F355 suspension analysis | Page 3 | FerrariChat

F355 suspension analysis

Discussion in '348/355' started by Mitch Alsup, Apr 2, 2004.

This site may earn a commission from merchant affiliate links, including eBay, Amazon, Skimlinks, and others.

Page 3 of 3
  1. mfennell70

    mfennell70 Formula Junior

    Nov 3, 2003
    586
    Middletown, NJ
    #51 mfennell70, Apr 20, 2004
    Esprits don't have a rear bar at all and a tiny (17mm, I think) front bar.
     
  2. Mitch Alsup

    Mitch Alsup F1 Veteran

    Nov 4, 2003
    9,265
    #52 Mitch Alsup, Apr 20, 2004
    I never found this tidbit of information in my suspension and vehicular dynamics books either. It came to me while I was doing the suspension analysis. The least amount of chassis movement, when taking a car in pure dive (brakes) into pure cornering, occurs when the outside front tire and the inside rear tire do not move and the inside front transfers its weight to the outside rear. In effect, the chassis pirouettes around the fixed wheels. Any more movement than this will lessen the forces that the wheels can apply during this transition.
     
  3. Jonas Jarlmark

    Jonas Jarlmark Rookie

    Apr 7, 2004
    3
    #53 Jonas Jarlmark, Apr 22, 2004
    True, Mitch. I'll run some more simulations and see if I can get the low frequency load variations to minimise at that setting of anti-roll bars. As you say, the combined pitch/roll axis of the car will stay directly on the diagonal outer front/ inner rear, so the variation should be minimal. Thanks for giving me another thing to keep in mind! Then we have a total amount of anti roll bar to have on the car and just needs to distribute it front to rear to get the balance. Maybe this could be one reason why drivers of cars with little or no anti roll bar feels that the car "falls over" as the turn in progresses to pure cornering.

    / Jonas Jarlmark
     
  4. tonyc

    tonyc Formula 3

    Oct 19, 2003
    1,641
    Monterey, CA
    Full Name:
    Tony C
    #54 tonyc, May 13, 2004
    Mitch,

    Here is the old F355 setting I had:
    Left Front Right Front
    Camber -.8 -.5
    Caster 6.7 7.6
    Toe .15 .10
    Left Rear Right Rear
    Camber -2.1 -2.5
    Toe .15 .29

    Often during agressive driving, the back end would twitch back and forth. Changed them to this:

    Left Front Right Front
    Camber -.8 -.9
    Caster 7.1 7.6
    Toe .16 .14
    Left Rear Right Rear
    Camber -2.3 -2.4
    Toe .11 .13
    Front tires are: 225/40R16 Bridgestone Potenza RE050
    Rear tires are: 265/40R16 Bridgestone Potenza RE050

    At high speeds I never felt to secure, mostly likely because I have not had any training. I am going to take a 3 day Skip Barber driving school at Laguna Seca as soon as I can. Tomorrow I am going to redo my alignment again and could like to return the car to factory specs. I will be in the car during the alignment. Any recommentations are much appreciated. I would like to go into the shop armed with the settings that I want. What do you recommend to get the car set up to factory specs?
    Thanks in advance!
    --tony
     
  5. Mitch Alsup

    Mitch Alsup F1 Veteran

    Nov 4, 2003
    9,265
    #55 Mitch Alsup, May 13, 2004
    The first set of alignments would have made the car dart all over the road unless it was billiard table flat. The second would have taken some the edge off, but still left you with the feeling of "when is this car going to bite me"; that is; not very secure.

    Based on what you posted (car faster than driver) I would:

    back off the front camber to -0.5
    equilize caster (on center feel) target 6.5 to 7.0 but get it equal
    back off the rear camber to -1.8 to -2.0
    go up to -0.25 toe each corner (all 4)

    Ths will take the edge off the car. Later when you have learned how to drive the car like it wants to be driven, you may want to put more agressive camber settings. I would leae the toe alone until you have a reason to change the toe. I get perfect tire wear (inside wears out exactly when outside wears out::f/r and r/l) with these settings

    Your front toe is right on the edge of too small. You see, there is a dead zone in toe, either you want enough toe that the front end never toes out under braking, or you want enough toe-out that it never toes-in in cornering. When the front changes fron dynamic toe-in to toe-out (or vice versa) some of the loads change directions in the suspension links--the suspension gets confused until the bushing have deflected to the other direction. Stay on one side or the other. Street cars will want to stay on the toe-in side, race cars tend to stay on the toe-out side.

    You have more caster than desired, and you may have liked the heavyness at the wheel, I would lighten it up (decrease), but its only real important to get it as close to the same side to side as possible.
     
  6. tonyc

    tonyc Formula 3

    Oct 19, 2003
    1,641
    Monterey, CA
    Full Name:
    Tony C
    #56 tonyc, May 13, 2004
    You are too right. I went into a curve too fast and the back end started sliding. I made a big mistake and stepped on the brakes. The car kind a snapped straight and started sliding sideways. Not really sure since it happened so fast. I know I do not want that feeling of going for a ride
    again.

    Mitch,

    The proper setting for the "F355 faster than driver" settings I am going to ask for are:

    Front Camber -.5 right -.5 left
    Rear Camber -1.8 to -2.0 both sides
    Front Caster 6.5 to 7.0 both sides
    Front and Rear Toe -0.25mm (all 4)


    Sorry if this is a stupid question, but is there a way to test the caster/steering feel on the lift, or am I going to have to drive the car after every adjustment?

    Also what do you mean by dead zone in toe?

    --tony
     
  7. Mitch Alsup

    Mitch Alsup F1 Veteran

    Nov 4, 2003
    9,265
    #57 Mitch Alsup, May 14, 2004
    Any competent alignment shop has either a guage or its part of the measurement equiptment. In any event, it can be measured by turing the steering wheel full left, take measurement of camber, then full right, take measurement of camber, then use camber measurements in some horible looking trionometric equation and arrive at caster.

    Say you have a car that is just perfect in turns, braking, and accelerating; but wnaders around while driving straight down the road. You can add toe to "deaden" the car's response to road irregularities (straight line tracking). You can add so much toe that it takes a considerable steering input before the car moves off center, or you can back down the toe until the car responds to the slightest steering input. Once everything else is setup right, toe controls how lively the steering wheel feels "on center". {Caster controls how it feels just off center}
     
  8. tonyc

    tonyc Formula 3

    Oct 19, 2003
    1,641
    Monterey, CA
    Full Name:
    Tony C
    #58 tonyc, May 21, 2004
    Hi Mitch,
    The shop I used was not able to match the settings you recommended,
    but we got close. Below are the new settings in degrees:
    Left Right
    Front Camber -.6 -.6
    Front Caster 7.1 7.0
    Front Toe .01 .01
    Rear Camber -2.3 -2.3
    Rear Toe .01 -.01

    The car now feels very solid (sure footed), tracks straight, and is just a joy to drive. Do you see any problems with these settings?
    thanks,
    --tony
     
  9. Corsa

    Corsa Karting

    Nov 1, 2003
    109
    Stockholm
    Full Name:
    Peter
    #59 Corsa, Feb 24, 2006
    Where are the images in this old but superb thread?!?
     
  10. jmillard308

    jmillard308 F1 Veteran
    Owner Silver Subscribed

    May 29, 2003
    6,576
    Perth West Oz
    Full Name:
    John Millard
    #60 jmillard308, Mar 21, 2007

    +1
     
  11. Buckets

    Buckets Karting

    Sep 9, 2019
    86
    Seattle, United States
    Full Name:
    Nick Papagiorgio
    #61 Buckets, Mar 3, 2020
    Qavion and paulchua like this.
Page 3 of 3

Share This Page