Guides
Lap delta explained
Lap delta is the running time difference between your current lap and a reference lap, measured at the same point on track rather than at the same moment in time. A delta of -0.4 means you are four tenths ahead of the reference where you are now. Unlike a lap time, it tells you where on the circuit you gained or lost, which is what makes it useful for improving.
What it actually measures
A lap time tells you the session was three tenths slower. It does not tell you where.
Lap delta does. It compares your current lap against a reference lap at the same point on the circuit, and reports the running time difference. Stand at the exit of turn three and the delta says how much time you have gained or lost by the time you reach that spot, compared to the reference lap at the same spot.
The critical detail is that the comparison is by position, not by time. Two laps do not take the same duration, so comparing them second by second would be meaningless. Comparing them metre by metre is what makes the number useful.
Reading the sign
Conventionally:
- Negative: you are ahead of the reference. A delta of
-0.4means four tenths up. - Positive: you are behind.
Because a minus sign is easy to misread at 140 mph, overlays add colour: green when you are ahead, red when you are behind. TrackHero does this, and shows your current personal best alongside the running delta.
Why it beats a lap time
Lap times are a scoreboard. Delta is a diagnosis.
Watching the delta through a lap tells you the shape of your driving. A number that sits flat through the fast sections and climbs steadily through the infield says your problem is slow corners. A number that spikes at one specific braking point says you have one corner to fix, not a general lack of pace.
That is why it is worth having on the video. Reviewing footage afterwards with a delta on screen shows you the exact moment the time went, in a way that a lap time at the end never can.
Reading it properly
Watch the trend, not the instant. Delta is derived from position, so wherever positional accuracy is weakest the number gets noisy. Slow corners are the worst case: at 40 km/h a couple of metres of GPS error is a meaningful fraction of a second. Judge a corner by how the delta changes across it, not by the value at one frame.
A gain has to come from somewhere. If the delta drops through a corner, you were quicker through it. If it drops on the following straight, the real gain was the exit speed out of the corner before. Time appears on the straight; it is earned at the apex.
Compare like with like. Against your own best lap in the same session, the comparison is clean: same car, same tyres, same track temperature. Against a lap from a different day, the difference may say more about conditions than about driving.
What your data needs
A delta needs a reference, which means more than one lap in the file.
This trips people up when exporting. If you export only your best lap from RaceChrono, there is nothing to compare against and the delta gauge has nothing to show. Choose All laps at export time.
You also need position data good enough to locate you consistently on the circuit. A 10 Hz logger is workable; 25 Hz is noticeably smoother. Both work, and higher rates simply make the number steadier.
On your video
TrackHero renders a live delta into the footage, against your best lap in the session, green when you are up and red when you are down, with your current PB shown alongside. It sits next to the lap overview, which shows your last four laps with outlap and inlap badges and your fastest highlighted.
To set it up, see how to add a telemetry overlay to track video.
Last updated .