Materials for Machined Bike Parts
The material decides the weight, the fatigue life, the finish and much of the price. This page compares the materials that actually get machined into bike components and says which part each one suits.
Typical values for the stated condition, not a specification; the mill certificate governs. The full aluminum data with sources is in the alloy and finish reference.
Strength and stiffness per unit weight
Divide by density and the picture changes. Specific yield strength decides how light a strength-limited part can be; specific stiffness decides how light a stiffness-limited part can be, and most bike parts are stiffness limited.
| Material | Tensile | Yield | Density | Modulus | Yield / density (kN·m/kg) | Modulus / density (MN·m/kg) |
|---|---|---|---|---|---|---|
| Aluminum 6061-T6 | 310 MPa | 276 MPa | 2.70 g/cm3 | 68.9 GPa | 102 | 25.5 |
| Aluminum 7075-T6 | 572 MPa | 503 MPa | 2.81 g/cm3 | 71.7 GPa | 179 | 25.5 |
| Aluminum 2014-T6 | 483 MPa | 414 MPa | 2.80 g/cm3 | 72.4 GPa | 148 | 25.9 |
| Titanium Grade 5 (Ti-6Al-4V) | 950 MPa | 880 MPa | 4.43 g/cm3 | 113.8 GPa | 199 | 25.7 |
| Titanium Grade 9 (Ti-3Al-2.5V), annealed | 620 MPa | 483 MPa | 4.48 g/cm3 | 100 GPa | 108 | 22.3 |
| Steel 4130 (chromoly), normalized | 670 MPa | 435 MPa | 7.85 g/cm3 | 205 GPa | 55 | 26.1 |
| Stainless 17-4 PH (H900) | 1310 MPa | 1170 MPa | 7.80 g/cm3 | 197 GPa | 150 | 25.3 |
| Stainless 303 | 620 MPa | 240 MPa | 8.00 g/cm3 | 193 GPa | 30 | 24.1 |
| Stainless 304, annealed | 505 MPa | 215 MPa | 8.00 g/cm3 | 193 GPa | 27 | 24.1 |
| Brass C36000, half hard | 400 MPa | 310 MPa | 8.50 g/cm3 | 97 GPa | 36 | 11.4 |
| Delrin (POM) | 70 MPa | 70 MPa | 1.41 g/cm3 | 3.1 GPa | 50 | 2.2 |
| Nylon 6/6, dry | 80 MPa | 80 MPa | 1.14 g/cm3 | 2.8 GPa | 70 | 2.5 |
Aluminum, titanium and steel all land near 25 MN·m/kg in specific stiffness. That is why a part sized by how much it may flex weighs about the same in any of them, and why titanium against aluminum is usually a fatigue and cost question, not a weight one. More in weight against strength.
Fatigue
Bike parts fail in fatigue far more often than by a single overload. Aluminum figures are typical rotating-beam fatigue strength at 5 × 108 cycles; real parts sit well below them because of notches, threads and finish.
| Material | Fatigue (typical) | What it means for the part |
|---|---|---|
| Aluminum 6061-T6 | About 97 MPa | No true fatigue limit. Life is counted in cycles, so every structural part has one. |
| Aluminum 7075-T6 | About 159 MPa | Higher than 6061 in absolute terms, but notch sensitive. Radii and surface finish decide the real result. |
| Aluminum 2014-T6 | About 124 MPa | Usually forged for cranks; the forged grain flow helps more than the alloy. |
| Titanium Grade 5 and 9 | Shows a fatigue limit | Strong in fatigue for its weight, but sensitive to surface damage, galling marks and sharp thread roots. |
| Steel 4130, 17-4 PH | Shows a fatigue limit | Roughly 40 to 50 percent of tensile strength for a smooth specimen. Corrosion pits and plating reduce it. |
Anodizing lowers aluminum fatigue life and the penalty grows with coating thickness, so structural parts are tested in the finish they ship in. Background: material fatigue.
Anodize and finish response
Anodizing is an aluminum process. Every other material needs a different finish, and even among aluminum alloys the result varies. Coating thickness and dimensional effect per finish are in the reference table and the anodizing guide.
- Aluminum 6061Type II anodize takes dye evenly; the best choice when parts in a range must match color.
- Aluminum 7075Anodizes darker and less evenly than 6061. Color matching against 6061 parts is hard.
- Aluminum 2014Copper content gives a dull, uneven anodize and poor corrosion resistance. Usually painted or powder coated.
- TitaniumNot dyed. Anodizing by voltage gives a fixed palette of interference colors with no dimensional change worth measuring.
- Steel 4130Needs a coating: paint, powder coat, zinc or nickel plating, or black oxide with oil. High-strength parts need a bake after plating.
- Stainless 303, 304, 17-4 PHPassivated, sometimes electropolished or bead blasted. No anodize.
- BrassRaw, lacquered or nickel plated. Tarnishes if left bare.
- POM and nylonColor comes from the stock, mostly black or white. No finish.
Which part each material suits
Starting points, not rules. The part pages under parts by type go into the interfaces and tolerances for each component.
| Material | Typical machined bike parts |
|---|---|
| Aluminum 6061-T6 | Stems, brackets, collars, spacers, cages, derailleur hangers, motor mounts |
| Aluminum 7075-T6 | Cranks, chainrings, direct mount rings, thin-section parts, high-load clamps |
| Aluminum 2014-T6 | Forged crank arms and stems finished by machining |
| Titanium Grade 5 | Axles, bolts, pivot pins, spindles, boutique hardware |
| Titanium Grade 9 | Tube-based parts: seatposts, handlebars, frames, rails |
| Steel 4130 | Dropouts, yokes, fittings and brazed or welded frame parts |
| Stainless 17-4 PH | High-load pins and shafts, heat treated after machining |
| Stainless 303 and 304 | Axles, pivot pins, washers and hardware that must not rust; 303 machines faster, 304 resists corrosion better |
| Brass | Valve parts, bushings, small turned spacers, decorative hardware |
| POM and nylon | Pulley wheels, bushings, chain guides, spacers that must not mark the frame |
Comparisons written for a specific decision: 6061 or 7075, 2014 and 2024, Grade 9 or Grade 5 titanium, 4130 dropouts and yokes, 17-4 PH hardware and Delrin and nylon.
Inserts for carbon fiber parts
Carbon frames, cranks, bars and seatposts still need metal where a thread, a bearing or a clamp meets them. Those inserts are machined and bonded in.
Typical inserts are threaded pedal and spindle interfaces in carbon cranks, bottom bracket and headset sleeves, dropout and derailleur hanger mounts, bottle cage and accessory bosses and seatpost head clamps. 7075 and 6061 aluminum are the usual materials; titanium is used where the joint sees high load or must not corrode.
Carbon fiber is electrically noble. An aluminum insert touching it in the wet corrodes, a process called galvanic corrosion. The joint is isolated with a glass fiber ply, an insulating primer or a controlled adhesive layer, or the insert is made in titanium. Bonded surfaces need a defined roughness and bond gap from the adhesive maker's data; a sealed anodize bonds poorly, so ask before specifying it on a bond face. State on the drawing which surfaces are bonded and which are functional.
Questions
Is titanium stronger than aluminum for the same weight?
By yield strength per unit weight, Grade 5 titanium is ahead of 7075 and well ahead of 6061. By stiffness per unit weight the common metals are close, so a titanium part sized for stiffness is not lighter. Titanium earns its cost on fatigue, corrosion and small, highly loaded parts such as axles and bolts.
Why is 6061 the default when 7075 is twice as strong?
Most bike parts are sized by stiffness, fatigue or the interface, not by static strength, and 6061 anodizes evenly, machines fast and costs less. 7075 is worth it on cranks, chainrings and thin sections where strength really sets the size.
Can an aluminum insert be bonded into a carbon part?
Yes, and it is common, but carbon fiber is electrically noble and an aluminum insert in contact with it corrodes in wet conditions. Isolate it with a glass fiber ply, an insulating primer or the adhesive layer, or use a titanium insert.
Which plastic for a pulley wheel or bushing?
Acetal (POM) for parts that must keep their size, because it absorbs very little water. Nylon where toughness under impact matters more, with looser fits to allow for moisture swelling.
Material chosen?
Send the drawing with material, finish and quantity. We match it with up to 3 shops that machine bike parts in that material, and you hear back within 24 business hours.