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Old 07-15-2003, 02:18 PM   #1
wcbjr
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Default Big difference in tire pressure needed to oversteer

I've got stock struts, Whiteline lowering springs, Whiteline ALK, f/r strut bars, f/r sway bars (26mm race on rear) and f/r endlinks. Even with that 26mm setting, it takes a difference of 15psi to get oversteer. ~30 front, ~45 rear.

Is this because the camber is a bit off from the springs, or the bigger front bar? My next purchase was going to be some adjustable KYB's so I could increase the damping in the rear, but should I instead go for some front camber plates and adjustable rear control arms? They are about the same price.

?
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Old 07-15-2003, 02:26 PM   #2
driggity
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Do you mean power on oversteer? Also what is your alignment right now? That will have a huge effect on handling. What size is your front sway bar?
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Old 07-15-2003, 02:34 PM   #3
wcbjr
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Power oversteer and just normal throwing the wheel to the side. I am stock in the power category, so I don't have all that much.

I have a 22mm front bar, the springs may have given me -1deg front and ~-1.5deg rear camber. I know the rear is more(negative) than the front. Which is why I was wondering if the camber adjustments may be of more importance than the struts. Both are going to happen eventually, but I was wondering which would be more appropriate at this time.
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Old 07-15-2003, 05:04 PM   #4
ripvw
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Driggity is correct - alignment will have a huge impact on your handling.

Higher rear pressure results in more understeer. Greater negative rear camber results in more understeer too. You want to pull things back to neutral by adjusting alignment and tire pressure. The reason that 45psi in the rear may be giving you oversteer is that pressure is so high for your tires that you are now losing grip by running on the crown of the threads. By the way, what tires are you running? Please don't say RE92 - if so forget everything written below this line and buy better tires first.

Since you are running Whiteline stuff, you should read the 5-part article "WRX on Rails" from AutoSpeed Magazine located on Whiteline's website.

http://www.whiteline.com.au/
Go to Reviews and Articles, then Technical and How To Guides.

In the 5th part of the article, Autospeed documents how they were able to max out the settings for the rear swaybar (24mm), 22mm front bar, combined with an agressive sports alignment to get totally neutral handling and maximum roll control. They also talk about tire pressures.

To start, if you want to add oversteer/reduce understeer, you want more pressure in the front tires than in the rear. The Autospeed article documents that, as well as web-site advice from Yokohama, Tire Rack, and this thread:

http://forums.nasioc.com/forums/show...hreadid=203801

Autospeed found that they got less understeer by running the front cold pressure at 37, the rears at 32 - street pressures, by the way. This setting proved to be perfect as they added rear sway and ALK. When they went to the front swaybar, they did another more agressive alignment to bring everything back to neutral and found that they could run better with equal pressure front and rear.

To sum up, if it was my WRX I would:

- Read the Autospeed article
- read the thread
- get the control arms and MRT or Noltec camber/caster adjustable plates (caster is a good thing, see Chris W, Cosworth and BigSkyWRX posts)
- get the alignment to Whiteline Sports settings, or somewhere close. Might even want to email Whiteline for some more specific guidance - they seem to be real responsive.
- reduce tire pressure to equal front and rear, probably endking up somewhere between 35 and 40psi depending upon your tires.
- add pressure to the front/reduce pressure to the rear if you need/want more oversteer in 2.5psi increments
- get better dampers - I'd consider Koni's - but if you go with the AGX's make sure you get the new ones designed for the WRX

Good luck,

Gary
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Old 07-15-2003, 05:24 PM   #5
wcbjr
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I am running Cobb 17x7.5" wheels with 225/45/17 Sumitomo HTR-Z tires.

Yeah, I know the reason I am now getting oversteer with the current pressures is because I am riding the crown. I lower everything to ~30 or 35, then will try the opposite and see what happens. Seems counter-intuitive, but whatever works.

I considered the Koni's, but the KYB's will be about $50 cheaper when I finally get around to ordering some. I had KYB's on my RS-T with great success.

Thanks for the useful info.
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Old 07-15-2003, 09:26 PM   #6
FYI
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If you want more oversteer, you need to do the following:

- set cold front tire pressure to 30 PSI
- set cold rear tire pressure to 35 PSI
- set rear camber to - 0.5 degrees
- set rear sway bar to full hard
- set front sway bar to full soft
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Old 07-16-2003, 06:13 AM   #7
ellisnc
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Did someone say track day

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the steering is not quick enough for you to be able to really catch the car... be careful
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Old 07-16-2003, 09:05 AM   #8
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WHY do you want oversteer? In what situations do you NEED it?

Fast driving is running the balance game with car control, oversteer is slower in cornering.
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Old 07-16-2003, 10:13 AM   #9
wcbjr
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Oversteer is more fun for everyday driving, in situations where you aren't really pushing any limits but still want to have fun.

I would like to get to the point where I can either change tire pressure or tone down the rear sway bar in order to get more neutral handling for auto-xing and the likes.
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Old 07-16-2003, 11:54 AM   #10
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Quote:
Originally posted by wcbjr
Oversteer is more fun for everyday driving, in situations where you aren't really pushing any limits but still want to have fun.
Please allow me to disagree...

You have stepped beyond 'pushing the limits' when you get oversteer.

Oversteer isn't something for 'everyday driving' either. I don't see it on the way into work from anyone... BMWs, Vettes, Mustangs... all RWD platforms.. no oversteer in 'everyday driving.'

I say this because once you start dialing in oversteer and altering your 'stock range' of alignment, which is what I was going suggest, you're going to get darty car control, and excelled tire wear.

Also not something for 'everyday driving', unless everyday, you run the car on a track.

So once you get your Oversteer, on under inflated tires going around a corner, and loose it, $10 says you blame the 'sucky' tires.

IMHO, you're an accident waiting to happen if you continue down your intended course.
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Old 07-16-2003, 12:02 PM   #11
wcbjr
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Maybe I shouldn't have said pushing the limits.

An example I can use is taking a u-turn under a highway bridge. You can't tell me that a bit of oversteer wouldn't make that turn just a bit more fun. Sure, if dialed in correctly, I can go faster with a neutral handling car. But "drifting" is much more entertaining. And yes, RWD cars drift all the time. That's what makes them so much fun.

I am not trying to go all-out, as fast as I can around the city. That's stupidity. But for the reasonable speeds I am going, I want to have some fun. Which is why I bumped the rear pressure up so much.

If I take the same car to the track, which I want to go all out with, then I will make it more neutral for faster cornering and exit speeds.

Call it my own passive variable center differential.
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