Connects the steering rack to the tie rod mount on the front upright, setting front wheel angle and front toe.
A tube with a bonded aluminium insert at each end and a rod end threaded in, so length and therefore toe is adjustable. From CR25 the tube is CFRP rather than steel.
From the CR25 Carbon Suspension Members one-pager, which is the decision document behind the move to composite rods. Carbon tubes for tie rods, actuation rods and A-arms were identified as "the biggest change and lowest hanging fruit" in pursuit of weight loss, with an estimated maximum saving of 8 lb from suspension members alone. The technical justification given is that less unsprung mass lets the suspension do a better job of suspending, giving a more reliable and smoother drive. Per-component risk was assessed up front: tie rods almost no risk because they are very lightly loaded, with a maximum estimated 1 lb saving; actuation rods carrying buckling and tear-out risk for a 2 lb saving; and cast aluminium spherical bearing holders carrying bending, tear-out and casting consistency risk for a 5 lb saving. Rockwest was preferred over McMaster for better material property documentation and better overall pricing.
Sized in the carbon component calculator: 390 lb axial load, 13.67 in length, 0.856 in OD, 0.75 in ID, buckling FoS 7.82. Proof tested tensile and compressive to a 1.5 factor of safety. From the design reports and one-pagers: Validation as planned: rigorous 251 lab testing to determine the pullout strength of the DP420 bond to the tubes and the compressive capability of the carbon tubes, with each manufactured part for CR25 to be tested before being driven on. That plan became the MTS Criterion 43 programme recorded on the main entry.
Tube cut to length with a diamond blade Dremel wheel. Surface prep with IPA and sanding. Bonded at a 0.005 in gap using a 0.0049 in silica bond gap controller and a 0.010 in clearance fit on insert diameters. Cured 24 hours at room temperature under static pressure. From the design reports and one-pagers: One-pager estimates: cut carbon tubes to length 2 days; adhesion bonding 2 days; casting 6 to 7 weeks lead time from the forge; milling the bearing surface 1 day; insert machining 2 days. Specification at that stage: 0.005 in bond gap with 0.005 in bond beads, DP420 adhesive.
Rockwest Composites 3k 2x2 twill CFRP tube, aluminium inserts, 3M DP420 adhesive, FK alloy steel rod ends.
None recorded. This part has no entry in Knowledge_Transfer/Issue Logging/Fault Vault.xlsx, in either Issue Log.xlsx, in CR22/Issue Tracking/Shakedown 7-15-23.xlsx, or in any design review issue list found in CrimsonStorage or Box.
Tube 0.750 in x 0.856 in, 13.67 in long, 2 in rod insert length, design FoS 2. Tie rod set weighs 434.5 g. Quantity per car, as costed: 1, 2
Nothing in CrimsonStorage covers these yet.