Double Wishbone vs. MacPherson Strut I:The Basics - Team Integra Forums - Team Integra
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Double Wishbone vs. MacPherson Strut I:The Basics

Posted 12-07-2002 at 12:00 AM by MichaelDelaney

PREFACE

The following article was written by Bampf many years back in my old Integra Forum Tech Archive Stickies, when I was a mod on another Honda board. It was such a good article that having found it again while purging my hard drive, I thought that it should go back up to educate people here regarding the Gen. 4 Integra's (RSX's) MacPherson strut suspension compared to the Gen. Integras' Double Wishbone suspension. My thanks goes to Bampf once again for investing his own time and effort to assist in making the Integra enthusiasts community become a more informed knowledgeable group.


I. INTRODUCTION

Tuan asked me to post something on MacPherson Strut type suspensions versus Double Wishbone type suspensions, so here it is (even though its a lot later than I had promised it to him sorry it took me so long Tuan). This is probably going to be fairly long, but I wanted to make sure that I covered all of the important points (plus I'm long-winded), so please bear with me. Well, let's get to it...

MacPherson Strut




Double Wishbone





Nearly all cars in production today use either a MacPherson Strut type suspension or Double Wishbone type suspension for the front and rear of the car (the MacPherson Strut is known as a Chapman Strut when used on the rear of the car, but they are identical in every way but name).

Both of these suspension types are [U]independent sus] meaning that on whatever end of the car they are installed on, vertical movement of the suspension on the right side of the vehicle does not directly effect the suspension on the left side; basically the two sides of the car are not directly linked to each other so they can move independently of each other. Both of these systems also use a "coil-over-oil" design for the springs and shocks on the car, meaning that the shock absorbers are mounted inside the coils of the springs.

Now let's talk about what each of these are designed like, and then we'll go on to the advantages and disadvantages of each of these
systems.



II. MACPHERSON STRUTS

I'll start with the MacPherson Strut (Chapman Strut) design. This was invented by Earl S. MacPherson in the 1940's. The MacPherson Strut is basically the simplest of the front independent suspension designs.

Like I mentioned above, this system uses a "coil-over-oil" design. The piston rod of the shock absorber is used to serve as a kingpin axis at the top of the strut. At the bottom, the spring and shock combo pivot on a ball joint on the single lower arm (which is often an A-arm). When turning, the entire strut column (basically the shock body) is twisted in order to turn the wheel, which would cause the spring to "wind-up"(the strut is twisting, but the spring wouldn't, causing the spring to be twisted, or wind-up). In order to solve this problem a thrust bearing is placed at the top of the spring to prevent spring wind-up during turns. Now in a MacPherson Strut type suspension design, the strut itself is the load bearing member, with the springs and shocks merely performing their respective duties instead of also holding up the car.

There is a lot of confusion surrounding this, so I would like to
address that quickly before moving on:

Many people believe that the MacPherson Strut design doesn't use shock absorbers at all, that it uses what they call "a strut" which they think is completely different from a shock absorber. So when they talk about MacPherson Strut type suspensions, they will tell you that MacPherson Strut type designs do not use shock absorbers, that they use struts. I have encountered many other misconceptions about this issue, but that one is by far the most common. Now there isn't anything that you can do to damage your car if you use the term strut instead of shock absorber, but I thought I'd better clear up the terminology problems here. These misconceptions are completely understandable, as there are so many different people in the business using almost as many different terms. (hehehe, I told you I am long-winded)

I'm going to try and explain the difference as best I can. A strut is the load-bearing member of the MacPherson/Chapman Strut suspension design. A shock absorber, or more correctly a damper, is the thing in your suspension that counteracts the movement of the springs in order to stop the car from constantly bouncing up and down over and over after you hit a bump in the road.

Now here's where the confusion comes from: The strut and the shock absorber are integrated together in a strut type suspension. They are two different things, but they come in one package all integrated together. It is not a major problem, but since I'm writing this anyway, I thought I'd clear that up. So even though the strut and shock absorber are integrated into the same housing basically, they are two different things...the strut bears the weight of the car, effectively holding the car up, and the shock absorbers counteract the movement of the springs. So cars with a MacPherson Strut suspension have BOTH struts and shocks.

Ok, back to the MacPherson Strut. So, we've got the wheel of the car attached to the bottom of the strut by a lower A-arm (in almost all cases today), and a near vertical strut. Steering is accomplished by the steering gear being connected either directly to the lower part of the strut, or to an arm from the front or back of the spindle.

Before I move on to Double Wishbone suspensions, a quick side note about the way the MacPherson Strut allows the twisting that takes place when the steering wheel is turned. The spring is seated in a special plate at the top of the strut assembly. When this plate, or the springs get worn, a loud "clunk" is usually heard at full lock (the steering wheel turned as far as it will go in one direction) as the spring frees itself from the proper place on the plate and then snaps back into place. The reason that I mention this is that this noise is often confused with a CV joint knock, so if you're hearing something that you think is a CV joint problem, you may want to have the springs and plate checked as well.


DOUBLE WISHBONE

All right, now onto the Double Wishbone suspension type. Unfortunately, it is very difficult to explain all of the parts of this type of suspension and how it works, so I'm just going to do a quick overview so you understand basically what is going on. With this type of suspension, the upright supporting the wheel is attached to the frame of the car with a pair of links in the shape of a wishbone. These links are connected to the frame by bearings called suspension pivots (which are either metal or rubber, or now-a-days polyurethane). These links (arms) are not always parallel, and are usually of unequal lengths. The Double Wishbone suspension is a type of Double A-arm suspension. Double A-arm suspension systems have been around for about 50 years now. Early versions had equal length arms, but this caused the wheels of the car to lean outboard in turns (increased positive camber). When unequal length arms were developed the positive camber change problem was solved, and in fact was changed to a huge advantage because it made the wheels develop increased negative camber during vertical suspension movement. Double Wishbone suspension also use the "coil-over-oil" design, much like the MacPherson Strut, which often leads to people calling the shock absorbers on their cars "struts" even when their cars don't use a strut type suspension.

I've included pictures of each suspension type to try and make what I'm saying a little clearer. Especially with the Double Wishbone suspension, the pics can probably give you a better idea of how the suspension works than I can with words. Of course, the best way to figure it all out is to get under a car with a Double Wishbone suspension type and look at it to try and figure out how everything works. Don't feel bad if it doesn't make sense though, there are plenty of mechanics out there that don't understand how a Double Wishbone suspension works, it's a very complicated system. Today, engineers use computers to help them design the systems because there are too many variables to deal with to do it by hand without taking an extremely long time.
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