How to reduce power steering assist in an '05 LGT

I switched to an '05 LGT (wagon) after a decade of German RWD cars and found the LGT to have pretty decent steering feel but too much power steering boost for my taste.

 

After driving another car for a week, then coming back to my GT, I've decided to try to do something about it.

 

I talked with some other car guys at work and the consensus is that by finding and installing the appropriate flow control valve between the power steering pump and the rack that I should be able to fine tune and reduce the amount of power steering boost.

 

Does anyone here have experience with doing this? Do you see any problems with this approach?

im guessing hat you want more weight in the steering? If thats all you want, get the perrin or fulcrum LCA offset bushings that give you more caster. that will increase the weight of the steering to what i consider the desired level.

I have a 2006 legacy 2.5i wagon (automatic); i also feel that the steering was vague, seem unable to find a straight line. The car will go left and right on both regular city road as well AS HIGHWAY. As usual, the dealer tech siad it's Normal!!

Is that a problem of too much power steering boost? Can anyone help?

More caster.

 

I am wondering why these cars don't have more from the factory.

 

Think of it like this.

 

no caster: a caster wheel that spins around in one spot.

little caster: caster wheels that are offset. (wheel axle is "forward" of the steering vertical axis.) pushing or pulling the wheel gets it back in line;

 

Lots of caster: a long rake chopper motorcycle. Wheel is way out in front, and the steering axis is at a shallow angle. The wheel axle is usually in front (or even above) of the steering axis

 

the angle of the steering axis from the ground is the rake angle. The distance between a theoretical vertical line through the wheel axle and the ground, and the point where the theoretical steering axis line intersects the ground, forward of the axle line, is called "trail".

 

The high amount of caster creates an effect that automatically uses the suspension to center the wheel. to turn the wheel either direction takes more effort, and actually tends to put force on the suspension. the natural state is straight ahead, and it tends to self-center.

 

A motorcycle with purely vertical forks would be nearly impossible to use, as the front wheel would be all over the place, all the time. Choppers on the other hand, are usually slow to turn, and once turning, tend to "fall into" the turn.

 

A sport motorcycle tends to balance those effects for short trail, and steep rake, to make steering as easy and quick as possible, at the edge of uncontrolled. That is why they put fluid dampers on the steering yokes... to tame down the steering oscillation while allowing such geometry.

 

Cars are slightly different, considering that there are two parallel front wheels, but the suspension principles are the same.

 

lack of caster is likely what makes the car so easy to turn, and also easy to wander, and get blown around. Grippier tires simultaneously help and hinder that. (more grip available for traction, but also more tendency to tramline and wander due to the road surface.)

 

With two parallel wheels also have a measurement for toe-in, which measures the distance between the forward side of the tire centerlines compared to the track dimension between the wheel centerlines at the hubs, which is fixed. toe out or toe in. adjusting half a degree or so in or out can have different effects on directional stability, but can also wear tires, and change the way the car enters turns (resisting turn in more, or falling into turns...)

 

Camber has a little less to do with turn-in, but can affect stability. more negative camber can make the car feel more stable in lateral motion.

 

Bottom line, before reducing power assistance to the steering, it would probably be better to fix the geometry problems.

 

Offset bushings for caster, camber adjustment, and perhaps some toe adjustment. (and keep in mind, that rear suspension settings can effect the way the back of the car follows the front, and make the car feel different, too.)

 

A good alignment shop should be able to set up a four wheel alignment that leans toward performance and stability. Sometimes settings from the factory can be different from side to side, within the wide range of acceptible specification, and could be on the comfort, easy steering, plush end of the adjustment range. Going the other way might help.

 

Offset caster bushings, and camber adjustment plates at the top of the struts, and a good alignment could shape things up well, while not underdriving the hydraulics, or degrading easy steering at parking lot speeds.

http://img186.imageshack.us/img186/4331/3060000000059090zi6.jpg

Could you elaborate?

 

More caster.

 

I am wondering why these cars don't have more from the factory.

 

Think of it like this.

 

no caster: a caster wheel that spins around in one spot.

little caster: caster wheels that are offset. (wheel axle is "forward" of the steering vertical axis.) pushing or pulling the wheel gets it back in line;

 

Lots of caster: a long rake chopper motorcycle. Wheel is way out in front, and the steering axis is at a shallow angle. The wheel axle is usually in front (or even above) of the steering axis

 

the angle of the steering axis from the ground is the rake angle. The distance between a theoretical vertical line through the wheel axle and the ground, and the point where the theoretical steering axis line intersects the ground, forward of the axle line, is called "trail".

 

The high amount of caster creates an effect that automatically uses the suspension to center the wheel. to turn the wheel either direction takes more effort, and actually tends to put force on the suspension. the natural state is straight ahead, and it tends to self-center.

 

A motorcycle with purely vertical forks would be nearly impossible to use, as the front wheel would be all over the place, all the time. Choppers on the other hand, are usually slow to turn, and once turning, tend to "fall into" the turn.

 

A sport motorcycle tends to balance those effects for short trail, and steep rake, to make steering as easy and quick as possible, at the edge of uncontrolled. That is why they put fluid dampers on the steering yokes... to tame down the steering oscillation while allowing such geometry.

 

Cars are slightly different, considering that there are two parallel front wheels, but the suspension principles are the same.

 

lack of caster is likely what makes the car so easy to turn, and also easy to wander, and get blown around. Grippier tires simultaneously help and hinder that. (more grip available for traction, but also more tendency to tramline and wander due to the road surface.)

 

With two parallel wheels also have a measurement for toe-in, which measures the distance between the forward side of the tire centerlines compared to the track dimension between the wheel centerlines at the hubs, which is fixed. toe out or toe in. adjusting half a degree or so in or out can have different effects on directional stability, but can also wear tires, and change the way the car enters turns (resisting turn in more, or falling into turns...)

 

Camber has a little less to do with turn-in, but can affect stability. more negative camber can make the car feel more stable in lateral motion.

 

Bottom line, before reducing power assistance to the steering, it would probably be better to fix the geometry problems.

 

Offset bushings for caster, camber adjustment, and perhaps some toe adjustment. (and keep in mind, that rear suspension settings can effect the way the back of the car follows the front, and make the car feel different, too.)

 

A good alignment shop should be able to set up a four wheel alignment that leans toward performance and stability. Sometimes settings from the factory can be different from side to side, within the wide range of acceptible specification, and could be on the comfort, easy steering, plush end of the adjustment range. Going the other way might help.

 

Offset caster bushings, and camber adjustment plates at the top of the struts, and a good alignment could shape things up well, while not underdriving the hydraulics, or degrading easy steering at parking lot speeds.

Could you elaborate?

 

Yeah, I think I need some diagrams and equations.

 

j/k, IWSS. Very helpful, actually.

Is the caster on an LGT significantly different from on similar cars?

 

I'm not sure changing the caster, which will to some extent change suspension geometry, is necessarily the best thing to do if all that is going on is too much power assist.

Don't forget that changing to a wheel with a higher offset (all other things being equal) will increase your scrub radius which can have a dramatic impact on steering feel and stability.

 

Scrub radius is the distance between the centerline of the wheel (if your looking at the car straight on) and the intersection of the steering axis inclination angle and the road surface. Our cars come with negative scrub radius from the factory which may contribute to the wandering feeling you get on the highway. Steering Axis Inclination is also affected by the ride height of your vehicle so it is a balancing act between SAI and wheel offset to produce the proper scrub radius.

 

Keywords:

Steering Axis Inclination (SAI)

Scrub Radius

Nice explanation, IWanna.

 

I've sometimes dreamed of finding a suspension expert who could tune a car to feel exactly like I want it to. But I suspect such people are very rare. A few times while having alignments done I've asked for tweaks to improve on-center feel. This always results in blank stares.

Nice job Iwanna... !Good Info.

 

Out here (in SoCal), we're lucky...we have a guy (Darrin at WestEnd Alignment) that really does know what he's doing. You can ask for various set ups and if it's possible on your car, he will do it: "Aggressive street", "all out autocross"," Track car", or "best tire wear", he can tweak it.

Moved to suspensio/brakes

Don't forget that messing with your caster will also affect your anti-lift and anti-dive geometry. Suspension design is all about compromise.

Increase in caster is generally a good thing

Increase in caster is generally a good thing

 

Vehicles usually have some positive caster specified since this promotes directional stability, however, excessive positive caster can cause two problems among other things. The first is that excessive caster will cause a higher level of road shock to be transmitted through the steering wheel. The second problem is that a tire/wheel assembly with positive caster has a tendency to toe inward when the vehicle is being driven. If one side has more positive caster than the other, this causes it to toe inward with more force than the other side, leading to wandering issues. Also, the toe usually leads to uneven shoulder wear on the front tires at low speed.

 

What I was trying to say was that increasing positive caster is good to a degree. You go too much and you'll encounter these problems, along some drastic changes to suspension geometry (which usually happens in very extreme cases) and you'll end up with a car that is less responsive.

Humbly appreciating this thread as I am learning much about alingment kudo's...

 

So, if we could get back to John's original question? What are the significant differences between the LGT setup and say a M3 or A4 setup. Seems that most german cars I have driven do have a heavier feel (or less twitchy) to the steering. Is it just caster? Is it "amount" of power-assist steering? This steering issue (and "twtchy" gas pedal) were the two things I noticed first in comparing it to my old A4.

 

Cheers,

Mike

Install a normal ratio steering rack from a 2.5i?

 

What are the steering ratio's on audi's and bmw's?

Humbly appreciating this thread as I am learning much about alingment kudo's...

 

So, if we could get back to John's original question? What are the significant differences between the LGT setup and say a M3 or A4 setup. Seems that most german cars I have driven do have a heavier feel (or less twitchy) to the steering. Is it just caster? Is it "amount" of power-assist steering? This steering issue (and "twtchy" gas pedal) were the two things I noticed first in comparing it to my old A4.

 

Cheers,

Mike

 

The caster idea was suggested because it's probably the only thing you can change on the car without having to do some serious fabrication and expense. The power assist (derived from the pump and pulley used to drive it), steering rack ratio, tire width, suspension geometry, bushing compliance, and even the offset of the wheels used all determine the feel of the steering.

dont add TOO much caster, as I come to realize that the steering will feel sluggish between the transitions... as you add more caster, you are also changing the range of the dynamic camber.. you'll start to notice that your car will lower and raise a good 1/4" from turning from lock to center.. hard to explain, but you can see it happen..

 

when you do that, you are physically LIFTING the car from 1/4" back up to center, which is where the heft comes from in the steering adding that to the change in direction as well..

 

If you want some heft, just disable the power steering completely, that'll really fix the "assisted" feeling.

Our cars use a variable displacement pump where the discharge volume per revolution is regulated by the movement of an eccentric ring which forms the pumping chamber. The ring is moved by a combination of oil pressure (from a control valve) and a spring. One could soften the spring to allow the pumping volume to drop more easily as revs pick up.

 

Alternatively a smaller pully could be installed on the pump so the pump spins faster and throttles back its output sooner.

 

edit: see ps-17 through ps-19 in the fsm. the spring on the RH side of the pump needs to be loosened

Underdrive pulley set :-)

 

Shawn Baumgartner

Just take the power steering belt off Popeye.

you'll have to drain your powersteering fluid too as it becomes a hydraulic lock and the steering wheel will be very hard to move... At least in honda racks :/

Underdrive pulley set :-)

 

Shawn Baumgartner

 

that's going to make things worse. our PS pumps throttle the output volume based on shaft speed. the slower the pump turns, the higher the volume (as long as you are above the minimum pump speed) .... it sounds counter-intuitive but that's the nature of the pump design.... see the fsm.

 

what we need is an overdrive pulley.

you'll have to drain your powersteering fluid too as it becomes a hydraulic lock and the steering wheel will be very hard to move... At least in honda racks :/

 

there's a much easier way on Hndas. just splice a pair of Ts in the hydraulic lines going to the vss and add a bypass between the two. as bypass is increased, the assist goes down. since the lines to the vss control the servo gain rather than act on the line pressure directly, there isn't a requirement for swaged fittings. wire clamps are enough to contain the pressure there.