Aug 15–16, 2026 · G29 Z4 M40i · HPDE, instructing Taylor Whatley
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.
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).
Chin 1 · canon row 1 · downhill, banked
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.
Chin 2/3 · canon row 2 · the double apex, one 247° arc
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.
Chin 4 · canon row 3 · the crest, top speed of the lap
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.
Chin 5/6 · canon row 4 · biggest single gain in May: −0.775 s
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.
Chin 7 · canon row 5 · "a non corner, just a bend in the straight"
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.
Chin 8 · canon row 6 · entry to the Museum complex
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.
Chin 9 · canon row 7 · T7a "Mount the curb", T7b the sharp apex
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.
Chin does not number this · canon row 8 · lowest point on the circuit, 181.7 m
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.
Chin 10 · canon row 9 · left-right chicane, climbing
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.
Chin 11 · canon row 10 · ends far left
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.
Chin 12 · canon row 11 · first half of the double brake zone
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.
Chin 13 · canon row 12 · the compression at the low point
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.
Chin 14/15 · canon row 13 · second-biggest gain: −0.757 s
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.
Chin 16 · canon row 14 · slowest point, highest point
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.
Chin 17 · canon row 15 · onto the front straight
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.
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:
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.
Taylor Whatley · novice · 2020 M4, car #33. More power and more weight than he can use yet, on a track with six blind apexes.
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.