Understanding spring rubbers

By Michael Guerrero, Stock Car Racing Magazine
August 9, 2001
2:25 PM EDT (1825 GMT)

You often hear a crew chief or reporter mention during a NASCAR broadcast that a team is going to add a spring rubber to the right front or left rear to tighten up the car on its next pit stop. But what does that really mean? How much of an effect can a piece of rubber have on the handling of a race car? And what exactly is a spring rubber?

Stock Car Racing magazine went to Robbie Loomis, crew chief of the No. 24 DuPont Chevrolet, for an explanation of how and why he uses spring rubbers to make Jeff Gordon's car handle so well.

"A lot of times you'll see people run them because you want to have the car be able to get down on the straightaway. It'll be soft or won't be as hard on rubber, yet, when the car travels in the corner and gets maximum travel, then it'll start getting hard on the rubber and pick up the spring rate."

Spring rubbers come in a variety of sizes and compounds.

What a spring rubber actually does is connect the coils in the springs, which drives the spring rate up and makes it stiffer. Spring rubbers come in 2 ¼" to the larger 5" version. They also come in full, half and quarter pieces for specific adjustments.

Crew chiefs, in consultation with the driver, make the call as to where and what size spring rubber to install or remove on a pit stop. The decision is based on whether the car is tight (meaning the car won't turn well and wants to head into the wall) or loose (meaning the rear of the car wants to spin around).

"Typically you'll see people put them in the right front of a car to tighten the car up, cause it'll add spring rate to that corner. You will also see people want to put them in the left front to make the car want to turn better, cause it will add spring rate just to the left side of the car." Often it's actually quicker to add a spring rubber to the left or right rear during a 15-second pit stop. It is common to begin a race with spring rubbers already in the rear.

A spring rubber is attached between the coils of the spring

"They'll add (spring) rate pretty quick to a spring because you can figure you're talking about a 300 to 350-pound spring by the time you put a rubber in it. If we want to loosen the car up, we'll put one in the right rear, which will gain the (spring) rate over there. If we're trying to tighten the car up, we'll put more spring rate in the left rear."

Spring rubbers are made in soft, medium and hard compounds. Some rubbers are harder, which increases the spring rate more than a softer compound.

"You might put one in a spring and it will add 25 pounds to the spring rate, and then you put another one in and add 50 pounds to the spring rate. There is a variance in the different hardness of rubbers that you can get that will really affect the rate of spring. Naturally the full rubber is going to give you a lot more rate between the coils than putting a half in."

A spring rubber is just one of the seemingly small adjustments that can mean the difference between winning and losing in the intensely competitive world of NASCAR.