Is 911 Engineering Actually Backward?

Just about every magazine article ever written about the Porsche 911 refers to the "flawed" engineering of having the engine behind the rear axle, the resulting rearward weight distribution, and the ill effects on handling. The writer then goes on to say the latest 911 is handles better than the last. It has been an accepted truth for at least thirty years.

So today I was reading about some new Ferrari thing, the 2013 F12berlinetta. For fifteen years Ferrari has undeniably been one of the very best sports car manufacturers in the world. This new F12berlinetta is their fastest yet (based on Fiorano lap times) and costs $326,000 so it has to be cutting-edge engineering and at that price, absolutely no-compromise, cost-no-object engineering. It is front-engined, yet it has a 54% rearward weight distribution.

So just how "bad" is the rearward bias of a 911? Well, Porsche has slowly moved it forward over the years. In 1969 it was 57%, a little higher than the 2013 Ferrari. Except for 1986 a Cabriolet was 58%. One source says the 2012 911 will be 61% rearward. Huh? It's moving in the "wrong" direction. And I haven't found other data. And of course, even Porsche said the 50/50 weight distribution of a 944 was "perfect."

So what's going on? If 50/50 is ideal, why isn't the Ferrari? This Ferrari isn't the first example I've found of other front-engined car having more weight on the rear wheels, there are others (but I don't have time now to google them). Maybe there's a general trend of high-end sports cars to move weight back? Did I google bad numbers? Can you tell me other modern front-engine cars with a rear weight bias? Basically, it boils down to this: why are high-end manufacturers spending lots of engineering money to move weight back, past a 50/50 distribution?

Begin!

David

If the Porsche 911's handling is so flawed, why has it won so many races?

The "Theory" is correct. But proper suspension design negates a lot of the " theory". FWD cars are the reverse of the "Theory" but some of them handle pretty well.

I've read that:

-40/60 disto is perfect (referencing the Maserati MC-12). I maximizes accelerative traction and braking.

-That the 911 is and has always been a triumph of development over engineering. One of those anomalies that engineers hate.

The original 911's were so good because the extreme rear weight bias gave them immense traction off of the line and in the corner exits. This same rearward bias gave it the tendency to pendulum, resulting in snap-oversteer. It was a compromise on the goods and bads.

The 944 had a "perfect" 50/50 distribution, making it neutral in cornering and transitions. This, however, means the 944 doesn't excel in any one area.

For an example of this, try and watch some old race footage and see how the 911's rocket out of corners, which was their advantage (being better than all others), and allowed many victories.

Front biased cars on the other hand actually excel at braking. Again, pulling up some vintage footage of Mini's racing, you can see them absolutely dive-bomb the braking zones as they could stop much shorter and with more G's than the competition. This advantage allowed them many victories.

So if we had 3 theoretical cars, a 911, a 944, and a forward-biased RWD Porsche (uh, let's say a 928?), all with identical overall weight, braking ability, grip, power, and torque and lined them up for a race, the 911 would rocket into first with the 928 last. The 928 would then be able to out-brake the other 2 into the bend and the 911 would rocket out of it faster. Every lap the 944 would make a steady lap in 2nd as the 928 and 911 swapped 1st and 3rd with each other.

With modern traction-control systems, the computer can negate the pendulum effect of rearward bias, and as such more manufacturers are moving there for increased performance (especially the almighty 0-60) without the inherent risk to the handling.

50/50 sounds good, but it's arbitrary, not ideal.

There are two things to think about when thinking about a 911's rearward weight bias. One is the location of the center of gravity fore/aft, which is what you're talking about. The other part is that big flat-six pendulum which is located all the way at the back.

Visualize for a moment a car driving down the road, about to enter a left-hand sweeper. Now erase everything except the wheels. In place of the chassis, imagine the wheels are all attached to a 1" bar running down the middle of where the car used to be. Imagine this bar is a weightlifting bar, and that we can slide the weights around along its length to mimic different weight distributions.

For the 911, we've got a pretty stout weight all the way at the rear of the bar.

For a Miata, the weights are more evenly distributed.

Now, let's say the rear end of our barbell starts to step out in the sweeper. Once the back of the bar gets some momentum going*, which one's going to be easier to put back in line?

My understanding of the ideal for a two wheel drive road car is that it will have a significant rearward weight bias, not 50/50 distribution. It will also have larger rear tires, roughly proportional to the rearward weight bias. In steady-state cornering, it should use its tires fairly evenly due to this proportionality. In braking, the rearward weight bias will help it not rely as heavily on the fronts as a 50/50 car, and in acceleration it will have more weight over the larger drive tires.

The 911 gains these rear-bias benefits, but by having its rear bias created by a big lump all the way at the back, it suffers more from this pendulum effect than a car of similar weight distribution would if its masses were more centralized.

That's my understanding, more or less. It should probably be taken with salt.

(*) To be correct, it already has momentum, and is simply trying to continue in a straight line. It's that rotational energy relative to the chassis that I'm trying to get you to picture. It's the old bit about trying to rotate a barbell first with the weights right next to your hands and then out at the ends of the bar.

Javelin wrote: Front biased cars on the other hand actually excel at braking. Again, pulling up some vintage footage of Mini's racing, you can see them absolutely dive-bomb the braking zones as they could stop much shorter and with more G's than the competition.

I don't think that's correct. Rear bias in a RWD car will get you better acceleration because you've got more weight over the tires doing the work.

But cars have brakes at all four corners. I believe the ideal situation for braking is a car which is rear-biased to the extent that it weights all four tires equally at maximum deceleration (assuming equal tire sizes).

The 911 should win this one, too. If you can keep it pointed the right direction

I don't believe anything I've read in this thread.

You guys get together and get me a few Ferrari's and Porsche's to play with and in a few months I'll come back with some quantitative results.

A bad idea, engineered to perfection.

it doesn't matter... it's a 911...

That's literally the answer to every argument regarding the 911. We have had a few, my GRM team mate and resident E36 M3 disturber Cam just got an RS america.. There are faster cars for less money...none of them have the soul of a 911..

I had a 72 911. An E. Except for doing something stupid like lifting or braking while cornering.. I never had an issue with it's handling. At least it was not a widow maker like the pre 69 cars with their shorter wheelbases

backwards engineered? Ok.. and?

Bah, anyone who says that (e.g. Clarkson) is just mouthing off to be contrarian. Pick the year of the worst "evil handling" 911 you can think of, then go find a Ferrari, Lamborghini, or whatever of the same year. Drive them all at 11/10ths. I guarantee the Italians will put you into the runoff backwards just as quickly as the 911 will. Back then the twitchiness & razor thin margins for error were seen as part of what makes a sports car sporty, and the idea was you had to be a better driver to use them fully.

There's more to good handling than 50/50 weight balance, and there are a lot of really excellent ways to work around that ratio when it's "imperfect."

It's flawed for the same reason fighter jets are intentionally designed to be statically and dynamically unstable. The'flawed' Porsche engineering solution these idiots rant over is because they've never had engineering courses in dynamics, or else they're trained in statics, anyone who knows the difference should understand what I'm saying, and why there's no question as to why a Porsche can still do what cars that are more 'balanced' and bigger engines can do, just sayin...

it's funny you say that Jay. I got into it with a guy on Saabcentral who proclaimed the 911 the "worst car ever"

here is an exact cut and paste

"Jump into a 911 and drive it like the SAAB and you will die, a 911 is not in the slightest bit forgiving, even the 427 AC cobra is better (and they are pretty bloody awfull, the 289 is the one to have) "

Yes, because it's totally logical to drive a 911 exactly the same way you'd drive a Saab. Clearly all cars should have identical driving dynamics regardless of their drivetrain & suspension configuration.

My head did meet the desk just there, if you were wondering.

Out of morbid curiosity, what model Saab was he comparing with?

he claims to have an "unwell NG900s convertable" so.. the floppiest noodle of a saab ever built

here was his opening post... I will admit that the 928 was a great car...

"I've driven a few.. the 911 was by far the worst car ever, the 928 is the one to have I am afraid if you are going to use it and more importantly drive it and not pose in it. I know its front engined and watercooled but it is by far and away the best all round car Porsche has ever built. The 924 abnd 944 are both excellent cars that show Porsche can build a proper car

The '76 911 turbo (930 flat nose, like the one trashed at the begining of the cannonball run) was the scariest thing ever, best thing I ever did was sell it! tried an '88 which was better but still a big beetle, recently tried a 98 911, which was better again, but for the money there are far far better cars out there. Like the boxter even! "

And the rest of his quote about the 911 not driving like a saab:

"All things are relative, but its is a big beetle (it even shares some parts not just engine location), compared to a 928, 944 or 924 the 911 does not handle at all well. Once you have crossed the line they will kill you just like a beetle, only problem being they will probbly do it faster. Put the same wheels on the back of a bettle and it will probbly also 'handle' possibly better than a 911 as the engine is shorter.

Jump into a 911 and drive it like the SAAB and you will die, a 911 is not in the slightest bit forgiving, even the 427 AC cobra is better (and they are pretty bloody awfull, the 289 is the one to have)"

David S. Wallens wrote: If the Porsche 911's handling is so flawed, why has it won so many races?

Well, when you start out with a design like that and turn a comprehensive engineering program on it with two goals (1. Retain aircooled, rear engine design. 2. WIN) then you get interesting results.

IMO, the 911s superiority in racing was in spite of, not because of, its peculiarities. They took heavy advantage of the better braking distribution, and the ability to put power down out of a corner, and sort of worked around the other problems.

mad_machine wrote: I had a 72 911. An E. Except for doing something stupid like lifting or braking while cornering.. I never had an issue with it's handling.

Note that those are bad ideas to do in ANY car, really.

Try those tricks in an early RX-7 with the good spring rates and the 18mm rear sway bar, and you'll also be looking at where you came from before you're done saying "Oh SH..."

At least it was not a widow maker like the pre 69 cars with their shorter wheelbases

And I want one of those, just because of their cussedness

Static weight distribution measured at the tires isn't everything either. Where the weight is placed throughout the chassis matters too for dynamic behaviour. Of course the suspension functionality and setup matters. As mentioned, optimal performance means a rearward bias. Find a purpose built race car with 50/50 weight distribution - it doesn't exist or if it does it's trying to satisfy an odd formula. :)

Obviously racing classes have a lot of factors involved in them, but 911s have always been competitive. I think it's fair to say the layout isn't terrible.

Let's see if you can sense what is about to happen before it happens. Makes the hairs stand up on my neck every time i watch this.

http://www.youtube.com/watch?v=s2A5WxWgAD4

ouch... I saw it coming.. what a shame, he was really earning his pay, making a turbo dance on such a damp and small road.

Knurled wrote:

mad_machine wrote: I

At least it was not a widow maker like the pre 69 cars with their shorter wheelbases

And I *want* one of those, just because of their cussedness

I want a SWB 912.. does that make we weird?

Just because something doesn't make engineering sense, doesn't mean it doesn't work.

Helicopters fly everyday, yet no one can explain exactly how.

Porsche wins races despite its flawed layout, not because of it. Much like macpherson suspension is not ideal, yet it can be made to produce the numbers etc...

Also, we (engineers at least) know exactly how helicopters fly, thats just a silly comment.

I could have made it more clear that I'm not doggin' on the 911. I love 'em. I'm just trying to wrap my mind around two seemingly contradictory "facts:"

1. 911s are "bad" because there is "too much" weight in the back, and

2. Ferrari put more weight in the back of their brand new supercar than in the front.

Clearly there is more at work here than meets the eye.

David