Why doesn't my 911 have double-wishbones?

[gtc]

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.

[Flieger]

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.

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

[Packy]

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

[studbike]

Originally Posted by AlfonsoR

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.

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.

Originally Posted by AlfonsoR

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.

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.

Originally Posted by gtc

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.

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)

[DanielDudley]

Originally Posted by randywebb

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.

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.

[Flieger]

Originally Posted by studbike

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)

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

[Flieger]

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.

[studbike]

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.

Originally Posted by Flieger

I like to brake late and hard and turn-in quickly as I am releasing the brake.

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!

[AlfonsoR]

Originally Posted by studbike

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.

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.

[Flieger]

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.

[Nine17]

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.

[Flieger]

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.