Speed Tech Performance Track Time Kit - Second to None

Speed Tech Performance’s Track Time Kit Changes the Way ’70– 81 F-bodies Handle for the Better … Without Changing the Whole Car

Chris Shelton Sep 1, 2012 0 Comment(s)
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It remained a secret for the better part of 40 years, but the second-gen Camaro has a distinct advantage over its older brothers: a better front suspension. The differences are numerous but the most profound was a knuckle revision that vastly improved the handling.

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But that doesn’t mean the design is beyond further improvement. Those taller knuckles may have improved the camber curve, but their integral caliper mounts make them weigh a ton and won’t let them accommodate big-brake kits without extensive trimming. Their steering arms also limit wheel widths and offsets. And that’s to say nothing of the steering geometry problems. Of the stock vehicles Speed Tech Performance tested, all suffered noteworthy bumpsteer issues, some in ways that were unique unto themselves.

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Speed Tech found the solution in a most unlikely place: in a steering knuckle it offers to correct a flaw in the first-gen suspension. Its design matched every parameter Speed Tech established but one: it doesn’t fit second-gen suspensions.

So Speed Tech designed a new suspension around that knuckle. What emerged is the Track Time kit, a complete system that promises performance improvements usually exclusive to aftermarket subframe systems. Only this one does it with a twist: it fits the stock subframe.

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As noted previously, the centerpiece of this kit owes its existence to a retrofit of a first-gen knuckle. A few years prior, American Touring Specialties, now part of Speed Tech, drew upon the second-gen’s taller knuckle design to create knuckles that improve the camber curve on ’64- 72 A cars, ’67- 69 Fs, and ’68 –74 X cars (hence the knuckle’s AFX designation).

The knuckle’s trump card in this application is weight, specifically its lack of it. The absence of an integral caliper boss accounts for a good deal of the savings, but materials explain the biggest difference. GM made the second-gen knuckle from iron whereas Speed Tech makes its version from aluminum.

And not just any alloy either, the 7075-series alloy Speed Tech employs has a minimum tensile strength of 75,000 psi whereas A536 Grade 65-45-12 iron, a material commonly used for knuckle castings, has a tensile strength of only 65,000 psi. General Motors makes its Corvette spindles from aluminum, but the 6061-series alloy it uses has a tensile strength of 45,000 psi. That’s only 60 percent of the tensile strength of the alloy Speed Tech uses.

Speed Tech also forges its knuckles rather than casting them, as GM does. Forging orients a metal’s grain structure in a way that improves its ductility (its ability to deform without breaking) and its fatigue resistance (its ability to withstand repeated loading cycles).

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But weight is only part of the knuckle’s advantage. Shape accounts for the rest. Like most aftermarket knuckles, it lowers the suspension; however, it does it in an intelligent way. Instead of simply relocating the wheel vertically (upwards) as is done with most knuckles, it relocates it vertically and slightly horizontally. In this case, the wheel migrated along the suspension’s steering-axis inclination (SAI).

This inclination plays a critical role in suspension design. It’s the line that passes through the upper and lower ball joints and it defines the axis about which the knuckle rotates as the car steers.

The SAI works with the tire centerline to establish an underestimated, if not misunderstood, dynamic: scrub radius. Scrub radius is the relationship between the SAI and the tire centerline. Imagine plotting the SAI to ground level. The scrub radius is the distance between that line—the pivot point for the steering system—and the tire’s actual centerline.

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A calculated degree of scrub radius is good; it leverages the wheels’ rolling resistance to preload the steering gear, which prevents the car from wandering. But excessive scrub radius is bad. It generates excessive leverage, which transfers more force to the suspension, steering, and driver. It wears parts prematurely, makes the car feel twitchy, and reduces stability, especially under braking.




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