What is the best Front Roll Center location for DIRT




















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  1. #1
    Join Date
    Apr 2008
    Posts
    26

    Default What is the best Front Roll Center location for DIRT

    Been to some other forums...and read many books, and everyone seems to have a diffrent take on where the roll center should be on a DIRT car. I'm thinking the RF camber gain/upper a-arm angle would be more important than actual "static".

    I'm actually building a new Late Model Sportsman (with a camaro stock front clip, stock lowers and spindles). Got it up on blocks and I've got 17 degrees on the uppers... 1-3 degrees on the lowers (LF has more than RF). The roll center draws out to 5 1/4" off the ground, and 4" to the right. My upper mounts are serated, so I can move the RC left to Right fairly easily. I have 2.5 degrees of camber gain in the first 2" of travel.

    I would love to hear everyone's opinion on this, and also try to see what seems to be the norm for some of these LM chassis builders (what seems to work for them)

  2. #2
    Join Date
    Nov 2007
    Posts
    173

    Default

    It's so hard to get acurate test data on a dirt track I've never been able to find a certain location that is better .All you can do is get the inner pivot of the lower a-arm 1/8 inch higher than the ball jiont then run a program to simulate the car in dive and roll .Then try to get the r/c to have linear movement as the suspension moves.

  3. #3
    Join Date
    Jul 2010
    Location
    Georgia
    Posts
    1,023

    Default

    Quote Originally Posted by Moose32 View Post
    Been to some other forums...and read many books, and everyone seems to have a diffrent take on where the roll center should be on a DIRT car. I'm thinking the RF camber gain/upper a-arm angle would be more important than actual "static".

    I'm actually building a new Late Model Sportsman (with a camaro stock front clip, stock lowers and spindles). Got it up on blocks and I've got 17 degrees on the uppers... 1-3 degrees on the lowers (LF has more than RF). The roll center draws out to 5 1/4" off the ground, and 4" to the right. My upper mounts are serated, so I can move the RC left to Right fairly easily. I have 2.5 degrees of camber gain in the first 2" of travel.

    I would love to hear everyone's opinion on this, and also try to see what seems to be the norm for some of these LM chassis builders (what seems to work for them)
    This is a question that keeps evolving. Most everything I've read or had experience with places the RC between 3 to 5 inches high. Left to right is debatable, I know Rayburn's were up until the last couple of years more to the right than some others and the cars tended to be tight on entry, but worked well on big tracks like Eldora. The Hook setup changed the way a lot of car builders thought about the RC lateral placement. I know for a while some builders worked towards having a migrating RC that moved towards the RF, but it ended up making the cars pretty tight. I knew of one car that had the RC climb up on top of the RF tire during roll. Now I've seen more builders putting the lateral RC more left to help the cars turn better. Bottom line is every choice is a compromise, usually better driveability means less forward traction or a lose in sidebite. The latest trend is to have way shorter LS lower control arms and longer RS lower control arms.
    "If racing were easy, everybody would do it."

    #77 Leon "Slick" Sells

  4. #4
    Join Date
    Nov 2009
    Location
    Glennville, GA
    Posts
    745

    Default

    If your reading and research is anything like mine Moose, google is your best friend. You might have already stumbled on this article browsing the internet.

    http://www.auto-ware.com/ortiz/Chass...ctober2010.htm

    This link might help.....or just confuse the bajeezus out of you. Good article though either way. Had me scratching my head enough to read it about 15 times.

    Not to get off topic on you but here is a link to their reference library. A lot of good info on that page.

    http://www.auto-ware.com/techref/lib_index.htm
    Last edited by joedoozer; 02-14-2011 at 02:59 PM.
    Crew Chief "Tip of the day":
    Most handling problems can be solved by adjusting the screw-ball. It can be difficult to fine tune at times. Explaining yourself loudly and striking it on top of the helmet with a dead blow hammer usually works well.

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