FAQ: How to reduce understeer

crofrog · 01-31-2005, 05:02 PM

How to reduce understeer on Subaru Impreza’s

There are many things you can do to reduce understeer on these cars. One of the first, cheapest and probably the easiest ways to reduce understeer is to follow the old axiom “slow in fast out” this really will do wonders with reducing understeer, and it is always cheaper and faster to "fix" the driver.

Now onto the car, the first step is to figure out when the car is under steering:

Corner Entry
Steady state (at the apex)
Corner Exit

Some of these fixes will help you reduce understeer during all three stages some during only certain stage. When you are trying to reduce understeer you are trying to add traction to the front of the car so the back gives way first. One of the best ways of doing this is controlling body roll.

Here are some good first steps to reduce understeer.

1.Proper tire pressure.
This is a great first step. You need to insure your tires have the correct
contact patch before changing anything else.

2. Max out the camber in the front and add camber to the rear, and zero the toe all the way around.
This will increase the amount of grip the front has because the tire will be more upright.
Reducing the front toe will help if the car turns and then washes out.

3. Adding a front and rear sway bar.
To many people adding a front sway bar seems to be counter intuitive at first because all the classic race car setup books will tell you to add a front sway bar to decrease oversteer. The reason Impreza’s benefit from increased front roll rates is because of the poor camber curve afforded by the McPherson strut suspension. The rear sway bar does work for the obvious reason's.

A long thread discussing front and rear sway bars can be found here.
http://forums.nasioc.com/forums/showthread.php?t=704926
a very relavant post can be found here in that thread
http://forums.nasioc.com/forums/show...2&postcount=19

4. Front anti-lift kit
This adds caster which in turns adds camber when the wheel is turned.
As well as reducing the amount of binding in the front suspension. A full
discussion can be found here in the ALK FAQ

You should also look into replacing the springs, struts, and bushings. As this will improve the over all handling of your car, and depending on spring rates, dampener settings etc can be used to effect chassis balance but this is beyond the scope of this particular FAQ.

Now onto some things that just help reduce understeer in one phase of the cornering:

Such as a Front LSD; this will probably make on of the single biggest changes if you are having problems putting power down coming out of corners. By not allowing one tire to spin up you will have more over all traction to utilize. You should probably utilize a 1 way differential up front, and a torsen style seems to be the most popular for that application.

The next thing to change as far as the drive line is concerned would be the center differential. Something that is either torque biased to the rear or has the ability to vary the torque between the drive wheels is important. So a DCCD, torsen style, or Cusco tarmac spec is advisable here. A visit to the Differential Information Thread is probably in order.

If you are having corner entry understeer and you have done the above. You should consider adding some toe out. To the front wheels to help it turn in more readily. Although this is very much a competition only adjustment and is not recommend for daily driven cars.

Of course there are many many more ways to skin this particular cat. So I recommend this button

This post was made from lots of lurking and searching here on nasioc, and because there were entirely too many threads entitled. “Just got my car. How to I get rid of understeer” (thanks Unabomber for the idea for the “editor’s note”)

I would also like to thank kwak for his help in firming up this FAQ, and changing the very scope of it.

If you have any corrections you want to make please feel free to let me know either via pm, AIM, or email, and I will make the corrections in a quick and timely manner.

* Registered users of the site do not see these ads.

imprezive one · 01-31-2005, 05:23 PM

Quote:

Originally Posted by crofrog

2. Max out the camber, and zero the toe.
This is a great second step to getting the car to turn.

Just wanted to add that maxing out your camber in the front won't do much to reduce understeer if your camber is maxed out or more negative in the back than in the front. If you really want some crazy oversteer then max out the camber in the front and have zero in the back and slide around on your sidewalls.

Also adding a little toe-in in the front and a little toe-out in the rear will reduce understeer/induce oversteer because the front wheels turn in more easily/the back wheels swings out more easily. However, I think pretty much everyone knows that too much toe will cause the wheels to scrub and cause them to wear quickly and unevenly. Just something I thought would be helpful. On my setup I have as much negative camber in the front as the stock camber bolts will allow me, about half a degree less negative camber in the back and zero toe all around but if I wanted to be a little more crazy I would go slight toe out in the back and maybe buy some camber plates.

crofrog · 01-31-2005, 05:36 PM

Quote:

Originally Posted by imprezive one

Just wanted to add that maxing out your camber in the front won't do much to reduce understeer if your camber is maxed out or more negative in the back than in the front. If you really want some crazy oversteer then max out the camber in the front and have zero in the back and slide around on your sidewalls.

Also adding a little toe-in in the front and a little toe-out in the rear will reduce understeer/induce oversteer because the front wheels turn in more easily/the back wheels swings out more easily. However, I think pretty much everyone knows that too much toe will cause the wheels to scrub and cause them to wear quickly and unevenly. Just something I thought would be helpful. On my setup I have as much negative camber in the front as the stock camber bolts will allow me, about half a degree less negative camber in the back and zero toe all around but if I wanted to be a little more crazy I would go slight toe out in the back and maybe buy some camber plates.

Your right I should have been more specific. Editing now

Trunk_Monkey · 01-31-2005, 05:37 PM

Was going to just make something like this.

crofrog · 01-31-2005, 05:38 PM

Quote:

Originally Posted by Trunk_Monkey

Was going to just make something like this.

If there is anything you want me to add please add it.

kwak · 01-31-2005, 05:56 PM

Alright, crofrog! This has been needed for a long time for something which gets asked every day. I'll read through what you have and see if I can add some additional useful information.

crofrog · 01-31-2005, 06:05 PM

Quote:

Originally Posted by kwak

Alright, crofrog! This has been needed for a long time for something which gets asked every day. I'll read through what you have and see if I can add some additional useful information.

Thanks please do, then we can get a mod to sticky it for a little while.

Cheers

EZ Rider · 01-31-2005, 07:50 PM

You guys see this? Under the sticky, "Threads of Note" > "Make your car handle how you want"

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

crofrog · 01-31-2005, 08:10 PM

Quote:

Originally Posted by EZ Rider

You guys see this? Under the sticky, "Threads of Note" > "Make your car handle how you want"

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

It deals in generalities and some of the information is wrong.

Cheers,
Chris

EZ Rider · 01-31-2005, 08:17 PM

Ahhh, then time for an update eh?

I did notice the "soften the front sway" advice...

kwak · 01-31-2005, 08:28 PM

EZ Rider, good idea. I had forgotten about that thread. It takes a huge amount of time to wade through.

crofrog, I recommend limiting the Understeer FAQ to things which apply to the street and to people new to track / autocross driving. And also limit it to low cost changes. Everytime I see the understeer question asked I think correct tire pressure, ALK, both front and rear bars. Things like coilovers, spring rates, shock tuning, toe adjustments are pretty advanced. It can often take major sections of a book to explain these things properly. These areas often have multiple tradeoffs going on at the same time.

0. Slow Down
You should not be driving on the street so fast that you feel the understeer Subaru built into the car.

1. Tire Pressure
Better tires do increase the overall grip level but do not effect chassis balance, which is the point of the thread. I would recommend instead saying Tire Pressure. It is important to have all of the contact patch working. If the tire is underinflated or overinflated the tire will produce less grip.

2. Camber
In a turn a tire will make the most grip when it is most upright. A related issue is Camber Gain -- see sway bars.

3. Sway Bars
There is some confusion on the forum created by some people saying only add a front bar and others saying only add a rear bar. Some additional comments are here http://forums.nasioc.com/forums/show...2&postcount=19.

Changing the front sway bar to something bigger than stock addressed a known Camber Gain issue with the car. Camber gain is when the outside front tire moves to positive camber because of body roll. This reduces grip. A stiffer front bar reduces the amount of body roll which reduces camber gain which increases grip at the front. Up to a point.

Adding a bigger rear sway bar increases the amount of weight transfer at the rear of the car. This reduces the amount of rear grip slightly but also increases the amount of front grip.

4. Springs
Springs do more than just that. Using springs just to address understeer is different from what you have said. I would not include springs in an understeer faq. It is for an advanced topic about how to increase overall performance.

5. Adjustable Struts / Shocks / Dampers can be used to effect understeer but that should be a more advanced topic.

6. ALK also reduces corner exit understeer by reducing the amount of binding in the front suspenion. See the ALK FAQ.

7. Bushings are not so much about camber as reducing unwanted / unpredictable changes in the suspension geometry which cornering.

I would never recommend toe out for a street driven car.

Just my opinions.

crofrog · 01-31-2005, 09:04 PM

Quote:

Originally Posted by kwak

Just my opinions.

I agreed with allot of your opinions and edited to the FAQ to reflect that.

01-31-2005, 05:02 PM	#1
crofrog Scooby Newbie Member#: 57430 Join Date: Mar 2004 Chapter/Region: MAIC Location: Severna Park, Maryland Vehicle: 2002 WRX wagon PSM	FAQ: How to reduce understeer How to reduce understeer on Subaru Impreza’s There are many things you can do to reduce understeer on these cars. One of the first, cheapest and probably the easiest ways to reduce understeer is to follow the old axiom “slow in fast out” this really will do wonders with reducing understeer, and it is always cheaper and faster to "fix" the driver. Now onto the car, the first step is to figure out when the car is under steering: Corner Entry Steady state (at the apex) Corner Exit Some of these fixes will help you reduce understeer during all three stages some during only certain stage. When you are trying to reduce understeer you are trying to add traction to the front of the car so the back gives way first. One of the best ways of doing this is controlling body roll. Here are some good first steps to reduce understeer. 1.Proper tire pressure. This is a great first step. You need to insure your tires have the correct contact patch before changing anything else. 2. Max out the camber in the front and add camber to the rear, and zero the toe all the way around. This will increase the amount of grip the front has because the tire will be more upright. Reducing the front toe will help if the car turns and then washes out. 3. Adding a front and rear sway bar. To many people adding a front sway bar seems to be counter intuitive at first because all the classic race car setup books will tell you to add a front sway bar to decrease oversteer. The reason Impreza’s benefit from increased front roll rates is because of the poor camber curve afforded by the McPherson strut suspension. The rear sway bar does work for the obvious reason's. A long thread discussing front and rear sway bars can be found here. http://forums.nasioc.com/forums/showthread.php?t=704926 a very relavant post can be found here in that thread http://forums.nasioc.com/forums/show...2&postcount=19 4. Front anti-lift kit This adds caster which in turns adds camber when the wheel is turned. As well as reducing the amount of binding in the front suspension. A full discussion can be found here in the ALK FAQ You should also look into replacing the springs, struts, and bushings. As this will improve the over all handling of your car, and depending on spring rates, dampener settings etc can be used to effect chassis balance but this is beyond the scope of this particular FAQ. Now onto some things that just help reduce understeer in one phase of the cornering: Such as a Front LSD; this will probably make on of the single biggest changes if you are having problems putting power down coming out of corners. By not allowing one tire to spin up you will have more over all traction to utilize. You should probably utilize a 1 way differential up front, and a torsen style seems to be the most popular for that application. The next thing to change as far as the drive line is concerned would be the center differential. Something that is either torque biased to the rear or has the ability to vary the torque between the drive wheels is important. So a DCCD, torsen style, or Cusco tarmac spec is advisable here. A visit to the Differential Information Thread is probably in order. If you are having corner entry understeer and you have done the above. You should consider adding some toe out. To the front wheels to help it turn in more readily. Although this is very much a competition only adjustment and is not recommend for daily driven cars. Of course there are many many more ways to skin this particular cat. So I recommend this button This post was made from lots of lurking and searching here on nasioc, and because there were entirely too many threads entitled. “Just got my car. How to I get rid of understeer” (thanks Unabomber for the idea for the “editor’s note”) I would also like to thank kwak for his help in firming up this FAQ, and changing the very scope of it. If you have any corrections you want to make please feel free to let me know either via pm, AIM, or email, and I will make the corrections in a quick and timely manner. * Registered users of the site do not see these ads. Last edited by crofrog; 01-31-2005 at 09:03 PM.

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01-31-2005, 05:37 PM	#4
Trunk_Monkey Scooby Specialist Member#: 71032 Join Date: Sep 2004 Chapter/Region: MWSOC Location: NW Chicago Burbs Vehicle: 2003 WRX World Rally Blue	Was going to just make something like this.

01-31-2005, 05:56 PM	#6
kwak Scooby Newbie Member#: 73476 Join Date: Oct 2004	Alright, crofrog! This has been needed for a long time for something which gets asked every day. I'll read through what you have and see if I can add some additional useful information.

01-31-2005, 07:50 PM	#8
EZ Rider Scooby Specialist Member#: 38224 Join Date: Jun 2003 Chapter/Region: NWIC Location: WA Vehicle: 2004 WRX White	You guys see this? Under the sticky, "Threads of Note" > "Make your car handle how you want" http://forums.nasioc.com/forums/show...hreadid=203801

01-31-2005, 08:17 PM	#10
EZ Rider Scooby Specialist Member#: 38224 Join Date: Jun 2003 Chapter/Region: NWIC Location: WA Vehicle: 2004 WRX White	Ahhh, then time for an update eh? I did notice the "soften the front sway" advice...

01-31-2005, 08:28 PM	#11
kwak Scooby Newbie Member#: 73476 Join Date: Oct 2004	EZ Rider, good idea. I had forgotten about that thread. It takes a huge amount of time to wade through. crofrog, I recommend limiting the Understeer FAQ to things which apply to the street and to people new to track / autocross driving. And also limit it to low cost changes. Everytime I see the understeer question asked I think correct tire pressure, ALK, both front and rear bars. Things like coilovers, spring rates, shock tuning, toe adjustments are pretty advanced. It can often take major sections of a book to explain these things properly. These areas often have multiple tradeoffs going on at the same time. 0. Slow Down You should not be driving on the street so fast that you feel the understeer Subaru built into the car. 1. Tire Pressure Better tires do increase the overall grip level but do not effect chassis balance, which is the point of the thread. I would recommend instead saying Tire Pressure. It is important to have all of the contact patch working. If the tire is underinflated or overinflated the tire will produce less grip. 2. Camber In a turn a tire will make the most grip when it is most upright. A related issue is Camber Gain -- see sway bars. 3. Sway Bars There is some confusion on the forum created by some people saying only add a front bar and others saying only add a rear bar. Some additional comments are here http://forums.nasioc.com/forums/show...2&postcount=19. Changing the front sway bar to something bigger than stock addressed a known Camber Gain issue with the car. Camber gain is when the outside front tire moves to positive camber because of body roll. This reduces grip. A stiffer front bar reduces the amount of body roll which reduces camber gain which increases grip at the front. Up to a point. Adding a bigger rear sway bar increases the amount of weight transfer at the rear of the car. This reduces the amount of rear grip slightly but also increases the amount of front grip. 4. Springs Springs do more than just that. Using springs just to address understeer is different from what you have said. I would not include springs in an understeer faq. It is for an advanced topic about how to increase overall performance. 5. Adjustable Struts / Shocks / Dampers can be used to effect understeer but that should be a more advanced topic. 6. ALK also reduces corner exit understeer by reducing the amount of binding in the front suspenion. See the ALK FAQ. 7. Bushings are not so much about camber as reducing unwanted / unpredictable changes in the suspension geometry which cornering. I would never recommend toe out for a street driven car. Just my opinions.