F1 Upright: Design & Geometry

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This 2014 Caterham front upright shows some of the key design features of F1 uprights, although as you can see it is both a 3D printed mock up part and also part of a pull rod front suspension set up. F1 Uprights are the part that completes the front suspension geometry, connecting the axle to the wishbones, whilst also providing mounting points for the brake caliper, pull rod and steering track rod.

Upright design in F1 has diverged from the previous typical practice of having an open design to allow cooling air to pass through the upright to the carbon brakes. With these previous designs, which went out of fashion in the early 2000’s, uprights were fabricated from a mix of sheet, cast and wire eroded parts, welded together. Now the upright wraps more tightly around the hub and bearings and cooling flow passes around the smaller upright, rather than through it. With this change the manufacturing went from fabricated steel or titanium, to cast or CNC milled. Materials for this new format were typically, Aluminium, (Ti for the cast versions) and MMC.

Now upright itself has to be made from aluminum by regulation, this change was brought in to prevent teams making them from MMC’s, which have a far higher material cost. However, I’m told the total cost to make an Aluminum upright as efficient (weight vs stiffness) as a MMC version ends up costing far more, due the extra R&D put into the design, so much for Alu being a cost cutting measure then!

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Milled from solid Alu the upright has mounts for the brake caliper, again regulations demand just two fastener connect the brake to the upright, these are space at 200mm. The suspension attaches at two points, for both the upper and lower wishbone’s outer ball joints. The trend in F1 is to have the lower wishbone mounted ever higher, typically for a push rod set up this is near the axle centerline, very high for any sort of racecar suspension. Then to reduce the load on the wishbones the upper wishbone is spaced as far apart as possible from the lower one. Thus the upright extends upwards to limit imposed by the 13” wheel.

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As Caterham have a pull rod front suspension, the lower wishbone needs to clear the pull rod and hence is mounted lower than other teams. The lower mount is some 40mm below the axle line and space 125mm from the uprights outer face. The upper mount is 150mm above the axle line and 140mm from the front face of the upright. Also near the wishbone mounts are the mountings for the two wheel tethers, the upper wishbone’s tether bolts into a clevis next to the upper mount, while the lower wishbone’s tether passes lower down inside the upright to connect near the brake mounting.

UPRIGHT
Camber is adjusted at the top ball joint mount, which is oversized to accept inserts. Different sized offsets move the upper outer ball joint to camber the wheel by specified amounts. The upright appears to have about 15mm of mechanical trail.

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The pull rod mount is 65mm above the axle line and 115mm from the uprights face. In this positon the pull rod outer ball joint is offset from the steering axis by 20mm, this it will affect weight transfer with steering, a common approach known as pull rod on upright (POU).
Lastly the steering arm is formed as its own shape extending from the upright’s body. Is some 85mm offset from the steering axis and 90mm above the axle centerline.

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Rotating within the Upright is the hub or axle, this is typically made from titanium, machined from a mix of turning and wire erosion, the latter used to get the splines to mount the brake bell. Making machining even trickier is the Hubs concave hollow shape, as the part diverges from each end to meet the outer bearing.
Caterham made no use of the void inside the hub, other teams blow air through the part, to vent through the open axle end, for a blown aerodynamic effect. While BAR\Honda\Brawn used to have an oversized inner diameter and spark eroded outlets in the waist of the hub fed the brake disc with its cooling air, rather than passing airflow around the outside of the upright\Hub.

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The Hub has six drive pegs for engaging with the wheel and there are 30 splines to engage with the brake bell.

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The hub is mounted to two bearings one larger outer race and a smaller diameter inner race, the hub and bearings being fastened and pre-loaded by the castellated nut on the inner end of the hub.

Outer bearing dimensions:
OD 112mm ID 89mm 12mm wide
Cerobear DSF 71818000010

Spaced 58mm from

Inner bearing dimensions:
OD 82mm ID 60mm 12mm wide
Cerobear DSF 71912000018

Hub dimensions:
Hub 200mm long
Wheel nut dia 65mm
Hub nut dia 55mm
Disc bell 150mm