C10 Chassis model
A Clean Slate C10 Chassis
Roadster Shop’s CNC-designed SPEC-Series Frame Brings the Squarebody Chevy into the 21st Century
By Ryan Manson | Photography by the Author

Building a custom, classic truck begins with the proper chassis. The foundation of your build needs to properly represent the intent of said build. For example, if you’re building a ’60s Ford truck and your vision calls for a truck that lays rocker, you’re going to be hard-pressed to make that happen with the stock twin-I beam suspension design. More than likely, that stock Ford chassis is going to need to be heavily modified. Labor is time, and time is money. On the other hand, if your build simply calls for an upgrade in brakes, suspension, and steering with perhaps an engine swap upgrade, rolling out the old in exchange for the new in one fell swoop might make the same amount of sense. With 40-plus years of use and abuse under these trucks, there’s no doubt you’re likely to find some kind of damage, modifications, or other “previous-owner-made repairs” that will need to be fixed before the modifications can even begin. So, whether your build calls for some serious modifications to the frame, a handful of stock upgrades, or you’d rather just have the peace of mind that comes with a brand-new chassis, swapping out that old twisted frame for new might just make the most sense. And it’s probably cheaper than you think!

rendering of our 1980 C10
We had Michael “Casti” Castiglione work up this killer rendering of our 1980 C10 sitting on the SPEC-series Roadster Shop chassis.
The Roadster Shop co-owner Phil Gerber’s Squarebody
Here’s The Roadster Shop co-owner Phil Gerber’s Squarebody sitting on its rockers, evidence of how low their SPEC chassis is spec’d to sit when equipped with an airbag setup at all four corners.

When we started our Squarebody build, our intentions landed us squarley in the “multiple modifications required” class. Stock, these trucks (1973-1987 Chevy C10s) are notorious for their bulldozer-like qualities of the front crossmember when lowered any more than a few inches. We didn’t want to have to revisit our mini-truckin’ days, avoiding every Botts’ dot and approaching every driveway at a 45-degree angle so as to avoid ripping out the suspension from under the truck. We also wanted to upgrade the suspension and brakes to something a bit more akin to our driving style and to properly support the supercharged LT1 engine planned for the build. After a conversation with Phil and Jeremy Gerber at Roadster Shop, it became clear that their SPEC-series chassis would be perfect for our C10 build.

fully assembled SPEC chassis
Our fully assembled SPEC chassis showcases a number of interesting details, including the front and rear frame kickups designed for increased ground clearance while still maintaining a 4.5- / 5-inch ride height. Precision CNC laser cut and contoured framerails ensure there are no kinks, bends, or stressed areas that are prone to flex, like mandrel bent tubing, and feature a unique interlocking key and slot design that ensures proper alignment of each section.
powdercoating on the chassis
Our SPEC chassis, fresh from a bath in the powdercoating booth at Eddie Motorsports, is ready for final assembly. After installing the Polyurethane bushings and pressing in the Moog balljoints, the control arms are ready to be bolted up to the chassis. First, the lower control arm is slid in place. Note the boxed design, which reduces flex and provides a solid foundation for the coilover shock to mount.
fabricated upper control arm
two eccentric fasteners
The upper control arm is another fabricated piece, though of a more industry-standard tubular design, and mounts via two eccentric fasteners, designed to make alignment adjustments quick, easy, and accurate.

Using CNC-based technologies, Roadster Shop designs and manufactures chassis that are lighter, stronger, and easier to assemble than those of the past. This allows the crew to design a chassis with a clean-sheet mindset, drafted specifically for a particular end goal as opposed to trying to modify an existing design to do something it was never meant to do. The SPEC-series chassis are assembled using Roadster Shop’s exclusive CNC laser-cut framerails contoured and joined using a series of interlocking keys and slots that, once formed to shape, ensure proper alignment of the frame sections and provide for a consistent welding gap. This procedure not only speeds up manufacturing but results in a stronger, lighter chassis with no kinks, bends, or stressed areas that are prone to flex. This streamlined approach to frame manufacturing results in lower costs without sacrifice.

Looking at a Wilwood Pro Spindle
A Wilwood Pro Spindle comes as standard fare on all Roadster Shop SPEC-series chassis, giving the end user a variety of options for brake components.
View of the coilover
We opted to go the coilover route with our SPEC chassis, using AFCO double-adjustable units, front and rear, with 575- and 250-pound springs, respectively. Roadster Shop now offers an RS SV 4.0 by Fox (soft valved) coilover shock as standard on all SPEC chassis.
9-inch Ford rearend housing
Roadster Shop ships their SPEC chassis with a 9-inch Ford rearend housing and a pair of 31-spline axles. All that’s necessary to finish the rearend appointments are a ring-and-pinion, differential, yoke, and third member housing.
Installing the upper and lower parallel four-bars
Out back, the upper and lower parallel four-bars are installed on their brackets and torqued to spec. Note the beefy lower four-bars and the triangulated design of the system, which negates the need for a panhard rod to keep the rearend centered.

In addition to these modern manufacturing techniques, the Roadster Shop’s engineering department took things a step further, by fully integrating a number of upgrades into the chassis design, namely, getting things nice and low. Lowering a stock-style chassis to the extent that their SPEC series does can result in a ride height where the suspension components were not originally designed to function, putting increased stress on items such as ball joints, shock mounts, and tie rods. Bumpsteer and incorrect camber and alignment situations are also common problems on extremely low applications. The crew were well aware of this, designing the one-off IFS and rear suspension system of their SPEC chassis for the ultra-low crowd. With stepped framerails, front and rear, Roadster Shop designed their new SPEC chassis for an aggressive 4.5/5-inch raked ride height whether equipped with airbags or coilover springs. Sprung on springs, the static ride height of a SPEC chassis puts the truck nice and low while still maintaning the aibility to drive it like a normal truck. Equipped with ride height-adjustable airbags allows the chassis to lay rocker when fully “aired out”, putting the pinch weld of the truck’s body literally in the weeds.

Renders of mid-production changes
Renderings of mid-production changes
Since we received our chassis, the guys at Roadster Shop have made a few mid-production changes to their SPEC-series chassis. One of those key changes is the swap from a triangulated four-link design to a parallel four-link design with a panhard bar (coilovers) or a Watt’s Link (airbags).
Installing a 3.70:1 gear ratio
We ordered an assembled third member from Summit Racing (PN CUR-9TT37OS) to fill our empty housing. One of the reasons the 9-inch Ford rearend is so popular in the aftermarket is the fact that the third member can be removed and installed as a complete unit. This makes installation easy since the pinion preload, backlash, and torque have all been prefigured. We opted for a 3.70:1 gear ratio since we anticipate running an overdrive trans in our C10 mated to an Eaton Detroit Truetrac differential. The Truetrac is a helical-gear style performance differential that maximizes wheel traction by operating as a standard or open differential under normal driving conditions, allowing one wheel to spin faster or slower as necessary. This allows it to operate as an open differential until a loss of traction scenario occurs, in which the helical-shaped gears transfer the torque to the high traction wheel. These gears mesh with increasing force until the wheel spin is eliminated. This operation is smooth, quiet, and automatic with no wearable parts and no required maintenance, unlike posi units of the past.
The rearend partially assembled
With the rearend partially assembled, all that’s left is to slide the 31-spline axles in place. We’re going to wait on that until we install the big Baer disc brakes at all four corners as the e-brake/caliper brackets retain the axles. This angle shows the double-adjustable coilover shock and the eccentric adjuster that the lower four-bar utilizes, which allows for quick, easy, and accurate wheelbase and pinion angle adjustments to be made.

With the height requirements set in stone, or rather programmed into their CAD program, the engineers at Roadster Shop set out to design a double-wishbone IFS setup using in-house-fabricated upper and lower control arms mated to Wilwood Pro Spindles. Eccentric adjusters are utilized on the upper control arms to make alignment adjustments quick, easy, and accurate. Sprung options include an airbag setup or a more traditional coilover shock. A front-mounted power rack-and-pinion and aggressive sway bar ensures the function of the front end reflects the form. Out back, a parallel four-bar setup is utilized, mated to a 9-inch Ford rearend housing. Both upper and lower four-bars are poly bushed, while the heavy-duty lower four-bar features eccentric mounting to make wheelbase and pinion angle adjustments quick, easy, and accurate, just like the front upper control arms. And like the front suspension, the guys designed the rear to perform just as well as it looked, with the allowance of a 12-inch-wide wheel equipped with a 345-series rear tire.

installing the 14-inch Baer disc brakes
We couldn’t wait to get the chassis rolling, so we skipped ahead and installed the 14-inch Baer disc brakes and slapped on a set of rollers to see how the chassis looked on the ground. Note the beefy front sway bar and front-mounted power rack-and-pinion unit. We’ll take a closer look at the brakes in a future story, but for now, consider this a teaser of things to come.
At this point, we were sold on the Roadster Shop’s SPEC chassis and placed an order on the spot. We knew we wanted to build something that could put those high and mighty muscle car guys in check and that it would require more might than, well, muscle. While the Supercharged LT1 should be more than enough to power our Squarebody, we wanted to be certain that the backbone of our C10 could effectively put the power to the pavement. Given the background on what the Roadster Shop guys put together in the form of their SPEC-series chassis, I’m feeling pretty confident that it will live up to our every expectation.
Baer Brakes

(602) 233-1411

Eddie Motorsports

(888) 813-93531

Roadster Shop

(847) 949-7637

Summit Racing

(800) 230-3030