Double Wishbone vs. MacPherson Strut3: 2nd Opinion - Team Integra Forums - Team Integra
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Double Wishbone vs. MacPherson Strut3: 2nd Opinion

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

PREFACE

Here is the debate. In Parts 1 and 2 of this series, Bampf presented the basics and the advantage differences between the 2 types. To generate provocative but civil discussions between members (but not a flame war between RSX owners and Gen 2 or 3 Integra owners please!!!), I'll now add a second opinion from my friend texan who is a knowledgeable fellow moderator I've known, since my previous mod days on another Honda board and from the Endyn BBS. Again, I am not the author here, similar to the case in parts 1 & 2: I'm just the messenger. The intention of this Part 3 is not to put down one type of suspension over another but to generate discussion in the forums about ways of improving each type. Again, thanks goes to texan for adding his editorial comments and opinions:


Quote:

Tuan-

So let's face it, the days of double wishbone front suspensions in economical Honda cars seems to be at an end (with the new Civic and Integra RSX), and what are we left with?

MacPherson struts, something many Honda people consider to be a terrible suspension design. But what's the upside to using this design?

Did the factory do it simply for cost cutting, and if so are they passing those price breaks along to the consumer? How much will handling and overall suspension performance suffer due to this change? Here's your answer:


MacPherson Strut vs. Double Wishbone

Double wishbones allow a suspension designer great freedom in creating the camber curve the suspension will see under compression and rebound.

They also ensure stable suspension geometry during body roll and turning, and provide the designer with great opportunities to tune the car's roll characteristics through changes in roll center height and roll axis (it's not important for you to know exactly what these are).

In fact, double wishbone setups are so good for performance applications, you seldom see anything else used for suspensions designed solely for maximum grip (aka nearly any race car).

However, all is not lost for the MacPherson design in the performance venue. MacPherson struts are actually a newer suspension design than the double wishbone setup, and have been used to create some incredible handling sports cars even today. They have their distinct design advantages, which include lower overall vehicle weight, lower cost to produce, and more efficient use of space under the vehicle. The weight savings is passed along through their being only 3 points on the chassis the suspension ties to, and these are spread far enough apart that the unibody and front subframe can be lighter (becuase they don't have to be so rigid). Both the design's compactness and lower cost comes through basic simplicity and the aforementioned chassis mounting setup.

BUT, they are at a disadvantage when looked at in raw performance venues.

Then again, none of us are using our cars as race only rides. Let's look at the potential problems with this design:

1- Inability to design in large amounts of camber gain during suspension compression.
2- Inability to design in large amounts of camber loss during suspension expansion.
3- Changing roll center height during body roll (specifically, the roll center drops quickly under suspension compression).
4- Transition to positive scrub radius when using wide, ultra high performance tires (particularly a problem on fwd cars).

Of these, the first two are us Honda faithful's main points of contention. With on-road cars, camber gain is incredibly important to cornering performance, especially on near stock suspensions that see a good bit of body roll during cornering. And speaking of body roll, that #3 up there means one thing: the more the body rolls in a corner, the more you tend to roll. Roll center height relative to vehicle center is the principle thing governing how much a car's body rolls during cornerning, and the lower the roll center becomes, the more the body will roll. With the MacPherson strut, the roll center drops significantly during suspension compression and body roll, thereby starting somewhat of a self feeding body roll effect. This is especially bad considering the MacPherson strut's inability to create good camber gain during suspension compresson, not to mention the effect body roll has on driver confidence. #4 is not something we can really get pissed about, as (to a lesser extent) increasing tire width even on our current cars has negative effects on scrub. This will be more of a problem for the drag racers among us, as vehicle steering stability and torque steer levels could be hurt significantly with wide drag slicks.

So after reading all that (sorry for all the technical jive talk, you
know me), where's the bright side?

Well, for us performance junkies, welcome to a new era of Honda suspension tuning. The beauty of MacPherson struts for a tuner's perspective is that you can easily change caster and camber angles with adjustable upper sturt mounts (most of you refer to these as pillow-ball mounts). Whereas in double wishbone suspension, you can't change camber or caster by moving the upper shock mount around, with a strut suspension design we now have tons of freedom to do so. Where before the only talk of camber and caster were in reference to stock suspension settings, now people can begin experimenting with optimized performance settings on the otherwise stock suspensions, and sharing their findings.

So what should the perspective RSX and Civic owners look for in aftermarket suspension upgrades? The most important will be increased roll resistance, in the form of stiffer anti-sway bars. On previous Honda cars, equally stiffer front and rear anti-sway bars did little to increase traction, they only helped in the driver confidence dept. and showed this in the lack of lap time improvements. And yes, the old rule of super stiff rear sway bars will still apply, as there is sure to be a good dose of understeer in the new cars. Just make sure to now match that with a significantly stiffer front bar for better road holding during cornering; it's gonna help for sure. Also, increase those caster angles some (and if anyone knows what the stock caster settings are on these cars, please post them here), see my alignment post to understand how this will help performance. And of course, all the old rules about suspension modification (good shocks and springs, height and damping adjustability if possible) still apply, however there will be increased importance on the upper strut mounting location. Front upper strut tower bars will be a necessity, and non-compliance pillow-ball upper mounts should now show real performance gains even without their being adjustable.


As always, I hope this helps explain things, and look to the bright side of MacPherson struts before knocking them too hard. Some of the best handling cars currently produced use this design (the BMW M3, Subaru WRX, etc...), and have proven it's not all that bad a thing.

Peace!
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