Coil binding and bump stops are terms we hear all the time. What are they? Fellow contributor “Dawg” Chapman brought up the fact that he was a little fuzzy about the subject and maybe some other fans were too. Let me attempt to bring in a little focus to the topic.
The Car Of Today chassis runs fastest with the front splitter just riding the racetrack, sealing off the air rushing underneath it. But that is a razor thin edge to walk on. The suspension can travel too much, the splitter can grind away from crashing onto the track surface, and the frame can drag the track to where the car is no longer even riding on the suspension.
Too little suspension travel and the front air is not sealed off. This is the slow way around the speedway, behind cars with their front-end travel figured out.
Coil binding setups were common in the nicknamed “Twisted Sister”, or the previous chassis version. This was another way to maximize travel in order to accomplish the same thing.
In a nutshell, coil binding was a combination of front spring rating and shock travel that allowed the front suspension to move during corner entry to get the car as low as it could without dragging the frame. The front coil springs were compressed to an exact point where the coils were touching one another. Like bump stops, this also is a very narrow target to hit.
Travel too far and the car would ride metal to metal on the front coils and the suspension would stop working. The car would loose grip and head for the wall, causing the driver to lift off the throttle.
Not travel enough and the ride height would let air rush below the chassis and speed is lost.
Teams mastered coil binding setups with testing, computer simulations, valence wear, and seven-post rigs. Multiple setups were tried with a very fine suspension travel goal.
A bump stop is a polyurethane doughnut inserted onto the front shock shafts to control the travel. They come in different sizes and stiffness ratings to provide adjustment. The COT has a four-inch clearance to the front splitter compared to eight inches of clearance to the former car’s valence. The bump stops therefore became a more effective way of controlling travel.
Splitter wear now became the variable replacing the valence when determining how stiff, how soft, and how many bump stops were installed on each front shock.
The bump stops are a different way to achieve the near same result as coil binding. And tire pressure, spring ratings, shock valving, body aerodynamic downforce, and suspension components must all work in harmony to a particular driver’s feel.
This is the bump stops’ second tour of duty. They became very popular in the late nineties. NASCAR outlawed the pieces before the start of the 2001 season, citing cost of adding material to the chassis for it to drag when dropping on the track surface.
But now the bump stops are back and a big part of the Cup tour. Like every other setup component, there is no magic winning adjustment. Each of the car’s pieces needs to work together as a single unit.
I have a pretty good idea which team had the bump stops figured out over the last few years.
Comments on this entry are closed.