Roll over obstacles instead of braking: unweight the wheels, use arms and legs as suspension. 5 steps with milestones, common mistakes and safety notes.
The honest answer first: you roll over small obstacles such as roots and rocks by unweighting the wheels instead of lifting them: unweight the front wheel, unweight the rear wheel, use arms and legs as suspension and let the bike roll [1]. You do not lift anything, you make yourself light at the right moment.
According to BASPO, an unbraked wheel rolls better over obstacles and the suspension works better without braking [2]. That is the opposite of the beginner reflex: see the obstacle, brake, stiffen up. Exactly this sudden deceleration led to going over the bars in 55.2 percent of 534 analysed crashes [3].
The Single Trail Scale assigns small obstacles to grade S1: small stones and flat roots that you roll over, with modulated braking and body displacement, usually standing [4].
How hard is it? You learn the principle in an hour. You become reliable on varied surfaces after many rides (experience-based).
Good rolling looks unspectacular because your body stays calm and only the bike works.
Before the obstacle you go from the base position into the active position: arms and legs slightly bent, centre of mass central to slightly back depending on the slope, elbows slightly out [6].
Milestone: you switch into the active position on command without the bars wobbling.
Just before the front wheel hits, your centre of mass goes low and slightly back. The pre-tensioned arms absorb the impact and the wheel keeps ground contact [1].
Milestone: you roll over the branch five times in a row, the front wheel stays down and does not deflect.
Before the rear wheel hits, your centre of mass moves forward again to the central position. The rear wheel rolls over the obstacle and your legs absorb it [1].
Milestone: you hear only a soft rolling sound, no hard thud.
Regulate your speed beforehand. You do not brake on the obstacle itself, because an unbraked wheel rolls better [2]. One or two fingers stay on the brake [7].
Milestone: you ride over the obstacle without front or rear wheel locking.
The technique also works for sequences of obstacles. BASPO names a rock garden with the front wheel unweighted as an example [1]. Then you return to base or active position.
Milestone: a row of three branches about two metres apart, clean and without putting a foot down.
Obstacles are the moment when wheels suddenly decelerate. Over-the-bars crashes made up 55.2 percent of the 534 analysed cases, mostly through sudden deceleration [3]. In mountain biking the head and upper extremity are the most common injury sites [9]. In a meta-analysis across cyclists, a helmet cut serious head injuries by about 60 percent [10], a figure for cycling in general.
Increase obstacle height and speed separately, never both at once (practice). Wet roots are slippery; the Single Trail Scale explicitly rates only ideal conditions, bad weather raises the difficulty [4]. This guide explains and motivates, it does not replace supervised training.
The trick is the sequence, not strength: first front wheel light, then rear wheel light. Say "front, back" out loud while practising. It sounds silly, but it separates two movements that beginners lump into one.
Second trick: hit the obstacle as close to a right angle as possible. A root you catch at a diagonal deflects the front wheel sideways, one you cross square simply rolls under you (practice). So choose the line where the angle is right while you approach, and your speed with it.
Switch into the active position, unweight the front wheel just before it hits, then the rear wheel, and let the bike roll over the root without braking. Arms and legs absorb the impact [1] [2].
Not for small obstacles, you only unweight. From a certain obstacle height unweighting is no longer enough and you lift the front wheel actively [11].
Regulate speed yes, brake on the obstacle no. An unbraked wheel rolls better over obstacles and the suspension works better [2].
Usually because you are too slow or hold your arms stiff. A rolling wheel stays in balance more easily [8], and slightly bent arms absorb the impact [1].
There is no fixed figure. From a certain height unweighting is no longer enough and you lift the front wheel actively [11]. Downhill, steps up to about 40 centimetres can be ridden at low speed [12].
Bike-Body Separation: Moving the Mountain Bike Under a Calm Upper Body