In between qualifying simulation runs on Fast Friday at the Indianapolis Motor Speedway, A.J. Foyt Racing’s Tony Kanaan opened the door to an interesting area of fine performance tuning at the Indianapolis 500.
Although the practice of manipulating the weight jacker device (highlighted in red, above) on the long IMS straights is far from secret within the paddock, its benefits deserve further exploration. Installed on the right-rear damper, the weight jacker is a hydraulic ram that drivers adjust from the cockpit using buttons on the steering wheel.
Placed between the top of the damper housing and the coilover spring, the hydraulic ram can be extended to push the spring away from the damper housing, and by doing so, the right-rear suspension is raised, which places added diagonal force across the car. By extending the weight jacker, the diagonal load puts more weight on the left-front tire, which helps to reduce understeer.
The weight jacker’s hydraulic ram can also be retracted, which lowers the right-rear suspension, and by doing so, takes diagonal weight off the left-front tire. It would be done to either reduce oversteer or induce a slight amount of understeer, if that’s the driver’s preference.
While the primary use for the weight jacker is to alter the car’s handling in the turns, that hasn’t stopped teams from exploiting the device’s capabilities to improve overall lap speeds between the corners. With the underwing on each of the 33 Dallara DW12s in the field producing downforce that is immensely valuable in the four turns, and a liability on straight-line speed between Turns 4 and 1, and Turns 2 and 3, drivers have become accustomed to rapidly working the weight jacker buttons prior to turning into Turns 1 and 3.
By retracting the weight jacker on the straights, a car will go slightly nose-up as the right-rear suspension is lowered, and by going nose-up, downforce is reduced beneath the car with the underwing. Per the IndyCar rules, the weight jacker has a half-inch maximum of travel, and while it is not a significant amount, the benefit is said to be upwards up 0.5mph on the straights. Drivers have to act quickly with the buttons to lower the rear, then return the weight jacker to its normal position on approach to Turns 1 and 3 — and can’t afford to forget…
“You’re basically moving weight in the front by jacking the rear up or down,” Kanaan said. “A lot of guys play with that. I think you guys will have some footage from last year. You see people playing along on the straightaways. And so on the straightaway, you want to bring your car really low, nose-up to pick up speed, but you don’t want to have that on the corner. Because once you get to the corner, you actually want the car to have the front grip. So, you have to play along with the buttons. Everybody has it.”