Engineering · Tool 05
Friction Coefficient Finder
Sliding · Rolling · Static & Kinetic
Pick sliding or rolling contact, then the materials or contact type involved, and the typical friction coefficient shows up — static and kinetic together for sliding, a typical value and range for rolling.
Reference only. Friction coefficients are notoriously sensitive to surface finish, cleanliness, temperature and load — published values vary between sources. Treat these as a starting point for estimation, and test the actual mating surfaces for anything load- or safety-critical.
Friction Coefficient Finder
Choose sliding (two materials in contact) or rolling (a wheel, ball or roller on a surface).
Sliding Friction — Quick-Scan Table
| Material pair | Static / kinetic by condition |
|---|---|
| Steel – Steel | Dry: μs 0.74 / μk 0.57 Greasy / Lubricated: μs 0.15 / μk 0.09 |
| Steel – Aluminum | Dry: μs 0.61 / μk 0.47 |
| Steel – Brass | Dry: μs 0.51 / μk 0.44 |
| Steel – Cast Iron | Dry: μs 0.40 / μk 0.23 |
| Steel – Copper | Dry: μs 0.53 / μk 0.36 |
| Steel – PTFE (Teflon) | Dry: μs 0.04 / μk 0.04 |
| Steel – Rubber | Dry: μs 1.00 / μk 0.80 Wet: μs 0.70 / μk 0.50 |
| Steel – Ice | Dry: μs 0.03 / μk 0.02 |
| Steel – Wood | Dry: μs 0.50 / μk 0.20 |
| Steel – Nylon | Dry: μs 0.35 / μk 0.25 |
| Steel – Leather | Dry: μs 0.60 / μk 0.50 |
| Aluminum – Aluminum | Dry: μs 1.05 / μk 1.40 Greasy / Lubricated: μs 0.30 / μk 0.30 |
| Cast Iron – Cast Iron | Dry: μs 1.10 / μk 0.15 |
| Cast Iron – Copper | Dry: μs 1.05 / μk 0.29 |
| Wood – Wood | Dry: μs 0.40 / μk 0.30 |
| Wood – Leather | Dry: μs 0.40 / μk 0.30 |
| Glass – Glass | Dry: μs 0.94 / μk 0.40 |
| Nylon – Nylon | Dry: μs 0.20 / μk 0.15 |
| Rubber – Concrete | Dry: μs 1.00 / μk 0.60 Wet: μs 0.70 / μk 0.30 |
| Rubber – Asphalt | Dry: μs 0.80 / μk 0.50 Wet: μs 0.60 / μk 0.25 |
Rolling Resistance — Quick-Scan Table
| Contact | Range (Crr) | Typical |
|---|---|---|
| Steel wheel on steel rail | 0.0010 – 0.0020 | 0.0015 |
| Ball bearing (rolling element) | 0.0010 – 0.0015 | 0.0012 |
| Roller bearing | 0.0010 – 0.0024 | 0.0018 |
| Rubber tire on smooth concrete | 0.0100 – 0.0150 | 0.0130 |
| Rubber tire on asphalt | 0.0100 – 0.0200 | 0.0150 |
| Rubber tire on gravel / unpaved | 0.0200 – 0.0300 | 0.0250 |
| Bicycle tire on asphalt (high pressure) | 0.0020 – 0.0050 | 0.0040 |
| Solid rubber tire (industrial) on concrete | 0.0150 – 0.0250 | 0.0200 |
| Cast iron wheel on wood floor | 0.0200 – 0.0300 | 0.0250 |
| Steel wheel on wood | 0.0120 – 0.0180 | 0.0150 |
Explanatory Notes
Why these numbers move around
Friction coefficients aren't material constants the way density or elastic modulus are — they depend on surface finish, contamination, humidity, temperature and even how long the surfaces have been in stationary contact. Two published tables can legitimately disagree by 20–30% for the same "clean, dry" pair. Use these values to size an estimate, not to certify a design.
The aluminum-on-aluminum anomaly
Clean, dry aluminum sliding on aluminum is one of the few common pairs where kinetic friction is reported higher than static — the surfaces tend to gall and cold-weld microscopically once moving, rather than settling into an easier sliding state. It's a real, documented effect, not a typo, and one more reason aluminum-on-aluminum sliding contacts are usually avoided or run with a lubricant or dissimilar mating material.
Dry, greasy and wet aren't interchangeable
A lubricant film (greasy/lubricated) separates the surfaces and can cut friction by 3–5×, which is the entire point of designing a joint to be lubricated rather than running dry. Water (wet) doesn't always help the same way — it lowers friction for rubber on smooth pavement, but can leave it largely unchanged or even raise it for some metal pairs by washing away a protective oxide or oil film.
Cross-reference with the other tools
Friction coefficient feeds directly into the torque/preload relationship in the Bolt Grades tool's nut factor (K) — a dry vs. lubricated joint is exactly the dry-vs-greasy distinction made here.
Basis: typical values compiled from widely cited engineering references (e.g. Marks' Standard Handbook for Mechanical Engineers, common engineering-toolbox tables). Presented as representative figures for preliminary estimation — always confirm against a measured value or the specific material datasheet for load-critical or safety-critical designs.