Hardtail, sag, singletrack scale? The MTB A-Z explains every term from our mountain biking guides in plain, friendly English – before you need it.
## Introduction "Hardtail or full-suspension, what's sag, and what does S0 mean on a trail sign?" That's exactly where most beginners tune out. Mountain biking has its own language, and our MTB guides assume you already speak it, so they don't turn into endless glossaries themselves. This MTB A-Z translates every term you'll run into across the Academy - with everyday comparisons instead of dictionary sentences. Read it once before you start the other guides, and everything will click.
Hardtail - a mountain bike with suspension only at the front fork, rigid at the rear. Lighter, cheaper, and lower-maintenance than a full-suspension bike - and because it forgives mistakes less, it forces you into cleaner line choices automatically. Plenty for getting started.
Full-suspension (Fully) - a bike with suspension front AND rear, usually through a rear shock. More comfortable and noticeably better at soaking up vibration than a hardtail - but it won't make you measurably faster on a normal trail. The choice is about terrain and comfort, not a speed upgrade.
Saddle height (Sattelhöhe) - how high your saddle sits, set so your leg is almost fully extended at the lowest pedal point. Too high costs control, too low costs power - the single most important, and cheapest, adjustment on the whole bike.
Dropper post (Dropper-Post) - a seatpost you lower and raise with a lever on the bar while riding. Drop it before a descent and you suddenly have room to get behind and under the saddle, instead of sitting on top of it like you do climbing.
Cockpit & brake levers (Cockpit & Bremshebel) - handlebar, stem, and brake levers together - everything you hold while standing on the pedals. Levers are angled and positioned so a single finger is enough to pull them, adjusted while standing, not sitting.
Disc brakes (Scheibenbremsen) - brakes that clamp onto a metal disc at the wheel hub instead of the rim. They bite far more reliably in wet or muddy conditions than old-style rim brakes and are the standard on mountain bikes today.
Tyre pressure & volume (Reifendruck & Reifenvolumen) - how much air is in the tyre (pressure) and how thick the tyre itself is (volume). Large volume at moderate pressure absorbs impacts and builds grip; pumped rock-hard, it buys you no measurable performance, only more vibration.
Tubeless - a tyre system with no inner tube at all, sealed instead with sealant inside the tyre. It lets you run lower pressure without risking a snakebite/pinch flat (Durchschlag) - the rim slamming hard into a rock through a tyre run too soft.
Sag - the amount your fork and shock already compress just from your body weight in riding position, before any impact hits at all. A practical target is roughly 20 to 30 percent of total travel, set via air pressure in the fork and shock.
Fork & shock (Federgabel & Dämpfer) - the suspension units at the front (fork) and rear (shock, on a full-suspension bike). Set correctly on sag, they absorb high-frequency vibration - left untouched and too firm, they pass every hit straight into your arms.
Thru-axle (Steckachse) - the axle that locks your wheel into the frame or fork, usually threaded today rather than a quick-release skewer as in the past. Worth a quick check before every ride.
Protective gear (Protektoren) - kit like knee pads or a back protector, chosen based on terrain. Not a free pass for more risk, but a sensible addition to clean riding technique - which remains your strongest protection.
Side knobs (Seitenstollen) - the tread on the tyre's shoulder that bites in corners. Worn side knobs are like worn brake pads: no amount of pressure fine-tuning fixes that, only a new tyre does.
Neutral position (Neutrale Position) - the base standing posture: pedals level, knees and elbows loosely bent, hips centred, eyes forward. Your bent joints act as your own built-in suspension.
Looking ahead (Blick voraus) - deliberately scanning 5 to 10 metres ahead instead of staring at your front wheel. The bike goes where you look - and a far, relaxed gaze calms your hands too.
Modulated braking (Dosiertes Bremsen) - using both brakes together, with the front brake supplying most of the stopping power and the rear brake mainly stabilising. Relying on the rear alone means braking longer and less securely.
Line/line choice (Linie/Linienwahl) - the path you pick through an obstacle or corner before you actually reach it. Chosen early and committed to, instead of improvised at the last second.
Arm pump - burning, cramping forearms, usually from gripping the bar too hard instead of letting the bike move underneath you. Holding loosely instead of clamping down is the fix.
Singletrack (Singletrail) - a narrow, usually natural path, often just wide enough for one bike. The counterpart to a wide fire road, and the actual reason most people start mountain biking in the first place.
Singletrack scale (Singletrail-Skala, S0-S5) - the common German difficulty rating for trails, from S0 (easy, smooth) to S5 (extreme). As a beginner, stick to S0 and only edge toward S1 once the current level feels effortless.
Flow trail (Flowtrail) - a trail deliberately built or chosen to be ridden rhythmically, without abrupt stops - few technical obstacles, plenty of momentum. Ideal for drilling the basics.
Root section (Wurzelteppich) - a stretch where many roots cross the trail close together. Slick when wet, and for beginners a good reason to avoid it at first rather than test yourself on it.
## Pro Tip Don't hang these terms as a loose list - anchor them along the bike itself: from the bottom up (tyre pressure, tubeless, side knobs), through the middle (sag, fork, shock), to the cockpit (brake levers, dropper post). And on the trail, in the same order: look up first, then pick your line, then brake with modulation. Hang each word on a real station instead of drilling it by rote, and you'll have it locked in after your first ride.
### What's the difference between a hardtail and a full-suspension bike? A hardtail has suspension only at the front, a full-suspension bike front and rear. The full-suspension bike is more comfortable and noticeably better at absorbing vibration, but it won't make you measurably faster on a normal trail. For getting started, a well set-up hardtail is completely sufficient - lighter, cheaper, less maintenance.
### What does sag mean on a mountain bike? Sag is how much your fork and shock already compress just from standing in riding position, before any impact hits. A practical target is roughly 20 to 30 percent of travel, set via air pressure - suspension dialled in correctly absorbs noticeably more vibration.
### What is the singletrack scale? The singletrack scale runs from S0 (easy, smooth) to S5 (extreme) and rates a trail's technical difficulty. As a beginner, stay at S0 and only move toward S1 once the current level feels effortless - build difficulty in small steps, not jumps.
### Why does tubeless make sense for mountain biking? Tubeless runs without an inner tube, sealed instead with sealant inside the tyre. That lets you run lower tyre pressure without risking a pinch flat/snakebite - the rim slamming hard into a rock through a tyre run too soft. Lower pressure means more grip and comfort on the trail.
### What is the neutral position on a mountain bike? The neutral position is the base standing posture: pedals level, knees and elbows loosely bent, hips centred over the bike, eyes far ahead. Your bent joints act as your own built-in suspension and keep the tyres on the ground - locked-out, straight arms transmit every hit straight into your body instead.