1x drivetrain: benefits and setup guide

Why 1x?

The 1x drivetrain (pronounced "one-by") has revolutionised bike transmissions, especially in mountain biking. The principle: a single chainring up front, no front derailleur, and a wide-range rear cassette to compensate.

The benefits

• Simplicity: one fewer shifter on the bar, one fewer cable, one fewer derailleur. Fewer parts = fewer breakdowns
• Weight: save 200-400 g (front derailleur + cable + second chainring + shifter)
• Chain line: straighter on average, less friction, less wear
• No chain drops: with a narrow-wide chainring and a clutch derailleur, the chain stays put
• Ground clearance: without the front derailleur, no risk of catching on rocks

The downsides

• Reduced gear range: even with a 10-52T cassette, the range is less than a 36/26 double with an 11-42T cassette
• Gear jumps: gaps between sprockets are larger (e.g., 10-12-14-16-18-21-24-28-33-39-45-52T). With 2x, the steps are more even
• Price: wide-range cassettes are expensive (100-300 EUR for a SRAM Eagle or Shimano XTR 12-speed)

Choosing chainring size

The chainring choice depends on your riding and terrain:

Simple rule: if you are walking uphills with your current chainring, go 2 teeth smaller. If you are spinning out on descents, go 2 teeth larger.

Narrow-wide teeth

A 1x chainring uses narrow-wide (alternating) teeth: one wide tooth, one narrow tooth, matching the outer and inner chain links. This is what prevents chain drops without a chain guide.

Wide-range cassettes

SRAM Eagle (12-speed)

• XG-1275 (GX Eagle): 10-52T, steel, ~380 g, ~90 EUR
• XG-1295 (X01 Eagle): 10-52T, XD driver, ~330 g, ~200 EUR
• XG-1299 (XX1 Eagle): 10-52T, XD driver, ~250 g, ~350 EUR

Freehub body: XD (SRAM proprietary). Incompatible with Shimano HG bodies.

Shimano 12-speed

• CS-M6100 (Deore): 10-51T, ~550 g, ~50 EUR — excellent value
• CS-M7100 (SLX): 10-51T, ~485 g, ~70 EUR
• CS-M8100 (XT): 10-51T or 10-45T, ~380 g, ~80 EUR
• CS-M9100 (XTR): 10-51T or 10-45T, ~340 g, ~250 EUR

Freehub body: Micro Spline (Shimano 12-speed). Incompatible with standard HG (10/11-speed) and XD (SRAM) bodies.

Freehub body compatibility

Rear derailleur setup

With a 1x drivetrain, the rear derailleur does ALL the work. The setup must be perfect.

Clutch derailleur

All modern 1x rear derailleurs have a clutch: a friction mechanism that prevents the chain from bouncing. The clutch must be engaged (lever ON). If the chain slaps on descents, check that the clutch is working — if worn, the derailleur needs replacing.

B-tension adjustment

B-tension (or gap) controls the distance between the guide pulley and the largest sprocket. This is critical with 50T+ cassettes.

• SRAM Eagle: use the SRAM gap tool. The guide pulley should be approximately 17-20 mm from the 52T sprocket
• Shimano 12-speed: the pulley-to-sprocket distance should be 10-12 mm on the largest sprocket (depending on the exact model)

If B-tension is too low, the derailleur hits the cassette on the large sprockets. Too high, and shifting becomes sluggish and imprecise.

High and low limit screws

• High limit (H): limits the derailleur on the smallest sprocket. On a 1x, it must not go beyond to prevent the chain falling between the sprocket and frame
• Low limit (L): limits the derailleur on the largest sprocket. Must be open enough to reach the 52T without strain, but no more

Cable tension

1. Put the chain on the smallest sprocket
2. Loosen the cable anchor bolt
3. Pull the cable by hand, tighten the bolt to 4-5 Nm
4. Shifting should be precise from small to large. Adjust with the barrel adjuster: 1/4 turn counter-clockwise if upshifting is poor, 1/4 clockwise if downshifting is poor

SRAM Eagle vs Shimano 12-speed

Both work perfectly well. The choice often comes down to personal preference and ecosystem (whether you already have an XD or Micro Spline freehub body).

To check the exact compatibility between your crankset, cassette, and derailleur, L'Atelier retrieves the compatibility tables from Shimano and SRAM documentation in seconds.