Pace converter
Type a pace, get it in every unit that matters — plus what it adds up to over the classic distances.
| Held to the line, that's… | Time |
|---|---|
| 5K | — |
| 10K | — |
| Half marathon | — |
| Marathon | — |
Where it bends: nowhere — this one is pure arithmetic. The only thing it can't convert is how the pace feels at kilometre 38.
Race time predictor
Take a recent race and project it onto other distances, using the Riegel formula — the same one behind most online predictors, just with the fine print attached.
| Distance | Projected time | Pace |
|---|
Where it bends: the formula assumes you're as prepared for the target distance as for the one you raced. The bigger the jump, the more flattering it gets — a 10K time projects a marathon you can only run if you've actually done the marathon training. Treat the long projections as a best case, not a promise.
Heart-rate zones
Five training zones from your max heart rate. Add your resting heart rate if you know it — the zones then use heart-rate reserve (Karvonen), which fits most people a little better.
Don't know your max? A rough starting guess is 208 − 0.7 × your age
| Zone | Beats/min | What it's for |
|---|
Where it bends: age formulas miss the real max by 10+ beats for plenty of people, and zone borders are conveniences, not laws of physiology. If your easy runs don't feel easy in "easy" numbers, trust the feeling and test properly — a hard hill session or a lab test beats any formula.
Climb calculator
Your FTP and weight, turned into watts per kilo — and into honest times on the famous cols and the big climbing sportives. Physics, not wishful thinking: weight against gravity, rolling resistance, and air that gets thinner (and trims your power) as you go up.
The famous cols
| Climb | Time | km/h | VAM |
|---|
VAM = vertical metres climbed per hour — climbing's own speedometer. Lengths and gradients are the classic published figures for each side named. Long climbs self-limit: past the one-hour mark the tool quietly caps your chosen effort at what's actually holdable for that duration, so a "95% all-out" Stelvio becomes ~88% — because that's what your legs would do too.
The big climbing sportives
| Event | Time on the climbs | Rough day, total |
|---|
Event climbs are ridden at 75% of FTP no matter what you pick above — nobody climbs Alpe d'Huez fresh after 160 km. The total adds the kilometres between the climbs at ±30 km/h and 20 minutes of stops. Treat it as a ballpark: give or take half an hour, more if the weather turns.
Where it bends: the model assumes a steady average gradient, no wind, no wheel to sit on, and a road-bike position (CdA 0.34 m², Crr 0.0045, 2.5% drivetrain loss). Thinner air up high trims your power too — we use the acclimatised altitude curve (Bassett et al. 1999), so if you sleep at sea level, add roughly 3–4% on the high cols. And an FTP from a fresh 20-minute test is not the FTP you have on day four of a cycling holiday.
Aero lab
Where do your watts actually go on a flat road — and what would the usual aero upgrades really buy you, at your speed? Build your setup in the list below: every row shows what it's worth at your speed, and the box at the bottom turns your ticks into a new speed — or the same speed for fewer watts. Add your average watts if you know them and we'll calibrate the model to you.
Blue = air · amber = rolling resistance · dark = drivetrain loss. Flat road, no wind, riding solo.
Position — pick one
Kit
Tyres — pick one
And the body
Compared with the plain baseline: hands on the hoods, regular kit, butyl tubes, today's weight — at your speed from the top.
Where it bends: flat-road physics with wind-tunnel-measured mid-range numbers (position CdA ≈ 0.40 / 0.36 / 0.31 scaled to your size; helmet −0.006, loose-to-race-fit jersey −0.012, socks −0.004 CdA; wheels ≈ −0.006 CdA at 50 mm, maxing out at −0.009 around 63 mm; tyres: butyl Crr 0.0050, TPU/latex 0.0043, tubeless 0.0040; weight loss shrinks only the body's share of drag; 8 kg bike, sea-level air, 2.5% drivetrain). Real bodies aren't mannequins: your gains can be half or double these. Some of these marketing claims are on our own list to take apart properly — until then we've kept the numbers deliberately conservative. Average-ride watts include hills, stops and wheelsucking, so the calibration is honest but rough — and it politely refuses numbers that imply an implausible CdA.
Missing a tool?
These five are the start. If there's a calculator you keep wishing existed — fuelling planner, heat-adjusted pace, whatever keeps you up at night — tell us: mail info@enduranceproof.com or ping @EnduranceProof_ on X, and we'll put the best ones on the bench.
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