MATERIAL GRADE
Alloy
4130 Chromium-Molybdenum Steel
Carbon Content
0.28–0.35 wt%
Chromium
0.80–1.10 wt%
Molybdenum
0.15–0.25 wt%
Tensile Strength
≥ 75 ksi (515 MPa)
Yield Strength
≥ 55 ksi (380 MPa)
Elongation
≥ 15% in 2"
Heat Treat
Normalize @ 1600°F, Temper @ 1100°F
Polar Moment of Inertia (J)
J = π × (OD⁴ − ID⁴) / 32
Target J for down tube: ≥ 2,850 mm⁴ @ 28.6mm OD
Source: Wikidata Q1070521 • AISI 4130 Specification
TUBE PROFILE
Down Tube
Ø28.6mm • 0.8→1.0→1.2mm triple-butted
Top Tube
Ø25.4mm • 0.7→0.9→1.1mm triple-butted
Seat Tube
Ø34.9mm (oversized) • 0.9→1.1→1.3mm
Chainstays
Ø22.2mm • 0.8→1.0→1.2mm tapered
Seatstays
Ø16.0mm • 0.7→0.9→1.1mm elliptical
Head Tube
Ø44mm integrated • 1.5mm uniform
Total Frame Weight
1,680g ± 40g (56cm)
Stiffness Target
12% > baseline Reynolds 531
Butt Transition Length (L)
L = (t₂ − t₁) × 12
Gradual taper prevents stress concentration at weld interface
Source: Wikidata Q167130 • Butler Cycle Engineering Handbook
JOINT GEOMETRY
Head Angle
72.5° (racing geometry)
Seat Angle
73.0°
Chainstay Length
415mm (fixed)
Bottom Bracket Drop
-68mm
Fork Offset
45mm
Trail
62mm @ 700×23c wheels
Weld Process
GTAW-TIG, DCEN, Argon purge (O₂ < 50ppm)
Filler Rod
ERCuNi (nickel-enhanced for fatigue resistance)
Cross-ref: Butt Schedule Calculator • Homepage