One age old question in racing is, “Why is one driver faster than another in the same car, all else being equal?” Simple question. The answer, not so much.
Let’s set up a scenario. Two drivers, one car, set up by a third driver. Each driver has their own set of identical tires. One driver with ballast, so corner weights are identical. Warm-up and cool-down laps, 10-lap runs, throw out fastest and slowest lap times. Each driver gets two 10-lap practice sessions. Neither driver has driven this car on a track neither has been to. Inevitably one driver will be faster. Maybe by a second a lap, maybe only by .1 seconds for all laps, but one will be faster.
The important question is not who is faster, but why. There are four criteria, which are easily determined with data acquisition. First, who has the highest average throttle position percentage? Second, who has the lowest average steering wheel angle? Third, who has the largest area under the traction circle curve? Fourth, who has the lowest percentage of longitudinal tire slip (wheel spin and wheel lock-up)?
Highest average throttle position is obviously critical. The more you are on the gas, the faster you will be. The lowest average steering wheel angle is an indication of tire scrub, which slows the car. It also wears the tires more quickly. The less you turn the steering wheel, the faster you go.
The largest area under the traction circle is an indicator of maximum accelerations – lateral and longitudinal. In other words, the highest average cornering G force, braking G force and acceleration G force. Last is longitudinal tire slip. We all know wheel lock-up during braking is a no-no, but what about wheel spin exiting a corner? Few cars have enough torque to spin the tires on anything beyond a very low speed turn. Peak acceleration occurs at 2-3 percent wheel spin. So a little wheel spin is good given enough engine torque and gearing to make wheel spin possible. When asked if the Porsche 917 Can Am car was too powerful, the late, great Mark Donahue, replied “No! I can’t spin the rear tires all the way down the longest straightaway.”
Improving skills in these areas should be the primary focus of any competition driver. These four factors are the essence of going fast. In our two- driver, same-car scenario, most likely one driver will be better in one or two of these criteria while the other is better in the rest. This is a good indication that both drivers could improve. The reality is that all drivers can improve. It’s only a matter of how much.
Each of the four criteria outlined above is all about traction. The most proficient in all of the areas above is making the best use of the traction provided by the four contact patches. When it comes to going fast on the track, at the end of the day, it’s about traction. But this includes many factors – perfect throttle control, smooth braking, a gentle touch with the steering, carrying maximum speed into and through corners, getting on the power as early as possible exiting corners, minimizing steering wheel inputs everywhere, managing tires, which each of these items influences.
But the driver and control usage are only part of the picture. Weather, track conditions, even track configuration are important. So are tires, power and many other agenda items. But we’ll start with, “What’s the fast line at this track?” a question asked countless times — and rarely answered accurately.
One of the most basic precepts of driving fast laps is the late-apex concept. It has been written about, taught in racing schools and preached by helpful fellow drivers since Denis Jenkinson wrote the great book “The Racing Driver.” Before we go further on this topic, it is important to understand that we are talking only about going fast, not racing tactics and strategy. Things change when you get into setting up passes under braking at corner entry or while accelerating at corner exit. So lets analyze the late-apex concept.
The late apex came about in the early years of racing when engine power technology was more advanced than tire or chassis technology. Take the Auto Union Grand Prix cars as a case in point. Massive power, flexing chassis and skinny little hard tires that Stuck and Nuvolari could spin all the way down many straights. When you have enough power to spin the drive tires more than 2-3 percent as we discussed earlier, the more important a late apex becomes. A late-apex line requires that you turn the steering wheel later, but more at the entry so that you can unwind the steering wheel sooner at the exit. This is done to counteract wheel spin. It is crucial if the car is not equipped with limited slip at the drive axle. The less steering lock being applied, the more power that can be used for acceleration.
Remember the traction circle. Tires make only so much traction, which can be used for cornering or longitudinal acceleration (braking or accelerating). Some percentage of traction can be used for lateral and longitudinal acceleration. This means that unwinding the steering wheel as you begin to accelerate out of a turn is extremely important. You want to use every available pound of force created by the tires. This is true with or without wheel spin. But is a late apex needed to accomplish this? The answer is no.
I can hear it already. Blasphemy! Heresy! Racing instructors gasping! Coaches cringing. A late apex is mostly needed when the tires can spin too much at corner exit as the throttle is applied. A late apex allows a straighter exit path, reducing wheel spin. How late the apex should be is a question debated for as long as drivers have talked about fast lines. The short answer is that it depends on how much wheel spin. More wheel spin requires a later apex, at least up to a point, and very smooth, precise applications of the throttle pedal. Remember, we are talking about the fast way around a track, not out-braking or inside corner-exit passing. Most likely, fewer than 15 percent of corner-car scenarios would involve corner-exit wheel spin. Thus most corners in most cars would benefit from a more geometric line. It’s also important to use every millimeter of racing surface at turn in, apex and track out points. That asphalt is there for you to use, not watch pass by.
Here’s why. First, a geometric line is the fastest path around a corner allowing for maximum speed through the corner itself. Second, the geometric line means turning the steering wheel the least amount overall from turn-in to track-out points. And this means less tire scrub, or drag, trying to slow the car. Finally, you can still apply more and more throttle as you unwind the steering wheel at the corner exit. The key is the geometric apex of the corner. This does not mean you turn in quickly, holding the steering angle steady until the track out point. It does mean that you increase steering lock as you approach the apex, then decrease steering lock as you exit to the track out point. Same turn-in and track-out points, but the line is not part of a circle path, but more of an elliptical arc. So an apex near or slightly beyond the geometric center of the turn is best. If the turn is flat out, the geometric circle line is fastest and scrubs the least amount of speed. The most important element of cornering is to get on the gas early, drive a line that allows the most speed and the least amount of tire scrub and do not over-drive the corner entry. This is more important than the actual line through the corner.
OTHER TRACTION ISSUES
All of the above assumes that traction is best on the preferred racing line. That is not always the case. Here are some examples:
SLIPPERY & WET TRACK CONDITIONS
This can include rain, dust, water leaks and spilled fluids. I was driving in an endurance race several years ago. One car dropped a radiator full of fluid on the track midway into the braking zone. This was before anti-freeze was banned, so it was crazy slick on the racing line. Several cars went off, including the car with no radiator fluid. I saw what was happening and slowed, took an early turn-in and made it through the mess. The driver who lost the fluid had stayed on line until he spun to the inside of the track, making it impossible to totally avoid the slick section.
But if you changed your line so you went fairly straight as you crossed the slick area, you could carry near racing speed, but well off the normal line. Some drivers slowed too much and lost ground and positions while others went a little too fast and either slid or went off the racing surface. Paying attention and problem solving make potential disasters an opportunity for the astute driver.
Rain can cause serious traction issues, but it can vary from spot to spot on the track surface. Try exploring alternate lines in the quest for more grip. The same can apply to dust and sand blowing across the track surface. Dust and sand can be worse than rain since gusting wind can change the surface conditions constantly. You will need to search for the optimum line in a given corner on every lap. And you may need to change your line for the best visibility based on wind gust and volume of dust or sand in the air at any given time.
TRACK SURFACE CONDITION
The most obvious cause of traction loss occurs when asphalt begins to break up on a track, usually at the apex of a turn. This happens often on temporary street circuits. It is obvious that areas like this should be avoided. Less obvious are conditions of smaller ruts and bumps that can upset the balance of the car, unweighting the tire instantaneously. Different lines can reduce or eliminate these issues and save time around the track.
I was testing a car with very little bump travel on the rear shocks after being lowered. There was a severe dip — at least by racetrack standards — between the apex and track-out point of a medium-speed corner. The rear would snap out in a violent oversteer slide. This surprised me the first time, since I had driven many other cars over this section with no issues other than a little unloading of the tires as they crossed the dip. This condition required radical maneuvering to keep the car pointed in the right direction and on the track surface. But it was not the fast way around. Since we were stuck with improper shocks, to make the best of the situation, I had to alter the line so I hit the dip straight. Not fast, but way quicker than a spin or even just going dead sideways for awhile.
But altering line on any track with a rough surface can pay dividends. You can even use the knowledge gained about alternate lines as a tactical tool in a racing situation. Think outside the box.
An interesting incident occurred when I drove the Banks Sidewinder Cummins Diesel-powered Dodge Dakota pickup at Bonneville. After more than 10 years, we still hold the diesel pickup land speed record at over 217 mph. The salt course at Bonneville is about 150 feet wide. But after many runs, the surface gets chewed up, mostly from wheel spin. It is not unlike driving on a wash board dirt road, just not as bad. The official monitoring my licensing runs — it was my first trip to Bonneville — was helpful.
He said the edges of the track were smoother. So on the first run, I drove close to the right edge. As he said the right was a little better than the left. But it was still causing a little bouncing and it made applying the throttle difficult since it helped induce wheel spin. And with nearly 800 horsepower and 1,500 pound-feet of torque on a slippery, salt surface, wheel spin was hard to avoid, even without bumps and ruts.
On the next run, I lined up on the left side. When I left the line, I angled across the course to the right, so I would reach the right edge at about the 2 mile marker, where the course was much smoother. By angling across the course, I was hitting the small bumps and ruts at a slight angle, reducing the effect slightly since the rear tires were not hitting the bumps at the same instant. This offered an additional benefit of lengthening the course by over 100 feet. The extra distance allowed more room to accelerate and was instrumental in gaining 1 or 2 mph through the timed miles. I only had a chance to watch a few cars make runs from the starting area. No one else ever tried this, but it worked.
By the way, if you race at a track where the last turn is in the opposite direction from the first turn, you can use the above trick to gain a tenth or two in qualifying. More precisely it’s the opposite from above. Don’t cross back over to the opposite side of the track until you pass the timing mark. You will be driving less distance, which will save a little time. If your track is 50 feet wide, less the car’s width, you can save driving about 45 feet. At 100 MPH average speed, you will save nearly.3 seconds. If the speed is slower, you’ll save even more time.
These last examples are intended to get you to think. Even to think outside the box. Look at problems as opportunities you can use to your advantage. They are, but most don’t see them that way. Search for traction. And work on turning the steering wheel as little as possible, staying on full throttle as much as possible, minimizing wheel spin and avoiding wheel lockup. Finally, integrate the traction circle concept into your driving, as well as the other skills to use those tire contact patches to their fullest. That will make you faster.
This video shows you how to use the traction circle for determining how close your are to the limit as you brake, turn in and accelerate at corner exit in a left-hand turn.
This video gives you a primer on how to use your pedals and steering wheel and reference your visual field as you negotiate a turn.
