Well, here's the bad news. You can carry two golf bags in the trunk, but if the clubs are in the bag, they don't fit. I used to carry mine in the back seat, but now they don't fit with the roll bar. So, I have to take some of the clubs and put them in the back seat, and the bag in the trunk. I feel like Lamont Sanford when I go to the course.

Finally I said, screw it, and take the 968 to the golf course.

Wow, so then, clearly the suspension configuration has missed it's most important design constraint. ;)

Chuck; nice obfuscated doublespeak . . . ."zero, which is exactly how much a lever arm of zero length moves.
. . . the motion of the strut is not a straight line "

So, it moves zero, but has motion in a non-straight line?:rolleyes:

Dude, stop trying to cover.

Looked in the R&T dictionary last night -- it confirms the above. Colin Chapman adapted the McPherson strut for use on the rear of a car, the Lotus model given above. So, a modified rear McPherson strut is called a Chapman strut.

The comments about non-optimal suspension geometry are all true -- here is my question: If these compromises had NOT been made, would we like the handling feel of our cars as much? Note the word feel, not just higher handling performance... At least some of the enjoyment - at low speeds anyway - seems to go away with later models that have more competent geometries (i.e. Boxster S; GT-2, even the 964 - those are just some I have driven in a "sporting" fashion). The complicating factor is the great increase in wt. of those models.

If you want to see a really nice light, compact suspension w/ excellent camber patterns take a look at Honda Accords. I don't know if they still use them but at one point then had a virtual unequal length arm set up that worked really well.

Seems to me I heard a lot of squaking that they were changed but I wasn't really paying to much attention.

Thanks for the mature and insightful reply, you've aided everyones understanding :rolleyes:

BTW, Everyone seems to be looking down their noses at the MacPherson Strut when in fact it really is an ideal compromise for the "GT" design that the 911 is.

1) Along with the fact that it is the lack of the upper A-arm (or as Chuck correctly describes, an upper link of 0 length), which allows a usable trunk space, To get an idea of what a double-A-arm suspension would do to the 911's front trunk space, just look inside a Ferrari 308's front trunk. You'd be hard pressed to fit anything more a small overnight bag in there.

2) the geometry is really not all that bad.
a) It has good camber charactoristics under braking -- almost better then a double-A-arm design -- because there is relatively little camber gain. Camber gain under braking is bad because it effectively reduces the contact patch by lifting the outer edge of the contact patch.
b) It has ample suspension travel.
c) The camber issue is generally manageable for road use by using a combination of static camber adjustement and caster settings.

3) The weaknesses are not that great.
a) Binding of the strut is not an issue as long as the loads are reasonable and the strut has a reasonable size.
b) Under peak cornering conditions, sure there is camber loss which results in a gentle traction loss. But given the terminal oversteer of the rear-heavy 911, this "weakness" actually results in a car which is "balanced" and forgiving under steady throttle conditions since both ends tend to lose traction somewhat in parallel. (I believe that the 911's drastic TTO condition is more a function of the rear suspension design then the front.) Basically, it results in a car that can be driven at high levels of performance successfully due to it's balance across 95% of the handling spectrum.

Yes, that is the way they designed stuff in the Early 60's, they would bring in one of the advertisements and say, "Butzi! Make it look like zees!"

Just kidding. That's an advertising poster from 1962, with a 356 coupe. The point I am making is that "brilliant engineers" were brilliant enough to realize that they had to sell cars, and couldn't just slap a set of houndstooth seats in a 904 and call it cool.

"Golf bag engineering" is one of the hidden themes of Porsche design. More anecdotal evidence: my cousin went to buy a Boxster S. Upon seeing the rear cargo compartment, she scoffed, "There is no way you can fit two golf bags in there!" At which point the salesmen produced two golf bags in the showroom, removed the woods, and demonstrated that you could, in fact fit two golf bags in the compartment.

It is a little-known fact that the 907 Langheck was designed with this in mind as the below image clearly shows.
http://forums.pelicanparts.com/uploa...1135004509.jpg

In summary.... the 356 design used the VW-inspired transverse front torsion bars ( to add insult to injury...STACKED one set on top of the other !)...so this took up a considerable amount of trunk space.

The 356 was getting long-in-tooth, and the design schrifft for the 911 was more room ( altogether..people were getting "bigger")...more power ( 6 cyl vs 4)...and very definately room for golf gear in the trunk.

The Macpherson strut ( named after the inventor at Ford-England) had very acceptable camber curve ( vehicle dynamic) qualitites as well as being relatively light and cheap...and mostly space efficient. It took re-packaging the TB's to be longitudinal to gain even more space advantage. Certainly more-so than if the strut had a co-axial spring. Altogether...it was an elegantly simple solution for a number of conflicting needs. As Chuck mentions, it's a testimony to the design that it has been successfully used for so long in competition. It wasn't an after-the-fact marketing ploy.....

Wil

Cramer, that's awesome. :D

As you can see, in a foto of a 904, 917 .. . whatever, the advantages of a compact suspension are significant. That is, a fast race car uses the saved space for better aero . . . bump it up and you've got room for clubs. (or whatever the marketing dept thinks is viable)


jluetjen- A typical wishbone link sweep an arc.
As that link gets smaller and smaller, it sweeps a smaller and smaller radius, right down to "zero-length link" -- would be a fixed point
Whereas, an infinite length link would sweep an infinite radius arc (aka, a straight line.)

Last I checked, the two ends of a strut have relative motion along an infinitely large radius. . . not a point.

Despite some sniping, this thread has some infromative value.

Many of us, including me, have been mis-spelling the man's name. It is Earl Steele MacPherson (note the Mac, not Mc; also in Scotland there is still a death penalty for not capaitalizing the letter after the 'c').

His design was first used on the French Ford Vedette in 1949.

Lots of interesting information on this thread but, when you go back to the original question of why Porsche didn't use double A-arms, it's my opinion it was purely a cost issue. I believe Porsche was looking for the best solution at the lowest cost and the strut offered that.

When they were designing the 911 in the early 60's it had already been established that a double a-arm type suspension was and an solution for racing and you will notice that all (to my knowledge) of the "purpose" built race cars in that period (this doesn't include converted street cars) were either double a-arm or multi link (like the 917's)

A strut works quite well in certain applications as long as the requirements don't exceed the geometry characteristics. There are many limits to a typical strut, one of which is the scrub radius. As you start putting wider front wheels on the car, this becomes an issue ... of which there are many semi solutions but never the less, issues. The bump steer range is also limited to about a 2.00" to 2.50" range and always has an "S" curve meaning "in to zero to out" with the zero holding for the 2.00". As an example, I recently designed an off road race truck with double A-arms in the front that had 25 inches of total travel of which over 21 inches are at ZERO bump change... that will NEVER happen with a strut. Another issue is the camber curve to desired roll center .

As far as the trunk size goes, the arms actually aren't a factor (unless you make them extremely long). I've built a hand full of double A-arm conversions for 911 fronts (can't find any pics right now) and they didn't need to take any trunk space at all. The a-arm just simply attached to a reinforcement that was attached directly to the side wall of the trunk (btw, once again, I did my first one of these back in 1980 something so, when someone reads this and later comes out with a set up like this saying "another original idea" say what you must but, it's already been done :) . In fact I've worked on some GT1's and those didn't lose any truck space do to the A-arms either.

A book could be written on all the speculations alone but, the bottom line is .... A strut isn't the worst thing and it's cheaper and good enough for what they wanted to accomplish.
Final note: The 959 was an experiment with no particular cost limits .... it has double a-arms...

959 front
http://forums.pelicanparts.com/uploa...1135029909.jpg

959 rear
http://forums.pelicanparts.com/uploa...1135029931.jpg

Aw man, no pics? You're such a tease. ;)

Did the converted cars actually handle noticeably better or just differently?

They were a bit easier to drive and for sure had a better scrub than a regular 911 which also helped the steering effort and bearing life with 12 inch fronts but, the car wasn't really much faster on the clock. The biggest improvement were from changing the rear to a multi link. I've not done a double a-arm set up on the rear of a 911 .. it would be fun but just haven't done it and I've only seen it done on one car. For all practical purposes the 993 and 996 "multi links are almost an A-arm

One of the ways to over come the camber loss on the front during turn in (someone had mentioned this earlier) is to put a lot of caster in and that will cause the wheel to gain camber as it turns at a high rate than it loses. However, it depends on what your tires want. Non of these are absolute answers... just more options.

remember up near the top of the thread where someone said that the macpherson strut begins losing grip towards the end of its travel? this allows the manufacturer to finely tune the understeer, which is extremely important on the 911 and on bmws (more my background). if these cars didnt reliably understeer, they wouldnt be called "neutral", they would be called tail-happy like corvettes and vipers that have double wishbones. even a civic gets darty near the limit in my opinion, but having so much weight teetering over the front axle, it achieves the hyper-opposite of 911s weight teetered out over the rear axle, but because these are the wheels you control the direction of, a good driver can compensate, thus making the double-wishbones more suitable. If you want a true performance car, you have to pony up the dough and get a spyder, ferrari, etc in my opinion. I love bmws and porsches, but they aren't no-compromise performance vehicles. that's what makes them so livable. and from a visual design standpoint, a double wishbone would have a tough time fitting under the hood of the classic 911, with the extremely low front hood line.

Or even better flip the motor/trans!

When I bought my first Porsche last fall I also wondered why it had back seats, but now I put my two kids in there and drive around town. This serves two purposes
1) increased chick magnetnetism
2) breading 2 future Porsche enthusiasts.

Are you sure about that? If the front end is slipping in relation to the rear (understeer) , that is not "neutral" handling. Neutral handling means front and rear slip at the same or almost the same mechanical grip. Maybe you meant "safe handling". A lot of magazine writters associate safe handling with cars that understeer.

Perhaps I misinterpreted his statement, but I thought he meant that they adjusted it to add enough understeer to take an otherwise oversteering car and make it neutral

Could be. I am no suspension or track expert, but if a car is understeering, it should not be said to have "neutral handling". I guess there are varying degrees of oversteer/understeer to consider, though.

Ignore that post... his assumptions are incorrect. You do not fine tune handling by switching from one basic suspension design to another.

Gah... needless thread resurrection. :(

A strut is as good as a double wishbone is as good as a semi-trailing arm, if you make the suspension stiff enough that it does not move. Look at F1 where the tires are the suspension. They just use the wishbones as airfoils.:rolleyes:

Colin Chapman had it right. Just use the lightest and button it down tight.

heh, my torsion bars have VW stamped on the ends of them. Damn beetles.

Yes, i am sure about that. If both wheels are slipping at the same time, you are understeering. oversteering means the rear wheels are slipping > then the front wheels. Understeering means the front wheels are slipping > their steering angle, not necessarily > the rear wheels. Most any situation where lifting off the gas results in a sharper turn angle is one of understeer.

wrong. neutral handling cars are cars that do as little understeering as possible, while still having an understeer bias. there is no such thing as neutral handling as you have somewhat defined it. if a car is slipping, it is either understeering or oversteering. the only exception is slipping straight sideways with no forward motion or slipping sideways with forward or rearward motion but no steering angle.... not things that ever really happen. either the front wheels are scrubbing more, or the the back wheels are scrubbing more.

you are dead wrong (especially when conversing about porsche 911s) because you have ignored the fact that there are two axles. you would be right if the 911 had multilink or double wishbone in the rear. but given that the rear has struts, and that this is probably necessary to accommodate the combination of the visual design and rear engine configuration, there is no way in hell they would design a rear-weight-biased car with a front suspension that has less propensity to lose grip then the rear. that would yield a car that kicks the back out too easily and unforgivably in certain extreme situations when the front wheels are weighted (for example, hard braking followed immediately by sharp steering inputs before the suspension has had a chance to re-weight the rear wheels)

I think a lot of the handling feel of our cars is due to the tires. Even with a well tuned and tweaked suspension, you are going to have more feel on 16 inch wheels with 50 series tires than you would with lower profile tires on larger rims. The car will feel tighter, but less communicative.

Of course part of the fun of an early 911 is the fact that it has to be manipulated into doing what you want, and you will feel that even at less than 9/10ths. Many other cars, like a Boxster or a Miata are going to do what you want without being manipulated. Of course a miata will often be on skinny tires, agan making them easier to manipulate at lower speeds, but a Boxster may have to be wrung out to make it sing.

BTW, I don't buy into the thought that other good handling cars are less fun than a 911. I do get that they are different, and that some cars may be too competent at everyday speeds, making many drivers feel as if they aren't really needed. I would still rather have a car that is sharp at the edge than a car that is entertaining at 8/10ths and less sharp at 9.

Well set up 911s are often absurdly competent at extremely rapid rates of speed, and don't really need a lot of set up in most turns. But then you have to execute the shift, the engine is always singing, and the steering wheel is always chattering away at you, even down a straight road. The front brakes will often do interesting things on uneven traction surfaces or undulations in the tarmac. What a 911 has is character. A Boxster also has character, but you need to get to know some cars, because they are subtle. A lot of really well known long term Porsche owners have said that the Boxster was the best handling production car Porsche ever made. Then they said it was the Cayman S, and now the Spyder.

These are guys who have been living with character for 30 or more years. They must know something I am guessing.

You are dead wrong. The rear of a 911 has a semi-trailing setup. The front has struts.:rolleyes:

I like to brake late and hard and turn-in quickly as I am releasing the brake. This sounds just like the "extreme" situation he mentions. I like how the car feels. The front rotates into the curve much quicker and has lots of nice grip. The rear, having a lower roll-center and effective roll stiffness, has a lower frequency of roll/load transfer than the front. This means that in transiton, the front will move laterally before the rear has time to roll over and begin to provide lateral acceleration. Therefore, in transition, an "understeering" car is quicker than an "oversteering" car. "Oversteer" describes a steady-state cornering situation where the front wheel's slip angle is less than the rear. The steering wheel must be turned less and the car is "nose-in" cornering yaw attitude. Steady state is rarely achieved- roll has completely stabilized and no suspension movement/rebound.

Absolutely right, of course, the 911 doesn't have struts in the back. Whoops. Semi-trailing arms are also extremely space efficient tho. I don't think it would be possible to design a 911 with multilink or double-wish without completely changing everything around.

Don't we all. The beauty of the 911. With so little weight on the front end, you can throw it to and fro as if the back of the car is the short end of a lever arm. The back stays planted like a tree. It's great fun, and it would be great fun with either struts or double wishbones up front.

But if you had double-wishbones up front, you'd be increasing the grip at the extreme travel of the front suspension. And when you're designing a higher-performance "people's car", you want to minimize the likelihood of crashes.

I think the 911 would see a bit of improvement on the track with a double wishbone setup, but significantly more chance of unrecoverable oversteer in inclement weather on the road. Hey, maybe with the advent of modern stability control systems, porsche will eventually come around, ditch the struts, and harness the greater grip of double wishbones and compensate for the danger factor with computers.

In any event, the mid-engined porsches ARE better handling cars, as the above poster hinted at. Rear engine is an inferior design. But so what? It lends the car the character all of us love about it, and for every shortcoming of the design there is an equal and opposite reward that you couldn't pull off with a more traditionally set up car. If the front wheels scrub out a bit earlier then they would with double wishbones, isn't that a small price to pay for a safer compromise on an already-dangerous vehicle, without sacrificing any fun?

To answer the original poster's question, I think porsche chose struts for safety, lighter weight, simpler design, compactness, and to help prevent oversteer when you really get on the gas exiting out of a turn. You're porsche isn't going to be much more satisfying with double-wishbones. Just slightly less prone to oversteer when the front wheels are all the way up in the fenders. The combination of all the other factors of the vehicle's design contribute more to its handling mannerisms then the basic design of the front suspension.

Please don't be upset at me for resurrecting an old thread!

So the way you define neutral handling is a car that is oversteering? That would have as little oversteer as possible??????

Ok, just messing with ya.

So you say oversteer as little as possible, as in the front and rear are scrubbing the same, to put it in your own words. I think that's what I said.

So if the car is oversteering just a bit, that could not be characterized as neutral, just because it had some slight oversteer? My point is that someone might still call this neutral handling. It's semantics and to some degree preferences. But hey call it what ever you want, I like my tail heavy 20+ year old 911 that has an inferior design that has won I don't know how many races over the far superior mid engined Ferrari in LeMans type racing. It appears that the inferior rear engine layout somehow works better than it should.

Again, the suspension design means little if it does not move. Racecars move a lot less.

Porsche used front struts almost entirely because of packaging reasons, it was much better for space the the 356 torison tubes in front. The lumps if iron in the bumper showed they did not really know what caused the wild handling, nor was ther so much concern over safety for drivers loosing control back then.

Packaging drives most suspension designs, even in racing. I think that the handling issues discussed here are more related to weight-transfer, not suspension geometry or wheel travel.

Anti-dive effects the rate of load transfer since it is much faster than the spring force. Other than that, it is just about dynamic camber and toe, which only mean much if the suspension moves alot.