EVOlutionary

iTrader: (38)

This thread is dedicated to discussing general suspension tuning methods, issues, and strategies for the EVO VIII and EVO IX chassis. This will be weighted toward Autocross, but many ideas will carry over to road course applications.

This discussion will be about GENERAL suspension tuning issues, not specific recommendations. For example - if you increase front sway bar stiffness, you can expect "X", NOT "what front sway bar should I run". For questions such as the latter, please post those questions here - https://www.evolutionm.net/forums/evo-tires-wheels-brakes-suspension-23/

We will start with very basics and I will try to keep this first post updated with a list of relevent tweeks and their expected results. More detailed information will be added to this post as it is discussed. If you find any errors or anything you feel is flat out wrong, please let me know. I am trying to learn as are most of us here. . .

SPRINGS - used to support the main weight of the car, as well as dive, roll, squat.
*Front - stiffer - reduces front dive on braking, reduces front roll on cornering
*Front - softer - increases front dive on braking, increases front roll on cornering
*Rear - stiffer - reduces rear squat on acceleration, reduces rear roll in turns
*Rear - softer - increases rear squat on acceleration, increases rear roll in turns

SWAY BARS - used to limit body roll without affecting straight line suspension stiffness.
*Front - stiffer - reduces front roll on cornering. Also help stop the "tripod" effect of picking up the inside rear wheel by limiting outside front dive.
*Front - softer - increases front roll on cornering
*Rear - stiffer - reduces rear roll in turns, generally makes the rear "looser" in corners.
*Rear - softer - increases rear roll in turns


SHOCKS - used to slow weight transfer from side to side and front to rear, as well as keep the tire in contact with the ground in case of bumps.
*REBOUND - generally used to keep the tire in contact with the ground. Keeps the car from bouncing or oscillating after hitting a bump. Think of a car with 200,000 miles on it - you push down on the front bumper and the car bounces up and down a couple times before coming to a rest. This would be something like ZERO rebound dampning. As you increase spring rates you need more rebound damning to exert the same amount of control over the spring. This is why you can't throw a 1000# spring on the stock shocks and expect it to work well.



TIRE PRESSURES - you want as much cornering traction as possible without sacrificing straight line traction for accel and braking. More air will bow the center of the tread out and give higher temps in the center of the tread. Less pressure will bow the center tread in and lead to higher temps on the outside edges. There is a sweet spot between too high and too low that will yield optimal traction.


CAMBER/CASTER/TOE
*Toe Out - generally equals less stable. More rear toe will make the rear "looser" and will make it come around easier in corners, under braking and under accel.
*Toe In - generally equals more stable. Less rear toe will make the rear "tighter" and will make it not want to rotate as easily, but will be much more stable under braking and accel.
*More Camber - generally offers better cornering traction, better turn-in response, but can diminish braking and accel due to smaller contact patch when pointed straight
*Less Camber - generally offers better accel and braking due to larger, flatter contact patch.



more to come . . . stay tuned!

jid2

iTrader: (62)

From Tirerack because I didn't want to type it all in myself. These are basic concepts for any car.


Adjustments - Decrease Understeer - Decrease Oversteer

Front Tire Pressure: Higher - Lower
Rear Tire Pressure: Lower - Higher
Front Tire Section: Larger - Smaller
Rear Tire Section: Smaller - Larger
Front Wheel Camber: More Negative - More Positive
Rear Wheel Camber: More Positive - More Negative
Front Wheel Toe: Toward Toe-Out - Toward Toe-In
Rear Wheel Toe: Toward Toe-In Toward Toe-Out
Front Wheel Caster: More Positive - More Negative
Front Springs: Soften - Stiffen
Rear Springs: Stiffen - Soften
Front Anti-sway Bar: Soften (Thinner) - Stiffen (Thicken)
Rear Anti-sway Bar: Stiffen (Thicker) - Soften (Thinner)
Weight Distribution: More Rearward - More Forward

inco9nito99

iTrader: (90)

Sticky this! Great information for those wanting to understand the physics of what happens when you change certain things. Here is more information:

griceiv

iTrader: (2)

http://www.amazon.com/Race-Car-Vehic...7996813&sr=8-2

http://www.amazon.com/Tune-Win-Carro...7996948&sr=1-1

the end.

DaWorstPlaya

iTrader: (31)

Agreed!

Adding to that:

http://performanceshock.com/index.ph...63ca89eb2f4835

EVOlutionary

iTrader: (38)

Keep the book recommendations coming. I just placed an order

Not everyone will be able to buy a $100 book, and not many will want to set down and read that book. I hope this thread can be a resource for your average weekend racer who wants to start trying to get the most out of that set of shocks he just bought, or who is thinking about trying to make his car more competitive so he can win his first Regional autocross championship . . .

boardkat

+1 - tune to win is on its way to my place

thanks for the heads up, marshall!

griceiv

iTrader: (2)

It's taken me years to understand even half of what is in RCVD. That is a HEAVY book but so good. I used to think getting my masters degree was tough....but it's got nothing on trying to understand this book.

http://www.amazon.com/Tires-Suspensi...ref=pd_sim_b_4
That's a good one if you really like doing mathematical derivations. It has a ton of equations.

i might have to pick up a copy of Rowley's book.

donour

iTrader: (6)

I haven't read that one, but Dixon writes awesome books. The SAE shock absorber handbook was really helpful for me when chosing suspension parts.

d

Dave Mac

iTrader: (2)

I can't read that heavy text and mathematical derivations. I'm in product design/marketing and sales. "My brain don't work that way."
I just drive the car and make changes based on the simpleton text at the beginning of this thread.

hokiruu

iTrader: (19)

Excellent thread. Thanks.
Most of you are probably familiar with all this, but here is assortment of links for other noobs like me that I can't seem to read enough times:

A super dumbed-down beginner explaination: http://www.ozebiz.com.au/racetech/theory/align.html

Reading THIS book now.

http://farnorthracing.com/autocross_secrets.html

http://zzyzxmotorsports.com/tech/papers

Corner balancing thread from this board:
https://www.evolutionm.net/forums/sh...=271668&page=2

EVOlutionary

iTrader: (38)

I've read and used DG's info. It's a good read. I am particularly interested in his thoughts on corner balancing vs. "the norm". I think a lot of people just shoot for 50/50 cross weights.

Anyone car to share what method you use and why you feel it's the best . . . ?

griceiv

iTrader: (2)

If you're cross weights aren't 50/50 you'll end up with a car that turns better one way then it does the other.

DaWorstPlaya

iTrader: (31)

Correct, but if you have too much of a ride height different on one side to make the cross weights 50/50 it'll negatively affect your straight line braking ....

Evolutionary, with all the stuff that's been done to your car I assumed you already knew all/most of this ...

griceiv

iTrader: (2)

you shouldn't have to go more then a max of 1/4" away from level to get the car corner weighted properly. Braking wouldn't be the only thing affected by having the car all wonky, you get funky roll centers, different motion ratios, etc.

Step 1: level car
Step 2: adjust one of the 'highest wheel rate' spring perch to balance cross weight.

it should only take a couple turns on one spring to get the job done after the car is level.