What gearing do you need to ride in the mountains?
Updated: Jan 12, 2020
If it's your first visit and you live in a less mountainous country, it can be hard to know what gearing you need for a road cycling holiday in the Pyrenees (separate post for gravel riding to follow). When your rides tend to feature short climbs of 5-10 minutes, you can afford to let your heart rate climb because you'll soon be over the top and able to recover. In the mountains, you have to settle into a rhythm that you can sustain for well over an hour.
The simple answer is to go low - it's way better to have gearing that’s a little too low than too high. And if you're less fit, or perhaps not quite as skinny as the pros, then of course you need to go lower still.
A good way to test is to find the longest hill near to where you live, 10 minutes and around 8% ideally, and to ride repeats of it until you have totalled 30 minutes of climbing. Keep the pace steady, as if you're on a big day in the mountains. The aim is to have a gear that allows you to maintain a manageable effort and a comfortable cadence even on the last ascent.
I'd say that 34x28 is pretty much the minimum, even if you’re really fit, because there are some really steep sections on many of the climbs and you will appreciate being able to tackle them without resorting to a lung-searing effort or knee-bursting low cadence. That's the gearing that I keep on my bike to ride here, and I'm 71kg and race-fit. This is no place for a 53/39 chainset!
If your rear derailleur has the capacity, a cassette that goes up to 30t or 32t will make a significant difference and is the most affordable way to lower your gearing. Shimano has now introduced an 11-30 at the more affordable Ultegra level and 11-32 is available in 105, though it's a tad weighty. Remember that you will likely need to extend or replace your chain, or be extremely diligent about avoiding cross-chaining into big-big.
The latest groupsets offer the lowest gearing. The new 12-speed SRAM Red and Force eTap AXS offers a sub-compact 46/33 chainset and 10-33 cassette, giving a 1:1 gear. Shimano isn't there yet, with 34x32 (50/34, 11-32) the lowest possible, matched by Campagnolo, despite the latter now being 12-speed, and by SRAM's non-AXS groups. The rarely seen Rotor Uno is limited to 34x30.
A 34x32, and especially a 33x33, makes almost any climb possible for almost any rider, but you have to remember that you will be travelling more slowly and a major climb could take well over two hours. The likes of the Col du Tourmalet, 19km on the Luz side, could represent an endeavour beyond three hours. Something to keep in mind when planning your days.
A 1x drivetrain - that is, with a single chainring - will be at its most limiting in the mountains where you will experience a greater breadth of speeds than anywhere else. Yes, you can achieve the range with, say, a 44x10-42, but the jumps between gears will be unpleasantly large. Alternatively, a less gappy cassette will limit the range and you'll either be grinding uphill or unable to pedal downhill even on the gentle valley descents. It can work, but it's compromised.