down guide.
No photos yet, but it has one pan hinge in front. Pans are heavy in rear, so I'm wondering if removing 4 grams from pans would make it more adjustable? (weight is 114 grams with body).
The car is fast tight, but tilts on two wheel if cornering too fast, rather than swinging out.

[stevphens]

drilled brass guide nut
floating pin mounts for body
small diameter bite bar

Would increasing or decreasing wheel base and/or guide lead make the car more adjustable?

[Noose]

The overall weight seems OK as these cars do run better in that weight range.

You may want to try and add a piece of .024 brass plate in the center of the chassis. For some reason these cars tend to like some weigh there. Also,
I noticed you said that your fronts are .225 wide. The IRRA F1 fronts need to be .375 wide minimum. I would run some firm ones up front too.


Added note: Re-read this and saw that it is not an F1. Please disregard the tire statement.

[dominator]

Noose is right about the brass.

If the the track is only 90 feet I would drop to a 7:28 but no lower than 7:27. This will allow the motor to stay spun up and make it more drivable. At the ROC race held at
http://needforspeedraceway.com/Content/Track_Information.htm we ran on the 100 ft hillclimb with F-7's and I was geared 7:27 at 12 volts. Had I remembered to put a flat spot in the axle I would have won instead of finishing 2nd but it was still good enough to have .2 tenths on the field. The trick with hillclimbs is not the straight, but how fast you can get around the bottom escpecially on the short ones.

As for the rolling out of the turns, I have found that if you go to a softer front tire the chassis will have a little more give and not roll out. Try using a pair of JK small hub untreated. I do use both soft and hard for my fronts but it also depends on the chassis.

[Phil I.]

..........;)

Personal preference. I like to set mine up loose on a very lite glue track. That way when it gets TOO sticky. I can still hit the turns harder than most with out tipping. I to have floating body mounts. When it loose. I tape the front part of the body to the wings to titen it up some. If more is needed. I tape the back.
Did you full float the bite bar? If you did. Kill as much of the movement as you can with out soldering solid. If its solid. Make a U brace,.055 or .047, under the bite bar to the main frame rails. Going down the rails to the rear about 3/4 to 1 in.

GOOD LUCK AND TEST...TEST:D
PHIL I.

[stevphens]

Thanks guys!
I'll try the weight, Noose. By the way, congrats on your two podiums this past weekend! The slot car god sure is smiling on you. I guess it's all those virgin lexan bodies you have sacrificed!
I'll try experimenting with gearing and front tires as dominator suggested. With my vintage reflexes I assumed the car would be less responsive and easier to drive if geared high (large pinion). Am I wrong?
As you have figured out, I'm new at scratch building. What does "full floating bite bar" mean? All I really know about bite bars is that with my old flexi's I could change the diameter and make the car tighter or looser. If I remember correctly, a larger bite bar resulted in loose handling? Is that correct? On this chassis, I soldered the ends of the bite bar to the side pans, and let the center part float in a square tube soldered across the main rails. Maybe I don't even have a bite bar? Maybe I just made an upstop for the pans on their front hinge, and a support for the pans so they don't hang below the rails?? What IS the best design for a scratch built retro chassis bite bar?
Hope I don't ask too many questions...

[Phil I.]

Thanks guys!


As you have figured out, I'm new at scratch building. What does "full floating bite bar" mean? All I really know about bite bars is that with my old flexi's I could change the diameter and make the car tighter or looser. If I remember correctly, a larger bite bar resulted in loose handling? Is that correct? On this chassis, I soldered the ends of the bite bar to the side pans, and let the center part float in a square tube soldered across the main rails. Maybe I don't even have a bite bar? Maybe I just made an upstop for the pans on their front hinge, and a support for the pans so they don't hang below the rails?? What IS the best design for a scratch built retro chassis bite bar?
Hope I don't ask too many questions...

The way you have the center of the bite bar, threw the square tubing, is a floating bite bar. Un solder it from the wings makes it a full floating bite bar. I have never had good luck with the bar soldered to the wings. You want the wings to move up & down on the bite bar. Some use square tubing, some round as the stops. I use bent .032 piano wire. You then can use a smaller bar for more movement, looser, or a bigger one to tighten it up.

There is no best design for a bite bar. It is ALL up to you & TESTING. Finding out what works best for that one chassis. I built a true tripod with a full floating bite bar. It SUCKED. I soldered it solid to the square tubing and it worked well. I then did the U braced. Soldered to the frame rails, in other reply, and it made all the difference...It screames. I have another simi tripod that was just the opposit..

TEST...change...TEST...change...and find what workes the best for you. I have one chassis that has been threw 3 wing configurations before I kinda liked it.:rolleyes:

With the crew around here. Ask and ye shall receive an answere.....And I hope you have a good sense of humer.....:D RIGHT 'MOM'!

OLPHRT
PHIL I.

[dominator]

Here's a pic of a solid bite bar from a build by Rick Bennardo.

[stevphens]

In other words, there is no simple answer. Just test, change, test and change until it works. Evidently every chassis is different. I suppose that is the beauty of it. Thanks to all of your suggestions, I have a lot of work ahead. But I enjoy that. Just didn't have the knowledge to know where to begin. With my vintage memory I suppose making notes is essential. Apparently I remembered the flexi bite bar wrong.
Don't worry if I have a good sense of humor. If you race at our local track, you have to have a great sense of humor!

[Phil I.]

You will gain a knowledge that can't really be tought, on each chassis. If you ask. You can get a good idea what MITE. Not what will work. If you copy a chassis. You mite come close but you will still have to dial it in...TO YOU.... Like on a dual rail I built that was good. I had only run solder down 1/2 of the rails on one side. I noticed it after testing one day. Got the iron hot and soldered both side rails together.....Went to too stiff....SOOO. I took it apart and rebuilt it into a split dual rail. soldering the 1/2 in hinges to the outer rail only... Worked much better...I thought...:D

PHIL I.