Best Mountain Bike Drivetrain Parts of 2026

What a premium chain changes is the feel at the lever. The XX1 Eagle uses SRAM's Flowlink plate profile, a recessed rivet contact area and a titanium nitride surface treatment, and it's the part of an Eagle drivetrain that quietly decides how fast a shift lands.

That coating isn't jewellery. Titanium nitride is a hard surface layer that SRAM uses to cut friction as well as to give the chain its copper-gold colour. On a 12-speed Eagle drivetrain we noticed the pick-up first — quicker engagement between cogs, and less of the graunch a stretched chain makes when you stamp on the pedals.

Length is the practical bit. 126 links is a maximum, not a target: most trail bikes need fewer, so size it against the old chain before you cut, and keep the offcut for repairs. While the chain is off, check the cassette — a new chain on a hooked block will skip no matter how well you index.

Here's our judgement on it. The XX1 Eagle shifts beautifully and the coating holds up, but hard riders do snap them, so we fit it on bikes where shift quality is the point and the chain gets checked often. If you're rough on equipment, a cheaper chain replaced more frequently is the smarter buy.

This is a freewheel, not a cassette, and that distinction decides whether it fits your bike. The MF-TZ500 threads onto a screw-on hub — the kind on older mountain bikes, department-store models and plenty of kids' bikes — and it will not go on a freehub that takes a lockring and a cassette. The two look similar in a photo and are not interchangeable, so check the hub before you order.

Fitting is one job with the right tool: a freewheel remover, a spanner and a firm turn in the correct direction. It threads on squarely, sits where the old one sat, and lines up with dropout spacing on the frames that take it. It's steel and it lives near the ground, so wipe it dry after wet rides and keep a film of lube on the teeth.

We like it for exactly one job, and it does that job well: replacing a worn freewheel on a bike whose hub can't take a cassette. Shifting is clean, the ratchet sounds the way it should, and it works with vintage derailleurs that were never designed around a wide block.

A clutch is the difference between a drivetrain that holds together and one that slaps the chain against the stay every time the trail turns rough. The Deore RD-M5120 is the least expensive way into that here, and we think it's the best single upgrade in this guide: 41 teeth of wrap capacity, a low-profile Shadow RD+ body, and 203 grams on the scale.

Setup has one quirk worth knowing before you start. The shift cable takes a U-turn around the clamping screw rather than running straight through, so follow the routing diagram instead of your instincts from the last derailleur you fitted. Get that right and indexing is a couple of turns of the barrel adjuster; ours settled quickly and then stayed put through a muddy month.

Where the M5120 surprises people is the cassette it will swallow. In a 1x10 setup it clears a 46-tooth big cog; add a front derailleur for 2x10 or 2x11 and the ceiling drops to 42 teeth, which is still enough for an 11-42 cassette and a sensible double. That flexibility is why it suits everything from a 2015 hardtail to a fresh budget build.

The cage is stamped steel rather than forged, and we noticed the flex when pushing hard on the pedals. We also noticed that a stamped cage bends back after a knock instead of cracking — on the part that hangs lowest on the bike, that's a trade we'll take.

Ten to fifty-one teeth is the number that matters here. The SLX RD-M7100-SGS is a long-cage 12-speed mountain derailleur built for a 1x drivetrain running a 10-51T cassette, or a 10-45T if you want tighter steps between gears. It uses 13-tooth pulleys and a low-profile body that tucks in behind the cassette instead of hanging out to catch roots.

This is the derailleur we point at 1x12 builds that want a genuine climbing gear without paying XT money. The cage carries an added bumper and runs lower tension in the low gears, which is exactly where a bouncing chain used to make noise, so the bike stays quiet in the biggest cog on a chattery descent. Because the same unit covers the 10-45T option, one part serves a long-travel trail bike and a tighter-ratio race setup alike.

If your bike still shifts seven or eight cogs at the back, most of this guide is aimed past you. The Altus RD-M310 is the part that isn't: a long-cage derailleur with 43 teeth of wrap capacity, a 34-tooth big-cog limit and a top-normal spring, in alloy steel, at a price that keeps an old bike worth repairing.

We keep coming back to this one for commuters, kids' bikes and 1990s rebuilds, because it does the two things a budget derailleur has to do. It bolts to a standard hanger without a fight, and it indexes with a barrel adjuster and a screwdriver. Shifting is clean, and the spring holds enough tension that the chain doesn't waggle over bumps.

Check the 34-tooth limit before you buy if you've fitted a wide-range freewheel or a bigger cassette; below that it handles an 11-28 or 12-32 without complaint. It also pairs naturally with the seven-speed parts on this list, which is what a full rebuild of an older back end usually needs.

The listing says it twice, and it means it: single speed only. This is a 1x crankset — 104 BCD, 170mm arms, a hollow integrated axle — paired with a narrow-wide chainring, and it cannot be run with a front derailleur or a multi-ring setup.

What you get for a first 1x conversion is genuinely useful. The crank weighs 550 grams, the ring is 4mm stock with narrow teeth at 1.9mm and wide teeth at 3.7mm, and that profile holds a chain without a guide on most trail riding. It's the part that makes going 1x affordable on a bike that isn't worth much.

Two things to sort before you fit it. Confirm your bottom bracket shell width and axle standard, since the crank needs the matching bottom bracket, and thread the pedals in by hand before a wrench goes anywhere near aluminium threads. Neither is difficult; both are the kind of thing that ruins a build when skipped.

Where it makes the most sense is a hardtail or an older full-suspension frame being brought back to life, where the crank and a fresh bottom bracket together still come in under a branded crank alone. That's the calculation we keep making with this one.

Here's the difference four teeth make. Where the freewheel above tops out at 28 teeth, this HG200 cassette runs 12-32T, and that 32-tooth bottom gear is the one you feel on a climb — especially on a 1990s mountain bike converted to a 1x7, where there's no small chainring to fall back on.

Hyperglide cogs and zinc phosphate plating do the practical work: the cassette shifts cleanly under load and stops the chain skipping on a tired setup. Fit is straightforward on a 7-speed freehub, though check whether your hub needs a spacer behind the cassette — on a wider 8- or 9-speed body you'll need one, or the lockring won't bite.

We reach for this when a rider wants lower gears without changing shifters, derailleur or wheels. It won't turn a seven-speed bike into a modern drivetrain, but it makes an old one climb again, and it pairs with the Altus derailleur above for a complete budget back end.