1x vs 2x gravel gearing: compare climbing gears, cadence and overlap

The tooth ratio is front teeth divided by rear teeth. For a direct engaged chain drive it describes how many times the rear wheel turns per crank turn. The smallest front and largest rear make the low endpoint; the largest front and smallest rear make the high endpoint. Compare those two numbers separately rather than starting with one overall percentage.

The 40 × 51 low is 0.784, lower than 30 × 36 at 0.833. At the other end, 46 × 11 is 4.182, above 40 × 10 at 4.000. Here the single has the lower first gear and the double the taller last gear. Those results describe these exact inventories; a larger single ring or a different cassette can move either answer.

The 1x example uses the CS-M8100-12 10–51 tooth sequence. The 2x example uses the CS-HG710-12 11–36 sequence. Shimano also publishes 10–45 and other 11-tooth-start variants; those do not inherit the same middle sprockets from a similar name. Read the exact model and variant at the source rather than filling the gap between the first and last tooth counts by guesswork.

The three ledgers below each stay on one ring. They run from the largest rear sprocket to the smallest, or easier to harder in the direct model. A positive step is the increase in ratio from the row immediately above, divided by that previous ratio. The first row has no previous step. Keeping the ring fixed makes each row-to-row change correspond to adjacent positions in its declared cassette.

The small ring covers 0.833 to 2.727 and the large ring 1.278 to 4.182. The intervals overlap, but each ring still offers only discrete tooth pairings. For example 30 × 21 gives 1.429 and 46 × 32 gives 1.438, about 0.6% apart using 30 × 21 as the denominator. They are close, not identical, and could be reached by two different combinations.

Changing the front ring at the same rear position is a different question. On the 32-tooth sprocket, changing from 30 to 46 at the front raises the ratio by about 53.3%. The near-match above changes both positions; it is a numerical relationship, not a shifting instruction. A sorted list of 24 ratios does not tell you a real shift sequence or which pairings are allowed, quiet or efficient on a particular bike.

Start from a ride observation rather than a gear label. If you run out of usable low gears, record the actual current pair and rolling circumference before comparing a proposed low endpoint. If a rear shift feels too large at a recurring pace, write down the two actual sprockets and the speed where you noticed it. If you regularly stop pedalling in the highest gear, first distinguish coasting from a genuine engaged-cadence observation.

For different tyres or wheel builds use separately declared rolling circumferences. A 700c or 650b label does not supply rollout under load. If you do not know the circumference, compare tooth ratios only and keep cadence and speed unresolved. If there is an additional transmission stage, do not interpret the direct-drive wheel calculations as that bicycle’s actual development.

Open the blank comparator and give the two configurations distinct names. For the worked example enter 40 in the first Front teeth field and 30, 46 in the second. Enter each full rear list from the matching ledger. You can check tooth ratios without a wheel declaration. To reproduce the rolling example only, declare direct drive for both and enter 2160 mm as the circumference. Keep crank length and hardware limits blank unless you have separate evidence.

To compare at one speed inside the tool, choose an explicit reference pair and enter a reference cadence. For example choose 40 × 24 and 80 rpm; the workspace reports same-speed cadence against that specific reference where development is known. The 80 rpm speed column in the article is a separate multiplication for each pair, not the tool’s fixed-speed reference output. Following the link transfers no numbers and does not start a comparison.