Gravel Bike Gearing Explained

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Gravel gearing is the one part of the category with a real engineering problem behind it. A road bike needs a narrow band of gears around a fast cruising speed. A mountain bike needs very low gears and doesn’t care about the top. A gravel bike is asked to do both, on the same ride, sometimes in the same hour — grind up a loose fire road at walking pace, then hold 40 km/h on the tarmac home.

That is a genuinely hard ask, and the industry’s answer has been the 1x drivetrain: one chainring, an enormous cassette. It is sold on simplicity and on range. The simplicity is real. The range claim does not survive division, and this page is the division.

The two numbers that describe any drivetrain

Your lowest gearis what decides whether you get up the hill. It’s the smallest chainring divided by the biggest cog. A 40T ring with a 44T cog gives 0.91 — for every pedal revolution the wheel turns 0.91 times. Lower is easier.

Your range is the spread between your easiest and hardest gear, expressed as a percentage. Highest ratio divided by lowest ratio. It tells you how much of the world the bike covers.

Both get more comparable in gear inches, which folds in wheel size: chainring divided by cog, times wheel diameter in inches. It’s an odd unit — it’s inherited from high-wheel bicycles, where it literally was the diameter of the driving wheel, as Sheldon Brown explains — but it survives because it makes a 700x45 gravel bike and a 700x25 road bike directly comparable. Brown himself argued for gain ratios instead, since gear inches ignore crank length. He was right and nobody listened, us included, because gear inches are what everyone quotes.

What 1x actually costs you

Here are two current gravel drivetrains, on the manufacturers’ own published tooth counts.

SRAM’s XPLR 1x. SRAM publishes its XG-1251 XPLR cassette as 10-44 with the exact cog list 10, 11, 13, 15, 17, 19, 21, 24, 28, 32, 38, 44 — and states a 440% range. Pair it with a 40T ring and your lowest gear is 40/44 = 0.91.

Shimano’s GRX 2x. Shimano publishes the RX820 crank at 48/31 and pairs it with the CS-HG710-12 cassette, published as 11-12-13-14-15-17-19-21-24-28-32-36. Lowest gear: 31/36 = 0.86. Range: (48/11) ÷ (31/36) = 507%.

So the 2x setup has a lower climbing gear and 67 percentage points more range. It is not close. The 1x drivetrain — the one sold on range — has less range than the 2x it replaced, and this is structural rather than a bad product: you removed a chainring, so you removed the range that chainring provided. A 440% cassette cannot make up for it, because the 2x has a 327% cassette multiplied by a 55% chainring step.

You can watch this happen inside a single model. Trek’s earlier Checkpoint ALR 5 ran GRX RX600 at 46/30 with an 11-34: lowest gear 0.88, range 474%. Trek’s current Checkpoint ALR 5 Gen 3 runs SRAM Apex 1 at 40T with an 11-44: lowest gear 0.91, range 400%. The new bike climbs slightly worse and has 74 percentage points less range than the old one.

Then why is everyone selling 1x?

Because range isn’t the only axis, and the other reasons are honest ones.

No front derailleur. Nothing to knock out of adjustment, nothing packed with mud, nothing to drop a chain off in a rutted descent. On a bike whose entire purpose is surfaces that throw grit at your drivetrain, deleting the most alignment-sensitive component is a genuine win.

No cross-chaining, no overlap. A 2x has roughly a third of its gears duplicated between rings, so a 24-gear drivetrain gives you maybe 16 distinct ratios and forces you to remember which. A 12-speed 1x gives 12 gears and 12 ratios, in one line.

Tyre clearance. No front mech and a single narrow ring frees up space exactly where a fat gravel tyre wants to be. Some of the clearance in gravel bike vs road bike is bought with the chainring you gave up.

Simplicity you can feel. One shifter, one cable or one battery, one thing to think about on a climb.

Those are real advantages. They are just not range, and being sold range is how people end up spinning out on descents wondering what went wrong.

The step size nobody mentions

There’s a second cost to 1x and it’s subtler than range: the jumps get bigger. If you spread 440% across 11 shifts, the average step is about 14.4%. Spread the GRX cassette’s 327% across its 11 shifts and the average step is about 11.4% — with the chainring providing the rest of the range in one deliberate jump you choose to make.

That difference is the feeling of not having the right gear. You shift, and you’re either spinning slightly too fast or grinding slightly too slow. Look at SRAM’s own published cog list and you can see where it bites: 10, 11, 13, 15, 17, 19, 21, 24, 28, 32, 38, 44. The step from 32 to 38 is 19%. From 38 to 44 is 16%. Those are the cogs you use on a climb, which is exactly where a big jump hurts most.

(Both average figures are geometric means assuming even spacing — real cassettes aren’t evenly spaced, as that cog list shows. Treat them as the shape of the trade, not a promise about any specific shift.)

Why gravel gearing differs from road gearing at all

It comes down to speed range and the surface. A road bike lives between roughly 25 and 45 km/h on a predictable surface; it wants small steps in a narrow band and a big top gear. A gravel ride includes stretches at 8 km/h where the limiter is traction and gradient, not power.

Road groupsets can’t just fit bigger cassettes to solve that, because the rear derailleur caps the cog it can wrap. That cap is the actual, physical difference between road and gravel gearing — more than the chainrings. It’s why Trek publishes a 36T max cog on the Domane’s road derailleur while gravel derailleurs handle 44 and beyond, and why fitting a huge cassette to a road bike usually ends in a derailleur that won’t reach. What your derailleur will take is in the cassette and chainring guide, and how the tiers differ is in the groupset hierarchy.