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.

Camp 1209 04 Stp Track Time Kit Shorter Steering 4/17

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.

As it stands, most A-arm front suspensions on rear-drive cars have a little bit of positive scrub radius (the tire centerline lies outboard of the SAI). Dropping a knuckle simply by moving its wheel-mounting point upwards increases the positive scrub radius; however, moving it along the SAI preserves the scrub radius. The same goes for a hub or brake hat that pushes the wheel out: it moves the scrub radius more positive. Speed Tech accounted for that, too.

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Speed Tech used the divorced steering arm design to solve another problem associated with scrub radius. Anyone who’s ever tried to bolt wider wheels to a second-gen Camaro can bear testimony that the tie rod location limits rim width and ultimately offset. Most enthusiasts simply fit a wheel with more negative offset (add more of the width to the wheel face). That, too, makes the scrub radius more positive.

Well, Speed Tech worked too hard to preserve geometry just to throw it away on a wheel-offset compromise. So it eliminated the interference between the tie-rod end and the wheel by shortening the steering arm.

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The clearance gained makes it possible to maintain the OEM-style wheel offsets when using wider wheels. For a baseline, consider that GM equipped most first- and second-gen Camaros with wheels that have a 0.25-inch (6.35mm) offset. Speed Tech designed the arm to fit a 17x9.5 wheel with at least 5.5 inches of backspace and a 20x10 wheel with at least 6 inches of backspace. Both examples maintain the same 0.25-inch offset as the OEM wheel. Correct-offset wheels offer another bonus: they’re less likely to interfere with the fender opening.

The shorter arm also speeds up the steering ratio in the same way a numerically lower steering box ratio does. Speed Tech takes it one step further by including in their kit a super-fast Lee Manufacturing 12.7:1 power steering box. But a shorter steering arm has one potentially negative consequence: it increases the angle from the tie rod to the steering arm.

Camp 1209 09 Stp Track Time Kit Ride Tech Coilover 9/17

Increasing that angle reduces the Ackerman effect, the dynamic that lets each steering wheel follow its own radius as the car turns. However, Speed Tech restored that angle and the Ackerman by moving the steering arm’s tie-rod pick-up point away from the car’s centerline.

And remember the bumpsteer issues mentioned? Speed Tech solved that with the revised steering-arm design. Moving the tie-rod mounting point down a smidgen reduced bumpsteer to 0.02-inch at full compression and 0.01-inch at full droop. But it didn’t solve it consistently on all cars.

The reason for the inconsistency is because not all F-bodies were created equal. GM equipped them with different parts depending on model and make (remember the Firebird?). And while those cars may have left the factory with matching parts, they may not have gotten the correct replacements over the years. So instead of accounting for potentially dozens of variations of matched parts, Speed Tech designed its suspension around a particular set of OEM and replacement parts, which it supplies with the kits. It even found the opportunity to correct a flaw inherent in the factory design with an offset idler-arm bracket that levels the drag link.

Though knuckles distinguish Speed Tech’s system, it should be obvious by now that they’re really only a part in an assembly: the kit includes special control arms and two coilover/damper options sprung and tuned specifically for the application. But by engineering everything around those parts, the company has created an entire system where everything works together to achieve a specific goal: superlative handling.

Camp 1209 10 Stp Track Time Kit Damper 10/17

Admittedly, these system-engineered suspensions aren’t a new idea; they’ve evolved to the point that some manufacturers dispense with factory subframes for custom ones. However, this one vastly improves handling by a somewhat traditional way: by preserving the vehicle’s chassis and as many of the OEM-style parts as possible. It’s certainly a factor in purchase price, but it facilitates long-term serviceability.

So you could say the Track Time kit is one that you and your wallet can enjoy.

Sources

Speed Tech Performance
N/A,
888-467-1625
www.speedtech-performance.com
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