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The Cyclist guide to the right gear ratios for climbing

George Wallis-Ryder
15 Nov 2020

Climbing a mountain is hard enough without doing it with the wrong gears, but how do you know what’s right for you?

When it comes to climbing, most cyclists would admit to wishing they could reach summits a bit quicker. This is particularly the case during the hillier Spring Classics and the mountains of the Grand Tours. Having the correct gear ratios is a hugely important factor, but what exactly is the correct gear for climbing?

An increase in the range of gearing options on sale has left just as many cyclists in a land of confusion instead of pedalling toward paradise.

At a basic level, gears allow a rider to vary the effort required at the cranks to turn the rear wheel for a given speed.

If your biggest chainring has 52 teeth and you’re turning a 26-tooth cog at the rear, the ratio is 2:1 - meaning a complete pedal revolution turns the rear wheel twice.

The greater the difference between the size of front and rear gears, the harder it will be to push. 

SRAM Rival 22 cassette

Inseparably linked to choosing gear ratios is the concept of cadence i.e. how many revolutions per minute you turn the pedals.

Although varying between riders, in the region of 90-110rpm is considered ‘standard’. If you wanted to trundle along the flat at 24kph, you might select a 36x17 combination, allowing you to spin at a reasonable 90rpm.

In theory you might instead select a 52x12 ratio, which only requires a cadence of 45rpm.

Although you may think turning the pedals fewer times a minute for the same speed would be beneficial, this would be a difficult gear to ride at relatively low speed.

Spinners are winners?

When the road starts heading upwards, efficiency becomes the name of the game and asking too much from your legs up a climb is a certain route to failure.

Finding the right balance between your strength, fitness and gearing will ultimately garner the best results.

This is arguably where the biggest difference between professionals and the average rider can be found; WorldTour level riders can turn much bigger and harder gears at the same or sometimes higher cadence.

Chris Froome attacks Nairo Quintana on Stage 10 of the 2015 Tour de France

Stage 10 of the 2015 Tour de France ended with a 15.3km climb toward La Pierre-Saint-Martin, with an average gradient of 7.4%.

Chris Froome averaged just over 22kph for the 41 minutes and 28 seconds it took to reach the summit. Gearing consisted of 52/38 chainrings, and an 11-28 cassette, which he turned at an average cadence of 97rpm.

Using this information, and some complicated maths, we can estimate that Froome spent most of his time using a 38x21 gear ratio.

What then of an ‘average’ rider? Those not blessed with the Team Sky leader’s abilities might choose a compact chainset offering a 34 tooth inner ring.

How much further behind then would our mere mortal rider be by the time Froome had finished?

Using a compact chainset and the same 11-28 range cassette allows for ratios as low as 34x28, but for this comparison we’ll use the same cog selection at the back.

How far then could a rider spinning 34x21 expect to travel up the same climb?

Based on a cadence of 97rpm, after the same time it took Froome to finish, the compact rider would have only covered 13.6km of the 15.3km ascent.

Even the semi-compact rider on a 36x21 ratio would find themselves almost a full kilometre behind the yellow jersey winner.

The tale of the cog and sprocket 

Where you ride is perhaps the most important consideration to make when choosing gear ratios. If your local roads are pan-flat, there’s going to be little need for a 30-tooth rear sprocket.

Likewise if you commute over a mountain pass, you’ll want to skip over that 11-23 cassette in favour of something more forgiving.

The length of cage fitted to your rear derailleur dictates the largest useable rear cog, and although this varies between manufacturer and groupset, most standard derailleurs will accept a 28-tooth maximum, while long cage derailleurs will take cogs of around 32 teeth.

Cassettes are only one part of the drivetrain puzzle however, and matching them with an appropriately sized chainset can unlock your full riding potential.

Similarly if you are growing in strength it might be time to spec larger gears to your bike.

Ideally you shouldn’t be wearing through one chainring at a much quicker rate than the other, as this is a sign that your inner ring is too small or your big ring too big.

Although climbing is a unique skill in itself, selecting your gears doesn’t have to be any scarier than the rest of your riding. The gears at your disposal should be appropriate for your surroundings as well as your ability.

Attempting to push pro level gearing can be a recipe for disaster if your bike is writing cheques that your legs can’t cash.

If you want to look pro, copy their cadence instead of their drivetrains, as they tend to spin a gear that allows them to stay in their most efficient RPM range - as you should too.

This article first appeared on Cyclist.co.uk in October 2016

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