trailbraking in a 996?

I've been sufficiently scared to death of even lifting in a corner when driving a Porsche because of what people have told me, but that only applied to mid corner right? One can still safely trailbrake into a corner in a 911, right? Actually, something I've never even considered is do they dumb down the brake bias for their street cars? Would it have horrible understeer if I tried to trailbrake in it?

I think trail braking will improve the understeer because the front will become heavier due to weight transfer. But from my experience on the road, I like to scream up on a turn, brake late and hard getting it done, initiate the turn and apply throttle thru the turn. This works for me in the canyons and twisties. I realize a track can be way different driving at 10/10 rather than 6/10 or 7/10 on the street. Also I'm driving a stock Cab and what works in it may not with your car. I haven't raced a 966 but I have a lot of motorcycle roadracing experience.

Well, as I understood it though with these rear engine cars you need weight on the back to keep it from swinging out because their is so much momentum back there that it'll break loose as soon as you take weight off of it. That makes sense to me because I know you can bring these cars back into line if you start to oversteer mid-turn by staying on the throttle.

You have to brake through turn in to go fast. How far you trail brake of course depends on the corner. In general you're better braking longer and not quite as hard as the car is capable of. The more stock your suspension is the more important it is not to upset the car too much with really hard braking. At least that's what I've found. If you are experienced you also probably want to turn in a little early and rotate the car under braking. Jim

That was then, this is now. Porsche's done a ton of work to dial out the dreaded trailing throttle oversteer. My car (a C4s) has a pretty pronounced understeel in slow to mid corners. I almost alway trail brake, at least until the initial turn-in is done. Try it on a wide-open corner sometime: you'll be pleased.

That's a little misleading. The weight in the rear is a blessing and a curse. The blessing comes from the weight providing traction. The curse is the polar moment of inertia. That is, the distribution of weight is not even along the long axis of the car. There is a significant amount behind the rear wheels. The center of the car's mass is less than the tail end. It is sort of like a dumb bell and that is called high polar moment of inertia (all the mass is at the ends). When you turn your car, that weight wants to travel away from the radius of the circle and tends to wash the rear end outward of the circle. The front is lighter, so it does not exhibit this same tangental force. If friction between the tires and road is lost, the rear will turn around on you. That is the simple version. Now the more complex version. In the above example we are only talking about angular acceleration induced by the circle that the car travels. It assumes a constant angular velocity (same speed around the circle). If you speed up or slow down, a different set of dynamics comes into play. When you speed up the front of the car gets lighter and the rear gets heavier. Actually, the mass stays the same, but the force that gravity exerts between tires and road changes. You will see this when you hit the gas and the nose of the car goes up. When you brake it goes down. When you exit a turn you want the weight bias on the rear tires for more traction. As you approach the limit of traction in a turn the rear wants to swing out because it is like a giant pendulum (more weight at one end). Staying on the throttle helps keep the traction by shifting the force onto the rear wheels. At the hairy edge, when you let off the throttle, that force bias now shifts forward again. The force on the rear tires gets lighter and the force on the front tires gets higher. Now the angular momentum exceeds the coefficient of friction in the rear tires because you were on the edge. The rear steps out and because of the high polar moment of the 911, you spin. There is a lot more going on than what I just told you. There is more down force on the outside set of tires than the inside. There are a lot of other parameters, but the long and short of it is all about force distribution on the tires as you go around a turn. Now you should have a basic understanding of polar moment of inertia. For instance , a mid engine car has less tendency to spin because more weight is closer to the center of mass of the car. A 911 has a the opposite mass distribution and has a higher tendency to spin, but it also has more force on the rear wheels, whereas the Cayman does not. This means that the two cars have different techniques to entering and exiting a turn. Oh, one more thought. When a car spins the distribution of weight also has an effect on the rate of spin. A car with a high polar moment will spin slower than one with the mass close to its center. A Cayman, when it does spin, will spin faster than a 911 under the same set of circumstances. You can use the higher spin to your advantage if you use it to rotate the car and shoot out. The 911 also has an advantage with the slower spin that allows you more time to aim and correct the car. All this leads up to how hard and where in a turn you brake. When you ride on the edge you must do a dance with gravity and angular momentum. You maximize your speed by adjusting the car's momentum and bias so that it works to the best advantage of traction at the specific point of a turn. You must do this both precisely and smoothly to achieve optimum results. Foe me, I am ungifted in the art, so I just stay below the car's limit and the shinny side stays up.

Marv, Good read! The 911 handles a lot like a motorcycle. You need to keep on the gas thru a turn which maximizes rear wheel traction and keeps the front end relatively light. A little too much trail brakeing or chopping the throttle in a turn near maximum lean on a bike will load the front tire too much and will induce a front tire slide, very difficult to recover.

Another consideration is powering out of a turn, the inside wheel gets lighter than the outside. If it gets too light it'll slip, and the differential will spin that wheel up faster, reducing drive on the more important outside wheel. Then you lose the rearward weight transfer and the back end comes around. This is one reason you might want a limited slip differential. Bill

Marv- Very nice description.

Good writeups but let's not get carried away with the do not lift scare. Just like every other car you have to use the brake and the thottle to manage your weight. You need to brake through the turn in, you need to feather the trottle to correct understeer, you sometimes need to lift to rotate, etc., etc. The 996 really doesn't spin that easily. And thats from someone that's done it a few times. Jim

Marv, you should write for one of the 911 magazines. Fantastic article. Jay

Jim is right. They're really hard to spin - especially in stock form. The cars are heavily biased toward understeer. I've upgraded my suspension, added neg camber up front and changed to wider front tires to reduce understeer. But to answer your question: yes - the most effective change has been to alter my driving style to include trail braking to make the fronts bite on turn-in & after. Now if I can learn to roll on the throttle quickly and smoothly...

Thank you!

Not quite. And actually they are much easier to spin in stock form b/c of the soft suspension. What Jim said was "not easily" which is vastly different from "really hard". It's not hard at all. Sure it's a game of semantics. But, what needs to be understood, is that the if you do NOT know exactly what you are doing (ie, lots of seat time and proper instruction) then spinning the car is VERY easy. Even worse, is if you do not know how you spun the car it will happen again and again and again.......... Much easier to understand the "spinning" ability of the 996 is based on the situation. Wanna see a spin? Take a HIGH SPEED sweeper and start to lose track out real estate. Whatta ya do next? Human nature tells you to "slow down" so lifting off the throttle would make instinctual sense. Bye-bye, please keep all hands and arms inside the whiel the ride is in motion. It takes time to gain the confidence to realize that you actually need to have that throttle mashed to keep the **** down. Not a good way to approach the corners. If you go in hot, brake hard, and try to rotate, and throttle out , you are (1) creating an unsafe situation for yourself.....especially in the canyons; and (2)taking corners the WRONG way. If you want to be fast and MORE controlled in the corners, brake smoother and sooner, keeping the brakes applied after turn-in to rotate the degree you need, then throttle through the apex and your gone! Pretty much dials out all the understeer you want. Yup! Excellent Job

Dell, I'm headed to the airport so you get the last word on this but I think the "don't lift" mantra needs to be tempered. In the situation you described above in the fast sweeper the most likely reason in a 996 that you're running out of real estate is that you're pushing. The only way to fix that problem is to lift. Not a full lift but just enough to shift some weight to the front and regain some front end stick. I instruct students in 996s all the time and one of the most important skills is how to manage the throttle. Sending the message that lifting is always bad is not a good message. I did our region�s "physics of racing" class if anyone is interested in the slides. They are very simplistic but ok for explaining the basics of weight management. Jim

Jim, excellent point. I didn't intend for my example to be an on/off switch with the throttle. Feathering it would have been better but I have no idea the skill level of some of the people here so I went to the basics (ie, don't lift).

This is great Dell, exactly what I learned in high performance driving school last week. It's actually somewhat counter-intuitive for a novice like me. FWIW I also learned that it's not just 911s, modern sports cars can be very similar irrespective of RR, FR or MR layout. They all understeer turning under hard braking and they all oversteer lifting off the throttle mid corner. The differences are in the incremental effort to push it over the limit and the incremental effort to bring it back from the brink.

How'd ya think I learned Let's just say that I have been pointing the wrong direction on many occasions in my early days. At least I wasn't the fastest guy out there so my spins were painless and a great learning example.

I should have provided some context rather than make a subjective statement like: "they're hard to spin". 4 years ago, just after I bought my car, I attended a PCA car control school where the goal was to get your car to spin by lifting mid-turn. Imagine a skid pad with large figure 8 course where you'd get about 80 feet of wide open throttle in a straight line followed by a sharp turn at the top or bottom of the 8. I watched as Boxsters, 914s, 944s and 911s of various vintages loop with screeching tires, smoke and applause from the on-lookers. My turn comes - foot to the floor, engine revving, turn the wheel, lift....nothing. The car just pushes to a stop. Instructor tells me to try again but get more speed if possible and brake with my left foot after I lift. Guns blazing, **** & vinegar, here I come....turn, lift, brake - nothing but plowing front tires. A chorus of boos can now be heard from the rest of the students. Instructor tells me I flunked but I have a "really safe car". I don't feel so bad when the only other 996 doesn't spin either. Story's not over. My 1st DE about a month later has a decreasing radius right hander which I approach with stones of steel in my "really safe car". The car is pushing past the apex when I notice I'm running short of track out area (sound familiar? - see Dell's post). No problem, I'll just lift and she'll plow to a stop just like the skid pad. Instructor says "here we go" and around she went (something more than once but less than twice). ...sure was easy to spin that time. There's still some dust in my car from the cloud I created - a safe but humbling lesson. 4 years hence, I know the car a lot better. I certainly get it 'squirrly' now and then but the spins are pretty rare now. So reading opinions on the internet is good to a point. Sorting these matters out for yourself in a safe environment with proper instruction is much better. Have fun and be safe.

Excellent point!

996 do not spin as easily as earlier cars. however DO NOT lift remains true. but you can feather the throttle all you want if you know what you are doing. trail braking isn't need for street driving. if you need to trail brk to make a turn on street, either your car is grossly misaligned or you are going way the hell too fast. it is not easy to explain trail braking, this is something you learn SLOWLY through YEARS of track driving.

Yeah, I would never drive at trail braking speeds in the streets...and to come clean (I've mentioned this before) it's my parents car so no track time with it for me, but I do play GTR2 which is extremely realistic and with the 996 cars I was having issues with brake bias adjustments and trail braking and got to wondering if it's faster with a Porsche to not trail brake (the game is realistic enough that if it were the case in real life it would be the case in the game).