How to quickly and easily find speed from data traces

Find the Flats

A flat line is a massive red flag and should be the first thing you tackle when trying to analyze data at a glance. Eliminating them will pay huge dividends as you stay on the gas longer or brake later–or, ideally, both. 

• Look for flat, horizontal areas on the speed trace. These flat areas represent distance covered at a constant speed, and there’d better be a darn good explanation for why the car isn’t accelerating or braking. 
• A horizontal area, though, can show up in extremely long, constant-radius corners–like, beyond 180 degrees. 
• Flat areas can also show up in very long autocross slaloms where you’re constantly transitioning several times before accelerating out of the obstacle. 
• Flat lines are frequently a hallmark of a novice driver or someone learning a track–nothing to be ashamed of–and can show up toward the end of straights or, more precisely, preceding braking areas. Ideally, you should accelerate until the moment you brake, but unfamiliarity or uncertainty can lift that foot off the throttle before the braking zone. 
• Mid-corner flats are also common in similar situations of unsure conditions or abilities. Ideally, the car should decelerate all the way to the minimum cornering speed–typically at the apex of the corner–where the throttle is picked up for corner exit. A mid-corner flat usually means straight-line braking, followed by steady cornering, followed by acceleration once the car is fully pointed toward the next corner.

Sharpen the Peaks

Next, sharpen those peaks. The transitions from acceleration to braking should, in most cases, be razor sharp. Remember what we said earlier: If a car isn’t accelerating or braking, you’re leaving time on the table. 

• The incoming trace should climb steadily and, depending on the speed of the straight in question, will either be fairly straight or have a steadily decreasing angle of attack. 
• Powerful cars at lower speeds tend to have a fairly constant rate of acceleration, but rate of acceleration decreases as speed increases due to air resistance and gearing. So it’s natural to see your acceleration curves trail off as speeds go up. 
• The goal here is to make that peak–the transition moment between acceleration and braking–as sharp as a knife. Anything that isn’t a sharp peak that instantly switches from up to down is lost time.
• A peak that shallows out and levels off before dropping is indicative of a slow lift entering the braking zone before transitioning to brakes. 
• A peak that rises steadily and then begins its drop with a rounded curve indicates brake initiation being too gentle before getting to max brake pressure.
• ABS intervention and surface irregularities can introduce “noise” into the deceleration rate as well.

Analyze the Bottoms

Moving to the bottom of the graph, you’re also generally looking for sharp transitions as you switch from braking back to acceleration. Other factors, though, like the shape of the corner and amount of trail braking, can give these troughs a more gradual transition. So instead of simply looking for sharp valleys here, your lowest-hanging fruit will be lines that flatten or even reverse direction just before or–far more commonly–just after they bottom out.

• Flattening prior to bottoming typically indicates braking that was initiated too early, then released, then reinitiated closer to the corner. 
• Flattening after the bottom shows up quite often in the graphs of aggressive autocrossers, especially those who are just starting to make the transition to road course work. They’re getting to the throttle too early or too aggressively, needing to back out a bit, and then finally committing to full throttle. (While this technique sometimes gains a driver a tenth or two early in the corner exit, that adjustment closer to the final exit point nearly always costs speed down the subsequent straight.)
• In a perfect and just world, your acceleration curve out of a corner should be ever climbing, and sometimes that means tempering your enthusiasm and delaying your throttle application until you can commit once and fully. An early throttle application is meaningless if it causes you to back off and lose momentum later in the cornering phase.
• Your goal for the bottom of the curve: Maybe a slight reduction in rate of deceleration right at the end of the braking event due to trail braking, but the line should always be trending distinctly downward before transitioning back to the throttle and committing to acceleration out of the corner.