Read the bike IFs Keiro returns for Tilda, Mark, and John on Lake Placid: 0.70, 0.66, 0.56. Low. By 70.3 standards, conservative. By a full-distance standard, what you'd ride if you had headroom. None of the three has any. The climbing has spent it for Tilda and Mark; the climbing and seven and a half hours of pedalling have spent it for John.
Here's the course, in race order. The swim is 3,853 m, two loops of Mirror Lake — calm freshwater, water 21 °C, wetsuit-legal historically (Keiro flags it legal but credits no buoyancy bonus in the model — the swim time stands on stroke speed and CSS). The bike is 179.4 km and 2,134 m of climbing across two loops through the Adirondacks. Each lap contains two long, low-gradient sustained climbs — roughly 16 km from the village out and 7.5 km on the inland return — averaging 0.8–1.0 %. The one sharp negative pitch is the Keene descent at km 51.4, averaging −6.1 % over a few hundred metres. The dozens of trivial rollers in between are statistical noise; the two long climbs and the one sharp descent are the day's structure. The run is 42.9 km with 311 m of climbing, two laps through the Olympic village.
We ran three athletes through Keiro's full-race simulation — which models the swim, bike, and run together to find the execution that produces the fastest finish, not the fastest bike split.
Athlete comparison
| Tilda | Mark | John | |
|---|---|---|---|
| FTP | 220 W (3.55 W/kg) | 260 W (3.33 W/kg) | 210 W (2.50 W/kg) |
| CSS | 1:35/100 m | 1:40/100 m | 2:05/100 m |
| Run threshold | 4:15/km | 4:25/km | 5:15/km |
| Bike NP | 153 W | 172 W | 117 W |
| Bike IF | 0.70 | 0.66 | 0.56 |
| Bike VI | 1.022 | 1.019 | 1.027 |
| Bike TSS (% of budget) | 265 (80 %) | 245 (74 %) | 229 (69 %) |
| Bike split | 5:26:55 | 5:33:54 | 7:24:20 |
| CdA (aero) | 0.280 | 0.299 | 0.337 |
| Run intensity | 80 %T | 77 %T | 75 %T |
| Run pace | 5:22/km | 5:50/km | 7:25/km |
| Run split | 3:50:29 | 4:10:40 | 5:18:43 |
| Run TSS (% of budget) | 240 (109 %) | 239 (109 %) | 265 (121 %) |
| Finish | 10:36:06 | 11:06:39 | 14:22:09 |
CdA values are aero-position estimations — the simulation separately models time spent upright for cornering and on steep climbs using grade-based position switching. Run TSS budget is the athlete's own run TSS ceiling (220 nominal for an experienced age-grouper); all three plans exceed it.
Look at the bike IFs and read them at face value. 0.70 reads as comfortable. 0.66 reads as soft. 0.56 reads as a recovery ride. For a competitive full-distance bike, these are the numbers you'd ride if you had headroom to spare. Placid means them.
The IF looks low because the course doesn't allow anything else. 2,134 m of climbing across 180 km, distributed in two long sustained climbs per lap, doesn't let you spend the flat sections at 0.78. Keiro picks the highest IF the climbing will accept, and at Placid that ceiling is structurally low — not because Tilda and Mark are being conservative but because the climbs return diminishing time-per-watt above it. Push above the climb target and you've banked seconds and spent minutes off the run.
For John there's a second compression on top of the same terrain cap. His bike takes 7:24:20 — ninety minutes longer than Tilda's. TSS scales with intensity and time together, so the same IF held for ninety extra minutes is meaningfully more TSS. The plan drops his IF to 0.56 — the lowest of the three — not because his climbing is gentler but because anything higher, held for that long, arrives at T2 with a run that won't finish. Terrain compresses everyone's ceiling here; for John, his seven-and-a-half-hour bike compresses it a second time, because TSS accrues with every extra minute in the saddle.
The cost shows in the TSS, not the IF. Tilda banks 265 TSS on the bike, Mark 245, John 229 — and Tilda's is about 80 % of what she can spend and still run. The reason her IF can't go higher isn't that she's coasting; it's that the climbing has already filled most of the day's account at a number that reads like she's holding back.
Some courses cap the bike through heat. Others let you ride hard because nothing external limits you. Placid does neither — the terrain caps you low, and the easy number lies about how much is left.
Heat is a secondary, stacked limiter, not the lead. Keiro ran the race-time profile at 22.9 °C with a soft heat advisory and an IF-ceiling reduction of 8.5 % for Tilda, 9.2 % for Mark, and 10.9 % for John. Real, but not the structural cap. The mountain is.
And the run arrives over budget. Read the Run TSS row in the table above: 109 %, 109 %, 121 %. All three athletes start the marathon already past their own run-TSS ceiling, carried by bike fatigue — not because the bike was over-ridden, but because there is no execution that brings them in under. The flat-course intuition — "ride conservatively to protect the run" — doesn't have an analogue here. Conservative still arrives over budget. The plan's job is to land the run in the smallest deficit, not to avoid it.
The two long sustained climbs are the first trap, and the most expensive one. Each is fifteen-plus minutes of low-gradient riding — long enough that ten watts over plan feels like nothing, short enough that you'll be back on the flat before the cost registers. None of the day's signal will tell you it happened. The TSS account drains on the climbs and the receipt arrives on the run two hours later, at lap two of the marathon.
Plan-Target Power Over the Bike Course
The Keene descent at km 51.4 (and again on the second loop) is the day's only sharp negative pitch. The plan asks for descent power — Tilda 131 W, Mark 146 W, John 96 W — and the reason matters. Time-per-watt is collapsing on a −6 % gradient; the next ten watts buy you nothing measurable in elapsed time, and they're the ten watts you needed at the climbing return that follows. Treat Keene as recovery, not free speed. Sitting up before the bottom makes the descent target easier to hit by default.
Course Gradient — Where the Bike Climbs and Descends
Each 500 m of the bike course coloured by its mean gradient. The chromatic story is the descents and the kicker pitches — Keene's −5 to −6 % near km 51 and km 141, and scattered 5–7 % kickers along the rolling sections. The two sustained climbs don't appear as broad terracotta bands because they net 0.8–1.0 %, below the strip's 1 % colour threshold. That visual silence is the first trap: the climbs don't look like climbs on a gradient scale, which is why the TSS cost arrives at the run without warning. The steepest single drop on the course is a sub-kilometre −12 % pitch at km 43, ahead of the second sustained climb — a separate feature from the longer Keene descent at km 51.4. Both are descents, not hidden steep climbs. Dashed line at the loop boundary marks the two-lap split.
The third trap is the two-lap run starting over budget. Run TSS over the run's own ceiling means the marathon's structure has to be re-framed: lap one isn't a "save energy for the second half" decision — that's the conservative-bike instinct, and it doesn't apply when the second half is already the harder one by the plan's accounting. Lap one at plan pace, lap two on what's left, and the goal of lap one is to leave lap two as cleanly as possible, not to add to it.
This is a typical-July characterisation from 2019–25 Visual Crossing data, not a race-week forecast — plans refresh as the forecast firms up. Expect around 21.6 °C through the day (range 8.7–28.6 °C across the dataset), wind near 10 km/h from the south/SSE, 69 % humidity, water about 21 °C and wetsuit-legal. Keiro's race-time profile sits a touch warmer than the average at 22.9 °C with 77 % humidity, triggering a soft heat advisory and the IF-ceiling reduction noted above. Heat is real here; it's not the day's structural limiter. Wind is light enough not to redistribute the bike plan — no chart for it.
Most of what matters has been decided. FTP isn't moving, CdA isn't moving, and the course isn't getting flatter. A few things still are.
Believe the low IF. The number on the head unit will read as if you have headroom — at km 30, into the climb, holding 153 W on a power meter, the legs will say the plan is too soft. The plan accepts the asymmetry between what feels available and what the day will tolerate. Riding the watts, not the feel, is the single most important call this course asks the rider to make.
Descend Keene at descent target, both times. The first time, at km 51, you'll be fresh; the second time, on lap two, you won't be. The discipline both times is the same: hit the lower target, get back to the climb account with VI under control, and don't trade real run minutes for visual speed.
Pace lap one of the run for lap two of the run. The run TSS is over budget before you start. Lap one held at plan pace, lap two on what's left — and the order matters. There's no separate plan for lap two; there's only what you leave it. Pushing the first half because you "feel good" is what turns a 4:10 split into a 4:45 one. Placid's 12.8 % DNF rate across 10,407 starters is high for a course that looks straightforward on paper.
These numbers come from Keiro — a physics-based race planning tool that models all three disciplines together, so the bike plan accounts for the run and the run plan accounts for the bike. The full IRONMAN Lake Placid course breakdown covers the Mirror Lake swim, the Adirondack climb profile, and the field statistics in more detail. See a plan for your fitness, your equipment, and the day's conditions.