Smearing: How to Trust Friction on Bad Feet

Sooner or later there is no foothold left: only blank wall, a rough patch or the face of a volume. You press the shoe on the surface and trust the rubber. That is a smear, and it is often where climbers stop trusting their feet and start overgripping.

Whether a smear holds is not a matter of faith. It depends on the direction of the force through your foot, the size of the contact patch, how you load it, and the rubber and surface. The general principles are covered in Footwork Principles: Precision, Timing & Force Direction and Contact Mechanics. This article goes deeper into smearing itself: what decides whether it holds, what research says, and how to train it.

1. What a smear asks of friction

The force through your foot can be split into two parts:

  • Normal force: the part that presses the rubber into the surface.
  • Shear force: the part that pushes the foot along the surface.

On an edge, the edge itself carries most of the shear. On a smear, friction has to carry all of it. The foot stays put as long as the ratio of shear to normal force stays below the friction the rubber and surface can provide. Once the ratio goes above that limit, the foot slides.

The important consequence: the ratio depends on the direction of the force, not on how hard you push. If you press twice as hard in the same direction, both the normal and the shear force double, and the ratio stays the same. That is why stomping on a smear rarely helps. Changing the direction does.

A simple slab example

Imagine your weight goes straight down through one foot on a smooth slab tilted at an angle θ from horizontal. The friction coefficient you need is then tan θ:

  • 30° slab: about 0.58
  • 45° slab: 1.0
  • 60° slab: about 1.73
θ θ W N = W·cos θ S = W·sin θ Friction needed: μ = S / N = tan θ 30° → 0.58 · 45° → 1.0 · 60° → 1.73
Your weight W splits into a normal force N that presses the rubber into the slab and a shear force S that pushes it down the slab. The steeper the slab (larger θ), the larger S is compared with N.

The need for friction rises steeply with the angle. At some point a vertical load on a smear cannot be held by friction alone, and the hands or a different force direction must make up the difference. Where that point lies depends on the rubber, the surface texture and the conditions.

2. Body position decides how much friction you need

When your hands carry little weight, the force through your foot points roughly from the foot toward your center of mass (CoM). So where your hips are decides the direction of that force:

  • Hips leaning into the wall: the force line tilts toward the surface. More of your weight pushes the foot along the wall, the shear-to-normal ratio rises, and the foot skates.
  • Hips stacked over the foot: on a slab, the force goes straight down and the ratio is close to tan θ.
  • Hips slightly further out: the force presses more into the surface and less along it, so less friction is needed. The hands then have to stop you from tipping backward, usually with light pressure or a palm.

This is the mechanical reason behind the classic slab advice to "stand up over your feet." Leaning in feels safer, but it increases the friction the foot needs.

On steep terrain the picture is different: the feet mainly press into the wall, and hips close to the wall help them push inward. On slab and vertical smears, the feet carry most of your weight, so the direction of that weight matters most.

What research shows about load on the feet

Bonelli et al. (2025) measured contact forces in 14 intermediate and advanced climbers holding static positions on a slightly positive wall (+5°), a vertical wall and a slight overhang (−5°). As the wall got steeper, load shifted from the feet to the hand: hand force rose by 4–17% and total foot force fell by 3–12%. Body position also mattered: a low position with the arm extended and the legs bent increased hand force by 23–32% compared with a high position, and this effect was largest on the slab. The limits are clear: a small sample, static positions only, wall angles within ±5°, and no elite climbers. It supports the basic idea that on less steep terrain, your feet carry more of the load and your position decides how it is shared.

3. Contact area and heel position

Rubber grips through two mechanisms: adhesion to the surface and deformation into its texture. Both need contact. The more rubber that touches the surface, and the more evenly it is loaded, the more of the texture the rubber can use.

Rubber friction is also not perfectly constant. Research on rubber friction (mainly from tyre science) shows that the friction coefficient can fall as contact pressure rises, partly because of frictional heating and because the real contact area stops growing in proportion to the load (Fortunato et al., 2015). Spreading the same load over a bigger patch keeps the pressure lower, which is one reason a broad smear is often more secure than a load concentrated on the tip of the toe.

Practical consequences:

  • Lower the heel slightly. This brings more of the forefoot into contact instead of balancing on the toe tip. It needs some ankle mobility and calf length.
  • Use the ball of the foot. The area under the big toe joint usually gives the largest, firmest patch.
  • Look for texture. A rough patch, a dimple or the face of a volume angled slightly toward you reduces the friction you need, because part of the force now points into the feature.

These cues follow from contact mechanics. They have not been tested directly in climbing studies, so treat them as principles to experiment with, not as measured rules.

4. Timing: load gradually, then keep it steady

Rubber is viscoelastic. It needs a short moment to flow into the surface texture, and it holds better while it stays still than once it starts to slide. Two errors follow from that:

  • Loading too fast. A sudden load spikes the shear force before the rubber has settled. The foot breaks loose on the first contact.
  • Adjusting under load. Shuffling or rotating the foot after you have weighted it starts a small slide. Once the rubber is moving, it rarely grips again in the same spot.

The sequence is: place the foot precisely, ramp up the load over about a second, then move your CoM smoothly over it. If the foot is in the wrong spot, take the weight off and replace it rather than twisting it into position.

5. Shoes, rubber and conditions

Rubber compounds differ, but hardness is not the whole story

Elkington et al. (2024) tested five climbing shoe rubbers against granite in the lab. At the lower load, the rubbers with the smoothest surface and the highest adhesion gave the most static friction. At the higher load, softer rubbers did better, and hardness was negatively related to friction. The softest rubber had the highest friction but also the most wear. The authors conclude that hardness alone is an incomplete guide and that roughness and adhesion matter as well. It is a small pilot study, done at one temperature (22 °C) on one rock type, with loads that were estimated rather than measured on climbers, and it did not test smearing movements directly.

Shoes and conditions

  • Stiffness. A softer shoe conforms to the surface and spreads the rubber; a stiff shoe supports the foot better on small edges. This is a mechanical trade-off, not a tested result.
  • Keep the soles clean. Dust, chalk and grit sit between the rubber and the surface and reduce the real contact area. Wipe your soles before a smear-heavy climb.
  • Temperature matters. Rubber friction depends on temperature. In tyre research, friction usually decreases as the rubber gets warmer (Fortunato et al., 2015). Many climbers notice better friction on cool days, but we found no controlled study on climbing rubber across temperatures, so take that as an observation, not a proven effect.

6. Why fear makes smears fail

Smears feel insecure because there is nothing under the foot. The typical response is to lean into the wall, overgrip and stiffen the legs. Mechanically, that is the worst combination: leaning in tilts the foot force along the surface, and stiff legs make gradual loading harder. If a past slip still makes you hesitate, Rebuilding Confidence After a Slip or Fall explains how to rebuild trust without reinforcing the fear. The drills below let you find the real limit close to the ground.

7. How to train smearing

Smearing is a skill. It improves with deliberate, low-intensity repetition close to the ground, not with hard attempts. Work on mats, low on easy walls, and step off before you fall awkwardly.

Drill 1: Smear-only traverse

On an easy vertical or slab section, traverse using good handholds but no footholds at all. Every foot placement is a smear on the wall or on a volume. Focus on placing, loading gradually and moving only when the foot feels set. 3–5 minutes as part of your warm-up.

Drill 2: Find the slip point

Stand on a smear just above the mat, holding a good handhold. Slowly lean your hips toward the wall until the foot starts to slide, then stand back up over it. Repeat a few times on each foot. The goal is to feel how much body position changes the grip, and where the limit actually is.

Drill 3: Repeat with one change

Repeat a smear-heavy problem and change only one thing per attempt: heel height, hip position or loading speed. Compare how secure each version feels. This is the same approach as the drills on our technique limiter page.

A note on ankles

Slipping off a smear low down often means an unplanned landing. Keep the drills close to the mat, and if your ankles feel unstable on landings, the Ankle Stability & Landing Mechanics routine is a good addition. An ankle that stays swollen or painful after a fall should be checked by a physio.

Putting it all together

  • A smear holds as long as the shear-to-normal ratio stays below the available friction. Pushing harder does not change that ratio; changing the direction does.
  • On slab and vertical terrain, hips leaning into the wall increase the friction you need. Stand over your feet.
  • A bigger, evenly loaded contact patch helps: lower the heel slightly, use the ball of the foot and look for texture.
  • Place, load gradually, then move. Do not adjust a foot under load.
  • Rubber compound, shoe stiffness, clean soles and temperature all play a role, but research on climbing rubber is still limited to small lab studies.

Next step

If you often overgrip on easy slabs or lose your feet on volumes, technique is a likely limiter. Add the smear-only traverse and the slip-point drill to your warm-up twice a week for a month, and check the other drills on the technique limiter page. Then return to a few slab problems that used to feel insecure and compare.

References

  • Bonelli et al. (2025). Climbers' muscle excitation and force distribution at different wall angles and body positions. European Journal of Applied Physiology.
  • Elkington RJ, Armitage JL, Khan T, Bryant MG. (2024). Sticky feet: a tribological study of climbing shoe rubber. Sports Engineering, 27, 30.
  • Fortunato G, Ciaravola V, Furno A, Scaraggi M, Lorenz B, Persson BNJ. (2015). On the dependency of rubber friction on the normal force or load: theory and experiment. arXiv:1512.01359.
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