Speed tracking in sim racing: the speeds that matter

What speed tracking means

A speedometer tells you one number at a time. Speed tracking keeps all of them: the car's speed recorded every few metres, all the way round the lap, and drawn as a line with distance along the bottom. That line is the speed trace, and it is the top panel of almost every telemetry tool, from an F1 team's screens to the broadcast comparisons you see on TV.

Read from left to right, a speed trace is the circuit drawn in speed. The peaks are the ends of straights, the dips are corners, and the shape of each dip is how you drove that corner: the steep fall is the braking, the bottom is the slowest point, and the climb out is the exit.

The four speeds worth tracking

• Entry speed — how fast you are going where the braking starts. On most corners it is just your speed at the end of the straight before.
• Minimum speed — the slowest point of the corner, usually near the apex. It is the number most worth watching: brake too much and you have thrown away speed the corner could have carried.
• Exit speed — how fast you come out. It sets your speed down the whole of the next straight until both cars reach their top speed.
• Top speed — the fastest point of the straight. It is the last to look at, for the reasons below.

Here are the braking zones of the demo lap, the faster target lap against a slower one, with entry and minimum speed side by side. Every figure was computed by StintLab's own analysis code from synthetic demo laps:

The entry speeds are within a km/h or two everywhere: both laps arrive at every corner equally fast. The difference is at the bottom of the corners, where the slower lap is 10 km/h down in three of them. That is the whole story of the gap, and top speed would never have shown it.

Why top speed tells you less than it seems

Top speed is easy to brag about and hard to learn from. On any straight it depends on:

• The corner before. Leave a corner 10 km/h down and you are slower all the way down the straight, so a low top speed is often a corner problem, not a straight-line one.
• The setup. Less wing means more top speed and less grip in the corners. A car trimmed for the speed trap can be slower over a lap.
• Other cars. A slipstream or an open DRS flap adds speed that has nothing to do with how you drove.

So use top speed as a check, not a target: if two laps have the same setup and no tow and one is still slower at the end of a straight, look at the exit of the corner before it.

Reading a speed trace against a faster lap

Overlay your lap on a faster one, by distance, and look for where the lines part. Here is the first corner of the demo lap, braking at 500 m:

Three patterns cover most of what you will see:

• A deeper dip — you slowed the car more than the corner needed. Brake a little less, or release the brake more gradually into the turn.
• A dip in the wrong place — your slowest point comes earlier or later than the faster lap's, usually a sign of a different line or turning in at a different point.
• A slower climb out — the same minimum speed but a shallower exit: the throttle came in later or more gently.

The delta under the speed trace confirms what it cost: it climbs wherever your speed line sits below the other one. From the brake point to 900 m this one corner costs 0.621 s — more than any other stretch of the lap, with the same brake point on both laps. That is why the slowest point of a corner is often worth more than a later brake point. The full method is in Compare two laps.

Speed tracking in StintLab

StintLab records speed with every trace sample of every lap you drive in F1 25 and Assetto Corsa, on your own Windows PC:

• The speed panel of every lap comparison, in km/h, with both laps on one distance axis and the readout following your cursor.
• Entry and minimum speed for every braking zone, with the gear at the slowest point — see Braking points.
• A top speed for every lap. In F1 25 this is the game's own speed-trap reading; in Assetto Corsa, which has no speed trap, it is the highest speed in the lap's samples.

Questions