Compact vs. Semi-Compact Cranks: Comparing 50-34, 52-36 and 53-39 by Gear Ratio

Crank types and their teeth

On a road bike's front gears (chainrings), the larger is called the big ring and the smaller the small ring. Combinations of teeth have names: a larger big ring is better at high speed on the flat, and a smaller small ring gives a lighter gear on climbs.

The jump when shifting at the front is how many percent lighter the gear gets when dropping from the big ring to the small ring. It's 36% on 53-39 and 47% on 50-34, so dropping to the small ring on 50-34 feels much lighter all at once. This difference in the jump is the one you notice most easily when riding.

Compared with the same cassette (12-speed 11-30)

These results use a 12-speed 11-30 at the rear, 700×28C tires (circumference 2130 mm) and a cadence of 90 rpm, changing only the front gears.

The lightest gear on 50-34 (34×30) is about 6% lighter than 36×30 on 52-36 and about 13% lighter than 39×30 on 53-39. Meanwhile, the heaviest gears differ by 4% between 50×11 and 52×11, a speed difference of about 2 km/h at 90 rpm. You only keep pushing above 50 km/h on descents or in sprints, so for most people the difference at the light end matters more.

What differs on climbs: cadence at 10 km/h

On hills, the lightest gear is what counts. Comparing the cadence needed in the lightest gear to climb at the same 10 km/h makes the difference clear. The lower the cadence, the heavier each pedal stroke.

10 km/h is a speed often seen when an ordinary cyclist climbs a 6–8% grade. On 53-39 you drop to 60 rpm and grind up the hill, while 50-34 × 11-34 gives 78 rpm, close to how you spin on the flat. Climbing speeds by gradient and power are calculated in How to Choose a Cassette: Teeth Needed for Hill Climbs.

After switching, where does your usual gear land?

When you change cranks, gears of the same weight move to different positions. Switching from 50-34 × 11-34 to another setup, these are the closest combinations to commonly used gears (excluding cross-chaining). The figures in parentheses are the weight difference from the original gear.

For gears of about 2.4–3.3 used on the flat, every setup offers a combination within ±5%. The big differences are at the two ends: switching to 52-36 × 11-30 makes the lightest gear 20% heavier, and 46-30 makes the heaviest gear 8% lighter. A simple way to think about a switch is that flat gears won't be a problem, and the ends are where it matters.

What's the problem with a big front jump?

The weak point of 50-34 is the big 47% jump between the big and small rings. Dropping to the small ring makes the pedals suddenly light so your legs tend to spin out, and getting back to the same weight takes 3–4 smaller sprockets at the rear. To match 50×21 (2.38) after dropping to the small ring, for example, you have to change the rear as far as 34×14 (2.43).

• 53-39 (36%): after a front shift, move back 2–3 gears at the rear. The small jump makes frequent front shifts easy in a group
• 52-36 (44%): after a front shift, move back about 3 gears at the rear. A compromise between racing and long rides
• 50-34 (47%): after a front shift, move back 3–4 gears at the rear. Suits dropping to the small ring at the start of a climb
• 46-30 (53%): after a front shift, move back about 4 gears at the rear. Treat the rings as one for the flat and one for climbs

If you shift rarely at the front (big ring on the flat, small ring on hills), the jump's size hardly matters. If you switch often on a rolling course, a semi-compact or standard crank's smaller jump keeps your rhythm better.

How does a single chainring (1×) differ?

A single chainring setup uses one ring at the front with a wide-range cassette such as 10-36 or 10-44. With no front derailleur, operation is simpler, and the chain is less likely to drop in mud or over bumps.

Speeds are for 700×28C at 90 rpm. A single chainring has both a narrower range and fewer usable gears (those at least 3% apart from the others) than a two-ring setup. Rear jumps are also larger, so it suits uses that put simple operation first, such as gravel or town riding, more than group rides where you want fine pace control.

Which to choose? Recommendations by rider type

If you're unsure, decide by your biggest current problem: legs giving out on climbs, or running out of gear on descents and with a tailwind. For the former, prioritize the light end; for the latter, the heavy end. Either way, first consider whether a new cassette (from a few thousand yen) can solve it, as that's often cheaper than a new crank (tens of thousands of yen).

FAQ

Which is better, a compact or a semi-compact crank?

Compact (50-34) if you want easier climbing, and semi-compact (52-36) if you value high speed on the flat and a smaller front jump. With the same 11-30, the compact's lightest gear is about 6% lighter, and the semi-compact's heaviest gear is about 4% heavier.

What's the top speed on 50-34?

In the heaviest gear, 50×11, on 700×28C: about 52.3 km/h at 90 rpm, about 58.1 km/h at 100 rpm, and about 63.9 km/h at 110 rpm. In normal riding you mainly run out of gear on descents and in sprints.

How different are 53-39 and 50-34?

With 11-30, the lightest gear is 1.30 for 39×30 and 1.13 for 34×30, making 50-34 about 13% lighter. Cadence when climbing at 10 km/h is about 60 rpm on 53-39 and about 69 rpm on 50-34. The heaviest gear, 53×11, is about 6% heavier and about 3 km/h faster at 90 rpm.

What happens with a big front jump?

Dropping from the big to the small ring feels suddenly light, and getting back to the same weight takes changing 3–4 gears at the rear. The jump is 47% on 50-34, 44% on 52-36 and 36% on 53-39.

Does a single chainring suit a road bike?

It has the advantages of simple operation and fewer dropped chains, but the gear range is narrower and the jumps are larger. 42 × 10-36 has a gear range of 360%, narrower than 455% on 50-34 × 11-34. It suits gravel and town riding, while two rings suit group riding with fine pace control.