More than 25 years ago, the shocks in use in the most technologically advanced open wheel racing series in the world were transformed in a way that forever changed motorsports at its most elite levels. Jeff Ryan, the founder of JRi Racing Shocks, played an integral role in the development of the four-way racing shock.
Working as a damping technician in the early 1980s for an open wheel team (CART) in New Mexico, Ryan says that, at the time, the team would carry as many as 30 different shocks that featured fixed inner elements, necessitating that he take them apart and re-valve them between races to cater them to specific race tracks.
That’s when Ryan, also a machinist by trade, built his first four-way shock, which he shares was much different than other, similar designs that had been developed around the same time period. The new shock saw immediate success, and soon, he says, his team drivers would ask for nothing less on their machines on race day. Ryan later took his experience to an upstart shock manufacturer that put his design to use with the Williams and Ferrari Formula 1 teams, who won races right off the bat with his shocks installed.
Fast forward to the present, and four-way shocks are essentially standard equipment in disciplines of racing the world over — including some segments of drag racing. From Pro Modified to Pro Stock to Drag Radial, these shocks feature both high- and low-speed compression and rebound, as well as — in JRi’s case — an air-assist element, and are proving a key asset in getting high-horsepower cars down the race track quickly and consistently.
Despite their presence in the sport — and the more commonplace use on UTV’s and other off-road vehicles — four-way shocks remain a bit of a black art to many. After all, when many racers find themselves lost with a simple rebound and compression adjustment, adding yet another set of dials can be daunting. And so, with the help of Ryan and JRi’s Drag Racing Manager, Marc Smith, we’re going to give you a layman’s terms look at what a four-way adjustable shock is, how they work internally, and how racers are taking advantage of the unparalleled adjustability.
What Is A Four-Way Shock?
A Shock: Simplified
A shock is, as JRi’s Jeff Ryan puts it, nothing more than a pressure relief valve. Hydraulic fluid provides the pressure (or resistance) needed to moderate the compression valve and the piston within the shock as it moves in one direction or the other. But there’s more to the system than that, as nitrogen gas is added to the backside of the compression valve in order to pressurize the system and prevent aeration in the oil.
Auto racing, however, particularly at its highest echelons, is an ultra-competitive sport where fractions of a second make all the difference. And there, the ability to adjust down the Nth degree is paramount. As well, because time is money, a four-way shock can be adjusted to work on any track in a matter of minutes, rather than the alternative of swapping shocks or re-valving the one you have.
So what’s high-speed and low-speed, and what’s the difference?
Imagine, if you will, riding a dirt bike into a large rock at speed — the shock is undergoing an instantaneous and particularly large degree of compression. This is akin to a high-speed motion. Now, think of a rider performing a jump and consider the forces of landing the bike. One is abrupt while the other is agile. As well, they represent two distinctly different motions: one is the wheel and tire going up into the frame while the other is the frame and its weight compressing into the wheel and tire.
It’s how you manage the pressures inside the shock and bleed it off that correlates to grip and feel. – Jeff Ryan, JRi Racing Shocks
Through the use of an additional means of pressure relief, a four-way shock absorber gives a racer access to both the high- and low-speed circuits so that they can cater it to the car and the track, be it the compression or the rebound. JRi’s four-way is a monotube design, in which both columns of fluid on each end of the tube are used to bleed off the low-speed or increase the pressure on that side of the tube in order to create the higher damping values. JRi tunes the low-speed right on the piston face through orifices that the oil passes through. A separate shim stack on the piston is then used for high-speed operation, which gives way to allow more oil to pass through and therefore a higher speed movement of the shaft.
Now, you might be wondering how the shock is able to differentiate the two. And, if you know how a wastegate on a turbocharger works, where a specified amount of air pressure forces a spring and valve open to release boost, then it will make perfect sense. The piston itself features a series of orifices (essentially a needle and jet) that fluid passes through, which are adjustable. This is your low-speed circuit. But as the velocity of the piston increases, there’s a need to flow more oil to decrease pressure against it so that it may rebound quicker. According to Ryan, this is generally from 0.1 to four inches per second for the low-speed bleed before it’s no longer effective and the high-speed shim stack begins to open up and take over. This is done by adjusting the preload against the shim stack, similar to the spring pressure in a wastegate.
“You can valve the shim stack to where the low-speed adjustment can be, say, from zero to two inches per second, but at that certain point, there’s a crossover where the low-speed bleed can no longer flow. Say you’re trying to push a gallon of fluid through a 1/8-inch hole, there comes a point where you can’t push it any harder. It’s then when it starts to modulate off the piston,” Ryan explains.
The compression side is operated through a compression valve located inside the external canister, that contains a bleed and a shim stack. A typical twin tube shock without this canister would house the compression valve at the base of the shock, and the storage chamber would be the outer tube of the shock body.
As a monotube shock, the JRi four-way utilizes the external canister to serve as the storage chamber for the hydraulic oil. Part of the job of the canister is to create a pressurized “overflow” for the oil within the working chamber of the shock to ensure there’s always fluid in the working (compression) chamber of the shock. The shocks are gas-charged, meaning that nitrogen is injected into the canister under pressure, on the opposite side of the compression valve, keeping it under constant pressure and preventing any aeration (air bubble formations in the fluid that would affect its operation) during movement of the shock.
On the rebound side of things, the adjustments to the high and low speeds are made on the eyelet of the shock. A metering rod runs down through the hollow shaft of the shock which controls the jet. In the JRi four-way, the design is comprised of two shafts, one inside the other, with the internal shaft containing the metering rod. When you adjust the high-speed rebound, a “cage” that’s attached to the rebound side of the piston preloads another shim stack that’s on the end of the piston. The low-speed, on the other hand, is operated through a needle and jet that’s screwed into the end of the shaft, that controls the orifices in the face of the piston. Adjusting this one way or the other, like compression, allows more or less oil to pass through. This jet can also be completely closed off if you so choose.
“I’ve really stayed with that initial design since the beginning. Obviously, we’ve refined it, but we haven’t changed it. I’ve gone away from it a couple of times, after looking at the way other manufacturers are doing it, with twin tubes and doing the damping around the outside of the body, for instance, but we’ve found that the dyno results are always right where their shocks are. So, I always go back to what I know. We feel the best performance comes from our original design,” Ryan says.
I’ve really stayed with that initial design since the beginning. Obviously we’ve refined it, but we haven’t changed it. – Jeff Ryan, JRi Racing Shocks
JRI has also built an air assist feature into their four-ways allowing a racer to completely shut off the low-speed circuit of the shocks, thereby overriding the low-speed rebound. With this, racers can virtually lock out the suspension for the initial launch, if they so choose, and release it when needed. This feature is operated with a separate air bottle and solenoid in the car and a controller. Jerry Bickel Race Cars sells a timed pneumatic air bleed system that’s compatible with the JRi shocks to operate the air assist feature.
“All we’re really doing with the air is using it as a switch, where you can go full-hard to full-soft or somewhere in between very quickly. So you have air pressing on that adjuster, and as soon as you release the air, that adjuster moves. It’s nothing more than a switch,” Ryan explains.
Once the air bottle is turned on, it charges the shaft inside the shock to 250 psi, shuts the needle off, and overrides the low-speed rebound. Once the timer releases the air — often at 1.5 to 1.8 seconds into the run, the needle unseats. This lets racers get more aggressive with their high-speed rebound on tracks that aren’t particularly great. “This way, you can put more rebound in than you could on a non-air-assist shock, because once you dump the air, you’ve smoothed the ride back out,” Smith explains. “If you tried to do the same thing a non-air shock it would hurt you on the back half of the track because when it hits the bumps you have so much rebound in there that it’s trying to pull the tires off the track.”
Pro Stock teams, in particular, have used a double air-assist setup that actually charges the low-speed compression (with a fitting where the low-speed compression adjustment screw would be), and a second air bottle, solenoid, and timer. With the air put to it, the needle is shut off and causes it to hit the tire harder on the hit, but once rolling, the air is dumped and the car can settle down into the race track to allow the air to flow over the car and the spoiler.
Four-Ways In Practice
“When I first introduced the four-way to McLaren Formula 1, when I was in Europe, their engineers asked me to put together a set of rules on how they could use the four-way adjustables. They were coming off shocks with no adjustments,” Ryan shares. “Basically, I explained that any motion of the chassis going down into the tire, I would consider a low-speed adjustment. Any motion of the tire going up into the chassis through the hub, I would consider a high-speed adjustment. And I’ve always stuck with that, haven’t strayed from it, and it seems to be pretty accurate.”
As Ryan goes on to explain, a four-way shock is able to change large amounts of damping, which is considered the high speed, while the low speed is the slope or the way in which the energy is delivered to that higher number of damping.
I explained that any motion of the chassis going down into the tire, I would consider a low-speed adjustment. And any motion of the tire going up into the chassis through the hub, I would consider a high-speed adjustment. – Jeff Ryan, JRi Racing Shocks
In drag racing, the very operation of a shock, regardless of the type, is very different depending on the tire you’re running, as Smith tells us. A car running on slicks, like Pro Modified, Pro Stock, or even Top Sportsman, are aiming to maintain a degree of wheel speed, without spinning or shaking the tires. And they use the weight of the car, among other things, to help regulate wheel speed. A radial tire car on a radial-prepped track, on the other hand, is intended to dead-hook and lacks that need for wheel speed. In fact, radial cars will typically rebound (or extend) at the launch, rather than compress like their slick tire counterparts.
On a slick car, the initial hit, as you might surmise, is a high-speed operation — once the car has gotten up on the tire, it becomes purely low speed as the car works its way over the small undulations in the racing surface.
As Smith shares, the bleed on the low-speed rebound jet is typically between .0020 and .0040 of an inch, which is relatively small. “You have to be able to control that bleed in drag racing because that’s a critical part of how you hold the spring together and keep the weight on the rear tires. If a shock has too much bleed, it doesn’t matter how much high-speed rebound you have in it, the shock is going to come apart and come apart too soon. So you have to keep that tight window on your bleed, or you won’t make it to that 60 to 100-foot mark before the rear tires unload and you lose traction.”
On a good track, or early or late in the season when tracks typically have a little more grip, Smith says that racers often don’t need as much rebound, especially high-speed rebound, because the track has enough bite. And, as he explains, the more rebound you put in the shock, the longer you hold the weight on the tires and the more you suppress wheel speed. So, when tracks can take it, you don’t want to slow down the wheel speed and therefore acceleration. As the tracks lose grip, you have to dial in more rebound to hold the weight on the rear tires. He says this can sometimes be as much as two seconds into the run before you want the shock to begin to release.
Once a slick car has endured the high-speed compression at the hit and the low-speed rebound has held the weight, the car begins to get ‘up on the tire’ and will settle down, turning to what Smith calls a “frequency” motion as it goes through low-speed compression and rebound over the bumps in the track.
“After the initial hit, compression is very minimal. Most drag racers, once they set their compression, it doesn’t change a whole lot from track to track. What really changes is how long you hold that weight on the rear tires.”
Despite this, slick cars rarely return to ride height, as by the time the low-speed bleed has begun to allow some degree of rebound, aerodynamics have taken over and begun to push the car down into the tire.
Radial cars, on the other end of the spectrum, are approached in reverse.
“With a radial car, you’re not trying to hold the weight on the rear tire, because it’s a hard tire with somewhere around 16 pounds of air. Because of that, you’re trying to give that tire as much grip as you can,” Smith says. “You actually don’t want any rebound in the shock at all holding the weight on the tire because then you’re restricting the spring or whatever suspension device you have from pushing the tire down into the race track. The tire is so hard and has so much air in that it’s about grip more than weight.
Most drag racers, once they set their compression, it doesn’t change a whole lot from track to track. What really changes is how long you hold that weight on the rear tires. – Marc Smith, JRi Racing Shocks
Regardless of the tire you’re running, or even the amount of power you’re attempting to plant to the pavement, the adjustability provided by a set of four-ways shocks is truly unparalleled. True, there a lot of intricate, moving parts housed inside the shock body, and while the engineering side of it might lean towards rocket science, for the racers, it’s anything but. Rather, it’s all about finding a baseline for their car and learning how to make the shock work to their advantage on any given surface in any conditions.