You are standing at the bottom of a climb in the Alps. You know it is 13.8km at 8.1% average — Alpe d'Huez, the most famous finish in cycling. You know your FTP. You have a rough sense of what you weigh in kit. The question hammering through your head is the same one that hammers through every cyclist who has ever looked up at switchbacks disappearing into cloud: how long is this going to take me?
The answer is not a mystery. It is arithmetic. And getting it right before you clip in is the single most important thing you can do for your pacing, your fuelling, and your chances of actually enjoying the final four kilometres instead of crawling them in a fog of lactate and regret.
I have spent over 1,400 episodes of the Roadman Cycling Podcast talking to coaches, sports scientists, and professional riders about climbing. The physics is simple. The application is where most amateurs get it wrong. This is the complete framework — the maths behind the prediction, the pacing strategy that protects you from yourself, and the benchmarks that tell you where you sit relative to the field.
The physics of climbing — why it is almost entirely W/kg
Three forces resist you on a climb: gravity, aerodynamic drag, and rolling resistance. Your power output has to overcome all three simultaneously, and the gradient determines which one dominates.
On a flat road at 35 km/h, aerodynamic drag consumes roughly 80% of your power. Rolling resistance takes most of the rest. Gravity takes nothing. The moment the road tilts upward, the balance shifts. At 3% gradient, gravity already claims about 68% of total resistance. At 5%, it takes 83%. At 7% — which is the average gradient of most famous Alpine climbs — gravity accounts for over 90% of the resistance you fight.
This is the fundamental insight that separates riders who understand climbing from riders who throw money at equipment. On a climb of 7% or steeper, your deep-section wheels, your aero helmet, your skin suit — they are worth seconds over 45 minutes. Your power-to-weight ratio is worth minutes. The physics does not care about marketing claims. It cares about watts divided by kilograms, multiplied by the gravitational constant.
The crossover point sits at roughly 4-5% gradient. Below 4%, aerodynamic drag still contributes enough that position, equipment, and CdA (your drag coefficient multiplied by frontal area) make a measurable difference. Above 5%, those factors shrink toward irrelevance. By 8%, aero drag accounts for about 3% of total resistance. You could ride Alpe d'Huez in an upright city-bike position and lose less than 90 seconds compared to a perfect aero tuck — but add one extra kilogram of body weight and you lose about 30 seconds. The numbers are stark.
Run your own power-to-weight through the W/kg calculator before reading further. You need a baseline number, because every prediction and every benchmark that follows depends on it.
How to predict your time on any climb
The full physics model that the climb time calculator runs balances power output against gravitational resistance, aerodynamic drag, and rolling resistance, then solves for speed using iterative methods. But for climbs above 6% gradient, a simplified formula gets you within 5-8% of the accurate answer:
Time (seconds) = (Elevation gain x Total mass x 9.81) / (Power output x 3.6)
Where elevation gain is in metres, total mass is rider plus bike plus kit in kilograms, 9.81 is gravitational acceleration, and the 3.6 conversion factor accounts for the unit mismatch between watts and the speed equation. This formula ignores aero drag and rolling resistance entirely — which is why it only works on steep climbs where those forces are negligible.
A worked example for Alpe d'Huez: elevation gain is 1,071m. A 75kg rider with a 9kg bike and 1kg of kit gives a total mass of 85kg. If that rider sustains 250W (3.33 W/kg), the formula gives:
Time = (1,071 x 85 x 9.81) / (250 x 3.6) = 992 seconds = approximately 99 minutes, or about 1 hour 39 minutes.
The full model in the climb time calculator — which includes aero drag, rolling resistance, altitude-adjusted air density, and drivetrain losses — gives about 1 hour 11 minutes for the same rider. The difference tells you something: on Alpe d'Huez at 8.1% average, the simplified formula overestimates by about 20% because the small contributions of favourable aero (you are moving slowly, so drag is minimal) and rolling resistance corrections net out to a material saving over 13.8km. The formula is a sanity check, not a race plan. For accuracy, use the calculator.
For Mont Ventoux from Bedoin — 21.5km at 7.5% average with 1,617m of elevation gain — the same 75kg rider at 250W gets:
Full model time: approximately 1 hour 51 minutes.
The critical variable in both cases is the power you can actually sustain for that duration. Your 20-minute FTP test number is not the number to use here. For a 60-minute climb, realistic sustainable power is 85-90% of FTP. For a 90-minute climb, 80-85%. For anything over two hours, 75-80%. Use the FTP zones calculator to establish those thresholds before modelling your climb.
Pacing strategy for long climbs
Here is where knowing your predicted time converts from interesting to essential. If you know a climb will take you 75 minutes at 240W, you can pace it. If you guess it will take 55 minutes and set off at 280W, you are in serious trouble by the halfway mark.
The research on pacing for sustained efforts is consistent and unambiguous. Even pacing — holding the same power from bottom to top — produces faster times than any variable-pacing strategy for efforts lasting over 20 minutes. A slight negative split — starting 3-5% below target and finishing 3-5% above — is marginally better still on long climbs because it accounts for the physiological cost of early intensity.
The cost of starting too hard is not linear. It is exponential. Going 5% above your sustainable power in the first third of a climb does not cost you 5% in the final third. It costs you 8-12%, because the metabolic debt from early anaerobic contribution depletes glycogen stores faster, raises blood lactate to levels that suppress fat oxidation, and triggers a cascade of neuromuscular fatigue that worsens as the climb continues. I have seen riders lose 10 minutes on the upper hairpins of Alpe d'Huez because they went out 15W too hard in the first 20 minutes. Fifteen watts. That is the margin.
When I had coaches like John Wakefield on the podcast — he works with the Red Bull-Bora-Hansgrohe riders — the consistent message was the same. The best climbers in the world pace climbs by feel and by numbers, but the feel is calibrated against thousands of hours of data. Amateur riders do not have that calibrated feel. So use the numbers. Set a target power that is 85-90% of FTP for climbs up to an hour, 80-85% for climbs of 60-90 minutes, and 75-80% for anything beyond. Tape the number to your stem if you have to. Then ride the first third thinking "this is too easy." If the first third does not feel too easy, you have already gone too hard.
The practical pacing protocol for a 60-minute climb looks like this. Minutes 1-20: settle at 85% FTP, keep the breathing controlled, eat and drink. Minutes 20-40: hold 88-90% FTP, assess how the legs feel, take in another gel or 200ml of drink. Minutes 40-55: if the legs are good, lift to 92-95% FTP. Final 5 minutes: empty the tank if you have anything left. That is a textbook negative split, and it will beat the rider who went out at 95% FTP and crawled the final 15 minutes every single time.
Seated versus standing — when each is faster
The seated-versus-standing debate has been running for as long as cyclists have been climbing. Contador danced on the pedals. Froome spun at 95 rpm seated. Pogacar does both, switching between positions with a fluidity that makes it look like a personal preference rather than a tactical decision. But the physiology is clear on the trade-offs.
Standing climbing recruits more muscle mass. The glutes, hamstrings, and core all engage more forcefully when you are out of the saddle because your body weight contributes to the downward force on the pedals. This additional recruitment means you can produce more peak power standing than seated — typically 5-10% more for efforts under two minutes.
The cost is energy. Studies measuring oxygen consumption at matched power outputs consistently show that standing costs 8-12% more energy than seated riding. That means a rider producing 300W standing is consuming the same oxygen as a rider producing 324-336W seated. Over a 10-minute effort, the difference is manageable. Over a 60-minute climb, it compounds into a significant metabolic debt.
The practical guidance is this. Sit for the vast majority of any climb over 10 minutes. Use standing for four specific situations: steep pitches above 10% gradient where the gear ratio demands it; brief accelerations or changes of pace lasting 15-30 seconds; muscular relief every 5-8 minutes on very long climbs, standing for 20-30 seconds to shift the load between muscle groups; and the final kick if you are racing or chasing a time.
The Contador-Froome comparison is instructive but misleading. Contador stood more because his physiology — lighter, more explosive, higher proportion of fast-twitch fibres — suited it. Froome sat more because Tim Kerrison identified that his cardiovascular system could deliver more oxygen than his musculature could use at low cadences, so high-cadence seated climbing was more efficient for his specific engine. Neither style is universally better. The right approach depends on your physiology, your power profile, and the gradient. But for most amateur riders on most climbs, the answer is: sit down, find a rhythm, and save standing for the moments when you need it.
The gradient threshold where weight beats aero
I touched on the 4-5% crossover above, but the data deserves a closer look because it changes how you think about equipment, body composition, and race-day choices.
At 3% gradient, a 75kg rider at 250W travels at roughly 22 km/h. At that speed, aerodynamic drag still accounts for about 21% of total resistance. A rider with a CdA of 0.30 (aero position, integrated cockpit, skin suit) gains roughly 45 seconds over 10km compared to a rider at CdA 0.40 (hoods position, loose jersey). That 45 seconds is real. It is worth chasing.
At 5% gradient, the same rider slows to about 16 km/h. Aero drag drops to 8% of total resistance. The CdA advantage shrinks to about 15 seconds over 10km. The rider who dropped 1kg of body weight instead of buying an aero helmet gained roughly 20 seconds. Weight has overtaken aero.
At 8% gradient, speed drops to about 11 km/h. Aero drag is 3% of total resistance. The CdA advantage is about 5 seconds over 10km. The 1kg weight advantage is now 30 seconds. And a 2kg body composition improvement — entirely achievable over 8-12 weeks of structured nutrition without crash dieting — saves a full minute. On the 21.5km of Mont Ventoux, that scales to over two and a half minutes.
This is why the race weight calculator matters for climbers. Not because lighter is always better — there is a floor below which power drops faster than weight — but because understanding where you sit on the weight-versus-power curve tells you whether your next marginal gain comes from the bike shop or the kitchen.
The power-speed calculator models the full interaction between aero, weight, gradient, and speed. Use it to test scenarios before you spend money. If your target event is a rolling sportive with no climb above 5%, invest in position and aero. If your target event is a mountain gran fondo with four cols above 7%, invest in body composition and threshold power. The physics will tell you exactly where the returns are.
Using climb data to set realistic sportive targets
Here is where prediction becomes practical. You have a local climb — say, 3km at 6%, roughly 180m of elevation gain. You ride it regularly. You know you can hold 260W for the 12-13 minutes it takes. That gives you a W/kg of about 3.47 (at 75kg). Now you want to know what that means for La Marmotte, or the Maratona dles Dolomites, or the Gran Fondo Stelvio.
The method is simple. Take your known W/kg at a known duration. Adjust for the duration of the target climb using the power-duration curve: for efforts twice as long, sustainable power drops by roughly 5-8%. For efforts three times as long, 10-15%. Then run the adjusted power through the climb time calculator for the target climb profile.
For La Marmotte — which includes Col du Glandon (23km at 5.1%), Col du Telegraphe (12km at 7.1%), Col du Galibier (18km at 6.9%), and the final ascent of Alpe d'Huez (13.8km at 8.1%) — you are looking at roughly 5,000m of climbing over 174km. The climbing alone will take 4-5 hours at 3.0-3.5 W/kg. Total finish time for that power range is typically 9-11 hours including descents, flats, and stops.
The benchmark I give to riders in the Roadman community who ask about mountain sportive targets: if you can sustain 3.0 W/kg for 60 minutes on a local climb, you will finish La Marmotte in roughly 10-11 hours. At 3.5 W/kg, 8-9 hours. At 4.0 W/kg, 7-8 hours. Those are honest numbers — not the optimistic estimates you see in magazine previews, but the times that actual riders on actual power data post.
For the Stelvio — 24.3km at 7.4% from Prato allo Stelvio, 1,808m of elevation gain, summit at 2,757m — the altitude factor becomes significant. A rider who sustains 3.5 W/kg at sea level will lose roughly 8-10% of that power at the summit altitude, reducing effective output to about 3.15-3.22 W/kg for the upper third of the climb. Factor that into your prediction or the final kilometres will be considerably harder than the calculator suggests.
The VAM calculator is useful here as a cross-reference. VAM — vertical ascent rate in metres per hour — gives you a single number that captures climbing speed regardless of gradient. A VAM of 800-900 m/hr is a strong amateur effort. A VAM of 1,000-1,200 m/hr is competitive amateur or low-level racing. The pros sustain 1,600-1,800 m/hr on major mountain stages. If your local-climb VAM is 850 m/hr, extrapolate that to the target climb's elevation gain for a quick duration estimate.
Altitude effects on performance
Altitude is the variable most amateurs underestimate. The first 1,500m of elevation above sea level has minimal physiological impact — the partial pressure of oxygen remains high enough that the body compensates without measurable performance loss. Above 1,500m, the decline begins and it is roughly linear.
The rule of thumb: sustainable power drops by approximately 3% per 300m above 1,500m. At 2,000m, expect a 5-6% reduction versus sea level. At 2,500m, 8-10%. At 3,000m — the summit of the Stelvio at 2,757m, the Passo dello Stelvio at 2,758m, the Col de l'Iseran at 2,770m — 10-13%.
The mechanism is pure physics. Atmospheric pressure drops with altitude. Lower pressure means fewer oxygen molecules per litre of air. Your lungs take in the same volume of air, but each breath delivers less oxygen to the blood. The cardiovascular system compensates partially by increasing heart rate and stroke volume, but above 1,500m the compensation is insufficient to maintain sea-level power output. VO2max drops. Threshold power drops with it.
The practical impact on a climber ascending from a valley floor at 800m to a summit at 2,500m is that power degrades progressively across the climb. The lower third at 1,000-1,400m feels normal. The middle third at 1,400-1,900m feels slightly harder than the power number suggests. The upper third at 1,900-2,500m feels materially harder — heart rate is elevated relative to power, breathing is laboured beyond what the wattage warrants, and the RPE drift can cause riders to overcook the effort or mentally crack.
This is why pacing on high-altitude climbs requires a deliberate adjustment. If your target power at sea level is 250W, your target on the upper half of the Galibier should be 225-235W. Not because you have become weaker, but because the air has become thinner. The climb time calculator accounts for altitude-adjusted air density in its physics model, so the predicted times reflect this — but you still need to adjust your pacing in real time.
Acclimatisation helps. Seven to fourteen days at altitude recovers roughly half the performance deficit through increased red blood cell production and improved oxygen extraction. If your target event is a mountain sportive at altitude and you can arrive a week early, do it. If you cannot, factor the altitude penalty into your pacing plan and accept that the summit kilometres will be slower than the valley kilometres.
One counterintuitive benefit: thinner air means less aerodynamic drag. At 2,500m, air density is roughly 22% lower than at sea level. On flat or rolling terrain, this is a significant free-speed advantage. On a 7% gradient where aero drag is 3-4% of total resistance, it saves about one second per kilometre. Marginal. Do not count on it.
The Alpe d'Huez and Mont Ventoux benchmarks
These two climbs are the gold standards for amateur climbing benchmarks because they are long enough to require real sustained power, steep enough that W/kg dominates, and famous enough that everyone has heard of them. Here is what the numbers look like for a 75kg rider on a 9kg bike.
Alpe d'Huez — 13.8km, 8.1% average gradient, 1,071m elevation gain, finish altitude 1,850m.
At 2.5 W/kg (188W): approximately 1 hour 31 minutes. This is a solid recreational effort. The pace is slow enough that fuelling and hydration are manageable. Most riders with a year of structured training can hit this.
At 3.0 W/kg (225W): approximately 1 hour 16 minutes. This is a strong amateur time. You are passing more people than are passing you. The effort requires serious threshold fitness and proper pacing.
At 3.5 W/kg (263W): approximately 1 hour 6 minutes. This is competitive amateur territory. You are among the faster riders at any mass-participation event. Breaking this barrier is the goal for most serious age-group cyclists.
At 4.0 W/kg (300W): approximately 58 minutes. Sub-hour Alpe d'Huez. This is the benchmark that separates recreational from properly fast. It requires exceptional aerobic fitness for a non-professional rider.
At 4.5 W/kg (338W): approximately 52 minutes. You are in the top fraction of amateur climbers. Most riders at this level are racing nationally.
The professionals? Pogacar's stage-winning efforts on Alpe d'Huez have been in the range of 36-40 minutes, corresponding to roughly 5.8-6.2 W/kg sustained. That is a different species of effort, and comparing yourself to it is pointless. Compare yourself to your last effort, and use the climb time calculator to set the target for your next one.
Mont Ventoux from Bedoin — 21.5km, 7.5% average gradient, 1,617m elevation gain, finish altitude 1,909m.
Ventoux is longer, more variable in gradient, and more exposed to wind — which means aero drag plays a slightly larger role than on the sheltered switchbacks of Alpe d'Huez. The gradient also varies dramatically: the first 6km through the forest averages 5-6%, the middle section through the tree line averages 8-9%, and the final exposed section to the summit averages 9-10%.
At 3.0 W/kg: approximately 1 hour 51 minutes. At 3.5 W/kg: approximately 1 hour 36 minutes. At 4.0 W/kg: approximately 1 hour 25 minutes. At 4.5 W/kg: approximately 1 hour 17 minutes.
The gradient variation on Ventoux demands a different pacing approach than Alpe d'Huez. On Alpe d'Huez, the gradient is relatively consistent — you can hold a steady power and the speed stays roughly constant. On Ventoux, the lower slopes are shallow enough that aero position matters, the middle slopes demand a power increase to maintain climbing speed, and the upper slopes above the tree line are exposed to wind that can either help or destroy your time depending on the day.
The strategy I use when riders ask me about Ventoux is power-based, not speed-based. Set a W/kg target for the duration. Hold it regardless of gradient. On the shallower lower slopes, that target power produces a faster speed and you cover ground quickly. On the steep middle section, speed drops but the power stays the same. On the exposed summit, adjust for wind — headwind means accepting slower speed at the same power, tailwind means enjoying the free assistance without pushing harder. The power target is the constant. Everything else is variable.
Putting it together — your pre-climb protocol
Before you ride any climb with a time goal, run this sequence.
First, establish your realistic sustainable power for the expected duration. If the climb will take 45 minutes, use 88-90% of FTP. If 75 minutes, use 82-85%. If over 90 minutes, use 78-80%. Be honest. This is not the time for aspirational numbers.
Second, weigh yourself with your kit. Add your bike weight. This is your total system mass. The race weight calculator helps you assess whether there is realistic weight to lose without compromising power, but that is a project for months before the event — not the morning of.
Third, run the numbers through the climb time calculator. Enter the climb profile (or select from the presets), your power, and your total mass. The calculator gives you a predicted time, an expected speed, and a VAM. Write down the predicted time and the target power.
Fourth, plan your fuelling. For climbs under 45 minutes, you can ride on what you have consumed in the hour before. For climbs of 45-90 minutes, take a gel at the 25-minute mark and drink every 15 minutes. For climbs over 90 minutes, eat 60g of carbohydrate per hour starting from the bottom.
Fifth, pace the climb. Start at the low end of your target power range. Settle into a rhythm. Resist the group around you — their pace is not your pace. Use your head unit or a heart rate cross-reference to stay honest. The race predictor can model your entire event including the flat and descending sections, so your climbing target sits within a whole-day energy budget.
The riders who predict their climbing times accurately and then execute the plan are the riders who finish mountain sportives feeling strong rather than shattered. The physics is knowable. The pacing is controllable. The only variable left is whether you trust the numbers enough to ride them.
What actually moves your climbing time
Predicting your time is the diagnostic. Improving it is the project. And the project has a specific order of operations.
First, improve W/kg through a combination of threshold training and body composition work. These are the two biggest levers and they are multiplicative — raising FTP by 10W while dropping 2kg of body fat improves your climbing time more than either change alone. This is a 3-6 month project done properly, not a crash diet before a sportive.
Second, fix your pacing. Most amateur climbers lose 3-5 minutes on a 60-minute climb purely through poor pacing — going out too hard, yo-yoing on gradient changes, or mentally cracking in the final third. Learning to pace by power is the fastest free improvement available. The FTP zones calculator gives you the numbers. The discipline is yours to develop.
Third, build climbing-specific endurance through repeated long efforts at or just below threshold. Hill repeats on a local climb of 10-20 minutes are the bread and butter of climbing improvement. Three sets of 10-15 minutes at 90-95% FTP with 5-minute descending recoveries, once or twice a week for 6-8 weeks, will measurably shift your sustainable climbing power. If you do not have a suitable climb, use the indoor trainer at a low cadence of 55-65 rpm with the incline simulation set to 7-8% — the power-speed calculator can model the equivalent outdoor effort.
Fourth, learn to use standing and seated positions strategically. Practice both in training. If standing on steep pitches is currently an emergency measure rather than a deliberate tactic, spend time on 10-12% gradients doing 2-minute standing efforts at threshold to build the specific muscular endurance and coordination.
The climb time calculator is the starting point, not the destination. It tells you where you are. Training tells you where you are going. And the gap between the two is the work.