這樣是最省力的。看見上坡就要提前準備換擋。不要前麵小輪，後麵也小輪，或者前麵大輪後麵也大輪， 這叫cross-chaining。
https://www.yellowjersey.co.uk/the-draft/bike-gears-explained/
沒有時間看，就注意下麵幾點。坡太陡，誰都有騎不上去的時候。
- Avoid ‘cross-chaining’: Cross-chaining is when you have a little/little or big/big combination. This puts stress on the drivetrain and can cause premature wear of the components. It’s OK if you occasionally find yourself cross-chained – say for a short, steep climb – but it is something you’ll generally want to avoid. The rule of thumb to follow is that when on the big ring, only use the smaller two-thirds of the cassette. When on the inner (or middle) ring, only use the inner two-thirds. When in ‘granny gear’ limit yourself to the largest two or three cogs.
- Anticipate your shifts: Keep an eye on the road ahead and shift before you have to. You’ll maintain a smoother power output, and you’ll be shifting at a time when there’s less stress on the drivetrain – so your shifts will be smoother too. As you approach a red light or stop sign you should also downshift a couple of gears, in anticipation of getting rolling again as smoothly as possible.
- Keep pedalling!: It is much more efficient to keep a constant, steady power rather than ‘burst and coast’ riding. It sure feels like you’re getting better exercise when you make that big effort, but you’re putting all the load on your muscular system, which isn’t really good at sustained effort. Spinning light and fast ends up putting out the same amount of power, but shifts the load to your cardio-vascular system, which is good at endurance activity.
