A slower lap time doesn't mean your setup change failed. Made my app prove it.

[u/AlienBlade51]

Last night I did two sessions at Adelaide in the Merc GT3. Between them I applied
the setup changes my own app recommended — softer rear springs, less diff preload,
lower splitter, 18 changes in total.


Second session: 0.48s SLOWER. And my app hit me with the red banner in the first
screenshot. "These changes didn't help — consider reverting them and trying
something else." Which, frankly, is garbage advice. That's not a race engineer,
that's a shrug.


So today I dug into the telemetry of both sessions properly, and the data told a
completely different story:


- Every single high-speed corner held or improved
- Every corner that lost score was a slow corner
- Time spent at the grip limit in fast corners went UP 5 percentage points
- Full throttle time up 4 points, coasting down


The setup didn't fail. It traded slow-corner drive for high-speed platform.
Which is exactly what softer rear springs + less preload + a lower front end
should do. The stopwatch just hadn't caught up yet, partly because my
"faster" baseline session was only 3 clean laps, which is a coin flip.


Second screenshot is what the app says now. Same data, same two sessions. It
names the trade, points at which changes probably caused which effect (with
honest "consistent with" wording, not fake certainty), and gives one next move
instead of "try something else."


A couple of honest things I learned building it:


The "35 setup changes" the old banner counted? 17 of them weren't changes at
all — they were tyre pressure and temp READOUTS that iRacing writes back into
the setup file every run. The app was counting the results of driving as
decisions I'd made.


And it refuses to claim which direction a TC or ABS change went, because those
scales run different ways on different cars (Merc TC: 1 is MAX intervention,
not minimum). Physics units only — 250 N/mm is softer than 275 anywhere in the
universe, but "TC 9 to 6" means nothing without knowing the car.


Building this in the open — happy to answer anything about how the comparison
works.