The rear weight bias thing...how does one live with it?

[dd74]

When I think about it, these 911s are screwy cars. As gas is depleted from the tank, the rear weight bias of these cars increases, so it becomes apparent the driver has to continually adapt to the changes in the car's weight dynamics.

Now, there are other cars like the Miata, the RX7 and RX8, and M3, which claim to have near 50/50 weight distribution, and from a physics point of view, it seems these cars will, during spirited driving, stay much closer to that weight split, whereas the 911 never begins to approach a 50-50 distribution.

My question is two-fold: what is the advantage of a car like the 911 with the majority of its weight placed in the rear? And if there is an advantage, assuming a car does not have adjustable sway bars or that the driver cannot exit the car to play with tire pressures, etc, as fuel is burned, how does the driver compensate for an increasingly heavy rear and increasingly light front?

Thanks all.

[dd74]

Yes, good point. I always thought mid-engine weight distribution was best - but is that, in most cases, 50-50?

[911mot]

hmm engine at the back cant be all bad,I wonder what the weight distribution of a Formula One car is?

[dd74]

Originally posted by 911mot
hmm engine at the back cant be all bad,I wonder what the weight distribution of a Formula One car is?

Right - so why is it an advantage?
I've read where pro drivers describe driving 911s on tracks as "sliding" the car around the track, using throttle steering mostly.

But then, with the engine in the rear, and a suspension that is softer than an F1 car, it seems one would be pushing the car more than sliding it.

Sliding actually seems more likely with a mid-engined car, or one with 50-50 weight distribution.

[bell]

the advantage of a rear weight bias....specifically is as the rear weight in the rear compresses the suspension it increases traction, there is a sweet spot in 911's under heavy cornering where the rear is simply planted to the road and you can feel the car clawing around the corner with the push from the rear.........that's the advantage....
and is also why 911's are considered a "drivers" car.
50/50 isn't always the ideal split.......especially in the wet.
imo of course.

[Bill Verburg]

The advantage of a 911's rear weight bias is traction on acceleration and traction under braking

the advantage of 50/50 is quick rotation in any direction, horizontal or vertical.

[Wrecked944]

FWIW, when I am at AutoX, I love to lift off the throttle in a turn and swing the back end around. Then smoothly apply the gas and she resettles herself and comes right back under control. I like it so much I've been told I need to consciously avoid it because I haven't bothered to learn any other driving skills. Persistant use of trailing throttle oversteer may not be the fastest way around the course, but it is the funnest!

[911mot]

With the weight on the rear it will grip better and let you put more power down but that weight also works against you in the corners with the 'pendulum effect' trying to make the car swap ends. If it goes you have to be very quick, brave and lucky all at the same time to catch it. You can't drift a 911 either, at least iv'e never seen it or done it. Maybe a 4wd could, anyone tried it?

[gestalt1]

on the track, corner entry is key to good lap times and a rear weight biased car has an advantage. under braking weight is shifted to the front and the weight distribution is more even at this point. additionally the front wheels have the stress of trying to change the direction of the car, at corner entry you want some weight on the front for additional grip but you do not want too much overloading the front tires and un-weighing the back too much. i feel this is why a rear weight biased car is better for the track. on a steady radiused long corner a 50/50 car may be more forgiving and easier to drive. most tracks are corners connected with straights.

[450knotOffice]

Didn't Vic Elford drift his 911's around most of the dirt and snow covered courses back in the late 60's?

[TimT]

there are a few types of weight distribution

944/928 have close to 50/50 yet these cars have high polar moments.

The 914 50/50 and the car has low polar moments.

and 911 which may have much more rear weight bias.

There is much info available regarding Porsche work arounds to get the 911 to handle well.. be it on the road, or on the track.

[TimT]

Oh and sliding a car, and using the throttle to squirt out of a slide is just so cool

[randywebb]

nobody mentioned packaging and lighter wt. (no driveshaft); also the wt. is over the traction wheels, and not over the steering wheels, consequently the steering feel is light and "alive"

- ever notice how much space there is in such a small car? rear engine...

[Wil Ferch]

Some years back Car and Driver magazine did a comprehensive test ( and long explanation ) of what the "ideal" weight distribution should be ....

It ended up being 45F/55R.... and specifically NOT 50/50

Darned if I can recite why....

- Wil

[Todd Simpson]

The rear engine layout is best for acceleration and it's best for braking.

Cornering...well, it's also the best. You want understeer, you got it. Oversteer, well you can have that too.

[JeremyD]

Originally posted by Wil Ferch
Some years back Car and Driver magazine did a comprehensive test ( and long explanation ) of what the "ideal" weight distribution should be ....

It ended up being 45F/55R.... and specifically NOT 50/50

Darned if I can recite why....

- Wil

I remember the one that expounded on the virtues of the 911 vs the corvette - how the rear engine layout helped in braking and acceleration.. and that "they thought there would be a bigger difference in cornering

[Wil Ferch]

I'll bet the article I'm thinking about was around the time the Fiero was inroduced and tested....around 84.

The test you're talking about, was likely the white '88 Club Sport vs. the black Z51 Corvette. I remember that one too.

- Wil

[Jack Olsen]

My less-than-expert two cents:

An M3 is 50/50, and a 911 is something like 62/38, right? Well, yes, except for this key fact: that's only true when the car is sitting still. In thinking about handling, it's important to consider how much the car's weight gets thrown around on its suspension when it's being driven. You're dealing with a constantly-changing situation. Under braking, for example, the 50/50 M3's front wheels are doing much more work than its rears. Under acceleration, it's the opposite.

Now, given the fact that brakes are capable of slowing a car down as much as ten times more effectively than even a race motor is capable of speeding it up, you see that in a straight line, the rear weight bias is going to offer some clear advantages. Anyone can lock the wheels with their brakes, but (sadly) most of us can't light the tires up as easily with the gas pedal. So it helps to offer more weight over the traction wheels under acceleration, like the 911 does, and it's less essential to throw a lot of weight over the front wheels for braking, which the M3 design does.

The flip side is in cornering. The 911's rear weight bias makes it less stable on a fast entry to a corner. You can throw an M3 into the same corner faster. But the 911 is going to be more sure footed as it plants and exits. Slow-in-fast-out allows 911's to beat up on cars that can enter faster but have to brake more before they're lined up, rotated, and and able to come out of the corner. When I drive mine, the 911 feels a little like I'm skiing. It kind of pushes itself out of the turns. With an M3, to me, it feels more like the car is pulling me out of the corner.

Trying to correct or change the car's course during a long sweeper, or dealing with things like decreasing-radius turns where you're trying to turn and decellerate at the same time? These are some of the areas where the advantage goes to a car like the M3.

And as has been already pointed out. The 911's configuration simplifies and lightens the drivetrain, and eliminates the need for power steering, cutting still more weight. Reducing weight is always goign to be more important than finessing weight distribution, in the larger scheme of things, so there's another advantage for the 911.

Either way, though, you can't have it all.

Taking a step back from the whole issue, it helps to remember that the difference in weight distibution is not an enormous factor at all. Lots of things (like absolute weight, suspension capability, braking ability, horsepower -- or even the tires being used) will have a much bigger effect on lap times. That's why front-, rear-, and mid-engine cars have been competing on more or less even footing for so many decades.

[masraum]

Many, many racecars have a rear weight bias. I believe that the main "problem" with the 911 rear bias is not as much the fact that the weight is more in the rear, but that the bulk of that weight is at the extreme rear. If the car still had a rear bias, but was mid engined it would rotate more quickly which is desired for a racecar or "sporting" car.

My guess is that a mid engined car with a rear weight bias would combine the traction/handling benefits of a 911 and the rotating handling prowess of the boxster and 914.

[Won]

Originally posted by Wil Ferch

It ended up being 45F/55R.... and specifically NOT 50/50

- Wil

I remember reading about the weight distribution of an F-1 car being something like that, 45/55.