Here we see the results of...
Here we see the results of stacking different rate spring rubbers. The stacked spring effect shows and the stack gains rate slowly until a defined travel is reached before the rate increases drastically. With this chart, you can match the stack to your specific shock travel.
A solid suspension doesn't promote
continued and high levels of adhesion. Loss of grip at any corner will cause loss of performance. When the suspension goes solid, the tire spring rate will need to control irregularities in the track. Most asphalt racing tires have a spring rate of upwards of 2,500 lb/in.
What is encouraged is a setup where you use as much rebound in the shocks as is needed, and no more. Jason stressed this in our conversation. I've seen some shock graphs where the rebound was unusually high and that concerned me. But now, knowing more about the process and the spring rates that are associated with bump rubbers, I've concluded the rebound rate must control the spring rate.
If the bump rubber rate is 1,500 lb/in, then the shock must control that rate. If the rebound rate is not high enough, then that corner of the car won't stay on the bump rubber and the setup won't be consistent.
Sure, the rebound rates I've seen appear high in relation to more conventional setups, but we're not comparing apples to apples when we compare shock rates. That is why going from conventional setups to the BBSS setups requires much different shock designs. Organizations like RE Suspensions can be utilized to get the correct shocks for your application. The above illustrations tell why.
The key to reliable setups that are fast and consistent is in the combination of spring rates, bump rubber rates, and shock design to produce a balanced setup. This is the same balance we have talked about for many years now. It's the same process with a different approach.
The trend in Dirt Late Model racing has been to force the front ends lower with softer springs and then to a higher-rate spring to control the roughness of the track. This is a tall order but it can be
Hyperco Springs produced this...
Hyperco Springs produced this illustration to show how the stacked, or dual spring configuration works for the dirt cars. This is known as progressive rate change due to the increase of rate with shock compression travel, but the progression is immediate as opposed to gradual. You are either on the stacked spring combined rate or the higher spring rate. The key to making this work is to know where to place the locking ring to time the rate change.
A dirt car can't run on bumpstops for 99 percent of the tracks it runs on. Sure, there are times when a track goes black and remains very smooth, but we can't rely on things being that way very often. So, what will work to accomplish the above stated goals?
Double, dual, or stacked springs were introduced to me back in March 1998. Kelly Falls and Dewayne Ragland put together a plan to use stacked springs to soften the ride at one ride height and then cause a much stiffer rate at lower ride heights. Many combinations of stacked springs were tried on different corners of Dirt Late Model cars with varying success.
Until recently, honestly, it was
hit or miss and I think the missing ingredient was in designing shocks that could work with that system to produce the desired results. Jason and I talked about this setup phenomenon and how racers can make stacked springs work.
If you read the asphalt section leading to this dirt section, you will understand the goals of going from soft to stiff spring rates. The goal is similar with dirt setups except that the corner in which we need to transition is the right front, not the left front as in asphalt racing.
The successful use of stacked springs at the right front on Dirt Late Model cars is becoming more and more popular. The result is an attitude that is lower to the track and a spring rate that handles the forces of rough dirt tracks.
The shock is fitted with a stiffer top spring and softer bottom spring. The softer combination of the top and bottom springs allows the car to reduce its ride height using the same mechanical downforce we talked about in the asphalt section.
The movement of the shock causes the bottom support ring of the top spring to contact a locking ring located on the shock body. Then only the stiffer top spring rate comes into play. Now the car is lower and on a sufficient spring rate.