What's the heirarchy of handling for a 911?

[Hotwatermusic]

Weight distribution

Center of gravity

Track width

Tire grip

Weight

How would one prioritize these characteristics to make a 911 the best handling car it can be, within its own constaints, of course? For example, is it worth sacrificing overall vehicle weight by having a heavier battery, spare tire, etc. up front giving better downforce and distribution, than not having them there at all (and losing the weight in doing so)? If you had to put these five attributes (and any others I might be missing) in a list, how would it look?

[Flieger]

Tires

weight

weight distribution

suspension tuning

[Dantilla]

I'm no expert, but tire grip is absolutely, without question, number one.

[Trog]

Driver skill.

[VFR750]

Driver skill is #1

Mild Suspension tuning w/corner balance
DOT-R Tires
Brake cooling
More suspension tuning
Aero
weight & distribution

IMHO, a heavy/low powered car teaches you about momentum and smoothness. Once you can hustle a heavy car, weight reduction is icing on the cake.

[Hotwatermusic]

Originally Posted by Trog

Driver skill.

Yes, but that's a given. It's read. I am asking if "the Stig" got into a Porsche to drive it, what handling attributes of the car would be most important to him getting around the "Top Gear track" the fastest? And forgive me if these aren't recognized references, as they're only thing I figured most of us might know.

[dtw]

I had been thinking in terms of...

0. Overcommit to corner
1. Don't lift
2. Don't lift
3. Don't lift
4. Don't lift
5. Lift
6. Countersteer
7. Counter-countersteer
8. Depress clutch pedal
9. Depress brake pedal
10. Kill ignition
11. Summon tow truck
12. Engage insurance adjuster
13. Post pics on Pelican

But that's really more of an order of operations than a hierarchy. Carry on.

[HarryD]

Check out Steve Weiner's Web pages on the topic:

Welcome to Rennsport Systems, Porsche Performance Products for the 21st Century

Draw your own conclusions.

[Captain Ahab Jr]

For a classic 911 ie limited to 150mph top speed being used on a road circuit I would go for

Tyres as nothing else comes in contact with the track and this ultimately controls which direction the car travels in.

weight as most lap time will be spent either accelerating or braking. Less is best as it reduces loads on components and your braking efficency improves

weight distribution/C of G as this will improve change of direction during cornering and the a low C of G will reduce lateral tyre deflection improving tyre grip. Sweet spot for front/rear weight distribution is 60-55% rear/40-45%front and as low as you can go on C of G

I would also add chassis torsional/beam stiffness, suspension camber/toe stiffness as being very importantas there is no point trying to make a jello go fast as it will wobble all over the place.

Obviously all this doesn't make up for the spacer betwen the steering wheel and the seat.

[Porsche-O-Phile]

Originally Posted by dtw

I had been thinking in terms of...

0. Overcommit to corner
1. Don't lift
2. Don't lift
3. Don't lift
4. Don't lift
5. Lift
6. Countersteer
7. Counter-countersteer
8. Depress clutch pedal
9. Depress brake pedal
10. Kill ignition
11. Summon tow truck
12. Engage insurance adjuster
13. Post pics on Pelican

But that's really more of an order of operations than a hierarchy. Carry on.

Touche.

I'd add:

4.5 Panic
9.5 Soil drawers
10.5 Bury head in hands, sobbing

[RSTarga]

slow in, fast out. for the track my priorities would be:
1) tires
2) minimize weight transfer front to rear with stiffer rear torsion bars.

[Grady Clay]

Tires
Tires
Tires
and more.

Yes on all the other but tires, tires, tires.

My racing used a new set of race tires every day.
Sometimes more.
Even then it took very careful tire management.

So long as everything else about a Porsche racer is just OK, tires are the single issue.


Search some of my prior admonitions.

Best,
Grady

[Hotwatermusic]

Originally Posted by Captain Ahab Jr

For a classic 911 ie limited to 150mph top speed being used on a road circuit I would go for

Tyres as nothing else comes in contact with the track and this ultimately controls which direction the car travels in.

weight as most lap time will be spent either accelerating or braking. Less is best as it reduces loads on components and your braking efficency improves

weight distribution/C of G as this will improve change of direction during cornering and the a low C of G will reduce lateral tyre deflection improving tyre grip. Sweet spot for front/rear weight distribution is 60-55% rear/40-45%front and as low as you can go on C of G

I would also add chassis torsional/beam stiffness, suspension camber/toe stiffness as being very importantas there is no point trying to make a jello go fast as it will wobble all over the place.

Obviously all this doesn't make up for the spacer betwen the steering wheel and the seat.

How "sensative" is center of gravity? Meaning, is it_at_all worth taking out the 1" risers my seats are on, so my 200lbs butt is that much lower in the car? I imagine it wouldn't make a bit of difference, but I would love a reasonable excuse to get rid of them.

[Grady Clay]

In the early ‘70s Porsche built a ‘variable center-of-gravity’ 911. It had a cubic foot of lead on a vertical track through the horizontal plane CG. This ‘lump of lead’ was on a track where it could be just under the roof or through the pan almost touching the ground. I was told it would change the vertical CG by more than 2”.

There is a Christophorus technical article in ’70-’72 about the car and tests. I drove the car on the Weissach skid pad in May ’74.

The conclusions were that a 2” change in vertical CG had about the same effect as the difference between Dunlap 165/78-15 street tires and the period Dunlap race tires. A BIG deal.

So … To answer your question, vertical CG counts a lot.

I understand one of the ‘tricks’ of F1 is to get the car very underweight and add the weight to spec with a tungsten plate under the chassis. This is so effective that F1 regulates the height with wood ‘rub strips’.

Best,
Grady

[RWebb]

Thx Grady - that is another amazing historical tidbit from you.

if pure lead, that would have weighed almost 708 lbs.

I'm surprised that the cubic foot was not some metric unit however.

[sig_a]

1. C/G
2. gross weight
3. tires
4. dynamic load distribution
5. track (baked in by design)

[Hotwatermusic]

Originally Posted by sig_a

1. C/G
2. gross weight
3. tires
4. load distribution
5. track (baked in by design)

Wow, that is a lot different than what others have listed, which is good, I like reading the differing opinions. I knew right off the bat though that I miss-communicated on my original post. By "track width" I meant the side to side distance between the tires--the wheelbase width-wise if you will--I guess I just didn't use the proper term for it. I knew immediately after posting it people would think I meant width of the track the car is driven on. Thanks for the responses everyone, this has been very educational for me.

[DanielDudley]

Originally Posted by Grady Clay

So … To answer your question, vertical CG counts a lot.

Best,
Grady

First you make sure your suspension is in good shape, not sloppy or worn. Then you make sure you have good dampers.

Then you get a corner balance, lowering, alignment.

THEN you get tires. BRAKES must work

[Fleming]

Tires,

but,
Let's not forget unsprung weight.

In talking with the guys at Jongbloed Racing Wheels, lap times (the effect of a good/bad handling car) was a common topic. Heavy to light wheels can be measured in "seconds per lap".

Driving a car with lightweight wheels turns in faster, takes less distance to brake, and had a slightly faster acceleration. The overall distinction is a tighter feeling car - which is much more connected. A by-product is more sensitive tuning of springs and shocks.

Having Fuch's has spoiled us. With 12 lb wheels we gain the handling without ever driving on 20 lb steel wheels to compare against.

Sherwood's wheel weight study is here:

911 Wheel Weights

The down side of very light wheels - they don't like potholes.

[sig_a]

[QUOTE=Fleming;5125569]Tires,

"Driving a car with lightweight wheels turns in faster, takes less distance to brake, and had a slightly faster acceleration. The overall distinction is a tighter feeling car - which is much more connected. A by-product is more sensitive tuning of springs and shocks."

I can agree with that. Moving from 17" Fikse at 25" diameter to 15" Fuchs at 23" diameter improved handling in three distinct areas: lower C/G by 1"; reduced unsprung weight by about 40 pounds total; lowered final drive gear ratio about 8 percent. This is the single most impactive suspension modification so far.