Taking a look at the three-link suspension with some of the industry’s experts
Photos Courtesy of the Manufacturers and Race Pages
When you are looking at the “late-model” Mustang, everything generally starts in 1979, when the new Fox chassis was debuted. Little did anyone know at the time, but that would not only be the start of a 25-model-year run, but also become one of the most prolific platforms in street-car drag racing – largely due to its triangulated four-link suspension from the factory. So it only stands to reason, that when the 2005 model-year rolled around with the new S197 chassis and a three-link suspension from the factory, everyone was a little leery with a ton of questions floating around.
Here we are, 12 years later and the questions have been answered – both by the performances we’ve seen on the race track and by the experts themselves, as we took an in-depth look at the state of the S197’s three-link suspension. Now that the aftermarket has had time to fully mature, and the three-link is a proven product, everyone gets to start the process all over again with the new S550 chassis and Independent Rear Suspension – but that is a topic for another article.
The Basic Setup
If you aren’t too familiar with the setup of an S197 rear suspension, its basic layout is a standard 8.8-inch rear-end, with a few changes from the familiar Fox four-link setup. Like the Fox suspension, there are two lower control arms, however unique to the S197, the rear coil springs aren’t on the control arms, but rather the axle tubes. A single, short upper control arm, centered on the differential housing makes pinion angle adjustment easier, but also loses the triangulation offered by the previous-generations setup. Because of that loss of triangulation, the S197 utilizes a panhard bar to locate the axle under the car. These changes resulted in what the average driver perceived to be a “better” factory suspension. However, as Eric Holliday from JPC Racing said, “As soon as you lower the car it starts doing really goofy things.” Dave Zimmerman of Team Z Motorsports explained, “The factory suspension wasn’t designed for drag racing. It was designed for a little more handling and ride comfort.” If you are reading this magazine, it’s probably safe to say you aren’t interested in a stock plush ride – you care about performance – and the performance potential of the S197 rear suspension is definitely there.
Passing Basic Geometry
Everyone we spoke with generally agreed, the first steps to getting the S197’s 60-foot times down was to get the suspension geometry correct. “The instant center is very long from the factory,” said Zimmerman of the OEM configuration. To remedy this, there are a variety of upper and lower control arm relocation brackets on the market. This might sound like an extreme modification, but is actually a common and relatively-simple change that applies to everyone from a lowered daily driver to a seven-second beast. Kelly Aiken of BMR Suspension explained, “When you lower the S197, it changes the angle of the lower control arms, and points the lower arms the wrong direction.” Steve Gelles of UPR Products agreed, “I recommend the control arm relocation kit whenever someone has lowered their S197. You want the lower arm as close to parallel [to the ground] as possible.” While getting the control arm parallel seems easy enough, Aiken related the formula BMR uses for a starting point. “The rule of thumb we use in-house is that a 1.0-inch drop should have the control arm mounting point dropped twice the amount. That would put it in the top hole, which is 2.0 inches lower than stock. A 1.5 inch drop would use the middle hole, which is 3.0 inches lower than stock. Anything lower than that we start using that lowest point, and we generally work with the customer on dialing-in their car, working on their specific geometry issues.”
With the lower control arms sorted, then there is the upper control arm to look at. Being so short from the factory, even the smallest of changes can have a large impact on performance. Aiken elaborated, “The single greatest downfall of the S197 three-link is the short upper control arm.” Holliday agreed, pointing out the need for relocation of the upper arm isn’t dependent on anything else, “While we recommend the lower relocations brackets as soon as you lower the car, the upper bracket should be done pretty much immediately.” Another advantage to the single control arm, is the ease in which pinion angle can be adjusted. While most of the folks we talked to mentioned that they adjusted pinion angle the same on a three-link as a four-link, Charles Epperson from London Chassis Dyno did say he tends to use less pinion angle on a three-link. “I try to achieve the right amount of separation in the suspension for the tire to work. Pinion angle needs to be adjusted so the driveshaft is happy during this range of motion; I try to achieve -1 degree by the finish line.”
Beyond the Street
At this point, you might be thinking, “If I have to relocate all of the control arms just to lower the car, what on earth do I need to do to get it to work on the drag strip?!” Well, the answer is, not really much more. Once you get the lower control arms relocated and pointing in the right direction, the rest of the suspension setup is almost exactly the same as any other suspension. You already have the adjustability you need, from that point on, it’s all standard suspension theory, as Epperson said, “Both the S197 three-link and Fox/SN95 rear suspension work in theory the same way.” Holliday agreed, saying, “If you know how you want a certain power and tire combination’s suspension set up, in general, it would carry over from a four-link to a three-link. You might need to change it a little for the S197, since it’s a longer car, and you can do a couple of things with that, but generally it’s the same. You have to set instant center, get your anti-squat right for the tire you’re on. It’s similar to the four-link with the same angles that you’re chasing.”
So, rather than go into suspension tuning theory – which could be another whole separate article – we’ll focus on the main differences the three-link offers high-performance cars at the dragstrip, and how the experts handle them.
With the loss of triangulation by going to the single upper control arm, there had to be another form of rear-end location used. The factory decided that a panhard bar was the solution. A panhard bar is a diagonal brace that attaches to the rear-end at one end, and the chassis at the other. It is a simple fix, but not without its problems in a drag racing application. “The panhard bar is really where the monkey wrench is. The rear-end moves around side to side when it goes up and down through its range of travel with the panhard bar,” said Holliday. That side to side movement can unsettle the tire and cause some odd, unwanted behavior. There are a number of adjustable panhard bars on the market for fine-tuning and trying to dial the car in as much as possible, but if your car is a purpose-built drag car, and the class rules allow it, pretty much everyone agreed that the solution is to eliminate it altogether. “On a racecar, we get rid of the panhard bar and go to a wishbone locator,” said Craig Pachar of Triangle Speed Shop. Epperson elaborated, “The wishbone allows the axle to stay centered during the entire range of motion. With the wishbone you can utilize separation without rear axle being shifted by a track bar. We have been fast with track bars but it is much easier with the wishbone setup.”
The next issue with some differences is the drag race anti-roll bar. “The three-link doesn’t have the opposing arms to combat roll of the rear axle, so you run into the tendency of the 3 link to roll over to the rear passenger side because of the single pivot point and the rotation of the driveshaft,” said Aiken. Zimmerman elaborated as well, “It’s like a tricycle. The driveshaft’s rotational forces play more of a role in the three-link’s behavior. You can cancel out driveshaft rotation by having the lower bars on different settings, but if you do run a parallel configuration, your anti-roll bar becomes much more critical.”
With more force to combat, it only stands to reason that you need a stronger anti-roll bar. “With off-the-shelf shocks, you generally don’t have enough anti-squat to fight the excess roll, even with a standard roll bar, so the solution is a bigger, stiffer bar,” said Aiken. “Or, you could run the smaller bar and dampers with valving strong enough to make up the difference, which is a solid option as well.”
This might sound relatively minor, but bushings play a large part in any suspension’s efficiency, and even more so in the three-link. Holliday explained, “There is a lot more load put on the upper control arm in a three-link, since it’s the only control arm doing the job. We like to put poly bushings on every car, even stock ones. The factory stuff is made for NVH and just too compliant.” Aiken elaborated on the upper arm’s bushing, “In factory trim, [the upper control arms] have huge rubber bushings on a short arm, so the amount of deflection you get is huge – almost 0.75-inch. That is essentially extending the arm 0.75-inch on launch.”
Of course, that leads to the issue of when to go from a polyurethane bushing to a solid bushing (A.K.A. heim joints or rod ends). Holliday pointed out that polyurethane bushings tend to have a little less life expectancy in a three-link setup than a four link, due to the increased forces. However when to make the switch is based on a wide range of variables – including the owner’s comfort threshold – making it a case-by-case decision. “I prefer heims joints over polyurethane,” said Eperson. “In really high-power applications, the typical poly bushing can create bind, and bind is the enemy of performance. I also understand the typical daily driver is more suited for poly ends but when you are trying to go 1.0-second sixty-foot, it becomes a toughness issue and a bind issue.”
Pachar also said, “In a street driven application, sometimes we’ll do half and half, with rod ends on the rear-end and poly on the car. I’d like to run rod ends all the time but some people request that the noise level be kept in check.” Aiken added, “It’s not all about power, it is about the shock load, and that is really what determines when to make the change, and what kills poly bushings. If you look at a streetcar with 1,000 horsepower and 19s or 20s on it, poly is fine. Then, you can go to the opposite extreme of something like a high-winding N/A Coyote-powered stick car only making 500 horsepower, but launching at 5,000 RPM, and you need to run a solid bushing.”
It has been proven that a three-link can be incredibly quick down the quarter-mile. The aftermarket support for it is incredible and the S197 platform will work with everything from off-the-shelf bolt-on street suspension to solid-bushing race parts. So the last question we had for everyone was what their personal opinion of the three-link was. Aiken said, “You could take our upper control arm mount which has three mounting positions, and a set of lower adjustment brackets, a set of the arms themselves, and an anti-roll bar, and you have a suspension capable of 1.2 sixty-foot times. The Fox suspension is a lot more complicated to get to the 1.2-second sixty foot than a three-link.” Zimmerman felt similarly, saying, “Talking factory versus factory, I like the three-link better. There are actually two 2016 Cobra Jets built with a three link, and they are both outperforming the 55 Cobra Jets that were built with a four-link in them. It’s been a 1.18-second 60-foot in a 3500-pound car with a 9-inch wheel on it. There is a ton of potential if you know how to use it.”
Pachar was of the same opinion as the first two, “I have a lot more experience with the Fox stuff in racecar applications, but I’ve had zero issues with the three-link stuff working phenomenally. If the reinforcement is there and it’s built properly, the three-link is a perfectly decent suspension.” Epperson rounded out the field of proponents with some more numbers to back his opinion, saying, “When you compare full-tilt triangulated four-links to full-tilt three-link setups, I think the three-link has the advantage every time. I think the S197 cars are typically heavier than Fox bodies and people tend to judge the cars by what they see and not what the specs are. The typical good-running S197 is solidly in the 1.3-second zone and Foxes of similar power levels go 1.2s, so people think the three-link is inferior. However, when you level the playing field as to weight and power, the three-link will hold its own. We have been 1.10-second 60-foots with a turbo Fox at 3340 pounds, and we have been 1.12-second 60-foots with a three-link turbo car at 3340 pounds. That’s comparable to me.”
The two holdouts – Holliday and Gelles – weren’t against the three-link at all, but rather just preferred the tried and tested four link. Holliday explained, “I like the four-link because it’s triangulated, so it stays straight in the car. A four-link will hold more true throughout its range of movement. I think with big power cars, it’s easier to setup a four link,” adding the following to support his opinion, “Obviously the Fox cars are the most prolific stock-suspension drag race cars in the free world.” Gelles supported his preference by citing the adjustability of the four-link. “The four-link gives you more options when it comes to setups. When you are going with a full-out drag racing setup, I feel something like a Fox body with a well set-up four-link will dominate. The three-link has been proven to be capable, but the four-link has been proven time and time again. In my opinion, the four-link has much more to offer a racer.”
Regardless of everyone’s personal preference between the two, the fact remains, that the three-link has gone from a scary new configuration that no one knew what to expect out of, to a proven, capable performer than can hold its own in the quest to 1.0-second 60-foot times.
BMR Suspension 813-986-9302 www.Bmrsuspension.com
JPC Racing 410-729-0005 www.Jpcracing.com
C&C Racecraft/London Chassis Dyno 606-309-7988 www.Londonchassisdyno.com
Team Z Motorsports 734-946-7223 www.Teamzmotorsports.net
Triangle Speed Shop 409-792-9744 www.Trianglespeedshop.com
UPR Products 561-588-6630 www.Uprproducts.com