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fine tuning STEADY STATE cornering

Old 09-03-09, 11:56 AM
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fine tuning STEADY STATE cornering

Hi all,

I want opinions here in order to apply to my car. A few rule here: don't suggest something that reduces overall traction. An example: you have found the perfect tire pressures but you are suggesting higher rear pressure to compensate for oversteer.

I think it comes down to stabilizer bars and to springs but want other suggestions such as corner weights or lower CG (if even applicable). If it is only bars and springs, how do you easily fine tune?

thank you,
Ben
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Old 09-03-09, 12:25 PM
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Do you own a tire pyrometer? Have you corner balanced the car? What are your current camber settings?
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Old 09-03-09, 12:31 PM
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Btw, do you have access to a skid pad - preferrably one that's 200ft or greater in diamater? Do you also have access to any kind of GPS based datalogging device such as Max Q data?
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Old 09-03-09, 12:53 PM
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In regards to specifics on my car and how it is set up, I didn't want my settings to come into play and distract us. Hence why I mentioned nothing specifically about issues with my car. However your questions, I feel, are important.

I was looking for a general philosophy and I think your comment on a skid pad is relevant. I wish I knew where to go to do this in Phoenix, AZ.

I don't have access to GPS logging but that can be purchased no doubt.

Another point of clarity, I was thinking along the lines of how do you fine tune stead state not "how do you find stead state".

thanks,
Ben
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Old 09-03-09, 02:09 PM
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Ben,

The best way to fine tune steady state cornering is on a skid pad. Using a tire pyrometer (which measures tire temperature), you'll want to run a number of laps in one direction and check tire temps in three places on each tire -- outside, middle and inside. Depending on which part of the tire heats up the most, you'll want to adjust camber, tire pressure, etc. to try and even out temps as much as possible. If you find you're running on the bump stops, then you may want to raise the car slightly or run more spring rate or a stiffer swaybar, etc. This process will need to be repeated in the opposite direction on the skidpad.

Couple things to keep in mind:

1) Only change one thing at a time, then re-test (tire pressures, camber settings, spring rates, etc)
2) Try to do the testing in a fairly controlled environment (dry, clean pavement, similar air temps, etc)

There was a recent Grass Roots Motorsports article detailing some skidpad testing on an '08 WRX iirc. The basic principles of skidpad testing are outlined and it's a good read. It probably came out about 2-3 months ago iirc.

P.S. Unless you plan to compete in skidpad competition, maximizing your car's handling in a steady state turn is probably going to make it handle like crap in many other scenarios. There's no corner entry or corner exit in a skidpad. There's no slaloms, or increasing/decreasing radius turns. These are the type of elements you'll encounter in an autocross and/or on a road course, and that's why maximizing steady state grip has only limited benefit. My $0.02.
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Old 09-03-09, 03:27 PM
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Well said. Maximizing steady state often screws with the car's ability to transition; and slolom is a HUGE part of autox most places you go.

EDIT: Oh and btw, I have found that fine tuning any adjustable shock will yield a gain in stability while cornering. Too much rebound and you might bounce on the inside tire (lifting up, letting down) Too little and you might have too much weight transfer. Stuff like that and its more technical but Its hard for me to explain because I don't fully understand myself.

Last edited by dpf22; 09-03-09 at 03:31 PM. Reason: Forgot something
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Old 09-03-09, 06:07 PM
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Originally Posted by Chiketkd View Post
P.S. Unless you plan to compete in skidpad competition, maximizing your car's handling in a steady state turn is probably going to make it handle like crap in many other scenarios. There's no corner entry or corner exit in a skidpad. There's no slaloms, or increasing/decreasing radius turns. These are the type of elements you'll encounter in an autocross and/or on a road course, and that's why maximizing steady state grip has only limited benefit. My $0.02.
You made me think here and so maybe I am putting too much emphasis on this. The reason I bring it up trying to tune for it is twofold:

1. My car has not achieved it yet

2. I can only find 2 ways to truly adjust for it: springs and bars.

Seems all other modifications regarding camber, toe, pressures is only a way to get around the issue by compromise of traction on one end or the other. Now correct me if I am wrong here, but springs and bars do not compromise traction but only the change the bias of full given traction between the front and the rear (as well as inside and outside).

FYI, I road race and the car's entry, exit, acceleration and braking are fantastic...or I have not pushed it to the limit where I know there is an issue in these other areas.

Ben
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Old 09-03-09, 06:11 PM
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Steady state is all springs and bars in the limits you're placing with the rest of the car and info. You can do the computer modeling method and look for numbers that you know work(which only comes from experience with the program). Or you can do the trial and error method of buying springs and adjusting bars.

You will need a method to your madness so something besides the butt dyno is needed. A pyrometer tells you what the tires are doing but don't maximize for cornering because you'll lose more braking. A stop watch or other tracking method over the same course with each set up will be key.
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Old 09-03-09, 08:43 PM
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Originally Posted by jgrewe View Post
You will need a method to your madness so something besides the butt dyno is needed. A pyrometer tells you what the tires are doing but don't maximize for cornering because you'll lose more braking. A stop watch or other tracking method over the same course with each set up will be key.
+1 It really sounds like Ben needs to use some sort of data acquisition system for a few track events before making any changes to the car.

Ben, I'd save up and get one and then do a track day where you drive your car for a session and then have an instructor drive the car for a session. Later, you can overlay your session with the instructor's and see how closely you're driving the car to its limits. I'd also talk to the instructor about changes they feel the car needs. Sometimes "cornering balance" can be improved/corrected not just by changing springs and swaybars, but also with a switch to a different rear lsd (Kaaz, Quaife, OS Giken, etc.)
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Old 09-14-09, 09:39 PM
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Camber, Camber, Camber. You can check tire temperatures with a pyrometer or by feeling with your hand. You don't want to have cold spots. Too bad it's not a turn of a **** away, like with damping, but it's the main way you are going to maximize the tire's grip once the chassis has settled.
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