Comparative Technical Report:
1. Introduction
This document provides a scientific comparison of the FOX Upside Down Podium fork 20mm axle (6061-T6, hollow) versus a 15mm solid axle made from 7075-T6 aluminium, specifically for use as supporting evidence regarding strength, stiffness, and ride characteristics.
2. Technical Specifications
| Specification | FOX Axle (20mm/16mm, 6061-T6) | New Axle (15mm solid, 7075-T6) |
|---|---|---|
| Outer diameter | 20mm | 15mm |
| Inner diameter | 16mm | – |
| Construction | Hollow | Solid |
| Material | Aluminium 6061-T6 | Aluminium 7075-T6 |
| Weight (approx) | 105g | 110g |
Material properties
| Property | 6061-T6 | 7075-T6 |
|---|---|---|
| Young’s modulus (E) | 68.9 GPa | 71.7 GPa |
| Tensile strength | 310 MPa | 572 MPa |
| Yield strength | 276 MPa | 503 MPa |
| Density | 2.70 g/cm³ | 2.81 g/cm³ |
3. Calculation Results
3.1 Bending Stiffness (Flex)
Calculated using standard engineering formulas for the second moment of area and Young’s modulus (E × I):
- FOX axle (20/16mm hollow): E × I = 319 Nm²
- 15mm solid 7075 axle: E × I = 178 Nm²
Result: The FOX axle is about 1.8× stiffer against bending loads. This means it flexes less under lateral force.
3.2 Tensile & Yield Strength
Based on cross-sectional area and material strength:
- FOX axle (6061):
- Tensile force before failure: 35,060 N
- Yield limit: 31,215 N
- 15mm axle (7075):
- Tensile force before failure: 101,081 N
- Yield limit: 88,887 N
Result: The 15mm solid 7075 axle is structurally stronger despite its smaller diameter, due to its solid construction and higher-spec material.
4. Practical Implications for Ride & Safety
- FOX 20mm/16mm 6061 Axle
- Provides maximum lateral stiffness, essential when replacing a fork bridge; results in sharper steering and less flex under high load.
- 15mm solid 7075 Axle
- Exhibits more flex, which can lead to higher comfort (compliance), but remains much stronger and safe for use with extremely low risk of yielding or failure.
5. Summary Table
| Feature | FOX 20/16mm | 15mm Solid 7075 |
|---|---|---|
| Bending stiffness | 319 Nm² | 178 Nm² |
| Relative stiffness | 100% | 56% |
| Max tensile strength | 35,060 N | 101,081 N |
| Max yield strength | 31,215 N | 88,887 N |
| Weight | 105g | 110g |
| Ride characteristic | Direct, stiff | More compliance |
6. Conclusion
Both axles are structurally safe and suitable for intended use. The FOX axle offers maximum stiffness and directness, replacing the need for a fork bridge. The 15mm 7075 solid axle is much stronger and safe, with increased comfort due to greater flex. The most important difference is the feel on rough terrain versus steering precision.
Disclaimer:
The information and comparisons presented in this report are based on standard engineering calculations and data publicly available for 6061-T6 and 7075-T6 aluminium alloys. The results represent theoretical estimates and are intended for general informational purposes only. While every effort has been made to ensure accuracy, real-world performance may vary due to manufacturing tolerances, assembly conditions, and practical usage. For definitive assurance of safety and durability, we strongly recommend product-specific laboratory, fatigue, and field testing. No guarantees or certifications are implied or provided beyond these calculations.