11-30 vs 11-34: what actually changes
The internet's favorite cassette question, computed. On a compact 50/34 crank, moving from the 12-speed 11-30 to the 11-34 makes your lowest gear 12% easier — at 65 rpm on the steepest pitch, the same legs that ground along at 5.8 mph now spin the climb at 5.2 mph with identical effort per pedal stroke. The bill arrives in the cruising zone: the 11-34 gives up the 16-tooth sprocket, so where the 11-30 tiptoes from 15 to 17 in two gentle steps (6.7% then 6.3%), the 11-34 takes it in one 13.3% jolt — right where you hold steady speed and shift most. Whether that trade is worth it is exactly what the calculator above answers for your gearing and your candidate.
11-28 vs 11-30 vs 11-32 vs 11-34: the whole family on a compact
Before you pick two to compare above, here is the road cassette family side by side on a 50/34, computed from the manufacturers' published sprocket sequences:
| Cassette | Lowest gear | Climb speed at 65 rpm | Range | Biggest jump | Average jump | Capacity needed |
|---|---|---|---|---|---|---|
| Shimano 11-25 (11sp) | 1.36 | 7.0 mph | 334% | 11.8% | 8.6% | 30T |
| Shimano 11-28 (11sp) | 1.21 | 6.3 mph | 374% | 13.3% | 9.8% | 33T |
| Shimano 11-30 (11sp) | 1.13 | 5.8 mph | 401% | 14.3% | 10.6% | 35T |
| Shimano 11-32 (11sp) | 1.06 | 5.5 mph | 428% | 14.3% | 11.3% | 37T |
| Shimano 11-34 (12sp) | 1.00 | 5.2 mph | 455% | 14.3% | 10.8% | 39T |
| Shimano 11-36 (12sp) | 0.94 | 4.9 mph | 481% | 16.7% | 11.4% | 41T |
50/34 chainrings, 700×28 tires. Lowest gear = 34 ÷ largest cog; capacity = (50 − 34) + (largest cog − smallest cog), the number to check against your rear derailleur's spec.
Two patterns worth seeing whole. The average jump barely moves across the family — 12-speed spreads the extra teeth thinly — while the biggest jump grows from under 12% to nearly 17%, and it's the biggest jump that lands in the middle of the cassette on the wide ones. And the climbing speed column is the real purchase question: each step down the table is a few tenths of a mph at the same cadence on the steepest pitch, which is either irrelevant or everything depending on where you ride.
Every rear derailleur has a published maximum cog and a total capacity — the teeth it can take up across both shifts, computed as (big ring − small ring) + (big cog − small cog). The worked pair above needs 35T of capacity for the 11-30 and 39T for the 11-34; road short cages typically top out around 30–34T on the cog and the mid-30s on capacity, depending on generation, and going past the spec sometimes works with a longer B-screw and sometimes shifts like a bag of spanners. The pre-purchase checklist: your derailleur's max cog and capacity, your freehub type (an 11T cassette and a 10T cassette need different bodies), and a chain — a four-tooth-bigger cog wants roughly two more links, and a chain sized for the old cassette will bind in big-big. It's all on the derailleur maker's spec page; read it before the cassette page.
What about 10-tooth cassettes (10-33, 10-36)?
SRAM's road cassettes start at 10 teeth and pair with smaller chainrings (48/35, 46/33): the idea is the same top gear from a smaller, lighter, easier-shifting ring, and a lower low gear for free. The arithmetic mostly holds — 48×10 is 5.6% taller than 50×11, and 33×33 is a genuine 1:1 — with two costs the marketing skips: a 10-tooth cog runs the chain around a tighter bend, which costs a couple of watts of drivetrain friction in the gear you use for descents and sprints, and it needs an XDR freehub body, so it's a wheel question as well as a cassette question. Type any of them into the calculator (10, 11, 12…) to see them against what you have.
Bigger cassette, or smaller chainring?
The cassette isn't the only way down. Keeping your 11-30 and swapping the 34T inner ring for a 32T gets you a 6% easier low gear — most of the 11-34's climbing benefit — while keeping the 16T sprocket and the tight jumps you cruise on. The trades: chainrings are fiddlier to source for some cranks, the front shift gets slightly bigger, and your top end is untouched either way. Rough guide: if you only run out of gears on climbs, a smaller ring preserves the cassette you like; if you also want wider range generally, take the cassette. Run both options through the calculator — the chainring comparison prices the ring side — and see the whole picture on the full gear chart.
A 15% jump at the 30→34 end of the cassette barely registers — you're grinding uphill and grateful. The same percentage between 15 and 17 teeth lands mid-pack, where you hold steady speed on flats and shift constantly: at 19 mph on the 50 ring it's the difference between 81 rpm in the 17 and 72 in the 15, with nothing in between. That's why riders who "upgraded" to a wide cassette sometimes hate it on the flat commute and love it in the hills — both reactions are the same table above, read at different rows.
Reading the comparison
Three numbers decide most cassette choices. Lowest gear: if your knees or your hills say you need easier, this wins and the jumps are the price — pay it. Biggest jump and where it sits: below ~13% you'll barely notice; 15%+ in the middle of the cassette you will. Range: more range always costs either jumps or sprockets — 12-speed exists precisely to soften that trade, which is why the 12-speed 11-34 hurts less than the 11-speed version did. And if you're weighing 1x against 2x rather than two cassettes, that's a different question with its own trade-offs — the 1x vs 2x calculator runs both drivetrains side by side.