Subscibe to our feedShocks, Springs Deliver Aerodynamics, Speed
When Jimmie Johnson hits the road in his personal car, the springs and shock absorbers on his car work together to smooth out the bumps and give him a comfortable ride. The springs support the vehicle, and the shocks keep the springs from bouncing like a pendulum, so there’s little lurching and swaying even when driving around corners and on curvy roads.
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When he gets behind the wheel of the No. 48 Lowe’s Chevrolet, it’s an entirely different story. The principal use of springs and shocks on that car are to help give the car grip and to help with the all-important aerodynamics, therefore making it go faster. Johnson’s smooth ride is sacrificed at the altar of speed. Softer springs on the front help keep the nose low and stiffer ones on the rear keep the back of the car high, the best alignment aerodynamically but certainly not the best for driver comfort.
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When he gets behind the wheel of the No. 48 Lowe’s Chevrolet, it’s an entirely different story. The principal use of springs and shocks on that car are to help give the car grip and to help with the all-important aerodynamics, therefore making it go faster. Johnson’s smooth ride is sacrificed at the altar of speed. Softer springs on the front help keep the nose low and stiffer ones on the rear keep the back of the car high, the best alignment aerodynamically but certainly not the best for driver comfort.
“That race car is not a Cadillac,” crew chief Chad Knaus acknowledges. “It doesn’t ride real comfortably.”
Knaus and the other members of the Lowe’s team have been working with springs and shocks as long as they’ve been working on racecars. From the beginning of the sport, the springs and shocks on the four corners of the car have been used to manipulate the car’s handling. What has evolved is the technology and the knowledge about the components.
“It’s the management of them that has changed,” Knaus said. “We’ve learned more about the products, about the valves and pistons inside the shocks.”
Indeed, there are sophisticated machines today, like seven-post and shaker rigs that are used to test shocks and springs – as well as other suspension pieces – without ever leaving the race shop. The devices can simulate conditions at almost any race track and under varying conditions.
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“We use the seven-post every day at Hendrick Motorsports,” Knaus said.
Much of the simulation work is done by team engineer Greg Ives, who uses computer programs as well as the seven-post rig to develop a starting point for each racetrack on the circuit.
“That’s my strong main area,” Ives said. “I can run every racetrack as long as we have data in a matter of a day.”
Ives test numerous combinations of shocks and springs and narrows the choices down to the ones that will be used for the opening practice sessions, which is even more important now that most on-track testing is prohibited by NASCAR.
“You can go through so many shocks and bump stops in a short amount of time,” he said.
Lately, engineers, shock specialists and other crew members have been tasked with the challenge of maximizing the performance of the Car of Tomorrow, or as it is now often called, the Car of Today.
The shocks have become a key tool in managing the splitter at the bottom of the front end of the car. Teams try to maximize a car’s aerodynamics by keeping the splitter as close to the track as possible without actually scrubbing the asphalt. To keep the splitter off the track, teams use bump stops, which are pieces of material that are fastened to the bottom of the front shock. They work much like the old-fashioned rubber stoppers that are placed on a wall behind a door to keep it from punching a hole in the drywall every time it’s flung open.
Ron Malec, car chief on the No. 48 Lowe’s team, explains that bump stops on a race car, unlike bump stops on a door, are complex creatures.
“Bump stops are basically a cushioned spacer that goes on the front shock to hold the car to a certain height,” he said. “The amount of cushion the spacer has depends on how rough the track is. You don’t want a solid front suspension, because it’ll have zero grip. You want the tire to have compliance to the racetrack to a point, yet hold the car down as flat as you can for aerodynamics.
“It’s a fine balance, and it’s very track dependent and tire dependent.”
The spring and shock choices vary from track to track. Knaus said aerodynamics isn’t quite as big an issue at the road course at Infineon Raceway, but at most other places, even the short tracks like Martinsville and Bristol, the shocks and springs are tuned with aerodynamics in mind. At Talladega and Daytona, NASCAR makes the call, issuing shocks and springs to the teams during inspection.
The restrictor-plate tracks are the only two places where the team’s shock specialist Pete Michel isn’t one of the busiest people in the garage. At most other tracks he’s toiling away inside the team hauler, swapping pieces inside shocks or whole shocks to help Knaus and Johnson tune the car.
“We bring 50 different shocks to the track every week,” Michel said, adding that there are about 50 different parts inside each shock, many of which can be swapped about.
As Knaus, Johnson and the crew decide which way they want to go on the set-up, Michel makes the necessary adjustments, often with a five-minute turn-around or less.
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“During practice most adjustments are to the bump stops, and that’s very quick,” he said.
When it comes to making adjustments to springs and shocks during races, the team often puts a round of wedge or adds or removes the rubber spacers that are placed between the coils of the springs.
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The key player once the car gets on the track is the bearded one in the blue-and-silver firesuit – driver Jimmie Johnson. Johnson explains that adding or subtracting a spring rubber is almost like changing the spring itself.
“What you’re doing is changing the spring rate in the spring that you put it in,” he said. “So if you put it in the left rear, when the car lands and vertically loads it would put more spring rate in the left rear. And in our situation since we’re turning left it loads up the left rear and makes the car more comfortable to driver. And in a lot of cases it makes the car tighter. A spring rubber in the right rear would do the opposite.”
Johnson describes wedge as the amount of weight that sits on the tires in a diagonal fashion, so from left rear to right front and from right rear to left front. In most cases, there is a little over 50 percent of the weight on the right front and left rear of the car.
“As you put more wedge in and out it adjusts that weight percentage and makes the car do what you want,” he said. “If you imagine a chair sitting there and you cut off one of the legs -- it rocks back and forth.
“You need enough wedge to keep all four tires stable and balanced but at the same time too much wedge will just over-run the right front tire and make the car really tight,” he added. “We tend to see wedge be more effective on entry and exit of the corner than in the center, although it does work in the center, but it’s more of an entry and exit change. Where the spring rubber works more on vertical loading which is closer to the center of the turn.
“So depending on how the car’s handling – if I’m loose in we’ll look at wedge, if I’m loose landing we’ll look at a left rear spring rubber and kind of piece the corner together from there,” he noted.
Johnson’s ability to weigh in knowledgably about the chassis is a bonus on top of the computer simulations and seven-post testing back at the shop.
“We go back to data and look at it and see what could be the best,” Malec said. “But Jimmie’s input is definitely what matters most.
“Once you get on track is what matters. The seven-post can only give you so much information. You have to get on track and actually feel the car, feel each corner,” added Malec. “He can actually feel which tire is slipping on the track and tell is that the car is tight because the left front or the right front doesn’t have enough grip. He’s very good at that.”
And Johnson has three championships to prove it.