Eh, it's really quite small, unless you have stupid heavy wheels (meaning, that the wheels are a significant percentage of the mass of the entire system). If t

Eh, it's really quite small, unless you have stupid heavy wheels (meaning, that the wheels are a significant percentage of the mass of the entire system). If the mass of the wheel is 100% located at the rim, the energy goes 1/2 into straight line energy and half into rotational. But -- if you slow down, you don't lose that energy, it just redistributes to gravitational potential. The flywheel effect from heavy wheels may actually help, as it tends to smooth out pedal strokes. The energy to go up a hill is just mgh - friction. Some cadences are less efficient than others (e.g. for me, standing is more power but lower efficiency), and bikes that are too stiff may not help you get the best rhythm. In a totally unscientific test -- I've got a 12kg Aluminum gravel bike, wide tires, rack, fenders. I've also got an 8kg carbon racing bike, skinny tires, aero rims, etc. They have similar riding positions (reach/drop), though the gravel bike has a wider seat, which is better for one climbing cadence. I usually ride the gravel bike these days, because comfort. Two weekends in a row, I did a 12x rep climbing workout (2.5 hours), one on each bike. First weekend, Road bike. It felt _fast_. Quick, lively, accelerated from the stoplights on the way to the hill. Second week, back on the gravel bike, grinding up the hill. Total ET difference: 5 seconds. Sure there are differences.