Inside Smith Racecraft’s Advanced Hi-Tech Assassin Traction Bar, Part 3

Wayne Scraba

9 Aug 2018

Click Here to Begin Slideshow In our last issue, we left you with a set of basically assembled Smith Racecraft Assassin traction bars. With that issue, we looked at the knowledge behind the bars (Kim Smith) and showed the basics of assembling the bars, as well as providing insight on how they work. This time around we’ll examine bar tuning. As we’ve mentioned several times before, you’ll find these bolt-on traction bars are some of the most sophisticated available when it comes to tuning. Before we go any further, let’s stop and consider rod clocking in the bars. When a pair of rod ends is used in a single component (such as the link in the Assassin bar), the orientation of the rod ends on either end is important. This is what chassis builders refer to as “clocking” the rod end. Stop right here for one second: When you make very small adjustments in a suspension link that sees pre-load, it turns out you can make a huge difference in the way the car works or handles. In a four link, one-sixth of a turn at a time is all that is required in order to see a change in the way the car works. The rationale is similar with the Smith Racecraft Assassin bar. Keeping this in mind, counting the number of “flats” (the flat side of the rod end jamb nut) you turn on a link is critical. Included are a couple of photos that detail clocking. The first one shows you how a typical link is configured: One side of the link is fitted with right hand threads while the other end of the link is fitted with left hand threads. By simply loosening the jam nuts, you can lengthen or shorten the entire link bar. What about clocking? It’s easy. Check out the second clocking photo. When the rod ends are properly “clocked,” they are aligned. When aligned you won’t encounter binding in the suspension. At the same time, a link with clocked rod ends makes it easy to determine if the link is under tension. Simply grab the link by hand and rotate it back and forth. You’ll be able to tell if the link is neutral or under load (under load means it is binding). With the rod ends clocked, you can make adjustments to the traction bars. Keep in mind something of which we made mention in the last issue: During the initial setup, the car should be on the ground at ride height and “race” weight. The driver should be in the car (or matching weight should be placed on/around the driver seat). At this point, adjust each rocker so that the nose makes contact with the spring eye. Lock the jam nuts (and keep the rod ends “clocked”). What about preload? It’s not always necessary, but some racers add a small amount to the passenger side. How much is a small amount? Approximately ¼-turn. Don’t forget to count the “flats” on the jam nut. It's a good idea to keep that number in your tuning notebook or file. How about angle? According to Kim Smith, you should be in the range of negative 3 degrees. That places the pinion angle at approximately zero under power and going down the track. You’ll note that there are multiple adjustment holes on both ends of the Assassin bar. What you have are ½-inch holes on ¾-inch centers. This provides you with much, much finer adjustments in comparison to any other bolt-on traction bars. Once you have the initial adjustments sorted out, you can then fine tune by way of shock absorber settings. More on the initial settings below: For the initial setup, the traction bar should be positioned in the bottom hole, front and rear. If you need a soft hit, keep the bar in the lower holes. Smith Racecraft notes that for a harder hit, move the bar up one hole at a time. According to Smith Racecraft: “Generally speaking, the ideal adjustment will have the angle of the bar higher in the back than in the front. This will keep the tire planted to the ground for a longer period of time. Angling the bar higher in the front will result in a hard initial hit, but often it will result in the tire not staying planted to the track.” In the end, when it comes to hook with a bolt-in bar, the Smith Racecraft Assassins are pretty much in a class of their own. It’s easy to see the Assassin traction bars offer considerable adjustment and at the same time are easy to adjust - no special wrenches or other tools needed. Most users claim they regularly pick up performance over the other guys too, without bending springs. And the other big plus is the fact the parts are beautifully built. Ultimate hook? For a leaf spring car, we’d have to say these are at the top of the heap.

Inside Smith Racecraft’s Advanced Hi-Tech Assassin Traction Bar, Part 3 — Click Here to Begin Slideshow In our last issue, we left you with a set of basically assembled Smith Racecraft Assassin traction bars. With that issue, we looked at the knowledge behind the bars (Kim Smith) and showed the basics of assembling the bars, as well as providing insight on how they work. This time around we’ll examine bar tuning. As we’ve mentioned several times before, you’ll find these bolt-on traction bars are some of the most sophisticated available when it comes to tuning. Before we go any further, let’s stop and consider rod clocking in the bars. When a pair of rod ends is used in a single component (such as the link in the Assassin bar), the orientation of the rod ends on either end is important. This is what chassis builders refer to as “clocking” the rod end. Stop right here for one second: When you make very small adjustments in a suspension link that sees pre-load, it turns out you can make a huge difference in the way the car works or handles. In a four link, one-sixth of a turn at a time is all that is required in order to see a change in the way the car works. The rationale is similar with the Smith Racecraft Assassin bar. Keeping this in mind, counting the number of “flats” (the flat side of the rod end jamb nut) you turn on a link is critical. Included are a couple of photos that detail clocking. The first one shows you how a typical link is configured: One side of the link is fitted with right hand threads while the other end of the link is fitted with left hand threads. By simply loosening the jam nuts, you can lengthen or shorten the entire link bar. What about clocking? It’s easy. Check out the second clocking photo. When the rod ends are properly “clocked,” they are aligned. When aligned you won’t encounter binding in the suspension. At the same time, a link with clocked rod ends makes it easy to determine if the link is under tension. Simply grab the link by hand and rotate it back and forth. You’ll be able to tell if the link is neutral or under load (under load means it is binding). With the rod ends clocked, you can make adjustments to the traction bars. Keep in mind something of which we made mention in the last issue: During the initial setup, the car should be on the ground at ride height and “race” weight. The driver should be in the car (or matching weight should be placed on/around the driver seat). At this point, adjust each rocker so that the nose makes contact with the spring eye. Lock the jam nuts (and keep the rod ends “clocked”). What about preload? It’s not always necessary, but some racers add a small amount to the passenger side. How much is a small amount? Approximately ¼-turn. Don’t forget to count the “flats” on the jam nut. It's a good idea to keep that number in your tuning notebook or file. How about angle? According to Kim Smith, you should be in the range of negative 3 degrees. That places the pinion angle at approximately zero under power and going down the track. You’ll note that there are multiple adjustment holes on both ends of the Assassin bar. What you have are ½-inch holes on ¾-inch centers. This provides you with much, much finer adjustments in comparison to any other bolt-on traction bars. Once you have the initial adjustments sorted out, you can then fine tune by way of shock absorber settings. More on the initial settings below: For the initial setup, the traction bar should be positioned in the bottom hole, front and rear. If you need a soft hit, keep the bar in the lower holes. Smith Racecraft notes that for a harder hit, move the bar up one hole at a time. According to Smith Racecraft: “Generally speaking, the ideal adjustment will have the angle of the bar higher in the back than in the front. This will keep the tire planted to the ground for a longer period of time. Angling the bar higher in the front will result in a hard initial hit, but often it will result in the tire not staying planted to the track.” In the end, when it comes to hook with a bolt-in bar, the Smith Racecraft Assassins are pretty much in a class of their own. It’s easy to see the Assassin traction bars offer considerable adjustment and at the same time are easy to adjust - no special wrenches or other tools needed. Most users claim they regularly pick up performance over the other guys too, without bending springs. And the other big plus is the fact the parts are beautifully built. Ultimate hook? For a leaf spring car, we’d have to say these are at the top of the heap.

This is a typical link removed from the Assassin traction bar. Note the orientation, or “clocking,” of the rod ends.

A properly clocked link (shown here) will allow you to move the bar through its range of motion (rotate) within the rod ends. See the text for more info.

Both ends of the Assassin traction bars (front and rear) are built with multiple adjustment holes.

These are ½-inch holes on ¾-inch centers, which in turn provide you with much finer adjustments than any other bolt-on traction bar.

For a starting point, Smith Racecraft suggests you begin with the bars in the bottom hole, front and rear. The text offers some ideas with regard to preload as well as pinion angle.

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