Shocks on the open wheel Sprint Cars are subject to damage not only from racing incidents,
Another view is voiced by Thiesse: "In dirt racing, the left-rear shock in a Modified or Late Model seems to become the droop limiter, although we don't recommend the shock to be used in such a manner. In asphalt racing the huge rebound forces on the front [usually more on the left front] of the car can create high internal pressures and heat. These conditions tend to stress the O-rings and seals and may require a higher maintenance program."
"In pavement cars, we find that the most abuse is put onto the front shocks," Keyser says. "Most pavement cars are running a big sway bar along with very soft front springs that are run close to or totally coil bound. This type of setup puts a lot of the load of the chassis on the shocks themselves.
"In order to get the cars to pin the nose to the ground for optimum handling and aerodynamic reasons, the front shocks are often built with six times the amount of rebound found in a typical dirt car shock. That adds stress to the valving system and oil in the shocks, and header heat from a pavement car's exhaust has a huge wear factor on the front shocks," explains Keyser.
"Hiked up dirt chassis tend to top out the left-rear shock and bottom out the right-front shock. Asphalt race cars that use soft front springs can bottom out the front shocks during braking. Severe shock bottoming out can be very detrimental to the life of the shock. Shock bumpers can help prolong the life of shocks that tend to bottom," Bush suggests.
9. What typically causes premature failure of a racing shock?
"All of what we have talked about above!" exclaims Bush. "Hiked up dirt race cars tend to bind the shocks [top and bottom], which can damage shafts, seals, and rod guide bushings."
"The most damage that occurs to shocks are from track conditions, wrecks or poor maintenance," Keyser says. "All shocks need to be maintained weekly and put on some type of rebuild schedule. Dirt shocks are more likely to develop imperfections in the shafts because of the track surface and rocks or debris that they may encounter."
This coilover spring and shock combination is popular with all forms of racing. The racer
"A shock is a mechanical device with many components such as seals and O-rings that can fail at any time due to dirt and grit, heat and binding," Sandt adds. "Spring collapse will also create rubbing on the shock, which will wear it out. However, crashes still seem to get more shocks than anything else."
From Henquinet's experience, "Premature failure usually is the result of crashes. The other main cause is bottoming out or spring contact."
QA1's Thiesse agrees: "Anytime a shock is bottomed or topped out it can cause premature failure. One of the biggest issues with today's dirt Modifieds or dirt Late Models is the extreme indexing of the birdcages. If your shock is attached to this birdcage, it could travel the bearings past its full misalignment range and bind the shock. The bind will cause a side load to the piston rod and will prematurely wear the O-ring and bushing in the closure nut and ultimately cause the shock to leak."
10. Is there a preferred mounting height for shocks (piston position in the tube) in relation to the amount and direction of travel each shock will experience?
"The rule of thumb used to be 60 percent of the travel was allowed for the compression stroke. Today, there is no right or wrong answer, as long as the shock can function without topping or bottoming out," Thiesse offers.
Henquinet tells us, "Generally, you want the shock to be mounted so it is as close to the middle during the actual use on the track. However, you have to make sure it does not bottom out or top out. Where the main piston is located within the shock body has an effect on the efficiency of the shock, but it is very slight."
Bush offers a different view: "Ideally, the piston should operate as deeply in the shock body as possible. This arrangement provides the most stability for the shaft and piston assembly and enhances seal, bushing, and shaft life."
"Integra recommends that the shocks be mounted in a manner which is bind-free, with about 50 percent of the shaft showing with the chassis at ride height," according to Keyser. "This mounting procedure will aid in the prevention of the shock bottoming or topping out, both of which may cause damage to the shock."
The bottom line is that racers need to help their shocks by installing them properly to eliminate binding, checking them often, and having them rebuilt periodically. Think about how you use your shocks and what they go through. Then you will be able to avoid the pitfalls that go with shock problems.