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Author Topic:   I NEED EVERYONES HELP PLEASE
DirtTrackRacingRules 3 8
Dirt Maniac

Total posts: 101
posted April 13, 2004 07:53 PM  
What are some good length differences in the top and bottom bars of a 4 bar on the left rear? Is having 4 inches shorter on the bottom too much is only having 1 inch enough, and would it even work having the bottom bar longer than the top bar?

Thanks in advance for all your help!

dirtbuster
Dirt Forum Champ
Total posts: 2007
posted April 13, 2004 08:38 PM  
Anything can work with enough practice. A well tested and proven setup is roughly 17 uppers and 15 lowers.

nvracer
Dirt Maniac

Total posts: 127
posted April 13, 2004 09:06 PM  
2" difference is the norm this give a good ratio when the birdcage indexes.
Like dirtbuster said, anything will work with.

zeroracing
Dirt Forum Champ
Total posts: 1875
posted April 13, 2004 09:31 PM  
most 4 bars are 2 inches shorter on bottom.
i run 4 inches longer on bottom. and it works well.

NJantz
Dirt Forum Champ
Total posts: 755
posted April 14, 2004 07:28 AM  
The 4bar lengths that I just designed for my 4bar/zlink suspension are 14.75 on the bottom and 17.5 on the top. Works good on a 1/4mile track. Depending on what holes I place the links in, I can generate anywhere from 1.3"-2.7" of wheel base change on the left rear. Sure helps to hook up a car.

Everywhere I've read they say keep the bars within 2" of each other. Doing this keeps the motion ratios in check. It's really about where your car "gets up on the bars" at in the corner and where you want that point to be. Shorter bars make it happen quicker, longer bars delay that action.

The shorter you make your bottom link the more horizontal travel the birdcage will see as will the axle. Keep this in mind. You don't want your tire running into your frame.

It is best to design some sort of working model where you can experiment with different linkage lengths and mounting points. Then you'll know where things are going to be in a dynamic world. I designed mine in CAD as well as made a working model out of posterboard. I was like a kid in a candy store playing with different linkage combinations.

[This message has been edited by NJantz (edited April 14, 2004).]

[This message has been edited by NJantz (edited April 14, 2004).]

NJantz
Dirt Forum Champ
Total posts: 755
posted April 14, 2004 07:31 AM  
I've found that most mods run 14 and 12 and the late models are on 15 and 17 inch 4bars with the tops being the longer bar.

DirtTrackRacingRules 3 8
Dirt Maniac

Total posts: 101
posted April 14, 2004 04:17 PM  
Thanks Everyone!

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