Can someone explain to me suspension?

dkhl

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I believe I've read enough about suspension mods to understand the majority of the possible upgrades out there...

But can someone explain to me the most common basic suspension upgrades and what they do specifically? What's the difference between a Sway Bar and a Strut Bar for example? Thanks.
 
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Michael Yount

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A strut bar goes between the upper MacPherson strut towers to help stabilize the unibody in that area.

A sway bar - more properly called an anti-sway bar - is a steel-spring bar that limits the amount of body roll when a car turns. In order for the body to roll or lean, it must twist the sway bar. The larger the bar, the more it resists body lean in turns.
 

autoXr1

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This is from the Griggs Racing ( www.griggsracing.com ) site. Before you get into a discussion about suspensions and/or the components, you will need a basic understanding of the terminology.

"Before going into too much detail, let's take a minute to define some of the terms we commonly use that you might not be familiar with.
Roll Center - Both front and rear suspensions have a Roll Center. This is an imaginary point around which the body of the car will rotate in a turn. The attachment points of the suspension components determine the Roll Center.
Roll Axis - A line between the front & rear Roll Centers.
CG (Center of Gravity) - The center point of the vehicle's mass.
Understeer - When the front tires lose traction first.
Oversteer - When the rear tires lose traction first.
Neutral Steer - The ideal balance when the front & rear tires gradually give up traction at an equal rate.
Spring Rate - Expressed in pounds per inch, it is the force necessary to compress the spring, i.e. a 200 lb spring requires 200 lbs to compress it 1", 400 lbs to compress it 2", etc.
Motion Ratio - Specifically we usually refer to the relationship between the motion of the wheel and the motion of the spring; i.e. If the spring is half the distance from the control arm pivot as the wheel is, the motion ratio relative to the wheel is .5 to 1.
Wheel Rate - The combined effect of spring rate, motion ratio, friction and/or binding of other suspension components measured at the wheel
Roll Bind - Any binding of suspension components that occurs as the body of the car leans over in a turn
Roll Steer - Generally refers to a steering effect on the rear axle as the car leans over in a corner. Caused by the rear control arms pivoting around their forward mounting point, drawing the axle forward as the arm moves up or down.
Bumpsteer - Toe change as the suspension moves up & down
Ackerman - AKA "Toe out in turns". When turning the inside tire must turn more than the outer tire because it is turning on a smaller radius
Camber - Expressed in degrees, it is how much the tire leans in or out
Caster - The forward inclination of the spindle or strut - like the forks on a bicycle
Toe - The difference in the distance between the leading and trailing edge of the tires
Specifically the Mustang's shortcomings are:

Too much flex through the floor of the unibody.


Rear upper control arms whose function is to locate the axle housing laterally as well as control it's rotation (they don't do either very well). They give the car a very high rear roll center, and bind as the car leans into a corner. The binding causes a sudden increase in the wheel rate that results in the Mustang's characteristic "snap" oversteer.


a. The current front suspension geometry yields only about 2 degrees of caster, which was fine for the skinny whitewall tires that were used on the '78 Fairmont, but is inadequate for today's low profile high performance tires.

b. The front suspension also has a very low roll center (it can actually be below the ground if the car is lowered too much), which combined with the high rear roll center gives you a very steeply inclined roll axis.

c. The angle at which the front A-arms are mounted promotes brake dive.

d. Bumpsteer-The stock suspension has too much bumpsteer.

e. Ackerman-The steering rack is not positioned correctly, and does not provide enough toe out while turning, causing the outer edge of the outside tire to drag through the turn."
 

Michael Yount

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As you can see, autoxr1 knows his stuff (nice post!).

All I would add is keep studying before making any changes. There are many, many changes you can make, but almost any of them affect other things too - said another way, the suspension/chassis/wheel/tire package is at it's best when it works together. If the car is to be street driven, many things must be taken into consideration. It's not that difficult to make some mods that will make the car handle better on smooth, dry pavement. However, it's VERY difficult to make changes that will allow the car to handle better in those conditions without compromising the handling for other situations that you face on the street everyday. Think about the implications of your changes with regard to how the car handles in the rain or snow; what happens when you hit a big pot hole with lowered suspension and lowprofile stiff-shouldered tires on lightweight alloy wheels (bent wheels are often the result), etc. Sticky tires with racing alignments are wonderful for generating higher cornering loads - but on the street, you'll be replacing tires more often than you otherwise would. The factory actually does a pretty good job of producing a car that handles all the street can throw at it - but it's a compromise.

So, understand when you start changing things, there can be unintended side effects in other areas. I'd also add that the most overlooked, yet most important pieces of any handling package are tire selection and driver training. There are literally thousands of people out there who invest hundreds and even thousands in suspension changes only to ask a mediocre tire and driver to put it to best use. You'd be absolutely amazed at how quickly a basically stock car can be hustled around the autocross or road course with quality, properly sized, sticky rubber by a skilled/trained driver.

So, if you're really trying to improve the car's potential, I'd recommend you do these 4 things before you begin to significantly modify the car's suspension:

1)Be certain the suspension bits are in good working order - bushings/bearings/ball joints/tie rods all functioning properly, and aligned correctly. Install a set of welded-in sub-frame connectors to stiffen up the chassis.

2) Install a high quality set of aftermarket shocks/struts - Bilstein, Koni, Tokico - there are a number to choose from, although I'm partial to Bilstein.

3) Pick a high quality set of tires with a compound matched to the type of driving/racing you intend to do.

4) Go to driver's school - learn about the dynamics of car control; and then autocross or spend some track days with your car to learn what it's gonna do. If you're gonna track the car you'll probably find that you're gonna want to invest in a brake upgrade -- you'll find the stock fox body's brakes quite lacking.

Once you've done that, then it'll be clearer to you what if anything you want to further change about the car's stock suspension.
 

Michael Yount

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Addendum - true story. Back in 81/82 when Toyota introduced the then-new Supra with the DOHC six, they invited journalists to test drive it at Riverside Raceway in CA (no longer there). One of Car&Driver's testers was flogging (his words) the new Supra around Riverside when he noticed a car in his rearview mirror. Seeing he was being slowly reeled-in by this little car, he tried his best to move the Supra around as quick as he was able. It didn't help-the little car kept gaining. After a few more laps, his mirrors were filled with a 1982 Toyota Tercel. Yes, he'd pull away on the straights, but eventually, under braking, the little Tercel slipped by. Completely humiliated, the journalist in the Supra pitted on the next lap, and the Tercel came in the the lap after that. None other than Dan Gurney stepped out of the Tercel. That's how much difference a good driver can make.

Give that lots of thought before tackling changes to your car's suspension. Tighten the nut behind the wheel first.
 

autoXr1

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Tighten the nut behind the wheel first.[/QUOTE said:
:hail2: Can I use that? Perfect. :D

There was nothing more humbling than having my driving instructor driving my car, with me in the passenger seat, and having him destroy my own lap times...all that with the car carrying two people (an extra 200+lbs), instead of one.

Bottom line...whether you are driving on the road course or on the strip, proper instruction and practice, practice, practice, is invaluable. The vehicle can only perform as well as the "nut behind the wheel" will allow it.
 

Michael Yount

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Know what you mean - I've been to [email protected], [email protected] Point (the "old" more dangerous version), Daly at Vegas and Panoz at Road Atlanta. I got better with each school. Nothing like watching 19 year old For. Ford and For. 2000 hot shoes moonlightling as instructors, young and dumb and full of....rhymes with, throwing the school cars around with abandon - and usually quicker than I could. I was lucky enough to be SW Div. champ in SCCA's ITC class in 89 and again in 91. And I learned stuff and found people faster than me at every school.

Go to school. WAY better investment at first than throwing a bunch of parts on the car.

There's a local fellow who drives a 2000 GT/5 spd. Stock 4.6L w/5 speed - it's got an exhaust system on it, 4.10 gears and a cold air kit. Healthy wheels/tires, different shocks and subframe connectors. That's it. Stock sway bars, bushings, no Panhard rod, stock brakes. He ROUTINELY humbles everything around at the local PCA and SVT autocrosses - including all the Cobras and Z06 Vettes. Why? He knows his car, he's got great grip, and he's an excellent driver. There's usually a Rotus and a couple of turbo RX7's that squeak out better times - but he's quicker than everyone else. And the great thing is - he slaps the street wheels and tires on it for the ride home -- and it rides and handles just like the factory intended in all the other stuff the street throws at you.
 
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