NASCAR New Car 101: Bump stops are back

Dodge Motorsports recently began a program called NASCAR New Car 101 to help explain the technologies used by their new racecars. The most recent edition focused on the use of bump stops - rubber and urethane devices used to stop the car's suspension travel before metal-to metal contact happens.

Although bump stops simply look like pieces of rubber, there is a nearly limitless way to make them out of combinations of rubbers and urethanes, and they play a major role in a car's handling.

Before bump stops, drivers relied on coil binding - when the metal suspension coils make abrupt contact with each other - to stop suspension travel. Bump stops are used today because the Car of Tomorrow has less suspension travel than previous cars - four inches as opposed to eight inches.

"We've cut the amount of space that we've got to work in by half," explains Hartwell Pritchett, shock specialist for the Gillett Evernham Motorsports #10 team. "And that has pushed us to come up with new technology."

Howard Comstock, Dodge Motorsports, Program Manager for the Sprint Cup Series, explains how this new technology is put to work.

"We stack up rubber and urethane parts with aluminum spacers to try to control the amount of travel that the front wheels will see (during) corner entry and hard braking," he says. "We took an automotive application that's on every car that's made today and what we've tried to do is use that application for racing in the Sprint Cup Series."

The goal with creating and using bump stops, Comstock says, is achieving the "maximum amount of control with the minimum amount of loss." They need to control the travel of the shocks without restricting it.

One measurement of how finely tuned a car's bump stops are is to determine how far the car's front splitter - a piece on the front of each car that impacts down force and aerodynamics - is from coming into contact with the track pavement.

The way this is done, explains Pritchett, is to insert plastic screws through the front splitter and measure them after practice.

The cars have "holes drilled in the splitters and they've got a plastic screw with a stop nut that extends down through the splitter," says Pritchett. "What they do in practice is they will run the car, come back, look at the amount of plastic that's still hanging below the splitter and know how close they're getting to splitter-to-ground contact."

From there, the bump stops can be fine-tuned to get the front splitter as close to the pavement as possible without touching it.

Bump stops on each side of the car are tuned separately because they experience different forces since the cars travel in circles on the track.

"There's a tremendous amount of load on the right side (of the car) so we've got to have a lot more resistance on the right side. ... What we'd like to do is get the front end to travel perfectly in concert so it ends up flat on the track on the right side and the left side."

As bump stops are put to the test on the track, they are continually being developed off the track.

"We don't know what we don't know yet," says Pritchett. "There are so many materials that are available now and so much development that goes on all the time (that) by the end of the season I would suspect that we're going to be a lot farther along in our development."

After hearing it from the experts, it becomes clear that bump stops are not just bits of urethane. They're a tiny yet very important piece of the massive equation that is tuning the Car of Tomorrow. As the NASCAR New Car 101 program continues, more pieces of the equation will be solved.