What are the advantages of Double Wishbone suspension over conventional MacPherson Struts?

 

Double wishbone is also known as "SLA" (short-long arm) being as how the upper wishbone or "A-frame" is shorter than than the lower. This particular architecture gives more freedom for locating the roll center, and can be packaged very efficiently. One of the big disadvantages of the McPherson strut is bending loads in the strut, and they require more height to package than SLA. SLA is the choice of all race car classes such as F1 where there are no limits on suspension architecture choice.

SLA was invented by GM engineer Maurice Olley in the 1930s, and he can be considered the founder of modern vehicle dynamics. It has been in use on GM cars in various forms on the front since the late thirties, and was first used on the rear by GM on the C5 Corvette.

Many "multilink" rear supensions are essentially SLA in concept as each wishbone is effectively two links. Free bodies in space have six degrees of freedom that can be defined as translation or rotation about the three orthagonal axes, and it is desireable to keep suspension movement to just one degree - up and down motion. This implies five links and a SLA with a steering tie rod (front) or toe link (rear) is effectively five links.

Duke




[Modified by SWCDuke, 7:43 PM 1/2/2004]

 

Very intresting thanks still we see some expensive cars still using MacPherson struts.......

 

All I know is that the double wishbone setup is better.

What are the high end cars that use MacPherson struts?

 

Yes, but notice how strut towers intrude on the interior and raise the cowl on sports cars such as Nissan 350Z.

If you give an engineer a clean sheet of paper and tell him to design a car with no cost limits on the suspension, I guarantee you he will choose SLA for both ends.

Duke

 

Yeah the 911 uses struts in the front and i think the Boxster uses in all the 4 wheels.....

 

I don't even consider a Boxster to be a Porsche. That thing is crap. 911 must have a good reason for using struts in front. All super and sports cars I know of, such asMB, Acura, Bentley, Audi, Lotus, BMW, and practically all others use wishbone. Also, Lambo, McLaren, Maserati, Aston M, Viper, Prowler(crap), S2000, etc. Save the struts for the slow cars.


[Modified by Dsob15, 4:54 AM 1/3/2004] :thumbs:


[Modified by Dsob15, 4:56 AM 1/3/2004]

 

That's funny, I always thought the C5 had equal length upper and lower A-arms, which would keep the wheel camber constant.

Are they unequal length so that negative camber increases on the outside wheel in a turn? I guess you could use that to keep the tire flatter to the road surface as the vehicle leans, but never thought about it much before.

 

Honda uses double wishbone almost to perfection.. I had an Acura CL and I loved that suspension

 

BMW uses Macphersons.

The reason they are used so much is because they package better horizontally, which important in small cars where space is at premium. The Germans seem to believe that their strut suspensions come close enough to SLA performance. The numbers say otherwise.

BTW, I don't think Porsche handling is all that great, frankly. I just drove my firend's 2001 911 Coupe on GMR two weeks ago. It was competent, but not what I'd call impressive. The best thing that could be said is that they really have exised the evil out of the rear. It is truly neutral now. But it's certainly not in the same class as a Z06, Viper, RX-7, or S2000, for example. I'll never understand why people pay so much for those cars.


[Modified by TTRotary, 12:47 AM 1/3/2004]

 

Porsche finally went to a multilink rear suspension on the 911 (996) back in the mid-ninties as I recall. It replaced the previous semi-trailing arms, which is one of the worst rear suspensions ever devised - too much camber change combined with lots of toe change.

Shorter upper arms give more flexibility in roll center location and some camber change with jounce and rebound. Negative camber on rebound and positive on jounce helps compensate for track change and compensates for body roll to help keep the tire vertical to the pavement during cornering.

It's interesting to note that all C6 major suspension pieces look the same - A-arms, knuckles springs, shocks, but are all NEW parts. GM spent some money to retool the suspension in order to refine it even more.

Equal length parallel arms yield a roll center at ground level and no camber change to compensate for track change as the suspension moves. That's why the short upper A-arm is used, and they take up less lateral space higher up, which helps make for a wide engine room.

Duke

 

Part of what makes automobiles (and motorcycles) interesting is that so many different and "wrong" approaches to a problem can still yield a good and satisfying vehicle performance. Who wants every car to be the same?

Didn't the latest-generation Honda Civic switch from SLA to struts up front to improve crush characteristics in an accident? Caused a brief furor in the import tuner market, in no small part because the little Honda lost some of its long-standing performance snob factor over other subcompacts... same change affected the Civic-based RSX nee Integra, if I'm not mistaken.

I wonder... is the camber change set up for the higher-roll base suspension, or the lower-roll Z51? Don't you want less camber change in a flatter-cornering car?

.Jinx