Steps to reduce understeer

[ScottyS]

This has probably been covered a gadjillion times on message boards across the universe, but how about a simple list of things to adjust/swap to reduce understeer on, lets say, a stock wagon. :wink: As a total idiot where suspension is concerned, I believe that I am fully qualified to ask the question. :?

I'll just compile a list like this, in order of importance, sticking with the MAJOR items and shying away from ultra-fine-tuning:

1) Rear sway bar
2) Solid front and rear endlinks
3) High-performance tires with tuned air pressure
4) item four

Make sense? If not, I could always turn the post into something involving exterior ballistics.

[sperry]

Part of the ordering on your priority list will have to do with your goals and budget.

For a daily-driver, where cost vs. performance if most important:

1) Air pressure. On performance tires, raising the rear pressure will help the car to rotate by reducing rear traction.. On all seasons or cheaper tires... well air pressure won't really help you except at the very limit... and then lowering pressure will cause the tire to roll onto the sidewall more and rotate the car at the cost of tire life.

2) Rear swaybar. A stiffer rear swaybar is a good (and affordable) way to get the car to turn. Since you've got a wagon, switching to a stock sedan bar usually helps a bit. Aftermarket parts will help even more, but will cost you since you'll need mounts too. Check w/ JC, BAN SUVS or sybir about particular bars that will fit on your wagon, since I don't remember which bars will "cross-breed" properly.

3) Endlinks. While endlinks don't actually make the rear swaybar any stiffer, it makes the bar react more quickly to roll, providing "crispness" to the bar's anti-roll response. I'd suggest doing both front and rear endlinks, since solid front endlinks really help with turn-in resonse.

[JC]

Ya what Scott said. Getting better tires should help a lot. The RE92s will roll over and cause your car to push.

[ScottyS]

Ok, I have a rear WRX wagon bar, but maybe a 20mm rear should be in my future. Those who know about front bars can tell me if that should stay stock and just change the endlinks or if an upgrade would be advisable.

I'm not likely to get high-end tires, so I'll just have to deal with the RE92s.

[MikeK]

On my WRX, the two things that had the biggest effect to reduce understeer were the tyre choice, and the rear swaybar. In terms of bang for the buck, get a rear swaybar. On the stiffest setting you will be asking how to reduce oversteer

I got the swaybar, endlinks and stronger mounts for about $300+

[sperry]

Originally Posted by ScottyS

Ok, I have a rear WRX wagon bar, but maybe a 20mm rear should be in my future. Those who know about front bars can tell me if that should stay stock and just change the endlinks or if an upgrade would be advisable.

I'm not likely to get high-end tires, so I'll just have to deal with the RE92s.

A WRX sedan rear bar is 20mm.

Also, a stiffer front bar will *add* understeer. I have a 22mm front bar on my WRX to help turn-in and counter roll, but I have a 24mm rear bar to counter the added understeer.

Also, it may be impossible to dial out all the understeer on RE-92's... they don't have a lot of traction so they will tend to plow if you're going too fast... just slow down more before turning, and drive around the understeer.

[JC]

Originally Posted by ScottyS

I'm not likely to get high-end tires, so I'll just have to deal with the RE92s.

You don't need high-end tires to be better than RE-92s. :wink: I'd get front and rear endlinks. Adding front and rear strut braces and steering rack bushings should sharpen up handling quite a bit too but won't do anything for understeer really.

[sperry]

Originally Posted by JC

You don't need high-end tires to be better than RE-92s. :wink: I'd get front and rear endlinks. Adding front and rear strut braces and steering rack bushings should sharpen up handling quite a bit too but won't do anything for understeer really.

A front strut brace probably won't make much of a difference... but a rear one on a wagon sure would! Make sure to get one that's easily removeable so you can take it out to carry cargo however.

[Dean]

[Disclaimer]Let me start by saying pushing is not a bad thing... Pushing/understeering is "safer".... Average drivers are more likely to respond correctly to a car that is pushing/understeering than one that is loose/oversteering.

Changing this tendency in the car should not be taken lightly. If semi experinced drivers like some of us can still screw up and spin in the controlled environment of an autocross with more nuetral cars, you should be very careful about changing the handling of your car for the street...[/Disclaimer]

0. 500lbs of sand in rear cargo area.

134. Move the engine to the center console.

Stiffer rear bar and possibly a rear strut bar will help the wagon a ton as compared to the sedan. Part of the reason Subaru put a softer rear bar on the wagon is because it has more rear weight up higher than the sedan, so to make it push equally bad, they softened the rear bar.

Tires do not actually remove understeer, they just make it harder to reach in the dry. In the wet where not even the RE92s are likely to roll over, everything will still push without changing the suspension, or raising rear tire pressures more than they probably should be.

[dknv]

alignment settings, anyone?

[AtomicLabMonkey]

Originally Posted by dknv

alignment settings, anyone?

I second that one. Dial in as much positive caster and negative camber as you can, and toe out the front wheels a bit to help the car turn in. This will increase the grip of the front tires. Tuning with swaybars is a perfectly valid tool, but always remember that as you add roll stiffness (e.g. stiffen the springs or swaybar) at one end of the car, you're decreasing the available grip at that end. It's always better to *add* grip at the pair of tires that is not working, rather than decrease it at the pair of tires that is working, whenever you can.

[Dean]

OK Scotty, are we talking about the street or for the track/autocross, or both? And if either of the last two, do you care what class it puts you into?

Castor is fine for the street, but Camber and toe out aren't necessarily great for tire wear...

3. Remove front swaybar.

[JC]

Originally Posted by sperry

A front strut brace probably won't make much of a difference... but a rear one on a wagon sure would! Make sure to get one that's easily removeable so you can take it out to carry cargo however.

A front was a noticable change on my car and probably would be on his too.

[JC]

Originally Posted by AtomicLabMonkey

Tuning with swaybars is a perfectly valid tool, but always remember that as you add roll stiffness (e.g. stiffen the springs or swaybar) at one end of the car, you're decreasing the available grip at that end.

Care to explain that one?

[ScottyS]

Originally Posted by Dean

0. 500lbs of sand in rear cargo area.

134. Move the engine to the center console.

HA!

Actually Dean, I was just looking for some simple options for street driving on less-than-grippy surfaces. On the street I don't usually push the car into the magical realm that you guys are used to. I see a lot of dirt though, and while the Suby gets around super, a lot of times the front end just pushes too much. I realize there are a lot of factors here, such as throttle control in the turn, etc, but I just wanted to hear the options on this one aspect.

My old 2WD longbed XtraCab Toyota pickup it's not.

[Dean]

OK...

Dirt is a low friction surface, so the heavy end of the car is going to want to keep going in the same direction, period. Anything you do is really just trying to make the rear less sticky.

Slowing down at corner entry and smoothly powering out as you unwind the wheel through a late apex is probably a could change to your driving style and will suit the car quite well.

For the street, more camber in the front is not a great option. You could try making the rear less negative, or bumping rear pressures 2-5 pounds.

More front caster such as an ALK would definitely help, and would actually increase front traction instead of lowering rear traction.

Assuming you don't want a rocking beast, removing the front swaybar is not a great idea, so upping the rear is probably next easiest.

[AtomicLabMonkey]

Originally Posted by JC

Care to explain that one?

Sure - springs & bars control load transfer of the sprung mass, which is one of the components of overall load transfer due to lateral acceleration in a corner. As you stiffen the springs and/or bars at a pair of wheels (front or rear) more load (weight) transfers from the inside wheel to the outside wheel. Due to the inherent characteristics of pneumatic tires (lateral force produced vs. vertical normal force), a pair of tires will produce their maximum possible total lateral force when they are equally loaded. Consequently, the more load transfers from inside to outside in a corner, the less total lateral force that pair of tires will be able to produce - i.e. you have decreased the available grip at that end of the car.

[Theo]

My wagon has enough oversteer to be a little dangerous on the street. The camber plates and alignment adjustment made the biggest difference. The rear bar helped but it added the high speed instability that makes you feel on the edge (snap spin). I don’t let anyone drive her now…

In the dirt the thing handles awesome. No push, throttle controlled slides and a great ride. This is what a WRX is for. This weekend we were tearing up the ranch road for fun. I can’t get over how well the WRX handles the dirt roads. I want to Rally Cross!

I ran some toe out in the rear during last autocross season and it was great for eliminating push and helping turn in but I had to return to normal due to tire wear.

So far: Camber plates, Rear Sway bar, eibach springs and a couple of alignments have put the wagon into a setup that I love. Not great for autocross but perfect for street and dirt.

Theo

[sperry]

On thing to elaborate on regarding Theo's post:

If you have adjustable camber plates, you can actually adjust your camber and gain toe out at the same time. Because of the WRX's suspension geometry, adding negative camber (which is good for autoX) also adds toe out (which is also good). Dean and I've found that -1deg camber and a about 1/16" toe in (perfect for the street) translates into -2.5 to -3deg camber and about 1/8" toe out (perfect for the track/AutoX)!

So, if you're willing to take the time to adjust your camber at each event, you can have the agressive handling for the track w/o the awful tire wear on the street.

[Dean]

Originally Posted by sperry

On thing to elaborate on regarding Theo's post:

If you have adjustable camber plates, you can actually adjust your camber and gain toe out at the same time. Because of the WRX's suspension geometry, adding negative camber (which is good for autoX) also adds toe out (which is also good). Dean and I've found that -1deg camber and a about 1/16" toe in (perfect for the street) translates into -2.5 to -3deg camber and about 1/8" toe out (perfect for the track/AutoX)!

So, if you're willing to take the time to adjust your camber at each event, you can have the agressive handling for the track w/o the awful tire wear on the street.

Actually, Neither of us can add... 1/8+1/8=1/4, not 1/16...

Each degree of front camber = 3/8" total Toe... Right now I am at 1/4" at -2.5 degrees camber for the street which translated to 1/8" out at -3.5 degrees camber.

The extra in is actually good for cars with a lot of camber as it rudeces the inside wear a bit by making the tire roll a littel more like an ice cream cone.

[sperry]

Originally Posted by Dean

Actually, Neither of us can add... 1/8+1/8=1/4, not 1/16...

Each degree of front camber = 3/8" total Toe... Right now I am at 1/4" at -2.5 degrees camber for the street which translated to 1/8" out at -3.5 degrees camber.

The extra in is actually good for cars with a lot of camber as it rudeces the inside wear a bit by making the tire roll a littel more like an ice cream cone.

I was just trying to pull the numbers out of my ass from memory. I thought we were setup for less toe-in on the street than toe-out on the track... if you've got the actual numbers, that's better. Ignore mine.

All I know is that my tire wear has been very good on the street, and I consistantly get even 120/120/120 tire temps across the front tires at the AutoX assuming I'm not over-driving the car. The car's dialed.

[Dean]

Originally Posted by sperry

All I know is that my tire wear has been very good on the street, and I consistantly get even 120/120/120 tire temps across the front tires at the AutoX assuming I'm not over-driving the car. The car's dialed.

IIRC, I am running slightly more camber than you to minimize shoulder roll/wear at the slight cost of slightly higher inside temps.

We both need freaking Caster!!! It would be so nice to only run 2 degrees or so of camber and a butt load more caster...

[sperry]

Originally Posted by Dean

IIRC, I am running slightly more camber than you to minimize shoulder roll/wear at the slight cost of slightly higher inside temps.

We both need freaking Caster!!! It would be so nice to only run 2 degrees or so of camber and a butt load more caster...

I usually run -2.5 to -3 depending on the track (more camber for the tighter/slower courses). Are you running more than -3deg?

[Dean]

Originally Posted by sperry

I usually run -2.5 to -3 depending on the track (more camber for the tighter/slower courses). Are you running more than -3deg?

-3.5 front, -2 rear.

[AtomicLabMonkey]

I might try a little more toe out for auto-x use, especially if the car is still a little reluctant to turn in. I'm going to be trying 6mm (~1/4") out at the next auto-x on my car. That would actually make your street toe setting closer to zero, too.

And yes, caster is really nice if you can get more of it... the camber change & weight jacking effects as the wheels steer are good stuff. I've watched the scale numbers on a car as the wheels are steered off center and the weight jacking effect is very noticeable; it raises the weight on the diagonal you're turning towards, so it makes the car want to turn the corner easier.