Compare fast and slow laps at the same point on track
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Source path: content/lms/data-interpretation-for-drivers/02-reading-speed-traces/02-comparing-laps.md
Course: Data Interpretation for Drivers
Module: Reading Speed Traces
Estimated duration: 60 minutes
This lesson is about one narrow but powerful habit: stop looking at a fast lap and a slow lap as two whole laps, and start comparing what happened at the same physical piece of racetrack. You are not trying to admire the prettier trace. You are trying to answer a driver question: at this exact entry, apex region, exit, or straight, what did the faster lap do differently, what did the slower lap do differently, and what should you change next session?
The important word is same. Same car location. Same braking zone. Same turn-in region. Same exit curb. Same piece of straight. If you compare by time, the traces drift apart as soon as one lap is faster than the other. At ten seconds into one lap, the car may be in a different place than it is at ten seconds into the other lap. That makes the comparison noisy before you have even started. For this skill, you compare speed traces against covered distance, not elapsed time, so both laps are being judged at the same place on the track.
Speed is the first channel because speed is the result channel. It tells you where the lap time changed. It does not, by itself, tell you why the lap time changed. The driver mistake is to see a lower speed and immediately invent a cause. You were too early on throttle. You braked too much. You missed the apex. Maybe. But the disciplined sequence is first locate the gain or loss with speed and time compare, then use brake pressure, throttle, steering, RPM, gear, segment times, GPS line, G-sum, and curvature when available to explain it.
This lesson does not repeat the sibling lesson on reading the general shape of the speed trace. Here you already know that a speed trace rises under acceleration, falls under braking, and bends through cornering. The new skill is comparison. You will learn to overlay two laps, align them by distance, choose the piece of track that matters, separate result from cause, diagnose entry versus minimum speed versus exit speed, and turn that diagnosis into one objective for the next session.
The core principle: compare location before interpretation
Most useful driver data work is comparative. A single lap can show you what happened, but two properly aligned laps show you what changed. The reason overlays are so powerful is that driver performance is not abstract. It happens at a place. You released the brake at a place. You reached minimum speed at a place. You opened the throttle at a place. You straightened the car at a place. When two laps are plotted against distance, you can compare those events directly at the same piece of track.
A speed overlay gives you two immediate readings. First, it shows the absolute speed difference at each location. Second, when your software provides a cumulative time compare or delta channel, it shows whether that local speed difference is actually gaining or losing lap time. Use both. A small speed deficit that lasts through a long acceleration zone may matter more than a larger momentary difference in a short section. A higher minimum speed may look impressive but cost time if it delays throttle or lowers exit speed onto a meaningful straight. A lower entry speed may be faster if it lets the car rotate and exit harder.
That is why comparison starts with the speed trace but cannot end there. Speed tells you where to dig. The cause may be brake pressure shape, throttle hesitation, an early throttle application followed by a lift, inconsistent pressure, a light and long brake zone instead of a hard and short one, a gear difference, a line difference, or how quickly the car was turned and straightened. Your job is to avoid guessing until the other channels either confirm or challenge the story.
For an intermediate driver, the main discipline is restraint. Do not try to fix the whole lap from one overlay. Pick one piece of track where the fast and slow laps separate, preferably a corner followed by a significant acceleration zone. If the corner leads onto a long straight, exit speed gets amplified. If the corner is short and followed by another braking zone, the same speed difference may matter less. Sector times can help you decide whether a difference is worth chasing, but the speed and time compare overlay is where you locate the event.
The six-step comparison method
Step one is to choose the pair of laps with a reason. Usually you compare your fastest clean lap to a slower representative lap from the same session. That keeps car setup, tires, fuel, driver, and ambient conditions as similar as the session allows. You can also compare different sessions, setup changes, different drivers in the same car, or different ambient conditions, but then your interpretation has to stay honest about what changed. The overlay can show differences in driver consistency, setup effect, driving style, or condition change. It cannot tell you which variable matters if you mix too many variables and then pretend the comparison is pure.
Step two is to plot the laps against distance. This is non-negotiable for this lesson. If the x-axis is time, the laps diverge as the time gap grows. If the x-axis is distance, you can ask what both cars or both laps were doing at the same location. For long tracks such as the Nürburgring, this matters even more because a small early lap-time difference can make a time-based overlay misleading over the rest of the lap. Distance alignment keeps the question physically meaningful.
Step three is to turn on speed and time compare together. Speed shows the local result. Time compare shows whether that result is accumulating into a real gain or loss. Begin by scanning for the places where the time compare line changes slope or direction. Those are the sections where the faster lap is pulling away or the slower lap is recovering. Then look directly above that section on the speed trace and ask how the shapes differ.
Step four is to divide the section into entry, middle, and exit. Entry is the approach and brake zone into the corner. Middle is where the car reaches its lowest or most constrained cornering speed. Exit is where the car is straightening and accelerating away. The same speed difference can mean different things depending on where it appears. A higher entry speed with a lower exit can mean the driver carried speed to the wrong place. A lower entry with a better exit can be the faster method on a corner that feeds a straight. A similar minimum speed with a delayed throttle trace can mean the loss is not minimum-speed capability but confidence or timing on the release and application.
Step five is to check cause channels. If the slower lap loses time before the minimum speed point, inspect brake pressure shape and initial application. Was the braking long and light compared with the faster lap? Was the peak inconsistent? Was there a long tail into the corner that kept the car from rolling speed? If the loss appears at exit, inspect throttle. Was there coasting? Was application hesitant? Did throttle come in early and then require a lift? In a fast corner, was there a lift that the faster lap avoided? If the line may be the difference, inspect GPS line or curvature. Curvature tells you how much the car is turning, where it starts turning, where the turning peaks, and where it returns toward straight. It is not the same as steering-wheel angle, because vehicle balance affects how much the car turns for a given steering input.
Step six is to write one next-session objective. The objective should describe the location, the intended trace change, and the safety guardrail. For example: in the second right-hander before the back straight, match the fast lap brake release location and commit to one smooth throttle application only after the car is opening. The success criterion is not bravery. It is a trace that changes in the expected place without creating a new lift, a new correction, or a worse exit.
Sub-skill one: pick the right reference lap
Your reference lap is the lap you use as the comparison target. It does not have to be a perfect lap. It only has to be useful for the question. If your fastest lap contains one unusual heroic section and several messy sections, it may still be useful for one piece of track and useless for another. Intermediate drivers often make the mistake of treating the fastest lap as the perfect answer everywhere. The better habit is to compare section by section.
A fastest rolling lap or theoretical fastest report can help you identify which sectors or pieces of track contain your best known performance, but the lesson is still the same: compare at the same distance. If your software can show segments or section times, use them to choose where to dig. The trace work happens after that. The segment report tells you the neighborhood. The distance-based overlay tells you the street address.
When comparing your own laps, look for repeatable differences before changing your driving. If one lap has an odd spike caused by traffic, a missed shift, a GPS dropout, or a cool-down interruption, it is a poor teacher. If three laps show the same slow pattern through a corner and one lap shows a cleaner pattern, that one clean lap is valuable. You are looking for something you can repeat, not a magical outlier.
When comparing two drivers in the same car, be even more careful. The overlay may reveal style differences, but the faster driver may not be faster for the reason you first notice. One driver may brake later but release poorly. Another may brake earlier but carry a stronger exit. One may use a different gear. One may accept a different line. Use the same process: speed first, time compare second, cause channels third, objective last.
Sub-skill two: read the delta without worshiping it
The time compare channel is useful because it converts the speed difference into lap-time consequence. If the fast lap is gaining through a section, the delta shows the gap growing. If the slow lap is recovering, the delta shows the gap shrinking. This keeps you from being fooled by a dramatic speed difference that does not last long enough to matter, or by a small speed difference that persists down a straight.
But the delta is not a driving instruction. It is a locator. If the slow lap loses two tenths between turn-in and exit, the instruction is not simply go faster there. You need the reason. Did you enter too fast and wait? Did you brake too long? Did you coast between brake and throttle? Did you apply throttle early, force the car wide, and lift? Did you choose a line that gave a higher minimum speed but a worse exit? The delta tells you where your attention belongs, not what your hands and feet should do.
A good intermediate habit is to mark three places on the lap where the delta changes most clearly, then choose only one for the next session. The purpose of driver data is to improve the next time the vehicle hits the track. It is not to create a long list of sins. If you leave the laptop with seven corrections, you will drive worse. If you leave with one correction tied to one location and one measurable trace change, you have a workable plan.
Sub-skill three: separate entry speed, minimum speed, and exit speed
A corner is not one number. The speed trace through a corner has an entry story, a minimum-speed story, and an exit story. You compare all three because a driver can be faster in one part and slower overall. This is especially common when drivers chase minimum corner speed. They see the fast lap has a higher low point in one corner and assume the goal is simply to make the slow lap higher there. Sometimes that is right. Sometimes the faster lap wins by giving up entry or minimum speed to improve exit speed.
Minimum cornering speed matters because it shows how much speed the car carried through the most constrained part of the corner. Exit speed matters because it determines how much speed you carry into the following acceleration zone. The longer or more important the following straight, the more the exit matters. That does not mean you ignore entry. It means you judge entry by what it does to the exit, not by how impressive it looks at turn-in.
Use this simple diagnostic. If the slower lap is slower before the corner and remains slower through the exit, the problem may begin in braking or entry confidence. Check brake pressure and release. If the slower lap has the same entry and minimum speed but loses after apex, check throttle timing, throttle confidence, gear, and how the car is being straightened. If the slower lap enters faster, reaches a similar or higher minimum speed, but exits slower, suspect that the speed was placed too early and cost the driver the ability to accelerate. Use GPS line or curvature if available to see whether the car turned too late, stayed turned too long, or failed to straighten cleanly at exit.
The clean comparison question is not which lap had the highest number at one cursor point. The clean question is which lap spent less time through the section and why. The speed trace gives you the visible result. The time compare tells you whether the result mattered. The other channels explain the driver action.
Sub-skill four: use throttle and brake traces as witnesses
Throttle and brake traces are witnesses, not decorations. After you locate a speed difference, ask the throttle and brake channels to testify. On the brake trace, look at the shape of the initial application, the release, the trail, and whether there is a long tail. Compare hard and short against light and long. Look for inconsistent pressure from lap to lap. On the throttle trace, look for coasting, hesitation, early application that leads to a lift, and lifts in fast corners.
The most useful question is not whether the trace is beautiful. It is whether the trace explains the speed and delta change at that location. If the slower lap loses time on corner entry and its brake pressure stays on longer, you have a plausible cause. If the slower lap loses time on exit and its throttle opens later or opens then closes, you have a plausible cause. If the speed difference is real but brake and throttle look the same, keep digging. Check steering, gear, RPM, line, curvature, or conditions.
This is where the instruction to look for incongruencies matters. An incongruity is a mismatch between the story you expected and the channels you see. You may expect that the slower lap braked earlier, but the brake trace shows the same brake point. You may expect that the faster lap had more throttle, but the throttle trace shows the same percentage and the gear trace shows a different gear. You may expect that the line was the same, but curvature shows one lap started turning earlier and peaked differently. Do not force the data to confirm your first guess. Ask why until the channels agree or until you admit you do not know.
Sub-skill five: use line and curvature without pretending they are steering
A speed overlay can point toward a line problem, but it cannot prove the line by itself. If the faster lap exits with more speed after the same minimum speed, the car may have been pointed and straightened better. GPS line can show the path. Curvature can show where the car started turning, where it was turning most, and where it returned toward straight.
Curvature is especially useful because it describes the car trajectory, not the steering wheel alone. The car can turn more or less than the steering input suggests depending on balance. That means you should not use curvature as a moral judgment of hand movement. Use it as a picture of what the car actually did. If one lap starts turning earlier, reaches peak curvature sooner, and straightens sooner, the speed trace may show a cleaner exit. If another lap delays turn-in, peaks late, and keeps curvature high at exit, the throttle trace may show hesitation or a lift because the car was still too turned to accept acceleration.
This is also where the phrase same piece of track becomes practical. When you compare two speed traces at corner exit, place the cursor at the same distance. Then check whether the curvature is returning toward zero at that same distance. A lap with slightly lower speed but a straighter car may be ready to accelerate harder. A lap with higher speed but more remaining curvature may be using tire capacity to turn when it needs to be accelerating. The right answer depends on the corner and the following straight, which is why you prioritize corners that lead to significant acceleration zones.
Sub-skill six: choose the corner that pays you back
Not every difference deserves the same attention. The most useful corners for comparison are the ones followed by meaningful acceleration. A higher exit speed reduces the time spent on the following straight. That makes exit analysis more important on corners that lead onto long straights or full-throttle zones. Sector time analysis can help you identify these areas, but the driver decision is still practical: which change will pay back the most time and can I safely practice it next session?
This is where intermediate drivers often waste effort. They see a local difference in a slow complex and spend a session chasing a tiny gain while ignoring a worse exit onto a straight. Or they see a higher minimum speed in the faster lap and try to copy it in a place where the real gain came from earlier throttle and better straightening. You are not trying to win the overlay everywhere. You are trying to find the highest-value difference that you can convert into a driving objective.
A useful rule is to ask three questions before choosing the target. Did the time compare move meaningfully here? Does this section feed an acceleration zone or important sector? Do the supporting channels suggest a driver action I can practice? If the answer to all three is yes, you have a candidate. If the answer is no, leave it alone for now.
Worked example: Silverstone speed overlay method
The Silverstone example in the source material is useful because it demonstrates the basic workflow: two laps overlaid, speed first, then gains and losses, then causes. You do not need the actual figure to practice the method. Imagine you have two of your laps from a session and you overlay them by distance around a full circuit. The fast lap is your reference. The slower lap is your comparison.
You begin with the time compare channel. On one section, the delta begins to grow against the slower lap just before the middle of a corner and continues growing down the following straight. That tells you the loss is not only a momentary corner number. It is being carried after exit. Now you look at the speed traces. At entry, the slow lap is similar to the fast lap. At the minimum-speed region, the slow lap is only slightly lower. At exit, the slow lap opens a gap and remains slower for a long distance.
Do not conclude yet. Check throttle. If the slower lap shows a delay before throttle application, the cause may be hesitation or confidence. If it shows an early application followed by a lift, the driver may have asked for acceleration while the car still needed to turn. Check brake pressure. If brake release has a long tail compared with the fast lap, the car may have been held down into the corner longer than needed. Check curvature or GPS line if available. If the slower lap stays in curvature longer at exit, the car was still turning when it needed to be straightening.
The next-session objective from that comparison is not drive the corner faster. It is more specific. Match the fast lap release and exit shape at that section, then commit to one clean throttle application as the car opens. The success criterion is that the speed trace begins to recover at the same distance as the fast lap and the time compare no longer keeps bleeding down the following straight.
Worked example: Nürburgring and the danger of time-based overlays
A long lap makes the distance-axis rule impossible to ignore. On a long circuit such as the Nürburgring, a small difference early in the lap means that a time-based overlay quickly compares different physical places. At the same elapsed time, one lap may already be farther along the track. If you then try to interpret a braking point or corner speed from that view, you may be diagnosing the wrong part of the circuit.
Use distance instead. Now the cursor sits on the same location for both laps. If the speed traces differ at a specific part of the track, you know you are comparing that same place. That lets you make a real driver judgment. Did the slower lap arrive with less speed because of the previous exit? Did it lose speed under braking? Did it recover at exit? Did the time compare continue to move after the corner, suggesting that exit speed mattered?
The practical lesson is that the longer or more complex the lap, the less you should trust a time-axis comparison for local driving analysis. Distance alignment keeps the overlay honest. It lets you compare vehicle speed directly for every location on the track and then decide where to dig.
Common mistakes and what good looks like
Mistake one is comparing by time. It feels natural because lap time is the thing you want to improve, but it is the wrong x-axis for local driving technique. What wrong looks like: you place the cursor at the same elapsed time on two laps and interpret a speed or brake difference even though the cars are not at the same place. What good looks like: you plot against covered distance so the comparison is anchored to the same piece of track.
Mistake two is treating speed as the cause. Speed is the outcome of the driver and vehicle actions. What wrong looks like: you see the slow lap is three miles per hour slower at exit and simply tell yourself to exit faster. What good looks like: you use speed and time compare to locate the loss, then inspect throttle, brake pressure, steering, RPM, gear, GPS line, G-sum, or curvature to explain it.
Mistake three is chasing minimum speed without checking exit. What wrong looks like: you copy the lap with the higher low point and then lose time down the straight because the car was not ready to accelerate. What good looks like: you compare minimum cornering speed and corner exit speed together, especially in corners followed by a significant acceleration zone.
Mistake four is trying to fix too many places. What wrong looks like: you leave the analysis with a list of six corners, two brake zones, and three throttle changes. What good looks like: you choose one section where the time compare moves, the speed trace shows a clear difference, and the supporting channels suggest a concrete action.
Mistake five is ignoring incongruencies. What wrong looks like: you decide the problem was late throttle even after the throttle trace does not support that story. What good looks like: you let mismatches send you deeper. If throttle does not explain it, look at brake release, line, gear, RPM, steering, or curvature.
Mistake six is confusing curvature with steering input. What wrong looks like: you see a curvature peak and assume it directly describes how much steering wheel the driver used. What good looks like: you remember that curvature measures how much the car is turning, and that vehicle balance influences the relationship between steering input and path.
Drill: the three-overlay comparison drill
At your next event, use this drill after each of three sessions. The count is three overlays, one after each session. The working time is ten to fifteen minutes per overlay. The success criterion is one written objective per session, tied to one location, one expected trace change, and one safety check.
After session one, choose your fastest clean lap and one slower representative lap from the same session. Plot speed against distance and turn on the time compare channel if your software provides one. Mark the three locations where the time compare changes most clearly. Do not solve all three. Pick the one that is followed by the most meaningful acceleration zone, or the one where the supporting data is easiest to understand.
For that one location, divide the speed trace into entry, minimum speed, and exit. Write one sentence describing where the slow lap loses time. Then check brake and throttle. If the loss is entry-side, inspect brake pressure shape and release. If the loss is exit-side, inspect throttle timing, hesitation, early application followed by lift, or a lift in a faster corner. If the story still does not make sense, check gear, RPM, steering, GPS line, G-sum, or curvature.
Before session two, turn the diagnosis into one driving objective. Keep it small enough to execute. Do not write a vague instruction. Write a location and a trace goal. For example: at the selected exit, avoid the early throttle and lift pattern; wait until the car is opening, then make one committed application. Or: in the selected brake zone, reduce the long light tail and match the cleaner release shape from the reference lap. The exact wording depends on your data. The point is that the trace tells you what to attempt.
After session two, compare the best lap from session two to your reference. Did the speed trace change at the intended distance? Did the time compare stop losing there? Did the supporting channel improve without creating a new problem? If yes, keep the change and look for repeatability. If no, ask why. Maybe you changed the wrong thing. Maybe the line was the cause. Maybe the corner does not matter as much as you thought. Maybe the objective was too large.
After session three, repeat the same comparison. The drill is successful if you can show one of three outcomes: the loss shrank in the target section, the data disproved your first diagnosis and gave you a better one, or you learned that the section was lower priority than another location. All three are useful. The failure is leaving the data session with only a general feeling that the fast lap was better.
How to carry the lesson forward
The habit you are building is simple: overlay, align by distance, locate with speed and time compare, explain with other channels, then set one objective. This is the driver version of keeping data simple. You do not need every channel to start. With only GPS speed and distance, you can locate where the lap changed. With throttle and brake, you can often explain the main driver action. With line and curvature, you can test whether the car was being turned and straightened differently. With sector reports, fastest rolling, and theoretical fastest tools, you can choose where to spend attention.
The end product of analysis is not a beautiful screenshot. The end product is a better next session. If your comparison does not change what you will do at a named piece of track, it is not finished. If it gives you one clear, safe, testable change, it has done its job.
Worked example: Silverstone speed overlay method
Use the Silverstone-style workflow as a process example rather than as a claim about a specific corner. Overlay the fast and slow laps by distance. Begin with speed because speed shows the result, then use the time compare channel to find where the fast lap gains or the slow lap loses. Once the section is located, split it into entry, minimum-speed region, and exit. If the loss grows down the following straight, do not focus only on the lowest number in the corner. Check whether the exit speed was lower and whether throttle, brake release, line, gear, RPM, or curvature explains why. The objective for the next session should name the location and the trace change you want, such as a cleaner release, a later but single throttle application, or a straighter exit shape.
Worked example: Nürburgring and distance alignment
A long circuit makes time-based overlays especially misleading because the two laps can be at different physical locations after only a small early difference. Plot the laps by distance so both traces describe the same place on the track. Then compare speed directly at each location and use time compare to decide whether the difference matters. If a speed loss appears before a long acceleration zone, inspect exit speed and the supporting channels before blaming the entry. The lesson is not specific to one Nürburgring corner; it is the alignment discipline that matters. The longer the lap, the more important it is to compare by location instead of elapsed time.
Common mistakes
The first common mistake is comparing by time instead of distance. That turns a location question into a misleading elapsed-time question. The second is treating speed as the cause instead of the result. Speed tells you where to dig, while throttle, brake pressure, steering, RPM, gear, GPS line, G-sum, and curvature help explain why. The third is chasing the highest minimum speed without checking exit speed and the following straight. The fourth is trying to fix the whole lap from one overlay. The fifth is ignoring incongruencies when the supporting channels do not match your first story. The sixth is reading curvature as steering angle, when curvature describes how much the car is turning rather than how much the driver turned the wheel.
Drill: the three-overlay comparison drill
Run this drill after three sessions at your next event. After each session, spend ten to fifteen minutes comparing your fastest clean lap with one slower representative lap from the same session. Plot speed against distance and turn on time compare. Mark the three clearest places where the time compare changes, then choose one target section, preferably one followed by meaningful acceleration. Divide that section into entry, minimum speed, and exit. Check brake and throttle first, then steering, RPM, gear, GPS line, G-sum, or curvature if available. Write one objective for the next session that names the location, the intended trace change, and the safety check. The drill succeeds if the next overlay shows the loss shrinking, the diagnosis improving, or the chosen section being deprioritized for a better-supported reason.
When to use other channels
Use other channels after speed and time compare have located the problem. Brake pressure helps explain entry losses, inconsistent pressure, light and long braking, hard and short braking, trail shape, and long tails. Throttle helps explain coasting, hesitation, early application followed by lift, and lifts in fast corners. Steering, RPM, gear, segment reports, fastest rolling, theoretical fastest, G-sum, GPS line, total steer angle, throttle histogram, and curvature can all check the story when the first explanation is too simple. The point is not to use every channel every time. The point is to ask why and then use the available channels to confirm or challenge the answer.
Author Review
No quiz questions are attached to this lesson.
Sources
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|---|---|---|---|---|---|
| 1 | Analysis Techniques for Racecar Data Acquisition | 2eefac2f-4698-d1cf-0f29-7c28c364bf3a | 6 | 1 | uio_books_raw_v1 |
| 2 | Analysis Techniques for Racecar Data Acquisition | 298d8370-448d-3f4a-4164-cc740c02801e | 7 | 1 | uio_books_raw_v1 |
| 3 | Analysis Techniques for Racecar Data Acquisition | f283c211-228e-e2d7-1c5f-9fd276068a07 | 18 | 1 | uio_books_raw_v1 |
| 4 | Data for Drivers | cabda699642b26311b0a7ef998da2c71 | 15 | 1 | uio_books_raw_v1 |
| 5 | Analysis Techniques for Racecar Data Acquisition | d0db9128-dc9a-aec3-14a8-5f101654753f | 3 | 1 | uio_books_raw_v1 |
| 6 | Going Faster Mastering the Art of Race Driving - Carl Lopez | fa01ec16-aace-9079-2afa-de127b8272a9 | 300 | 1 | uio_books_raw_v1 |
| 7 | Going Faster Mastering the Art of Race Driving - Carl Lopez | 3732f6fd-13ee-73b1-76ed-abcba9b17590 | 27 | 1 | uio_books_raw_v1 |