Here you can see a great view...
Here you can see a great view of the left-rear suspension setup on this Rocket Chassis dirt Late Model. The top link is mounted at an upward angle in the center-hole position on the chassis, while the bottom link has no angle but is shorter in length than the top link. This setup enhances side bite but also controls roll steer through the corner.
This illustration shows how...
This illustration shows how adjusting the four-link bars can actually change the wheelbase of the race car. For instance, if a racer moves both links up three inches, the axle will move forward about a half-inch. When tuning a four-link, it is essential to understand what each adjustment means in the overall picture.
This photo illustrates the...
This photo illustrates the increasingly popular left-rear shock-behind setup (shock and spring), with a stabilizing rebound shock (shock without spring) mounted in the front as well.
Notice the straight Panhard...
Notice the straight Panhard bar attaching to the left side of the pinion. This is used in instances where the racetrack is slick, with big, slow corners.
Here, instead of a straight...
Here, instead of a straight Panhard bar Rocket Chassis has used a J-bar that wraps around the rearend and attaches to the right side. Notice the number of setup holes available, allowing racers to tune by changing the angle of the J-bar.
One of hottest items in dirt...
One of hottest items in dirt Late Model racing is an aluminum birdcage. Unlike the beefy cast floaters of the past, these billet pieces come with a variety of adjustable mounting options and save nearly 11 pounds of unsprung weight over their predecessors. This example from TWM Racing Products is made from 6061-T6 aluminum and can be ordered with numerous options, including floated or clamped brakes, various coilover mounts, and more.
Only a few years ago, achieving the right setup with a four-link suspension was no easy task on a dirt Late Model, and one reserved only for the elite tuners and racers. But over the past three to four years, four-link suspension tuning has undergone some radical changes and today offers almost limitless setup possibilities for all types of race conditions. We have more ways to tune the four-link, and thats good. But that means there are now more ways to mess it up. Theres certainly more to learn for a proper four-link setup, which makes it more difficult for a typical Saturday-night racer to master. However, if a race team can maximize the performance of todays four-link suspensions, theyll find themselves in victory lane on a consistent basis.
To help explain some of the four-link tuning tips top-level race teams and chassis builders use to win races, we turned to Joe Garrison of GRT Race Cars, who co-authored Dirt Track Stock Car Fabrica-tion & Preparation with Steve Smith Autosports. We also got the expert opinion of Rocket Chassis Mark Richards, whos helped fuel the success of racer Steve Francis. Randy Jordan of Dave Poskes Performance Parts told us some tips he and driver Steve Shaver have learned over the years, and Matt Long of Clewell Racing revealed how the Ohio-based team has used four-link tuning to help them get to victory lane in more than 248 feature wins behind veteran driver Tye Long (who has 245 of those wins) and young Cortney Clewell.
With the help of these professionals, well explain the different tuning components of a four-link suspension and how each change affects a dirt Late Model race car. For the purposes of this article, well assume most racers know the basics of the four-link suspension. Our primary focus is how to tune the suspension for specific conditions. If you would like to refresh your understanding of the four-links basic principles, and dirt race car setup in general, we recommend picking up a book such as Stock Car Dirt Track Technology, available through Steve Smith Autosports, before reading this article. The four-link suspension is a complex system that the average racer has a tough time totally comprehending.
I think where most racers miss the boat on any rear-suspension setup, especially four-link suspensions now that chassis builders place all these adjustments into it, is they overadjust and make the car tighter, says Mark Richards. That happens 90 percent of the time for most local racers. They are under this big misconception that they can drive the push out of the car, but you cant because these cars simply have way too much traction available.
Traction is important in dirt Late Model racing, and thats one of the primary functions of the four-link suspension, but the answer to every tuning problem is not always more traction. If the race car is too tight, the driver may actually have to break traction just to get the car to turn. That results in no traction or control through the turn, and the driver is then forced to find some trick to regain traction to exit the turn. All this serves to slow down the car rather than speed it up.
The key word is momentum, says Richards. When you have momentum, you dont need nearly as much traction.
Racers run into the same problem of lost momentum when they attempt to give the car too much induced roll in hopes of gaining more bite.
I have found that on this four-bar stuff, Friday- and Saturday-night racers have a real bad conception of what a four-bar should do to a race car, says Randy Jordan of Dave Poskes. They think its traction. They think theres magic in them bars to give them traction. And theres not. Instead of looking for magic, Jordan suggests racers find a neutral setup that works, then start moving the four-link suspensions tunable components one hole at a time until they understand what works and what doesnt on the race car. He also suggests not trying to tune too much on race night, or racers might end up chasing their tails and missing the setup entirely.
With some of these guys, the racetrack will be heavy when they arrive. Their car is pushing because they had it set up for slick conditions last week. Theyll want to come in and change bars and everything, he explains. Well, the tracks going to be back the way it was last week, or close to it, later in the evening. If they know they had the bars the way they liked last week, they should be tuning the wheel offsets, stagger, air pressure, and stuff like thatand leave the bars alone!
Four-Link Bar Angles Its the heart of the four-link suspension, so we might as well start with the four links them-selves. Racers have a variety of ways to tune the bars, but there are basically two main items being adjusted: the rod angle and the rod length. And within those adjustments, the upper bars are usually concerned with corner exit, while the bottom bars mostly affect the entry.
The more upward angle you have, top or bottom, the more weight is going to be induced through the trailing rods to the rear axle, making more traction, says Richards. But at the same time, you have a factor of roll steer that has to be considered. Too much upward angle will cause too much roll steer.
During a roll-steer condition caused by top links that are sharply angled, the right-rear tire actually moves rearward and the left-rear tire forward, causing the rear axle to steer toward the outside of the track. If this roll steer is too excessive, handling the car will be too difficult and actually negate any advantage gained by increasing the bite. However, some roll steer can actually help the race car through the turn. The trick when tuning the angles of the upper bars on a four-link suspension is finding a happy medium between traction and loose roll steer on different track conditions.
On the bigger tracks, says Richards, where you have to carry more momentum in the turns, less upward angle is needed. Conversely, for a short heavy track, where racers need to get lots of bite to exit the turn quickly, the upper links need to be angled more sharplybetween 15 and 20 degrees.
The angles we try to run on the upper bars are anywhere from 15 to 18 degrees for a normal track, but if it gets slick we can set the angles anywhere from 20 to 24 degrees, says Long.
As stated, the steep angle also creates more loose roll steer, but there is another concern with severely angled bars: out-tuning the shocks. The higher you adjust the left-side upper link, as the car goes into the corner and rolls over, it lets the rear end roll forward and shove up on the car, says Jordan. If that happens, the shock and spring arent doing a whole lot, and youre using mechanical rods to apply traction to your race car. You have to be careful with both links on the left side. Dont get them at such an angle that it tops the shock out. When it tops the shock out, itll actually jerk the left rear tire up off the ground.
To control entry into a turn, racers will look to tune the bottom links instead of the top. Lets say youre loose going into a turn; on the right, you can lower the bottom angle and shorten the bottom bar length, says Long. On a slick, short track, limiting the roll steer by angling the lower bar either level or negative up to five degrees will help the race car get through the corners faster.
But even finding the right balance between traction and loose roll steer over a certain track is sometimes not enough. Racers also have to consider high and low lines around the course and factor how each plays into the four-link setup. Imagine youve found a nice groove around the track, the setup is perfect, and youre flying high on the outsidebut you run into traffic. To pass, you might have to forsake your high line and dive to the bottom. If you have the suspension set up only to run wide, you might not be able to drive under a car and pass coming out of the turn. Thats why its best when tuning the four-link suspension to have a setup that is adaptable for the driver. Often, that means a setup that is more neutral so the driver has a better chance of manipulating the race car through different lines around the racetrack.
Four-Link Bar Lengths In conjunction with altering the bar angles, racers have the option of tuning the length of the bars as well. Some racers we talked to never change the length of their bars once they find their ideal setup; they choose only to adjust the angles and other factors from week to week. On the other hand, some of our experts admit they may change the length of the bars at the track to adjust for conditions.
In general, if the right-bottom bar is shortened and/or the left-bottom bar lengthened, the car will tighten up on entrysimilar to the effect lowering the right-bottom bar angle has. In contrast, if the right-bottom bar is lengthened, the car will become looser on entry.
Our normal bottom right bar is around 14 to 15 inches, and we might go as short as nine or 10 inches to tighten the car up, says Long.
If we get to a track that is wet and heavy for qualifying a speed race, and our hot laps are real tight, he continues, well just throw our standard long bar on the bottom right, which is about 15 inches long. Then if the racetrack slicks up for the feature, well put a shorter bar back on the bottom right.
As for the top bars, those lengths are usually left between 17.5 and 18.5 inches but can be different lengths on the right versus the left. Joe Garrison of GRT Race Cars actually runs longer bars on the left and slightly shorter ones on the right to prevent the car from becoming too tight. He says this bar lead should be anywhere from a quarter to a half inch difference in the length of the bars.
On a track with sweeping corners, you probably want just a little more lead in the bars, versus a track that is real tight and stop-and-go, says Garrison. Trailing rods that are too equal in length can cause too excessive roll steer. What youll find on most dirt Late Model setups these days is a long upper link and a shorter bottom link. This setup induces traction but helps limit roll steer. Figuring Saturday-night racers already have enough to worry about with tuning the bar lengths, this may be a feature most choose to setup once then never touch again.
Shock and Spring Setup When you talk shock and spring setup on a dirt Late Model, the possibility for tuning with double-adjustable race shocks and a variety of spring rates is a monumental task, and one that probably deserves an entire article unto itself. But there is a recent development in the position of the shock that warrants attention, enough so that Mark Richards credits it with saving the four-link race car. Were talking about moving the left-rear shock behind the axle. Developed about three years ago, this setup actually places the shock and spring behind the axle, instead of its traditional location in the front.
In general, the left rear behind shock has a similar effect increasing traction as another tuning setup racers have used for a long time: clamped-up. If there is traction available on the racetrack surface, the left-rear clamped setup provides lots of forward traction, says Richards. But when theres no traction available, the left-rear shock-behind setup is body-roll controlled, where the left-rear clamp is throttle controlled. So you dont have to have quite as much traction on the race surface for the shock behind to work. All you have to do is cause the car to have some sort of roll. Thats why you see a lot of the cars today rolled onto the right side through the corners, with the left side almost airborne.
What racers mean by clamped up is instead of attaching the shocks in the standard position on the birdcages, leaving them floating with the axle, the shocks are clamped straight to a fixed position on the axle.
As Long describes it, clamped up is instant traction. Or you can run double-clamped, says Richards, in which both shocks and springs are mounted to the axle. That allows both rear wheels to be loaded when the torque is applied to the rearend. Now one of the downfalls to that setup is, there has to be some traction there for the tires to make adhesion for that setup to work.
Essentially, forcing more traction into the rear tires will only work when there is traction to be had. Otherwise, running double-clamped on a slick track might leave racers spinning their wheels, literally.
We find on a double-clamped setup that it works best in extremely heavy, short-track conditions where you need the right-rear wheel to drive equally with the left rear, says Richards. But with a large number of racetracks, the high cost of digging them up these days seems have influenced operators to leave their tracks slick, even at the beginning of the night. Therefore, a double-clamped setup is rarer than in years past.
We still run left-rear clamp setups quite regularly. And where we find that a left-rear side clamp setup works well is on a tacky, usually short racetrack, Richards continues. The reason why is because a clamped bracket setup is controlled by the throttle. So it makes a real drivable setup on a short, tacky racetrack. We use the unclamped setup mostly on high-speed momentum racetracks, where we dont need quite as much bite.
If it gets really slick, the problem with clamped up is theres a lot of roll steer, says Long. When you hit the throttle, it pushes the left rear clear out from the car. Thats why many of those guys have just switched to the left-rear shock-behind setup.
Although a left side clamped is still effective and widely used, a left-rear shock-behind setup puts a lot of diagonal weight force in the car, which allows the driver to steer off the left rear and right front. It also helps increase traction, which is why this setup has become so popular. But a racer cant just decide to throw the shock behind the axle and expect the car to be fastertheres more to it than that.
With your shock behind, the biggest problem you have is usually being too tight coming off the corner, but you also have a lot of bite, says Long. That can be a dangerous combination. To combat that, racers can adjust the spring rate on the left rear, taking wedge out of the car.
Richards says, With the shock and spring behind, a high-wedge setup seems to work well most of the time on a high-speed racetrack. On a high-wedge setup, the springs need to have more split between them. Lets say you ran a 300-psi left rear and a 200 rightthat might be a good split for a high-wedge setup. However, on a low-wedge setup, the springs need to be more equal, like 250 and 225 psi.
You can also adjust the shocks to help stiffen the right or left rearand its all quite simple if you have a double-adjustable racing shock. With those advanced shocks, you can easily tune rebound and com-pression between heat races or practice laps.
What happens is when you put the shock behind, continues Long, you want maximum torque but also the least resistance so that the spring pushes the shock out. Everybody started off running whats called a dummy shock on the front of the axle.
While the shock behind has a spring around it, the shock in front serves as the control shock, limiting the distance that the rearend can fall down, and therefore does not need a spring. Basically, what we use that shock in front for is to control suspension travel, says Richards. We can help control the body roll, how much the car raises or drops, with the left-rear shock in front on a shock-behind setup. Sometimes youll even see guys use a zero, dead shock on the backside and use the shock in front as the control shock. The control shock in front actually moves at a little bit greater speed than when its used with the spring.
Panhard Bar or J-Bar In a dirt Late Model race car, this bar controls the cars roll center. While it has the same function, its name depends on its shape, which depends on where the bar is mounted to the pinion. A short, straight bar mounted to the left side of the driveshaft is a Panhard bar. A J-bar extends over to the right side of the pinion and is bent down in a J shape to mount lower on the bracket and maintain the desired angle depending on track conditions. Basically, all J-bars also are Panhard bars, but not all Panhard bars are J-bars. However, for dirt Late Models, J-bars are used in just about every situation except a slick, big, slow corner racetrack.
By raising the J-bar up on the frame to create more of an angle, it makes it easier for the car to roll over onto the right side, says Long. If youre drifting across the track going into the turn, then raise the chassis mount for the J-bar, and it will help the weight transfer to the right side.
We use a 19 to 20 inch, and it has probably anywhere from seven to nine inches of angle in it for our standard setup, says Garrison. By angle, I mean the mounting point on the pinion versus the mounting point on the chassis. If the track is extremely slick, you need a lot of angle in the J-bar to help induce roll in the car and create side bite and drive. On a bigger track where you can carry more speed, you dont need as much angle in the J-bar. You might even use a longer bar, say as much as 25 inches. On a real tight, stop-and-go racetrack, we might even use a short, straight Panhard bar if we have to get the car to turn quickly.
Garrison continues, Actually, on our standard J-bar setup, with it mounted on the right side of the pinion, I think it helps tighten the car on entry but allows it to turn through the middle and coming off. In contrast, the straight bar that mounts on the left side of the pinion makes the race car more loose on entry and gives the drive coming offperfect for a short, stop-and-go racetrack.
Again, you can see that while the basic principles behind the suspension are rather simple, a lot of variables are involved when it comes to tuning the four-link. Each adjustment on one end affects several factors on the other side. Unless you understand what how each change affects the rest of the race car, you might end up counteracting a change you just made.
If theres one theme most of these experts tried to espouse in our interviews, it was to make sure you understand its best to take things slowly when tuning the four link. Remember, its momentumnot tractionthat wins races.