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This is a discussion on How to: Suspension Tuning within the Suspension & Wheels forums, part of the Tech & Modifying & General Repairs category; Originally Posted by wrx wagone Also, since your dampers are limiting your spring rate selections, your suspension "tuning" will be ...

  1. #16
    Registered User jasonspeed's Avatar
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    Quote Originally Posted by wrx wagone View Post
    Also, since your dampers are limiting your spring rate selections, your suspension "tuning" will be limited to using swaybars to tune your roll stiffness. This is the situation that a majority of WRX owners end up with.
    OK, so if you plan on changing your suspension set-up on the cheap, start with upgrading swaybars?

    Also I know it's been covered before but I couldn't find a good answer about tower bars, especially in the back of a wagon. In the engine bay most call them a cosmetic type preformance upgrade. The concensus seems to point to get tham last, but would it be worth it to add them in the rear with a wagon?
    Bugeye Mafia #162
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  3. #17
    Moderator timber's Avatar
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    How did I miss this?

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  4. #18
    Registered User wrx wagone's Avatar
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    Quote Originally Posted by jasonspeed View Post
    OK, so if you plan on changing your suspension set-up on the cheap, start with upgrading swaybars?

    Also I know it's been covered before but I couldn't find a good answer about tower bars, especially in the back of a wagon. In the engine bay most call them a cosmetic type preformance upgrade. The concensus seems to point to get tham last, but would it be worth it to add them in the rear with a wagon?
    Swaybars are probably the best "bang for the buck". Strut tower bars are fairly pointless IMO. Subaru did quite a good job with the chassis stiffness of the GD/GG and newer Impreza, plus the front strut towers are essentially attached to the firewall. If you can honestly tell me that you feel a small bar of aluminum or carbon is going to stiffen towers that are that well tied into the structure of the car, then by all means add them.

    In a wagon, many people add a strut brace and report a positive difference. I don't run one mostly because I like to pack the back of my car for race day and don't feel like having a bar running right through the middle of my cargo area. My wagon is competitive nationally in SCCA Solo without a rear strut bar, and honestly often times with a WRX you are trying to get the rear end to grip less, not more. I dunno, I might add one at some point to see what the fuss is about but so far I haven't needed one.

    So overall, I'd skip on the tower bars, unless you really have some burning desire to get rid of perfectly good money on them.

    Get things in this order:
    1. Good Tires.
    2. Good Tires.
    3. Light Wheels (if affordable)
    4. Good springs and dampers (if affordable)
    5. Swaybars.
    6. Other fun suspension bits. (bushings, ALK, etc.)
    7. Chassis bracing.
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  5. #19
    Registered User wrx wagone's Avatar
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    Quote Originally Posted by timber View Post
    How did I miss this?

    Thanks, JR (and Mike)
    You need to hang out in suspension forum.
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  6. #20
    Moderator timber's Avatar
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    Quote Originally Posted by wrx wagone View Post
    You need to hang out in suspension forum.
    Sooooo much goodness in here.
    "Never Launched"
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  7. #21
    Registered User wrx wagone's Avatar
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    Quote Originally Posted by timber View Post
    Sooooo much goodness in here.
    Not for long, I just farted.
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  8. #22
    Moderator timber's Avatar
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    Quote Originally Posted by wrx wagone View Post
    Swaybars are probably the best "bang for the buck". Strut tower bars are fairly pointless IMO. Subaru did quite a good job with the chassis stiffness of the GD/GG and newer Impreza, plus the front strut towers are essentially attached to the firewall. If you can honestly tell me that you feel a small bar of aluminum or carbon is going to stiffen towers that are that well tied into the structure of the car, then by all means add them.

    In a wagon, many people add a strut brace and report a positive difference. I don't run one mostly because I like to pack the back of my car for race day and don't feel like having a bar running right through the middle of my cargo area. My wagon is competitive nationally in SCCA Solo without a rear strut bar, and honestly often times with a WRX you are trying to get the rear end to grip less, not more. I dunno, I might add one at some point to see what the fuss is about but so far I haven't needed one.

    So overall, I'd skip on the tower bars, unless you really have some burning desire to get rid of perfectly good money on them.

    Get things in this order:
    1. Good Tires.
    2. Good Tires.
    3. Light Wheels (if affordable)
    4. Good springs and dampers (if affordable)
    5. Swaybars.
    6. Other fun suspension bits. (bushings, ALK, etc.)
    7. Chassis bracing.

    New00bie question... Do you need to account for wheel weight in your suspension set-up, since this weight is unsprung? If so, where do you make the adjustment?
    Edit.. it smells like roses in here..
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  9. #23
    Moderating on the run! Big Sky WRX's Avatar
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    I don't think you need to account for it as in adjusting damping or spring rates- just understand that reducing unsprung weight effectively increases spring rates (along w/ improving acceleration/braking)

    when you calculate suspension frequencies you need the unsprung weights (wheels being one of them)
    "Simplify and add lightness." - Colin Chapman

  10. #24
    Registered User jasonspeed's Avatar
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    Quote Originally Posted by wrx wagone View Post
    Get things in this order:
    1. Good Tires.
    2. Good Tires.
    3. Light Wheels (if affordable)
    4. Good springs and dampers (if affordable)
    5. Swaybars.
    6. Other fun suspension bits. (bushings, ALK, etc.)
    7. Chassis bracing.
    OK, but would you see a problem with going straight to sway bars before doing springs and dampeners if I were to use my car as a DD mostly.
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  11. #25
    Registered User wrx wagone's Avatar
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    Quote Originally Posted by Big Sky WRX View Post
    when you calculate suspension frequencies you need the unsprung weights (wheels being one of them)
    And to complicate things further, I don't even bother with suspension frequencies.

    Quote Originally Posted by jasonspeed View Post
    OK, but would you see a problem with going straight to sway bars before doing springs and dampeners if I were to use my car as a DD mostly.
    There is nothing wrong with installing sways first, the only complication can be if you switch springs later you may not need or want the size swaybars you installed first. However, if you stick to "sane" spring rates and swaybars, you shouldn't have a problem with adding springs to a previous swaybar upgrade. Enjoy the swaybars. Read my Swaybar FAQ.
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  12. #26
    Registered User jasonspeed's Avatar
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    Quote Originally Posted by wrx wagone View Post
    There is nothing wrong with installing sways first, the only complication can be if you switch springs later you may not need or want the size swaybars you installed first. However, if you stick to "sane" spring rates and swaybars, you shouldn't have a problem with adding springs to a previous swaybar upgrade. Enjoy the swaybars. Read my Swaybar FAQ.
    So if you start with sways you would recommend adjustable ones to start with for future spring updates?
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  13. #27
    Registered User wrx wagone's Avatar
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    Quote Originally Posted by jasonspeed View Post
    So if you start with sways you would recommend adjustable ones to start with for future spring updates?
    Adjustable everything is good. Honestly, it is rather hard to find non-adjustable aftermarket swaybars. They do exist, but usually only front bars.
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  14. #28
    Administrator RayfieldsWRX's Avatar
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    Fantastic thread, JR.

    I also need to hang out in the Suspension forum more often.
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  15. #29
    Wrinklechops
    Quote Originally Posted by wrx wagone View Post
    Part 3: Suspension Components

    So how are all of the above changes to the vehicle dynamics accomplished? Luckily for us suspension designers have created suspension components that will allow us to control pitch, roll, and their rate of change.

    Springs - Allow us to control both pitch and roll.
    Swaybars - Allow us to control roll.
    Dampers - Allow us to control the rate of change in pitch and roll.

    With these suspension components and how they are able to influence the vehicle dynamics, this leads me to develop the following sequence for proper suspension setup:

    Step 1: Since your springs are the only suspension component that will control pitch, (while also affecting roll) you must first set your spring rates based on your pitch control.

    Note: This is the source of much compromise for a street setup. You may find that the spring stiffness that yields the best results for handling are not the most ideally suited for comfort and daily driving. Comfort may very well become the driving factor in your selection of springs.

    Step 2: Now that you have selected springs and those springs have not only changed the pitch but have also changed the amount of roll in the vehicle, we must set the swaybars to produce the desired roll stiffness.

    Step 3: With springs and swaybars in place and dampers which are properly matched to the springs, we will now adjust the dampers to create the proper rate of change of both pitch and roll.

    Damper tuning articles:
    Koni Road Racing Setup Guide
    Neil Roberts Article on Shock Tuning



    Part 4: Real World Tuning Procedure

    At least in my mind with the basis of this procedure routed in the procedure as outlined above, the process for proper suspension tuning as based on the performance of the vehicle through a corner becomes as described below:

    Step 1: Alignment
    Start with a basic alignment. At least -2.0 front camber and about -1.5 rear camber with zero toe.


    Step 2: Testing and Data Acquisition


    This step is where you must break a corner into three separate parts and focus on what the car is doing or not doing during each of these three parts.

    1. Corner entry:
    Corner entry is completely front suspension related. How the car behaves at corner entry will tell you all of the following things about your front suspension:

    a) Pitch. How hard have you stood the car on it's nose during braking into this corner? Do you need stiffer springs - too much dive and unloading the rear end of the car? Do you need softer springs - too little weight transfer to load the front tires sufficiently to maximize braking?

    b) Dampers. How was the rate of transition in the corner? Did the car react too quickly or too slowly? Did you shock the tire with to quick of a weight transfer, or do you not transfer weight quickly enough to allow the tire to find grip?

    c) Roll. How much weight transfer did you get going into the corner? Was it too much or too little? Too much and you've taken the tire over it's contact patch and lost grip through camber loss. Too little and you've never transferred the weight the tire needs to stick.

    2. Mid-corner:
    This tells you about the steady-state balance of the car. Does the car have too much understeer or too much oversteer? This is the location of the corner where it becomes critical that the front and rear grip is very well matched.

    3. Corner exit:

    Just like corner entry is to the front end, corner exit is to the rear end.

    a) Pitch: Are the springs too soft - the car squats under acceleration and weight transfers from the front causing corner exit understeer? Are the springs too stiff - corner exit oversteer?

    b) Dampers: These are used to dial in oversteer on corner exit. Tight transition heavy course - dial the dampers back. Open sweeper corners - dial them up.

    c) Roll: Once you have your rear springs set, use your rear swaybar to dial mid-corner oversteer.


    Step 3: Tuning

    From the information gathered by understanding what a car is going throughout the corner, the proper procedure to car setup involves adjusting these components in this order:

    Start at corner entry.
    1. Front springs - Set amount of corner entry brake dive.
    2. Front dampers - Adjust to course layout and surface to control rate of weight transfer.
    Move to corner exit.
    3. Rear springs - Set amount of squat under acceleration.
    4. Rear dampers - Adjust to course layout and surface to control rate of weight transfer.
    Dial balance mid-corner.
    5. Front swaybar - Set amount of roll stiffness in mid-corner (understeer).
    6. Rear swaybar - Set amount of roll stiffness in mid-corner (oversteer).


    Step 4: Alignment and Tire Pressure


    With your suspension setup largely finished, you can now adjust your final alignment and tire pressure to tweak this setup to its full potential. These adjustments in alignment and tire pressures can be fairly effective adjusted based on tire temperatures. This is a very good article on this: Reading Tire Temperature

    Tire pressure:

    Increasing tire pressures will yield an increase in grip upto the point where the tire's carcass can no longer hold the shape of the tire tread area and the tread will balloon out decreasing the tire's contact patch.

    Decreasing tire pressure will yield and increase in the slip angle produced by the tire. Good for rear tires, bad for front tires.

    Front tires - Increase the pressure in the front tires to yield the maximum amount of front grip.

    Rear tires - To create oversteer, you can either increase the tire pressures to reduce the contact patch, or you can reduce the tire pressure to increase the slip angle produced by the tire. I would recommend lowering the pressure. This method of inducing oversteer is much more consistent.

    This is a great section from Dennis Grant on Tire Pressures: Autocross to Win: Tire Pressures

    Alignment:

    1. Adjust your static camber to produce the largest possible contact patch.

    2. Add toe out to the front to promote turn in and to the rear to promote rotation.


    Part 5: Conclusion

    I would like to leave you with these thoughts in regard to suspension setup:

    1. Maximize front grip first and then dial the rear suspension to match.

    2. You can steer the car with the rear tires. Loose is fast.

    3. Everything with suspension tuning must be done in balance. It is the ability of the suspension tuner through the understanding and experience of all the different variables that allows them to find this balance. This is the art of suspension tuning, mixing all the correct parts to make the end result the best it can be.


    Thank you very much for reading this setup guide. It is by no means complete and is very much a work in progress. Please feel free to discuss items, make suggestions for improvements, correct any errors, or clarify any over simplifications I have made. I'm still very much growing my understanding of car setup, and will continue to learn over many years to come.


    Interesting reading:
    Dennis Grant - Autocross to Win
    I know the stock front and rear tire pressures are different, and I suppose that's typically true for any set of tires and I know it probably depends on a zillion factors, but what would you say is a safe difference in front vs rear tire pressure? Like, say the front calls for 44psi and the rear 38psi (hypothetically)... is that TOO MUCH of a difference? Where do you draw the line? 2psi difference? 4?

  16. #30
    Wrinklechops
    Quote Originally Posted by wrx wagone View Post
    Part 3: Suspension Components

    So how are all of the above changes to the vehicle dynamics accomplished? Luckily for us suspension designers have created suspension components that will allow us to control pitch, roll, and their rate of change.

    Springs - Allow us to control both pitch and roll.
    Swaybars - Allow us to control roll.
    Dampers - Allow us to control the rate of change in pitch and roll.

    With these suspension components and how they are able to influence the vehicle dynamics, this leads me to develop the following sequence for proper suspension setup:

    Step 1: Since your springs are the only suspension component that will control pitch, (while also affecting roll) you must first set your spring rates based on your pitch control.

    Note: This is the source of much compromise for a street setup. You may find that the spring stiffness that yields the best results for handling are not the most ideally suited for comfort and daily driving. Comfort may very well become the driving factor in your selection of springs.

    Step 2: Now that you have selected springs and those springs have not only changed the pitch but have also changed the amount of roll in the vehicle, we must set the swaybars to produce the desired roll stiffness.

    Step 3: With springs and swaybars in place and dampers which are properly matched to the springs, we will now adjust the dampers to create the proper rate of change of both pitch and roll.

    Damper tuning articles:
    Koni Road Racing Setup Guide
    Neil Roberts Article on Shock Tuning



    Part 4: Real World Tuning Procedure

    At least in my mind with the basis of this procedure routed in the procedure as outlined above, the process for proper suspension tuning as based on the performance of the vehicle through a corner becomes as described below:

    Step 1: Alignment
    Start with a basic alignment. At least -2.0 front camber and about -1.5 rear camber with zero toe.


    Step 2: Testing and Data Acquisition


    This step is where you must break a corner into three separate parts and focus on what the car is doing or not doing during each of these three parts.

    1. Corner entry:
    Corner entry is completely front suspension related. How the car behaves at corner entry will tell you all of the following things about your front suspension:

    a) Pitch. How hard have you stood the car on it's nose during braking into this corner? Do you need stiffer springs - too much dive and unloading the rear end of the car? Do you need softer springs - too little weight transfer to load the front tires sufficiently to maximize braking?

    b) Dampers. How was the rate of transition in the corner? Did the car react too quickly or too slowly? Did you shock the tire with to quick of a weight transfer, or do you not transfer weight quickly enough to allow the tire to find grip?

    c) Roll. How much weight transfer did you get going into the corner? Was it too much or too little? Too much and you've taken the tire over it's contact patch and lost grip through camber loss. Too little and you've never transferred the weight the tire needs to stick.

    2. Mid-corner:
    This tells you about the steady-state balance of the car. Does the car have too much understeer or too much oversteer? This is the location of the corner where it becomes critical that the front and rear grip is very well matched.

    3. Corner exit:

    Just like corner entry is to the front end, corner exit is to the rear end.

    a) Pitch: Are the springs too soft - the car squats under acceleration and weight transfers from the front causing corner exit understeer? Are the springs too stiff - corner exit oversteer?

    b) Dampers: These are used to dial in oversteer on corner exit. Tight transition heavy course - dial the dampers back. Open sweeper corners - dial them up.

    c) Roll: Once you have your rear springs set, use your rear swaybar to dial mid-corner oversteer.


    Step 3: Tuning

    From the information gathered by understanding what a car is going throughout the corner, the proper procedure to car setup involves adjusting these components in this order:

    Start at corner entry.
    1. Front springs - Set amount of corner entry brake dive.
    2. Front dampers - Adjust to course layout and surface to control rate of weight transfer.
    Move to corner exit.
    3. Rear springs - Set amount of squat under acceleration.
    4. Rear dampers - Adjust to course layout and surface to control rate of weight transfer.
    Dial balance mid-corner.
    5. Front swaybar - Set amount of roll stiffness in mid-corner (understeer).
    6. Rear swaybar - Set amount of roll stiffness in mid-corner (oversteer).


    Step 4: Alignment and Tire Pressure


    With your suspension setup largely finished, you can now adjust your final alignment and tire pressure to tweak this setup to its full potential. These adjustments in alignment and tire pressures can be fairly effective adjusted based on tire temperatures. This is a very good article on this: Reading Tire Temperature

    Tire pressure:

    Increasing tire pressures will yield an increase in grip upto the point where the tire's carcass can no longer hold the shape of the tire tread area and the tread will balloon out decreasing the tire's contact patch.

    Decreasing tire pressure will yield and increase in the slip angle produced by the tire. Good for rear tires, bad for front tires.

    Front tires - Increase the pressure in the front tires to yield the maximum amount of front grip.

    Rear tires - To create oversteer, you can either increase the tire pressures to reduce the contact patch, or you can reduce the tire pressure to increase the slip angle produced by the tire. I would recommend lowering the pressure. This method of inducing oversteer is much more consistent.

    This is a great section from Dennis Grant on Tire Pressures: Autocross to Win: Tire Pressures

    Alignment:

    1. Adjust your static camber to produce the largest possible contact patch.

    2. Add toe out to the front to promote turn in and to the rear to promote rotation.


    Part 5: Conclusion

    I would like to leave you with these thoughts in regard to suspension setup:

    1. Maximize front grip first and then dial the rear suspension to match.

    2. You can steer the car with the rear tires. Loose is fast.

    3. Everything with suspension tuning must be done in balance. It is the ability of the suspension tuner through the understanding and experience of all the different variables that allows them to find this balance. This is the art of suspension tuning, mixing all the correct parts to make the end result the best it can be.


    Thank you very much for reading this setup guide. It is by no means complete and is very much a work in progress. Please feel free to discuss items, make suggestions for improvements, correct any errors, or clarify any over simplifications I have made. I'm still very much growing my understanding of car setup, and will continue to learn over many years to come.


    Interesting reading:
    Dennis Grant - Autocross to Win

    Also, I did read your Swaybars FAQ which was awesome, but I can't respond to anything in there cuz it's locked now? My question was...I just ordered a front CUSCO 22mm bar for my '05, cuz it was cheap on clearance, etc... I know I need to get a matching rear swaybar ASAP but...will I risk any damage or lack of performance just running the front bar until I can get the rear?

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