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How-to: Tune 101 for best suspension/handling: tune out under or oversteer

Posted by shempt, Oct 4, 2005

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  1. shempt

    shempt Proven Member

    Joined Sep 17, 2004
    Lakewood, Colorado
    If you want to print a 'take-along cheat sheet' for your tuning tips, just scan down below for the basics. But to best tune out understeer or oversteer issues, there is a lot to learn and conceder first. Best advise I can give is to try tuning on a race course for safety. Read and ask a lot of questions on how best to execute these steps for you particular car and current car's setup. You can ask advise from even a non DSMer if they are experienced in this genre. To do this first will maximize the tune time and level of success you will have when you execute these measures on your own car. Also, do one thing at a time and keep clear notes of each experience afterwards.
    There are several books on this topic and reading them first is probably a good idea to get the basic facts. However, many variables can change the affect of your outcome a bit differently than someone else's experience. Each car with it's related suspension parts, chassis, road condition, drivers experience and style will have a lot to do with how your car will respond.
    For a very basic example: An owner of a front wheel drive car, with a front mount engine, may have a tendency to understeer. Understeer is when the car looses traction on the front wheels first and continues on the same direction the car's momentum is carrying it at that time. Which, in a turn, can be disastrous! This will obviously cause the driver to end up not making the full turn and run right off the road. In other words "plowing".
    The rear wheel drive car that has a rear mount engine can be more prone to oversteer. In this condition, the car's back tires will loose traction first and will have a tendency to "kick out" the back end of the car easily. That may be fun if it's controlled, but not fun if it isn't. Your entry and exits out of every turn is crucial if you want to have both control and maximize the efficiency and speed of your turn. Even with the late and popular sport of drifting, oversteer is carefully tuned for the correct amount.
    Now this all sounds simple. The basic idea is, but the application is as hard to perfect as anyone would admit. When you are pushing you car to it's physical limits, the car will end up doing one or the other, just at a lesser degree.

    There are many basic principals to try and apply. But again, the best plan of attack is to try one thing at a time. Then take thorough notes as to how you thought the car was affected by it. And try again. Then you can best reflect on how to use this info wisely in certain combinations to make successful results happen.

    Understeer corrections Oversteer corrections
    Push, plowing, front tires slide out first. Loose, rear tires slide out first.

    Usually slight understeer is safer. /Oversteer can be dangerous, especially at high speeds.

    Raise front tire pressure. Lower front tire pressure.

    Lower rear tire pressure. Raise rear tire pressure.

    Soften front shocks. Stiffen Bump. / Stiffen front shocks.

    Stiffen rear shocks. Soften rear shocks.

    Lower front end. Raise front end.

    Raise rear end. Lower rear end.

    Widen front track. Reduce rear track.

    Install shorter front tires. Install taller front tires.

    Install taller rear tires. Install shorter rear tires.

    Install wider front tires. Install narrower front tires.

    Install narrower rear tires. Install wider rear tires.

    Soften front sway bar. Stiffen front sway bar.

    Stiffen rear sway bar. Soften rear sway bar.

    More front toe out. More front toe in.

    Reduce rear toe in slightly. Increase rear toe in.

    Increase front negative camber. Reduce front negative camber.

    Increase positive caster. Reduce positive caster.

    Soften front springs. Stiffen front springs.

    Stiffen rear springs. Soften rear springs.

    May need more front suspension travel. May need more rear suspension travel.

    Install wider front wheels. Install wider rear wheels.

    Use softer front compound if possible. Use harder front compound if possible.

    Use harder rear compound if possible. Use softer rear compound if possible.

    Remove weight from front of vehicle. Add weight to front of vehicle.

    Add weight to rear of vehicle. Remove weight from rear of vehicle.

    Drive a different line. Driver may be going in too deep.

    Use weight transfer to your advantage. Driver may be getting on the throttle to early.

    High Speed. Increase front wing downforce. High Speed. Increase rear wing downforce.

    Too much front brake. Too much rear brake.

    Vehicle is TWITCHY at limit and hard to keep/ Vehicle slides and is easy to drive at limit
    ahead of in the steering department. / but does not corner to full potential.

    Lower front and rear tire pressures slightly. Raise front and rear tire pressures slightly.

    Suspension may be too stiff. Suspension may be too soft.

    Shocks may be set too firm. Shocks may be too soft.

    Tires may be old or hard. Roll centers may be too high.

    Vehicle may not have enough suspension travel. Lower vehicle.

    Vehicle may have a toe problem front or rear. Tires may be too hard.

    Increase negative camber front and rear if possible. Widen track front & rear.

    A properly set up vehicle will usually push slightly on corner entry, be fairly neutral at the apex (STEADY STATE) and exhibit slight power oversteer on corner exit. Tight courses may require more oversteer, fast tracks understeer.

    Items recommended to have readilly available: An accurate tire pyrometer, tire gage, notebook and tape measure when testing.

    Note: This is a sample of the methods used to correct various handling problems. Books have been written on this subject. Again, not every correction will always work as expected. Stiffer front sway bars will, in many cases, decrease understeer because of reduced body roll and better camber control.

    Follow these suggestions at your own risk, I listed them to make your racing safer and hopefully have your car perform much better.

    I'm sorry for the right and left collums not being able to space apart. Best way is to cut and paste the list in Microsoft word, then allign and print to your favorite font size for a good glove box reference tool, if you'd like.

    I will later post a followup for better tuning with tires and brakes. Good luck and safe driving! :D

    Also. Under "search this thread" in the upper right hand corner, type in 'understeer oversteer' and you will be able to get a concise list of other threads that touched on some of this, in a different way, as well.

    ew :thumb:

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