How to Read a Speed Trace: What the Shape Is Telling You

A speed trace is the most honest thing in your telemetry. Inputs lie a little — you can be hard on the brake pedal and still be slow — but the speed line shows exactly what the car did, metre by metre, with none of the story you tell yourself in the cockpit. Learn to read its shape and you stop guessing about which corner cost you the lap. Most drivers open the graph, see two squiggles, note that the red one is lower somewhere, and close it again. This guide is about what the shape itself means.

What you are actually looking at

Plot speed against distance, not time. Against time, a slower lap stretches sideways and the two traces drift out of sync until nothing lines up. Against distance, every point on the x-axis is the same piece of tarmac for both laps, and you can put a cursor on the apex of Turn 4 and read both speeds honestly.

The trace is a sequence of three shapes repeating: a rising line (acceleration), a falling line (braking), and a bottom (the minimum speed through the corner). Everything worth reading is in how steep those lines are and how wide or narrow the bottom is.

Add the delta trace underneath if your tool shows one. The speed trace tells you what happened; the delta tells you whether it mattered. A corner where you are 4 km/h slower at the apex but the delta line is flat through the following straight is not where your lap time went.

Reading the bottom: V corners and U corners

The single most useful distinction on a speed trace is the shape of the minimum.

The V

A V-shaped minimum means you decelerated to a point and immediately began accelerating. The trace comes down, touches the bottom for an instant, and goes back up. This is correct for a hairpin, a tight chicane, a second-gear corner — anywhere the limiting factor is how quickly you can rotate the car and get it pointed at the exit. In those corners, time spent at minimum speed is time wasted. The sharper the V, the better, as long as you are actually hitting the apex.

The U

A U-shaped minimum means you held a roughly constant speed through an extended arc. This is correct for a long, fast, constant-radius corner — Turn 8 at Istanbul, Turn 3 at Barcelona, Stowe at Silverstone. The car is at the limit of grip for a sustained period and there is nothing to be gained from an abrupt rotation. In these corners, a V shape is the error: it means you over-decelerated, got the car turned too early, and then had to feed speed back in against a corner that was still going.

Why it matters

Drivers routinely apply the wrong shape to the wrong corner. The most common version is driving a fast sweeper like a hairpin: a quick stab of brake, a sharp minimum, then a long climb back up. You arrive at the apex slower than necessary and the corner punishes you for the whole remaining arc. The opposite error — a wide, flat U through a hairpin — means you are scrubbing speed on the brakes too gently and coasting round. Look at the bottom of each corner and ask: should this be a point or a plateau?

The early lift

Look at where the trace stops climbing on the approach to a braking zone. On a good lap, the line rises in a clean straight run and then breaks downward sharply — a hard corner on the graph. If instead you see a short rounded shoulder, a few tenths where the line flattens or sags before the real deceleration begins, that is an early lift.

It usually comes from one of three things: you are not confident in the braking point and you are feathering off to buy thinking time; you are easing out of throttle before moving to the brake pedal instead of going straight across; or the car moved under you on the approach and you reacted.

The cost is larger than it looks. A lift that drops you 6 km/h at the end of a long straight has already cost you time before braking even starts, and because you arrive slower, your braking point tends to creep earlier on the next lap too. The fix is mechanical, not brave: practice going from full throttle to full brake with no gap. If the rounded shoulder disappears and the braking line gets steeper, you found free time.

Over-slowing

Over-slowing is the most expensive and the least visible mistake in sim racing, because from inside the car it feels safe and tidy. On the trace it shows up as a minimum that sits clearly below the reference, followed by a long slow climb that takes most of the following straight to recover.

The tell is where the two traces reconverge. If you are 5 km/h down at the apex and still 5 km/h down a third of the way along the next straight, you did not lose the time in the corner — you are losing it continuously, all the way to the next braking zone. That is why a slow exit from an important corner is worth more than a brilliant entry into an unimportant one.

The other signature of over-slowing is a short flat section at the bottom of what should be a V. That flat part is coasting: you are off the brake, not yet on the throttle, and the car is simply running out of speed. Any flat section in the middle of a V is time you can delete.

Comparing minimum speeds

Minimum speed is the number everyone quotes and the one most often misused. Three rules keep it useful:

1. Compare at the same point on track, not at each lap's own minimum. If your minimum happens 15 metres earlier than the reference lap's, you are comparing two different corners.
2. Read entry, minimum and exit together. A higher minimum achieved by braking far too late, missing the apex and running wide is a slower corner with a better-looking number.
3. Weight the corner by what follows it. Two km/h at the apex of a corner leading onto a 1.2 km straight is worth several tenths. The same two km/h into a corner that leads to another braking zone 200 metres later is worth almost nothing. Fix the ones that feed the long straights first.

When your minimum is genuinely low and your exit is genuinely slow, the usual cause is entry: too much speed carried too deep forces you to stay on the brakes past the point where you should be rotating, which pushes the apex late and the throttle later still. Brake slightly earlier, release slightly sooner, and watch whether the minimum rises even though you braked earlier. It very often does.

Working through a lap

1. Overlay your lap on a faster reference, aligned by distance.
2. Find the three biggest steps in the delta line and ignore everything else for now.
3. For each one, look at the corner's shape: is the bottom the right shape, is there a shoulder before braking, is there a flat spot in the middle, where do the traces reconverge?
4. Name one change per corner — brake five metres later, release earlier, no coast — and run five laps on it.
5. Re-overlay. If the shape changed and the delta did not, the change was not the problem. Move on.

This is the loop every engineer runs, and it is also what P1 does live: an AI race engineer that reads your telemetry as you drive and coaches the exact corners and braking points costing you time, so you are not waiting until the session is over to find out which three corners mattered.

Read enough traces and the shapes start to arrive before the numbers do. You will glance at a corner, see a rounded shoulder and a flat-bottomed V, and know what the lap felt like without replaying it.