By now, you probably know that attention to details while driving improves the net result. This is again true to all types of driving: Road, Track and Stage -- and to all drivers and driving styles within them. One very important detail is how we turn through the corners. This has various aspects to it and it's the core of performance driving -- the ability to corner at the limit.
The Basic Racing Line Formula: Outside + Inside + Outside = The Racing Line
Cars don't like turning. It puts each and every component of the car (as well as the driver) under lateral loads that threaten it's stability and distrube it's otherwise plane intercourse with the road. Some drivers try to "help" the car turn by making the turns shorter and take a sharp line to the "inside" of the corner, which makes the corner very short but also very sharp and narrow.
Others prefer the "highside" -- they turn the car through a very wide arc around the turn, otherwise known as a "rimshine" line. This line suffers from making the corner very long. The real line is a combination of both. Let's take a left-hand, 90-degree angle corner as an example: We approach from the right, "dive" into the corner to "cut" it in the inside (left side) just in the middle of the turn, and than let the car run wide and back towards the right shoulder at the exit of the turn. This allows to make a very straight line because, unlike the two former lines, this line considers not only the length of the track, but also it's width.
On this line we mark three key points: The turn-in, which is obviously where we start turning the car into the corner. The second point is the APEX -- the "peak" of the turn. In every turn, in every line, there is a "peak" where the car is under the greatest load/steering input -- in the racing line, this point is inside the turn, just in the middle whereas in a tight line it would be at the end of the turn. The Third point is the Exit point, where we are after the cornering settle for the next straight.
This line offers to fastest possible speed in the corner. Even if you don't plan to attack the corner at speed, this line keeps you further from the limit and reduces the jerking of the car through the turn. However, it does have cons. I said it was the fastest possible line, but it also isn't. The key is the definition of a corner.
Physically speaking, this line allows for the fastest speed in the corner. However, in terms of driving, real-life corners appear as part of a more complex road: There are preceeding and following straights (or other corners...). In this respect, this line is not the fastest one available.
The Basic Driving line: In Late, Out Early
The racing line is theoretical, the Driving line is practical. Before a standard turn, say, at the track, we normally have to slow down. When we slow down for the corner, we want to squeeze as much braking as possible into as little space and time. By braking very hard, we are able to keep the throttle full untill the last possible moment and than brake just enough before the turn.
In the theoretical racing line, we would have to ease off of the brake pressure to allow the car to turn into the corner at the required turn-in point. But, if we would place the turn-in point slightly later, we could also brake later and keep full throttle a bit longer on the straight before the corner. The trade-off is that once you turn you have to make a sharper and slower turn. This is worthy because brakes are the strongest means of car control. Since they are stronger than the steering, they produce a greater change in performance.
But, this is still not the essence of the driving line. You brake a bit later and turn a bit later, but you also clip the APEX later, a bit after the geometric center of the turn. Again, this makes you make a tighter, slower turn from turn-in to APEX, but sets you up for a nearly-straight path from the APEX to exit, so you can put more power down more quickely and begin accelerating before the APEX.
This trade-off is very effective because instead of gaining a few tenths of-seconds in the few metres between turn-in and APEX, you gain several seconds over the several houndrends of meters of the following straight by accelerating into it earlier. This "cornering philosophy" also dictates a very important rule: "Slow-in, Fast-out." You take a sharp line going into the corner, to take a straight line out of it, so you have to weigh corner entry speed AGAINST corner exit speed, in which case the latter almost always wins. Slow corner entry speed + Fast corner exit speed = Cornering efficiency.
This trade-off is very clear in sharp corners. Ameatures are often surprised to find out just how slowly Rally drivers and Track drivers go into the really sharp turns. These ameatures are under the false belief that a skilled driver can enter a sharp corner in a fast speed and this is not true. The limits of cornering speed are the limits of physics, not the limits of a driver's skill.
Another thing to mention here is that sliding the car is not taken very kindly. Any serious sliding makes the tire work in a "slip angle" that it was not planned to function in, and this slows the car down. Sideways is slow-ways. It sometimes happens in rallying that drivers almost can't manage to make it through a slippery gravel turn without sliding, so they prefer to initate a slide intetionally and early, than try to drive without sliding only to slide more sharply later inside the corner. This is a compromise, not a desired situation.
The Last APEX line
The "Theoretical" racing line is called a "geometric APEX" line because it's based on clipping the apex directly in the geometrical center of the turn. The basic driving line is known as a "late APEX line". However, sharper corners demands a later APEX and very sharp corners, especially off of the track -- often require taking a very late APEX which I call the "Last APEX". This apex should be late enough to provide an almost straight driving line through the exit of the turn.
The last apex is not your usuall line because it makes turn-in so sharp that it's often not desirable in spite of the fast exit speed. This line forces you to "rock" the car into the corner by a relativelly rapid turning of the wheel to make the car to change it's direction at once (where in the other lines the car is progressively eased in towards the apex) from turn-in towards the APEX. However, it is advantagous in very slow bends, and in other conditions when it's required -- it keeps you prepered for what's coming next by allowing you to have a better look around the turn in advance and by giving a slow and safe turn-in and a steady state inside the corner.
This is a good place to define the relationship of the three points that make up a cornering line: Turn-in, apex and exit. We have already attributed the greatest importance to the exit -- it has the greatest effect on performance. The apex is significant for being the place where the greatest load is placed on the car. The turn-in is important because it initiates the turn. In order to exit a turn properly you first need to enter it, and properly.
In fact, we can say that the first 20% of the corner (=turn-in) make up for 80% of the cornering, but that the results of those critical 20% are only discovered half-way through the corner (at the APEX) and the net result is only experessed after the exit. Races are won over the straightaways.
The error line: Early APEX
The problem with "Slow-in, Fast-out" is that you first reach the corner's entry before you do the exit. Without planning in advance (by looking ahead), a driver is going to prefer fast entry speed anyhow. Because of the high straight-line speed the car is in, the driver is likely to try and smooth the corner by turning in from an earlier point and in a line even more straight than the geometric apex. However, cornering lines have some sort of "racing karma" to them -- a earlier, smoother and faster line at corner entry, will become into a tight and slow line at the corner exit. You will simply clip the apex too soon, and the car will not be in one line with the exit point, and would instead be facing the edge of the roadway, forcing a slow down.
If the driver's attempts to slow down are succesfull -- the real trouble begins. The driver might interprate this as a succesfull corner, without noticing that trying to be fast in entering the corner have made him to slow and brake on the straight where he should have been on full throttle.
A summary of Driving Lines:
1. Early apex: This line is normally an error. The driver turns-in too early, which lines the car up towards the edge of the turn after the apex. This sort of line sacrifices corner exit speed for corner entry speed, which is foolish.
2. Geometric apex: This line is fast but not very commonly used. It offers a very smooth line by clipping the inside the corner directly in it's middle, but it does not offer a very good corner exit speed.
4. Late apex: This is the normal driving line. You turn-in and apex later to achieve both later braking before the turn and earlier acceleration out of it. You sacrifice corner entry speed for corner exit speed, which is the best tradeoff there is.
5. Last apex: Popular in road driving because it enables to have a better look around the turn. Might require turning the wheel somewhat sharply in racing.
"Taking a Set"
At the Apex of the turn, the car essentially becomes a bike. After turning the wheel, the car's weight is being transferred to the outside wheels so they provide almost all of the cornering force. This is important because the "inside" wheels often become nearly fully neglectable. This enables to cut the inside of the turn so much that you drop the inside wheels off of the pavement. On the track, this helps in making a faster turn. On the road, the same ability can be used to avoid a car that strayed into your lane or to get around slippery parts of road that you find inside the turn (a puddle, a sheen of ice, an icy patch).
Sometimes, especially when you take a "last apex" into a very sharp corner, a relativelly sharp steering input should be made to make the car respond by "taking a set" earlier. This rapid turning of the wheel rocks the car somewhat, distributing the weight of the car on the outside wheels when slightly more biased forward. Another place where quick steering inputs are required is in some of the fast curves on the track. Some curves of the track are very fast and you accelerate all the way through them, but sometimes they are performed at a speed and/or over a surface/incline that makes the car push too much out of the turn, in which case rapid steering helps.
Camber and Castor
Camber and Castor are two principles in wheel alignment. Both of them change the way in which a given tire faces the road. However, the road also has a Camber and Castor. The Camber of the road, is a side-slope while the Castor is the uphill/downhill incline. Each of the two carries an effect on the driver, car's grip and car's handling.
Negative Camber is the classic example and it is seen on the road and track, particularly oval tracks, where the corner appears to be "banked" and inclined towards the inside. This is "negative camber" which helps increase the car's lateral grip. Think, if the corner was banked at 90 degrees, we would not have to turn the wheel at all. It keeps the car's weight lateally stabilized. In a negative Camber corner, it's vital to be smooth and gentle because the effect on car handling is a reduction of understeer. This also dictates that the driver should take the geometic line and sometimes even an early apex line.
An uphill incline has a similar effect on grip, but increases understeer by causing a weight transfer to the rear. A downhill incline would decrease the grip levels. The problem is that Camber and Castor are not nessecarily identical all the way through the corner. Some corners have an increasing Camber that makes the driver turn-in early, while other corners have a decreasing camber, where you want more turning effort done in the early, grippy part of the corner, and less in the final part of the corner.
Banking also carries an effect on the effect of grip reducing agents. If a part of the road is inclined, water and foliage would drain downwards, forcing the driver away from the inside edge of the corner. In fact, the road always have some camber that drains water sideways, so the edges of the road are categorily more slippery, and it often makes the driver adjust the line so that he does not turn so far from the edge of the track.
Corner prototypes
The track has three corner prototypes: A fast curve, a moderate bend ad a slow corner. The fast curve is the most simple but treacherous sort of corner. The line is normally geometric: You turn in and apex just in the center of the turn. Usually, some acceleration takes place all the way through the corner. The driver has to turn the wheel smoothly and once a steering angle is established, the driver controls the line by throttle maintainence -- more throttle will induce more understeer and a wider line. Less throttle would make the car tighten up the line.
Lifting-off completly usually undermines the car's stability and can lead to terminal understeer that has to be coped with by strong and instantanous acceleration without significant steering corrections. Steering corrections will rock the car, but the speed reduces the engine torque enough so that, in all drivelines, it's possible to use more engine power for recovery and less steering. In a fast corner, staying "at one" with the car obligates that the driver keeps his eyes high, usually all the way through the corner.
Sometimes, fast curves are very fast but due to the line, incline and/or car -- create too much understeer that threatens to push the car off of the right line. These turns might also require a quick turning input for "taking a set" earlier.
The moderate-speed corner is the normal racetrack corner. It is slower than the fast curves and does not allow to accelerate all through it and usually requires braking before it. The line is therefore -- the basic late APEX line. This corner requires finesse like the fast curve -- and a minimum of weight transfer -- but requires some decisiveness to get around nicely. You brake to reduce your speed in a straight line. As you turn in, you remain with brake pressure applied and "share" the tires' traction between cornering force and braking force. This is known as "brake-turning."
You start easing the steering into the corner as you start easing the braking force off -- the more steering, the less braking. from full 100% braking, you switch to 90% braking and 10% cornering force, and than to 75% braking and 15% cornering force. Once the full steering angle is achieved and the maximum cornering force is established -- you have to seemlessly lift off of the brakes and roll onto the throttle just enough to keep the car at a constant speed so that it's just cornering. This is called "Balanced Throttle."
Just before the apex, the car is lined up so that you increase balanced throttle to some acceleration and than, at the apex -- start to unwind the steering as you accelerate. This is the exact opposite of what you do with the brakes as you turn in -- the more steering you unwind, the more throttle you can apply. From 100% cornering, you go to 95% cornering and 5% acceleration, 70% acceleration and 30% acceleration up to full acceleration even before the straight.
Throughout the corner, the car has to behave around neutral -- either fully neutral or with slight understeer. If the car understeer, the driver needs to reduce speed and/or acceleration. Just slightly back-off of the throttle or brakes while you undo some steering. The car would regain grip faster and more smoothly if it only has to make up for extra 3 degrees of steering instead of 5 degrees, so straightening the wheel slightly helps. Once regripped, you can turn back into the corner. You actually saw the wheel slightly out of the corner and back inside.
If the car oversteers, the corrective input has to be faster and car-dependant: In a Rear-wheel drive and/or four-wheel drive, you will need to apply constant throttle and use the steering to balance the car. You actually need to reduce the steering angle and probably turn the wheel away from the corner (countersteering) and than straighten the steering back once the car is balanced. In a front-wheel drive, you need to recover early enough that you don't need to countersteer -- you just accelerate forward and start to straighten the wheel. The key in both cases is to to keep the eyes up to the next reference point.
A Sharp corner is not very common on the track. They are more common in rallying, especially road rallying, as well as in normal road driving. The apex here is even later and the braking is drawn ever deeper into the corner. You keep the car braking in a straight line a bit later and than begin to turn the wheel quite sharply into the corner while lifting off of he braking a bit later but less progressivelly. You set-up the car for the "last apex" and keep the constant throttle towards the apex, and accelerate just through it and out of the corner towards the outside.
Understeer and oversteer recovery are quite similar, except that some front-wheel driven cars can have enough torque in such a turn, that it can be utilized to help straighten the car out of oversteer. You start straightening the wheel while momentarily accelerating hard to spin the front wheels slightly. This spinning still allows some acceleration to take place, so there's still a rearward weight transfer that helps the rear grip again, but the sliding of the front wheels will cause them to slide outisde and straighten the car instead of countersteering. Once the car is straight, you reduce the amount of throttle to get you around the turn.
Successive corners
Let's assume a place on the track with one righthander followed directly by a lefthander. You stick to the left before the first corner, turn right and into the corner, apex and track out to the left again -- this would place you on the "inside" of the next corner and off of the right line. This is particularly bad because our priority is for corner exit speed, so the speed coming out of the last corner in the corner-set is most crucial.
The choice is to "prioritize" the second corner. You take the "last apex" line into the first corner, which enables you to keep the car "pitched" on the inside after the apex, allowing you to take the correct late apex line towards the next corner. Alternativelly, if you have two right-hand turns one after the other, you can take the first corner with a geometic apex and than track-out to the far left-end of the road so that you can carry a late apex into the next corner.
This is just theory. In real-life you sometimes don't track-out all of the way, and negotiate the following corner somewhere from the middle of the track. This is mainly true for the faster curves that are in times very easy to get around even when you don't use the whole track width.
On the road
Driving lines on the road can be used in one of two causes: To increase safety, or to increase speed while practicing racing lines in winding roads. The system is preety much like the lines used in a race. Fast curves normally have a field of vision which is open and wide around the corner. This enables to use the geometric apex to make the corner as smooth and grippy as possible. Of course, the line on the public road should be restricted to the bounderies of your own lane.
A moderate bend is the type of corner you might negotiate on the countryside rural roads and in winding mountain roads. On the road, we need to drive well within the car's grip limits, so the main problem in such corners is not the grip that gets us through it, but the limits of vision. This is why a late apex is very effective here. In fact, it's best to take an even later apex -- just like the last apex. Still, because we drive on the public road, we need to avoid the sharp steering input which is used in that line: You turn the wheel a bit earlier and bit more smoothly, but aim for the same "last apex." Sharp corners are negotiated in urban districts and in mountain roads. These corners are negotiated much like the moderate speed bends: You enter it very slowely, wait to a very late stage and turn the wheel into the corner. You try to be smooth, but sometimes smoothness has to be compromised for a clasic "last apex" line.
On the road, it's important to reduce the overalp between braking, steering and acceleration. Some overlap helps in achieving a weight transfer that makes for a bit of extra responsiveness of the car during transients. However, less overlap makes for easier, safer cornering and a larger grip reserve: You brake with feel in a straight line, turn the wheel smoothly (but as decisivelly as required) and ease off of the brakes. You than establish balanced throttle all the way through the turn. Even when you start winding the car through the corner, you don't accelerate much -- just a little bit of acceleration to help straighten the car.
On the road, very fast curves and very sharp and slow corners often require a different line than the above prototypes: Let's say you drive on the righthand lane of the highway and you follow a slight curvature of the road to the right. Moving to the left-edge of the lane is going to be really unnessecary. It's going to put you out of the normal position you should keep on the road -- so it's best to stay on the right or maybe move just a bit towards the middle of the road as you turn. The same happens in slow, sharp corners in the city -- you keep a tight line to avoid posing a hazard for motorcycles.
Even in corners where you do take a wide driving line you don't nessecarily use the whole width of the lane. In a righthander, you want to keep a short distance from the divider line to keep a certain gap from oncoming traffic. Even on lefthanders (in countries where you drive on the right) you can't always set-up from the rightmost edge of the lane, because it can be slippery due to dirt and especially when wet.
Eyepath
The eyepath is a major element in taking a corner properly. First, you need to drive straights with your eyes UP. This way, you will see the corners in advance from the largest possible distance. Once you see a corner, you need to to glance into it and as far as possible through it. You need to assest the corner's type: What type of corner is this? The next step is to visualize the cornering line you want to car to take through the corner. Once you established the line you want to take, you mentally draw the turn-in, apex and exit points on it.
While glancing around the corner, look out for the convergence point. This is the furthest point of the corner you can see. This point appears as an arrowhead that seems to "unwind" and get away from you as you get closer. Adjust your pace to fit to that of the convergence point - so that you can match the right speed, gear and pace for the corner.
Once you enter the corner, you use your eyes to guide you through the right line which you planned and visualized in advance. In fast curves, you just treat the corner as a twisting of the straight, and keep on looking through it. You don't even need to use the convergence point. On slower corners, however, a more advanced eyepath is used. You start driving towards the convergence point. You set the right speed and gear to the corner and adjust your position in your own lane so that you are ready for the line you want to take.
When you reach the point which you designated in your imagination as the point of "turn-in", you should evert your eyes and look towards the next point -- the designated apex. You should gauge the exact turn-in point through the corner of your eye, through your peripheral vision. As you start lining up towards the apex, you look through it and down the following straight. You gauge the exact clipping point based again on your peripheral vision.
On the track, you improve this system by using a system of reference points: You set permenant visual details as points where you want to turn-in, apex and track-out. Apart from the fixed points, you use you judgement to gauge when you brake, when to let up the brakes in a corner and when to begin accelerating out of the corner. The driver can also use his steering and engine/exhaust tone as points of reference.
Lesson learned:
For the next month, try and practice the effective driving lines: Both road driving lines and race driving lines. You can also practice racing line on the public road too. They are best practiced on deserted winding mountain roads. You first make a slow run and inspect the whole road and decide what is the right driving line and if there are any surprises to avoid. Than, you do a faster run with the right driving lines.
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