Aug 15–16, 2026 · G29 Z4 M40i · HPDE, instructing Taylor Whatley
Target
1:41.x
Theoretical best from today's own segments: 1:41.40. Every piece has been driven already.
PB — new today
1:42.70
L22, session 2. Beat the old 1:43.910 by 1.21 s.
Tires
~15 cycles
RE-71RZ set entering the falloff band. Grip from here is borrowed.
Fast laps
Done
Session 3 is T5 and T15 only — don't re-drive the whole lap.
Weekend live
Newest last. This section grows as sessions land.
Sat · Session 1Pressure lessonFIXED IN-SESSION
Started 30 F / 29 R cold. They came up to 40 / 39 hot and the car went loose — that is 10 psi of build, well past the window. Bled to 32 / 30 mid-session and the lap immediately responded: 1:44.789 (L14).
The data said the same thing before the seat-of-the-pants did: the fast right-handers T9 and T10 were collapsing — the corners that need a big, flat contact patch are exactly the ones over-pressure ruins first. T9 min speed was 87.0 mph on L14 against 91.1 mph later in the day; T10 was 83.4 mph against 88.8 mph.
Hot target set at 34 F / 32 R. Set cold to land there, don't chase it hot.
Sat · Session 21:42.70 — new PBPB · −1.21 s
L22. Old PB 1:43.910 (April). Beaten by 1.21 s, and backed up — L24 1:44.14, L26 1:44.19, L25 1:44.45, so the pace is real and repeatable, not one hero lap.
The star was T7: +14.7 mph over the M440i baseline (74.4 vs 59.7), and it found 0.20 s between session 1 and session 2 alone — the biggest single session-on-session gain anywhere on the lap. The brief said take it faster than most do; you did. T11 backs it up at +12.6 mph and T4 at +8.6.
Theoretical best from today's own segments: 1:41.40. Sum of your best 15 corner windows and 10 connecting straights across 18 flying laps — every piece of a 1:41 has already been driven today, just not on the same lap.
Sat ~11:00 CT · Session 3Assignment: two corners, nothing elseNEXT OUT
The lap is done except for two places. Everything else is at or under the M440i baseline and inside 0.1 s of your own session best — leave it alone.
1 · T5 Charlotte's Web — the only corner still slower than the baseline. 38.0 mph on the PB lap against the M440i's 40.5 mph: −2.4 mph, and the only positive window delta on the card (+0.128 s). You already ran 43.4 mph through it today on a slower lap, so the speed is available and you are choosing not to take it on the quick ones. This is a trail-brake release problem, not a courage problem — you are off the brake too early, the car sets on the off-camber and pushes, and you wait it out. Carry the release deeper toward the apex and let the rotation come from the pedal.
2 · T15 exit onto the front straight — the largest self-gap on the lap. The corner itself is fine (+3.9 mph on baseline), but the segment from T15 track-out to start/finish ran 5.23 s on L22 against 4.75 s best today — +0.48 s, bigger than any other gap by a factor of two. T15 was also the one assigned corner that did not improve between sessions (window 5.64 s vs 5.56 s in S1, min speed down 1.2 mph). Get the exit right and the straight pays you twice. Set up further right through T14a, then earliest possible throttle and use the exit curb.
The one idea
The 6.1 seconds in May came from minimum speed, not from braking later. Chase the same thing in the Z4.
Between Saturday morning and Sunday afternoon at Barber the M440i went 1:52.10 → 1:45.99. Minimum speed rose at all 15 corners, from +1.0 mph to +13.8 mph. The brake point moved meaningfully later at exactly one corner. Peak grip usage — p99 lateral g — went 0.89 → 1.18. Same car, same tires, same track.
Six of those seconds were found inside the 15 corner windows; 1.33 s on the straights. The instruction that transfers to the Z4 is U, not V: smooth deceleration in, smooth acceleration out, and no coasting plateau in the middle. Throttle pickup moved earlier at 9 of 15 corners.
Barber agrees. The coaching corpus says the same thing independently: sustained minimum corner speed matters more here than late-and-hard braking, and a V-shaped speed trace is the tell that you over-slowed. Paraphrased from Apex Pro Track Coach — see Sources.
Numbering. Cards below lead with the JTI label — the numbering on the map JTI hands you, and the one everyone in the paddock will be speaking this weekend. The grey line under each gives Chin's club numbering and the canon row index the data is actually keyed on. The three do not line up: JTI carries 18 labels to Chin's 17 because JTI numbers the T7b track-out and Chin does not, and JTI splits T7 into T7a/T7b. From the crest onward the canon row index runs one lower than the JTI label. Charlotte's Web is JTI T5 (Chin 5/6, canon row 4) — if an analyst hands you "T4", check which scheme they meant.
New this week — measured camber
LiDAR-derived cross-slope and elevation for all 15 corners landed Thursday (TDAI-124), fitted along your own 5/31 lap at 5 m spacing, 2.84 cm median plane-fit residual. Three things worth carrying in your head:
T8 is the sharpest off-camber reading on the lap — −6.36 % at entry, at the circuit's lowest point (181.7 m), and you arrive already unloaded off the T7a/T7b drop. It has never been on your list. Put it there.
There is a crest at 645–675 m that nothing names — −0.35 g, the single most car-lightening feature at Barber, on the climb between the T2/T3 double apex and T4, attached to no canonical corner.
T1, T2/T3, T7a/T7b, T14a and T15 are properly banked (+6.0, +9.1, +8.9, +7.6, +6.1 %). The bank is real grip. Trust it and stop treating T1 as a slow corner.
Corner by corner
Min speed = best-of-5 from the 5/31 M440i laps. Green = the gain that lap set found over Saturday morning. Camber: + is on-camber (inside low).
T1Left · 215 m
Chin 1 · canon row 1 · downhill, banked
ON-CAMBER +6.0%compression
Min speed
69 mph
May gain
+5.1
The bank rises monotonically to +6.0 % at the apex — you arrive with more grip than it feels like you have. Brake a touch earlier and lighter, release quickly after turn-in, carry it. A V-trace here means you over-braked. Track all the way out.
T2/T3Right · 415 m
Chin 2/3 · canon row 2 · the double apex, one 247° arc
ON-CAMBER +9.1%BLIND APEXcompression
Min speed
52 mph
May gain
+3.0
Window
−0.54 s
Second-highest bank on the lap. In May the whole gain came from throttle pickup moving 121 m earlier — from 110 m past the apex to 11 m before it. That is the change to repeat. One long arc, not two corners. Exit lands you on the climb.
T4Right · 900 m
Chin 4 · canon row 3 · the crest, top speed of the lap
≈FLAT −0.5%BLIND APEXlong gentle crest
Min speed
73 mph
May gain
+4.3
Elevation maximum 196.7 m and no brake event at all on the best lap — Saturday morning had one. Set up right, apex just past the crest. The car unloads −0.16 g at speed; the crest is long and gentle, so it is a float, not a bang. Don't add steering while it's light.
T5Left · 1055 m · Charlotte's Web
Chin 5/6 · canon row 4 · biggest single gain in May: −0.775 s
OFF-CAMBER −1.76%compression
Min speed
43 mph
May gain
+4.9
Peak lat g
0.8 → 1.1
Z4 April
41.6 mph
The textbook case for the whole brief. Brake point essentially unchanged (69.2 m → 67.6 m before apex); the 0.775 s came from entry 65.2 → 69.6 mph and mid-corner grip 0.8 → 1.1 g. Pure mid-corner commitment. LiDAR confirms it is off-camber from 1030–1070 m, worst at 1050 m — five metres before the apex, which is exactly where it will try to push. Threshold-brake in a straight line, then trail the release into the rotation; releasing before turn-in is the classic understeer here. Exit is uphill: wait for the second apex, then commit to full throttle.
LIVE · SAT S238.0 mph on the 1:42.70 against the M440i baseline's 40.5 mph — −2.4 mph, the only corner on the lap still below baseline, and the only positive window delta (+0.128 s). Best today was 43.4 mph on a slower lap, so the grip is there. Session 3 target #1.
T6Right · 1400 m
Chin 7 · canon row 5 · "a non corner, just a bend in the straight"
NEUTRAL −0.2%flat
Min speed
94 mph
May gain
+2.1
Flat, no brake event, 0.2 g. Nothing to do here but be already positioned for the T7 brake zone. Camber sign on a near-straight is not meaningful — ignore the badge.
T7Right · 1630 m
Chin 8 · canon row 6 · entry to the Museum complex
ON-CAMBER +2.3%crest
Min speed
63 mph
May gain
+5.3
Window
−0.43 s
Take it faster than most do. Brake only enough to make T7, then hard again before T7a. The corpus is blunt that over-slowing this entry is the #1 time loss in this section — soft and early, hover the pedal at the apex curbing rather than a late stab. If you get to full throttle easily before T9, you over-slowed.
T7a/T7bRight · 1745 m
Chin 9 · canon row 7 · T7a "Mount the curb", T7b the sharp apex
ON-CAMBER +8.9%BLIND APEXcrest, −6.2 m to apex
Min speed
44 mph
May gain
+5.2
Peak lat g
1.1
Third-highest bank on the lap (+8.9 %) and it drops 9.8 m from entry to exit. The bank is what lets you carry 43.5 mph through a sharp apex — use it, get throttle before the apex as the best lap did (pickup 13.8 m early). Then remember what you are handing the car into: T8.
T8Left · 1880 m · the track-out
Chin does not number this · canon row 8 · lowest point on the circuit, 181.7 m
OFF-CAMBER −6.36% AT ENTRYflat
Min speed
70 mph
May gain
+3.2
Exit
89.0 mph
The new finding, and the one to actually change something about. The sharpest off-camber reading anywhere on the lap sits at 1825–1835 m — right at the T7b track-out — at −6.36 %, and it is the lowest point of the circuit, so the car arrives unloaded from the T7a/T7b drop with the inside edge high. Historically you carry ~70.2 mph through here with no real brake event and treat it as track-out, not a corner. In the lighter Z4 that combination — unloaded, off-camber, 70 mph, running to the left edge — is where a snap would come from. Don't add mid-corner steering here; unwind and let it run out. This is the one place this weekend where the instruction is caution, not commitment.
Set up right and take T9/T10 as straight as possible. Run the whole left curb with the left-side tires at the edge; don't grab too much apex curb, it costs more than it feels like it gains. No brake event on the best lap. The lat-g jump 0.5 → 0.8 is the whole story: this got faster by being straighter, not braver.
T10Right · 2190 m
Chin 11 · canon row 10 · ends far left
ON-CAMBER +1.1%BLIND APEXflat, climbing
Min speed
85 mph
May gain
+7.5
Second-largest min-speed gain of the day and the brake event disappeared entirely (36 m before apex on Saturday, none on the fast lap). Banking at entry helps rotation and then fades — so late apex and let it run to the far left on exit. In the Z4 this should be flat.
T11Left · 2560 m
Chin 12 · canon row 11 · first half of the double brake zone
ON-CAMBER +2.8%flat
Min speed
82 mph
May gain
+13.8
Brake pt
63 m earlier
Window
−0.57 s
The clearest technique change of the weekend, and the one exception to "don't brake earlier." You moved brake application from 93 m to 156 m before the apex — 63 m earlier — but far lighter, and min speed went 68.6 → 82.4 mph, the biggest jump on the lap. Window time 3.43 → 2.86 s. What changed was the concept: you stopped treating T11 as a corner and started treating it as the setup for the real brake zone at T12. Brake early, brake gently, get it done, arrive at T12 straight and positioned. Do this from lap one Saturday — it is a decision, not a skill.
T12Right · 2675 m
Chin 13 · canon row 12 · the compression at the low point
NEUTRAL +0.2%BLIND APEXcompression +0.27 g
Min speed
63 mph
May gain
+1.0
Peak lat g
1.0
This is the second brake zone T11 exists to serve. LiDAR puts the elevation minimum at 192.09 m at 2640 m with +0.27 g of compression from 2630–2680 m: the track hands you grip right where you need it — brake hard into the squat, then climb to the apex. Apex flat-camber, so the bank does nothing for you; the compression does. Aim two-thirds to three-quarters through the right curb. Early entry makes you cut the steep curb and unsettles the car. Smallest min-speed gain of the day (+1.6) — there is time still sitting here.
Almost flat out across the flat curbing, then a 9.06 m climb from apex to exit — the biggest single elevation change on the lap. 1.17 g at 78 mph with no brake anywhere in it on the reference lap. Camber builds to +6.3 % through the arc and the compression at 2840–2890 m adds another 0.28 g of load: it takes more than it looks like it will. Use the whole apex curb. If the car drifts between here and T15, lift slightly to settle rather than correcting with steering.
T14aRight · 3050 m
Chin 16 · canon row 14 · slowest point, highest point
ON-CAMBER +7.6%crest, 203.5 m
Min speed
50 mph
May gain
+5.8
Window
−0.52 s
Hard right at the top of the hill — the slowest point on the lap at the highest point. Brake point identical both days (47.8 m before apex, to the metre); the 0.518 s came from min speed 70.3 → 79.7 and throttle pickup moving 41 m earlier, to the apex itself. Fourth-highest bank on the lap at +7.6 %. Same brake point, more commitment, earlier throttle — the T5 lesson, applied at the other end of the lap.
T15Left · 3210 m
Chin 17 · canon row 15 · onto the front straight
ON-CAMBER +6.1%flat, −6.6 m drop
Min speed
64 mph
May gain
+6.5
Peak lat g
0.8 → 1.1
Banked +6.1 % and dropping. Peak lat g went 0.8 → 1.1 here in one day — biggest grip-usage jump on the lap, and it is the corner that pays twice because it sets the whole front straight. The further right you are through T14a, the better this is. The exit curb is very usable and most people leave it alone. Compromise the entry if that is what buys the earliest throttle.
LIVE · SAT S2The corner is fine — 65.6 mph, +3.9 mph on baseline. The exit is not: track-out to start/finish ran 5.23 s on the PB lap vs 4.75 s best today — +0.48 s, the largest single self-gap on the lap. Also the one assigned corner that did not improve S1→S2 (5.64 s vs 5.56 s). Session 3 target #2.
Between sessions — the data loop
Laps land in tdai_scratch.barber_aug2026_weekend_laps. The per-corner comparison against the May baseline is one query away — chat runs it in the paddock between sessions and hands back a ranked list.
What to ask for, in order of usefulness:
Min speed by corner vs the 5/31 best-of. The one number that matters. Anything below the M440i's figure in a car 600 lb lighter is a corner you are leaving alone.
p99 lateral g for the session. Your summary stat. 1.18 was the May ceiling; April's Z4 sat at 1.19. Under 1.10 means you are not using the tire yet.
Corner window time delta, ranked. Tells you which two corners to spend the next session on. Don't work on more than two.
T8 and T12 specifically — the two with the most theoretical room, for opposite reasons.
Caveat on the April Z4 numbers: those sessions logged at ~1.05 Hz, one fix every 30–40 m, so the sampler usually misses the true apex minimum. Per-corner Z4 min speeds from April are an upper bound, not a comparable baseline. Compare at lap level, or compare this weekend's 25 Hz data against May's 25 Hz data. Don't diff April corner numbers against anything.
Instructing Taylor
Taylor Whatley · novice · 2020 M4, car #33. More power and more weight than he can use yet, on a track with six blind apexes.
Blind apexes are a seat-time problem, not a bravery problem. T2/T3, T4, T7a/T7b, T10, T12 and T13/T14 all hide the apex from the braking reference. Tell him that up front so he doesn't read his own inconsistency as a lack of commitment. Reps build the visual reference; nothing else does.
T5 Charlotte's Web is the one to be conservative at. Off-camber, downhill approach, the primary passing zone, and the corner that most tempts a novice into too much entry speed. Threshold braking in a straight line first; rotation later in the weekend.
T8 deserves a specific warning. Chin's numbering skips it entirely, so it may not appear on whatever map he's holding; it's the sharpest off-camber point on the lap, and it comes at 70 mph immediately after a drop. Frame it as "track-out, hands unwinding" rather than as a corner.
In an M4, T7 entry is where he'll lose the most time — over-slowing it is the corpus's #1 listed mistake and a heavy, powerful car makes it worse. Soft and early beats late and hard.
Give him one thing per session. Your own six seconds came from a single concept applied fifteen times, not fifteen fixes.
Managing your own weekend around it: instructing eats the sessions where the tires are best. Your fast laps are Saturday morning — go get the time before the teaching load and the heat cycles both build. By late Sunday the RE-71RZs are past 15 cycles and into falloff; when the lap times stop responding, that is the tires, not you. Don't chase it with setup changes at the track.