To carry the wheel, react every load the tire generates into the suspension linkages, and mount the brake caliper and rotor, while keeping the corner light and the geometry stiff.
A rotating 7075-T6 aluminium spindle runs in two deep groove ball bearings pressed into an upright. The upright is the structural hub of the corner: it carries the spindle bearing housing, the lower ball joint connection, the tie rod mount, the top mount connection, the brake caliper mounting holes, the wheel speed sensor mount and the rotor temperature sensor mount. The top mount is a separate 6061-T6 part carrying the upper ball joint, kept separate from the upright so that the machining stays simple. The wheel bolts to the spindle flange and is retained by a hard-anodised spindle nut. At the rear the spindle also houses the outboard tripod. The tie rod mount on the front upright provides one nominal and three alternate mounting points, giving Ackermann options of 16%, 23.64% nominal and 30.57%, plus an additional 23.65% larger-wheel-steering option.
The spindle is a fatigue part, not a strength part. It is a rotating shaft under bending, so the analysis chain is: wheel loads from lateral acceleration, axial stress from bending, alternating and mean stress, equivalent reversible stress by modified Goodman, then S-N fatigue life. Peak stress sits at the outboard bearing shoulder, which is exactly where CR22 failed. The criterion is fatigue life greater than 600 miles, plus the minimum yield safety factor for the system. Control the bearing fit deliberately. Interference fit of the shaft to the inner race (+0.0008 to +0.0011 in) eliminates manufacturing clearance and engages every ball; clearance fit of the outer race to the housing (+0.0005 to +0.001 in) means only the inner race deforms. Buy the drag reduction. Moving the rear bearing from a contact-seal SKF 61814-2RS1 to a non-contact SKF 61814-2RZ cut pressed drag effort from 3.4 to 1.8 lb-ft and calculated power loss at 60 mph from 0.8416 to 0.4455 hp, a 0.396 hp saving for no weight. 1. Take wheel loads from the cornering, braking and combined load cases. 2. Size the spindle shaft for fatigue at the worst case, then size up to an appropriate bearing and remove as much inner material as possible. 3. Select bearings on required bore, spacing and its effect on moment reaction, static load rating against worst-case load, dynamic load rating against average load and expected life, and then the lightest and smallest option that fits. 4. Design the upright to connect the geometry points, sizing every hole and tab. 5. Analyse. Wheel load applied as a remote load from the contact patch to the bearing faces; lower ball joint and tie rod mount bolt faces react lateral and longitudinal motion; upper ball joint reacts all translation; brake caliper bolt faces take a moment reaction for braking. Global element size 0.045 in, second-order wedge elements. 6. Cross-check with the full-corner model, then state the resulting compliance. CR26I effective angular deformation of the corner in cornering is 0.32 degrees of camber change, including spindle, bearings, upright, tie rod mount and top mount.
- Decrease manufacturing time by 15%. Top mounts alone dropped 63% (1.5 hours) by using straight tabs. - Improve structural and fatigue models. - Reduce rolling resistance in bearing retention. - Reduce weight and moment of inertia while providing a reliable load path from wheel to upright.
- Spindle fatigue failure at the outboard bearing shoulder. Seen on CR22; this is why the whole spindle process is fatigue-first. - Bearing size against wheel load. Front bore was increased from 35 mm to 40 mm on CR26I to accommodate larger wheel loads, which forced a larger upright housing. - Rear bearing bore is limited by half-shaft tripod geometry at 70 mm, so it cannot simply be sized for load. - Single-body FEA showing singularities near boundary conditions and modelling no bolt preload, which limits how far the parts can be weight-optimised with confidence.
SolidWorks FEA for single-body analysis and ANSYS for the full-corner model with bolt preload and bearings given a uniform modulus from radial stiffness at load (~165 GPa). Modified Goodman and S-N fatigue analysis for the spindle. A bearing fit calculator. Bearing life analysis referenced to SKF's rating at 1,000,000 cycles at basic dynamic load. Autodesk Fusion 360 for CAM; HAAS TL1 lathe and TM2P mill for manufacturing. MIL-A-8625F Type III hard coat anodising for the nuts.