Climb Gear Planner
Drop in a route. The tool pulls out the main climbs, works out how hard each one is for your athlete, and shows which 12-speed gearing, Shimano or SRAM, keeps them spinning on the steep bits.
The science
How the climbing power is worked out, and where it comes from.
Model and references
Climbing power starts from a fraction of FTP set by how hard the rider is racing the event, with a small adjustment so short climbs are ridden a touch harder than long ones. That base is then reduced by two effects.
Durability. Sustainable power falls as mechanical work accumulates over the day. The tool estimates kilojoules done before each climb from the route, then applies a decay anchored to field data: well-trained amateurs lost roughly 6.5 to 12.5 percent of their 20 minute power after only 1000 kJ of work (Barsumyan et al. 2025), the same pattern shown in professionals by van Erp et al. (2021) and Spragg et al. (2023, 2024). Maunder et al. (2021) set out durability as a distinct quality from FTP or VO2max.
Fuelling. Carbohydrate intake blunts that fade. Carbohydrate during prolonged cycling reduced the drop in critical power that durability describes (Clark et al. 2019), through liver glycogen and blood glucose rather than sparing muscle glycogen. The fuelling setting scales the durability decay up or down to reflect that, as a pragmatic adjustment rather than a precise dose response.
Altitude. Aerobic power falls in thin air. The tool uses the two phase model of Peronnet et al. (1991) and Wehrlin and Hallen (2006): about 1 percent loss per 1000 m below 1500 m, then about 6.3 percent per 1000 m above, applied at each climb's elevation. Acclimatisation recovers roughly half. Thinner air also lowers aerodynamic drag, which the speed calculation accounts for, so it offsets a little of the loss.
Heat. Sustained power drops in the heat through cardiovascular strain. Unacclimatised cyclists lost around 16 percent of time trial power in serious heat, about 0.5 percent per degree, falling to roughly 3 percent after two weeks of acclimatisation (Racinais and Periard; Casadio et al. 2017). The conditions setting applies a modest whole-ride decrement; note the high cols are cooler than the valleys, which the single figure does not capture.
Pacing. Sustainable intensity for a five to eight hour mountain event sits well below FTP. Practical power ranges put a gran fondo near 0.72 to 0.80 of FTP and a long mountainous day lower still (Coggan intensity framework; gran fondo and century pacing data). On a route that is up or down all day, climbing intensity tracks close to that.
Gearing. The grid judges the easiest gear on the steepest sustained ramp (about 200 m), not a single steep point, because that is the pitch you sit in. It flags combinations that exceed realistic road rear mech limits: on Shimano a 34T maximum sprocket for Ultegra and Dura-Ace and 36T for the 105 R7100 and GRX; on SRAM AXS a 33T maximum on the standard rear mech and 36T on the wide one; and about 39T of total chain wrap either way.
References. Barsumyan, Soost, Burchard (2025) Front Sports Act Living 7:1530162. van Erp, Sanders, Lamberts (2021) Med Sci Sports Exerc 53(9):1903. Spragg, Leo, Swart (2023) Med Sci Sports Exerc 55(1):133, and Spragg et al. (2024) Eur J Sport Sci. Maunder et al. (2021) Sports Med 51:1619. Clark et al. (2019) on carbohydrate and critical power. Peronnet, Thibault, Cousineau (1991) Int J Sports Med. Wehrlin and Hallen (2006) Eur J Appl Physiol 96:404. Racinais and Periard, and Casadio et al. (2017) on heat and endurance performance.