Parts

Using Tubular A-Arms to Improve Race Car Suspension Geometry

(Image/Wayne Scraba)

Decades ago, there was only one way to “fix” the front suspension on a stock suspension door slammer race car.

It involved cutting, pasting, and tweaking the A-arms to increase caster (which is the tilt of spindle) and at the same, reduce the camber change (as the suspension went through its travel) in the front end.

The stock front suspension components that rolled off Detroit assembly lines through the decades were not (and some are not still) optimized for drag duty or carving corners.

Early cars were built typically with little caster so that Aunt Bessie could park it easily without power steering.

The trade-off is the car being unstable at higher speeds (Aunt Bessie wasn’t going there anyway).

Camber is an issue too: It changes as the front end goes through its travel during a wheel stand.

It doesn’t take a rocket scientist to see how goofy the front wheels look on some cars as they dangle in the air. With some of these combinations, as the car comes down to earth, the drama can unfold rather quickly. Usually, it manifests itself as hairline cracks on stock A-arms (been there, done that and I’m sure more than a few of you have too). 

That was then. Today, for many fast “door” cars (race cars and street-strip cars that originated on a factory assembly line), you don’t need to cut and paste the front end components to fix the geometry. You can simply choose a set of aftermarket upper and lower control arms with considerable tricks already built in (obviously, not a NHRA/IHRA legal swap for a Stocker or Super Stocker, but those are another story).

There are plenty of companies offering tubular control arms that bolt right into place. But what should you look for?

Some companies are, for the most part, building road race-style hardware while others are dedicated to drag racing. Some A-arms can work well in both applications.

When it comes to A-arms we’ll show you what to look for in the accompanying captioned photos. In this case, the examples shown are from Detroit Speed, but the picking and choosing process applies to pretty much all examples.

You can’t see it here, but each A-arm from Detroit Speed is assembled in a fixture (in fact, more than one), then TIG welded. Some drag race a-arms out there are built from chromoly. Many are constructed from mild steel. Some of the less drag race oriented arms available have large diameter tubing and many are wire welded. (Image/Wayne Scraba)
Once complete, the Detroit Speed A-arms are detailed and sent off to be powder-coated in a gloss black finish. It’s a durable setup. Relatively light too. Depending on the application and the configuration, you can cut as much as 15-35 pounds off the nose of your car with some tubular A-arm systems. Much of the weight reduction is unsprung, which adds more to the performance benefit equation. (Image/Wayne Scraba)
Building A-arms from scratch also gives the manufacturer the opportunity to build in more positive caster. What’s the big deal with positive caster? It allows the car to track straight and true while at speed. FYI, Detroit Speed tells us you should shoot for 3-4-degrees of positive caster when aligning the front end (this set will allow for a maximum of six or more-degrees of positive caster, which is a lot). (Image/Wayne Scraba)
In order to adjust the Detroit Speed upper A-arms for caster, you remove the nut, and either flip or swap the caster tuner slug. The upper A-arms come with two complete sets of slugs, that allow for a range of caster between (approximately) zero to 6+ degrees. This also means that shims are only used to set camber. (Image/Wayne Scraba)
Here’s a better look at the caster slugs. They can be reversed (mount hole forward or hole backward), or you can use the second set for even more (or less) caster angle. (Image/Wayne Scraba)
Some of the replacement A-arms available use OEM-style attachment points to the frame, complete with OEM bushings. Others use urethane bushings of one form or another. Other options include rod ends for the top side, and finally others use Delrin bushings or a combination of the Delrin and rod ends. (Image/Wayne Scraba)
The Detroit Speed A-arms incorporate Delrin bushings top (previous photo) and bottom. The reason for using Delrin is because it eliminates “stiction” in the bushing. When you have “stiction,” the offending material (such as urethane) more or less freezes up the suspension component, rendering the shock (and more important, the shock adjustment) useless.  Bottom line here is “stiction” isn’t helpful. (Image/Wayne Scraba)
You can purchase tubular A-arms for three different spring configurations – coil-over and conventional springs along with hybrid tapered coil overs. Coil-over setups allow you to play with ride height and offer plenty of spring tuning capability. The tapered setup that we’re using (it’s from AFCO Racing) uses the stock Detroit Speed spring pocket, but it provides for adjustability like a conventional coil-over. (Image/Wayne Scraba)
Steering stops are important. Basically, this is where the steering arm comes to a stop on the A-arm when the steering is at full lock. (Image/Wayne Scraba)
Something important to me is “serviceability.” For example, if a ball joint goes south (and they do), how much trouble is it to replace? We asked those questions too. In this case, the bolt-in upper ball joint is a stock OEM piece. Ditto with the press-in lower ball joint. (Image/Wayne Scraba)
A suspension limiter is necessary too. This prevents the upper A-arm from crashing into frame rail at full droop. Drag race applications make use of adjustable stops (“travel limiters”) in this location. (Image/Wayne Scraba)
Detroit Speed mounts the lower control arm bumper here. The purpose for the bumper is to prevent the A-arm from contacting the frame at full lift. FYI, this lower A-arm fits a wide range of Camaros and Novas. Depending on the year, the bumper can be positioned on either the leading or trailing end of the A-arm. (Image/Wayne Scraba)
Here’s a look at the bumper. It simply screws into place. The Detroit Speed A-arms are built with both leading and rear trailing mounts, so they can fit early or late F-bodies or Novas. (Image/Wayne Scraba)
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One Comment

  1. Daniel Wilson says:

    There are a number of different manufacturers that offer tubular suspension component upgrades. Naturally each one insists that theirs are better because of an advantage in design. Anything would be better, especially considering the less than optimal OEM components on my’70 Mustang Mach 1 with its original “competition” suspension. Detroit Speed offers some impressive upgrades but a more in-depth article comparing some of the technical aspects of equipment available from different manufacturers would be appreciated.

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