Racing Arms – Part One

 

arm-1It’s no secret that bolt-in a-arms for the nose of a purpose built drag car are readily available from plenty of sources.  Some of those pieces aren’t really dedicated drag race components.  Some are road-race inspired.  Some are simply replacement parts and some are just pretenders.  A select few of those pieces can actually pack plenty of sophistication, particularly for cars that see drag strip duty.  Case-in-point are the a-arms spread out in the photos in front of you.  These are top of the heap components manufactured by TRZ Motorsports.

Why the need for aftermarket upper and lower control arms?  Simple.  The stock front suspension components bolted to the nose of your car as it rolled down the Detroit assembly line were never optimized for quarter mile use.  Vehicle manufacturers were typically conservative when it came to built-in caster (and actually super-conservative in the sixties).

Let’s stop right here for a minute: What’s caster?  Caster is the backward or forward tilt of the spindle as you view it from the side of the wheel and tire.  When caster is positive, this means the spindle tilts backwards, which in turn, places weight behind the tire contact patch.  If the caster is negative, this means the top of the spindle is tilted forward, which in turn places weight in front of the tire contact patch.  Caster is expressed in degrees, and measures the amount the centerline of the spindle is tilted from true vertical.   For the most part caster figures seldom go beyond -3/4° (negative), but in almost all drag race applications, positive caster is required.  Why is that?  Consider positive caster as a way to “self center” the steering.  Ponder bicycles for a minute:  A comfy long distance touring bike will have a fork that’s kicked out.  This fork “kickout” provides a big chunk of positive caster. In turn, the bicycle experiences a significant amount of directional stability.  Then take a look at a mountain bike. Here, the fork is much closer to vertical.  The benefit of the mountain bike is that it can turn very quickly, however it definitely lacks directional stability.  The bottom line is, you can easily ride a touring bicycle with your hands off the handlebars.  Try it with a mountain bike. It’s not that easy (!!!).

What about Camber?  Camber is the tilt of the wheel at the top (tilting in or tilting out). Camber is expressed and measured in degrees, and looks at the tilt of the wheel from true vertical.  If the wheel and tire package tilts out at the top, this means the camber is positive. If the top of the wheel and tire package tilts in, then the camber is negative.  The real idea behind camber is to keep the tire planted squarely on the pavement.  This creates maximum front tire grip. In theory, it sounds like zero degrees of camber is good but that isn’t always the case for race cars that were originally production line cars.  Most production line cars require different camber figures (while at rest) so that good grip and tire wear is maintained as the car travels down the road.  Typically, a car with a small amount of negative camber will exhibit better drag strip handling characteristics without killing the tire.

Back to cars:  A stock 1969 Camaro has a factory caster specification of ½-degree + or – ½-degree.  In order to adjust the caster in a stock 1969 Camaro, you transfer shims front to rear or from rear to front. If you transfer one shim (1/32-inch) from the rear bolt to the front will decrease positive caster by approximately ½-degree.  The opposite (transferring one shim from the front bolt to the rear bolt) will increase positive caster by approximately ½-degree. That same 1969 Camaro has a camber specification of ¼-degree, + or – ½-degree.  To set camber, you have to add or subtract an equal number of shims from the front and the rear bolts on the a-arm cross shaft.  One shim (again, 1/32-inch) at each location will change the camber by approximately 1/5-degree. Adding a shim at each end will decrease positive camber.

So far so good, but camber and caster are usually set together.   What that means is you’ll probably physically run out of room to properly adjust the caster and camber on a the car with stock a-arms.  This becomes very apparent when you try to get a reasonable (for drag racing) caster number in a first gen Camaro.  To get something like five or six (or even seven) degrees of caster is difficult, if not impossible.  That’s one big reason why the TRZ Motorsports A-Arm package is a serious problem solver for drag race applications.  When TRZ engineered the control arms, they built in 5-7-degrees of positive caster. TRZ points out:  “Caster varies on cars that have different ride heights.  If the rear of the car is higher than the front, it then has less caster.  In some cases people can only get 5 degrees or so due to variances in the frames, prior accident damage, front frame damage, or the rear of the car sitting too high.”  It all means it’s possible to come up with way more positive caster than stock. Now, with a lot of caster your car won’t like backing up so much, but it sure will track well at speed.  Besides, you don’t have to parallel-park a racecar very often!

Next issue we’ll dig deeper into the “A-Team”.  There’s much more here than you might expect.  Watch for it.

arm-2

Here's a look at the TRZ lower a-arm alongside a stock Camaro/Nova lower.  While you can't see it here, the geometry improvement is considerable.
Here’s a look at the TRZ lower a-arm alongside a stock Camaro/Nova lower. While you can’t see it here, the geometry improvement is considerable.

arm-4

This photo shows the difference between a TRZ race upper and a stock upper.  As you can see, there is quite a physical difference.  There's more to it than meets the eye.  See the text for more.
This photo shows the difference between a TRZ race upper and a stock upper. As you can see, there is quite a physical difference. There’s more to it than meets the eye. See the text for more.
The complete a-arm package from the folks at TRZ Motorsports will reduce the front end weight of a car by as much as 15 pounds per side (30 pounds total), depending of course, upon the application.
The complete a-arm package from the folks at TRZ Motorsports will reduce the front end weight of a car by as much as 15 pounds per side (30 pounds total), depending of course, upon the application.
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