The terms every track day driver runs into.

The point in a corner where you are closest to the inside edge. It is the geometric middle of your line through the turn, not the middle of the corner itself.

In practice: Overlay two laps on the map and a later apex shows as a line that stays wide for longer before touching the kerb.

The lap from the pit exit to the finish line. Tires and brakes are still coming up to temperature, so the time means very little.

In practice: The out-lap of the Autodrom Most session on 9 October took 3:21.85, more than a minute off the pace, and is correctly left out of the best lap.

The lap that ends in the pit lane. The final sector is a pit entry rather than a racing sector.

In practice: Lap 12 recorded a 46.730 s sector 3 against a session best of 35.190 s. That is the pit lane, not a mistake.

A continuous run on track between two pit stops. One track day session is usually one stint.

In practice: Tire and driver performance both drift over a stint. The last two laps often lose tenths for reasons that are not technique.

A specific route around a circuit. One venue can have several: a full course, a short course, a variant that skips a chicane.

In practice: Lap times only compare within the same layout. Vetkuro proposes the layout at session start and lets you correct it.

One recording, from the moment you hit record to the moment you stop. It holds every lap, the vehicle, the weather and any video.

In practice: 9 October 2026 at Autodrom Most: one session, 34:23 of recording, 49.8 km, 11 timed laps.

A raised or painted strip at the edge of the track, usually at an apex or exit. Drivers use low kerbs to straighten the line. High ones unsettle the car and can damage a kart.

In practice: Two laps overlaid on the map show who uses the kerb as part of the line and who stays inside the white line.

A layout whose lap starts and finishes on the same line, so one lap runs straight into the next. Most circuits are closed.

In practice: Cross the start-finish line at Autodrom Most and the next lap has already begun.

A layout with a separate start line and finish line, and sectors in between. It times a run rather than a lap: hill climbs, autocross and rally stages work this way.

In practice: With no sector lines drawn, the whole run from start to finish is the only sector.

A layout drawn by another driver rather than supplied with the track. It carries the name of whoever made it and the date, and anyone can copy it as a starting point for their own.

In practice: A track with no official layout points you at the community ones, so the first person to record there is not drawing from scratch.

The path a car or bike takes through a corner or a whole lap to carry the most speed, not to cover the least distance. It usually uses the full width of the track: wide on entry, close to the apex, wide again on exit.

In practice: A line that is 2 m longer but lets you hold 8 km/h more through the middle of a corner is usually the faster one.

The place on the track where you first press the brake for a corner. Drivers anchor it to something fixed: a distance board, a kerb, a change in tarmac color.

In practice: Moving a braking point from the 100 m board to the 75 m board adds 25 m of full throttle. At 200 km/h that is about 0.45 s of extra straight, if you can still make the corner.

Carrying brake pressure past turn-in and releasing it gradually towards the apex. It keeps weight on the front tires, which gives them more grip to turn the car.

In practice: On a brake trace it shows as pressure that fades out over 20–40 m after turn-in, rather than dropping to zero when the steering starts.

The moment you start steering towards the apex. Turn in too early and you run out of road on exit; too late and you miss the apex.

In practice: Turning in 5 m later is the usual way to change an early apex into a late one.

An apex reached further along the corner than its geometric middle. It costs some speed on entry and buys a straighter, earlier exit.

In practice: Most useful before a long straight, where the extra exit speed is carried all the way down it.

An apex reached before the middle of the corner. The car or bike then runs wide on exit and loses the speed it gained at the apex.

In practice: It feels fast at the apex and shows up later as a lower exit speed and a slower end of the next straight.

Using the width of the track on exit, letting the car drift to the outside edge as speed builds. It is the last third of the racing line.

In practice: Two laps overlaid on the map: the faster one reaches the outside kerb with the throttle already fully open.

The front tires lose grip before the rears, so the car turns less than the steering asks for and runs wide.

In practice: In the data it shows as steering angle still rising while lateral G stays flat.

The rear tires lose grip before the fronts, so the rear steps out and the car rotates more than the steering asks for.

In practice: With phone sensors it appears as a sudden rise in yaw rate while lateral G drops.

The shift of load between tires as the car brakes, accelerates and corners. Braking loads the front, acceleration loads the rear, cornering loads the outside tires.

In practice: At 1.0 G, a 1 200 kg car with a center of gravity 0.5 m high and a 1.5 m track moves about 400 kg onto its outside tires.

The difference between the direction a tire points and the direction it is actually travelling. A tire needs some slip to generate cornering force, and past a certain angle it loses grip.

In practice: Most tires produce peak cornering force at roughly 4–8 degrees of slip, which is why a little sliding is normal and a lot is slow.

Braking and blipping the throttle at the same time with the right foot while the left foot works the clutch, so the engine revs match the lower gear before the clutch is released.

In practice: Without the blip, the driveline snatches as the clutch comes out, which can unsettle the rear axle at the exact moment the car is turning in.

Releasing the throttle without braking. Used to settle the car before a fast corner or to rotate it on entry.

In practice: A flat-out corner shows 100% throttle all the way round. A lift shows as a short dip towards zero in the throttle channel.

The reduced air resistance directly behind another vehicle. The follower needs less power to hold the same speed and can gain on the car ahead.

In practice: A close tow can add several km/h by the end of a long straight, which is often enough to try a pass at the next braking zone.

The tilt of a wheel seen from the front. Negative camber leans the top of the wheel inwards, which keeps more of the tire flat on the road when the body rolls in a corner.

In practice: Road cars usually run well under −1°. Track cars often run −2° to −4° at the front.

The angle of the wheels seen from above. Toe-in points the fronts towards each other, toe-out points them apart. Front toe-out sharpens turn-in; rear toe-in adds stability.

In practice: Toe is measured in millimeters or fractions of a degree. A single millimeter per side is enough to change how the car feels on turn-in.

The backward tilt of the steering axis seen from the side. More caster improves straight-line stability and makes the steering self-center.

In practice: Road cars run roughly 3–7° of caster, which is why the steering wheel straightens itself after a corner.

The aerodynamic force that presses a car onto the road. It adds grip without adding mass, and it grows with the square of speed.

In practice: Doubling speed quadruples downforce. A wing making 50 kg at 100 km/h makes about 200 kg at 200 km/h.

The distance between the ground and the lowest part of the car. Lower means a lower center of gravity and, with wings or a splitter, more aerodynamic effect. Too low and the car bottoms out.

In practice: On a car with a splitter, a change of 10 mm can move the aerodynamic balance enough for the driver to feel it.

A torsion bar linking the left and right wheels of one axle to resist body roll. A stiffer front bar adds understeer; a stiffer rear bar adds oversteer.

In practice: Often the first change made at a track day, because it moves the balance without touching the alignment.

The split of braking force between front and rear axles. More to the front is stable but gives up some braking performance; too far to the rear locks the back wheels.

In practice: Road cars brake roughly 70% front. Race cars with an adjuster commonly run 55–65% front.

A differential that limits the speed difference between the two driven wheels, so the inside wheel cannot spin freely when power is applied in a corner.

In practice: An open differential sends power to the lightly loaded inside wheel and the car pushes wide on exit. A limited-slip one keeps both wheels driving.

The rubber mix a tire is made of. Softer compounds grip more, wear faster and work in a narrower temperature window.

In practice: A soft compound may be a second a lap quicker than a hard one and last a fraction of the distance.

The loss of grip as a tire wears or overheats. It shows up as lap times getting slower over a stint even when the driving does not change.

In practice: Lap times drifting from 1:42.0 to 1:43.5 over 12 laps with steady sector splits point at the tires, not the driver.

Cold pressure is measured before a run, hot pressure straight after it. Pressure rises as the tire heats up, so setups are written as a hot target and the cold pressure is set to land on it.

In practice: Starting at 2.0 bar cold and finishing at 2.3 bar hot is a normal rise. Set the cold pressure to hit the hot number you want.

Everything that can be adjusted on the car, kart or bike: tire pressures, alignment, springs, dampers, bars, aero, gearing.

In practice: Change one thing at a time and write it down. Otherwise the delta between two sessions cannot be traced to anything.

First place on the starting grid, awarded to the fastest driver in qualifying.

In practice: In most series pole is set by the single fastest lap, not by an average.

The session that sets the starting order by fastest lap. Drivers usually do an out-lap, a few push laps and an in-lap.

In practice: Club qualifying is typically 10–20 minutes, so tire temperature and track traffic matter as much as pace.

The starting positions on track, usually staggered pairs of cars with a few meters between rows.

In practice: On a staggered grid with 8 m between rows, fifth row starts 32 m behind pole.

The lap before a standing start. Drivers warm tires and brakes, check the car, then reform on the grid.

In practice: Treat it like an out-lap: the time says nothing about pace.

The road alongside the track that leads to the garages and pit boxes. It has its own speed limit.

In practice: Limits of 50–80 km/h are common. A 60 km/h limit over 300 m costs about 18 s.

Pitting earlier than a rival so that fresh tires produce faster laps while the rival is still on old ones. The gap closes without a pass on track.

In practice: Fresh tires gaining 1.2 s a lap turn a 2.0 s deficit into a 0.4 s lead after two laps, if the pit stops cost the same.

A car that leads the field at reduced speed after an incident while the track is cleared. Overtaking is not allowed.

In practice: It bunches the field and removes the gaps built up over previous laps.

Danger ahead on or next to the track. Slow down, no overtaking, be ready to change line or stop.

In practice: One waved flag means a hazard beside the track. Two waved flags mean be prepared to stop.

The session is stopped. Drivers slow down and return to the pit lane or the grid.

In practice: The laps before and after a red flag are not representative, and the stop is not part of any stint.

Shown to one driver, together with their number: come into the pits at the end of the lap. It means a penalty or exclusion.

In practice: A black flag with an orange disc means the car has a mechanical problem that others can see.

A faster driver is about to lap you. Let them through at the next safe place.

In practice: At a track day, a blue flag or a pointed arm from the car behind means lift slightly and take the next straight to let them past.

The end of a session or race. After it, drivers finish the lap and return to the pits.

In practice: The lap after the chequered flag is a cool-down lap, and it will not be a good reference.

The edges of the track, usually marked by white lines. A car with all four wheels outside is beyond the limit.

In practice: In qualifying, lap times set while exceeding track limits are commonly deleted.

A format where drivers race the clock rather than each other. The fastest single lap wins.

In practice: A session is often 20 minutes with an out-lap, a few flying laps and an in-lap.

A non-competitive event where drivers pay for time on a circuit. Groups are sorted by pace and the lap times are for your own use.

In practice: A typical day is 4–6 sessions of 15–20 minutes, which is where most amateur data is recorded.

Categories by engine, age and minimum weight. The common ones: Mini for the youngest drivers, OK with a 125 cc two-stroke and direct drive, KZ with a 125 cc two-stroke and a six-speed gearbox, and Rotax Max, a single-make two-stroke class.

In practice: Lap times only compare within the same class on the same layout. The same layout can differ by seconds between classes.

How much the steel frame flexes. A kart has no suspension and no differential, so frame flex is how it manages grip, mainly by lifting the inside rear wheel in a corner.

In practice: A softer chassis generally helps when grip is low, such as in the wet. A stiffer one generally suits a high-grip track.

The ratio between the engine sprocket and the rear axle sprocket. A bigger rear sprocket gives faster acceleration and a lower top speed.

In practice: 12 teeth at the front and 78 at the rear is a 6.5:1 ratio. Moving to 76 at the rear gives 6.33:1 and raises top speed.

Choosing the fuel jets and needle position so the air-to-fuel mixture suits the air density. Too lean runs hot and can seize a two-stroke; too rich is slow.

In practice: Cold, dense morning air needs more fuel than the hot afternoon. A setting that was right at 9:00 can be lean by 14:00.

Lead weights bolted to the kart to reach the class minimum weight. Where they sit changes the balance.

In practice: The minimum weight includes the driver, so a lighter driver carries more lead.

A rental kart has a four-stroke engine of around 270 cc and bumpers, and is built to survive. A racing kart has a two-stroke engine making several times the power and is built to be fast.

In practice: On a 800 m layout, a rental kart might lap in 55 s and a racing kart in 40 s.

A start where the karts move in formation at a set speed and the race begins at the start line, rather than from standstill.

In practice: The first lap is part formation, so it is not comparable to any other lap.

The angle between a bike and the vertical. It is set by speed and corner radius: faster or tighter means more lean.

In practice: Track-day riders on road tires usually reach 40–50°. Slicks on a fast bike go beyond 55°.

Pushing the handlebar on the side you want to turn towards. The front wheel briefly points away from the corner, which makes the bike fall into the turn.

In practice: Above roughly 30 km/h it is how every rider starts a turn, whether they know it or not.

Moving your body to the inside of the corner. The combined weight of rider and bike sits lower and further in, so the bike needs less lean for the same speed.

In practice: Hanging off typically saves a few degrees of lean angle at the same corner speed, which leaves more margin on the tire.

Touching the knee slider to the tarmac in a corner. It is feedback on lean angle, not a goal in itself.

In practice: The knee often touches somewhere in the 40–50° range, but how early depends on body position as much as on lean.

A crash where the rear wheel slides, then suddenly regains grip and throws the rider over the top of the bike.

In practice: Often starts as a rear slide under power that grips again as the throttle is closed too sharply.

A crash where a wheel loses grip and the bike slides along the ground on its side. The front tire losing grip at high lean is the most common form.

In practice: Usually less violent than a highside, and it often happens with no warning at maximum lean.

The slowing effect of the engine with the throttle closed. It acts on the rear wheel only, and it is stronger on big singles and twins.

In practice: On a hard downshift into a hairpin, engine braking can make the rear wheel hop.

A sensor on the shift lever that briefly cuts ignition so the next gear can be selected without the clutch or closing the throttle.

In practice: Cut times are typically 50–100 ms. Bidirectional systems also blip the throttle on downshifts.

A clutch that partly disengages under engine braking, so a hard downshift does not lock or hop the rear wheel.

In practice: Without one, dropping two gears for a hairpin can leave the rear wheel skipping across the tarmac.

An electronic system that cuts power when the rear wheel spins faster than the front. Modern ones use lean angle from an IMU to decide how much slip is acceptable.

In practice: Most bikes offer several levels. A higher level is chosen on a wet or cold track, where the tire has less grip.

A system that reduces power when the front wheel lifts, so the bike keeps accelerating without going over.

In practice: Useful on the exit of slow corners, but if it fires early it costs time.

Electric blankets that pre-heat slick tires before a session, typically to 80–90 °C.

In practice: Without them a slick needs several laps to reach working temperature, and the first laps on a cold morning are the riskiest.

How far the suspension compresses under the rider's weight, set with preload. It decides how much travel is left and how the bike sits.

In practice: Rear sag of around 30 mm with the rider aboard is a typical track starting point.

A sensor package with accelerometers and gyroscopes measuring acceleration and rotation on three axes. It is what produces lean angle, pitch and yaw rate.

In practice: Every modern phone has one; Vetkuro reads it at 25 Hz. Akso, our own logger, samples its IMU at over 200 Hz.

A named part of the lap, bounded by fixed points on the track. Sector boundaries come from the layout, so they are identical for every driver and every session.

In practice: Autodrom Most has one sector line, at 2 472 m. Sector 2 of the session best lap on 9 October took 45.885 s.

The time taken to cover one sector. Reading splits instead of lap times turns one number into one per sector.

In practice: 1:58.333 and 1:57.838 are half a second apart. The splits say where: 0.071 s of it in sector 1 and 0.424 s in sector 2.

How far ahead or behind you are compared to a reference, measured at the same point on the track. Negative means faster, positive means slower.

In practice: After T4-T5-T6, lap 9 was +0.208 s against lap 4. By the finish line it was −0.495 s, the session best.

The lap everything else is measured against. Usually your best clean lap of the session; sometimes your theoretical best.

In practice: Referencing a lap that caught traffic gives you a dramatic delta curve and nothing to learn from.

The sum of your fastest zone times from a session, treated as one lap. Every part of it was driven, just not consecutively.

In practice: On 9 October at Autodrom Most, twelve zones add up to 1:56.986, 0.852 s under the best lap of the session.

Your fastest completed lap on a given layout. Not the same as your theoretical best, which was never completed as one lap.

In practice: A PB is what you tell people in the paddock. The theoretical best is what you work on.

Lining laps up by how far around the lap they are rather than by how much time has passed, so the same corner sits at the same position on every lap.

In practice: At 2 100 m two laps are at the same braking point. At 57 s they are at two different corners.

Working out where one lap ends and the next begins, from your position crossing the finish line of the layout. No beacon and no transponder required.

In practice: It is also what makes LapNumber, LapTime and Sector exist as channels. All three are computed from position.

A small radio device fitted to a kart, bike or car and read by a loop buried at the finish line. It produces the official lap time.

In practice: Transponder times are the official result. Laps detected from GNSS are for your own analysis and can differ from them, by less the faster the receiver.

A section of the lap covering one corner, or the straight between two of them; corners taken on one braking count as one zone. Vetkuro derives the boundaries from laps actually driven on the layout, so a zone spans the corner the way drivers take it: it opens before the braking point or at the turn-in, whichever comes first, and closes where the car has stopped both accelerating and cornering. Zones are finer than sectors, the set is the same for everyone on that layout, and none of it is drawn by hand.

In practice: Autodrom Most has twelve zones. T4-T5-T6 is one of them: three corners taken on one braking are timed together, because splitting them would compare nothing.

A short line across the track where one zone ends and the next begins. Gates are placed by Vetkuro from laps that were driven rather than by hand, and every zone time is measured between two of them.

In practice: Autodrom Most is cut at twelve gates, so a lap there has twelve zone times.

All the gates for one layout, carrying a version number. When Vetkuro has seen enough laps to place them better it publishes a new version, and sessions are timed again against it.

In practice: While a set is still provisional the analyzer says so, because the zone times can move when the session is processed again.

How many times per second a device records a value. It sets the resolution of everything downstream: line, delta, sector split.

In practice: At 180 km/h, 10 Hz means 5.0 m between recorded points and 25 Hz means 2.0 m.

Global Navigation Satellite System, the umbrella term for GPS, Galileo, GLONASS and BeiDou together. Receivers using several constellations get a fix faster and hold it better.

In practice: “GPS” is one American constellation; most modern receivers are GNSS receivers using three or four.

A measure of how favourably the visible satellites are arranged. Low is good. It describes the geometry of the fix, not the receiver's quality.

In practice: Under a grandstand or a bridge, HDOP rises and your line starts to wander even though nothing changed in the car.

The standard text protocol GPS receivers use to report position, speed and satellite status. Because it is standardised, generic receivers work without device-specific code.

In practice: Vetkuro's generic BLE profile accepts any receiver that broadcasts standard NMEA 0183 sentences.

The diagnostic port fitted to essentially every car built from 2008. An adapter reads engine data from it, but which values are available is decided by the car.

In practice: RPM and throttle position are near-universal. Brake pressure and gear are not.

The command set almost all consumer OBD-II adapters speak. An app talks to the chipset, the chipset talks to the car.

In practice: Carista, vLinker and NEXAS adapters all speak it, which is why one integration covers several products.

Acceleration expressed in multiples of gravity. Lateral G is cornering load, longitudinal G is braking and acceleration.

In practice: A road car on decent tires reaches roughly 1.0–1.2 G lateral. Braking peaks are often higher than cornering peaks.

Vetkuro's own session file. It holds the raw sample stream with timestamps, so the session can be re-analyzed later without loss.

In practice: The VTF is written on the phone first, then synced. That is why a session survives a track day with no signal.

One named stream of values through a session: speed, throttle position, coolant temperature. Every channel carries a unit, a source, and a rule for what happens where samples are missing.

In practice: A session is a bundle of channels sharing one distance axis. “Throttle” is a channel; so is “SatelliteHDOP”.

A channel nobody measured directly. It is computed from channels that were. Lateral G, lap distance and turn radius are all derived.

In practice: A derived channel is only as good as its inputs, which is why it declares what it was computed from.

In telemetry software generally, a channel a user defines with their own formula over existing channels. The term belongs to the industry rather than to any one tool.

In practice: Not the same thing as a derived channel: a derived channel is computed by the tool, a math channel is computed by you.

Putting channels that arrived at different rates onto one common base, so their values can be read at the same point on the lap.

In practice: A GPS receiver, an OBD adapter and a heart-rate strap never share a timestamp. Resampling is what makes one cursor meaningful.

Estimating a value between two recorded samples. The right method depends on the quantity: continuous values interpolate in a straight line, angles have to wrap around zero, and discrete values must not be interpolated at all.

In practice: Halfway between gear 3 and gear 4 is not gear 3.5. A gear is held until the next real sample arrives.

A graph of speed against distance around the lap. Each corner shows as a valley, and the laps can be overlaid to compare them.

In practice: The depth of a valley is minimum corner speed. Its width shows how long you braked and how early you got back on the throttle.

The lowest speed in a corner, usually at or near the apex.

In practice: 3 km/h more at the apex before a long straight is carried to the end of the straight.

Brake pressure, or brake on/off, against distance. It shows where you braked, how hard, and how it was released.

In practice: Brake pressure is not on standard OBD-II. Many setups only know on or off, or infer braking from deceleration.

Sideways acceleration, the load you feel in a corner. The sign shows the direction of the turn.

In practice: Peak lateral G at the apex shows how much of the tire's grip you were using.

Acceleration along the direction of travel. Negative under braking, positive under power.

In practice: Braking peaks of 1.0–1.5 G are normal for a car on good tires. A kart is closer to 1.0 G.

Any device that records sensor values against time. A phone, a dedicated GNSS unit and a car's ECU all do it.

In practice: They differ in what they record and how often: a phone typically gives GPS at about 1 Hz, an external receiver 10 to 25 Hz.

Speed, g-force and lap timing drawn onto the video frame itself, so the numbers travel with the clip instead of staying in the app.

In practice: A lap exported with the overlay carries the speed dial, the g-force box and the running lap time, laid out wide or tall to match the clip.

The offset between a video's own clock and the session's. Set it once and the player, the map and the graphs all land on the same moment of the lap.

In practice: A camera started before the out lap needs that shift applied, or the braking point on screen arrives before the one on the trace.

Two ways of encoding brightness in video. HDR holds a wider range and looks right only where the player understands it; SDR is the one every player understands.

In practice: Vetkuro converts HDR footage to SDR when it renders an overlay clip, so the export looks the same wherever you post it.

How much data a video spends per second. Raise it and fine detail survives compression; lower it and the file is smaller, but kerbs and tarmac turn to mush in a fast pan.

In practice: A higher bitrate on export keeps the overlay's thin digits legible while the camera is panning hard.