Weight Transfer


Weight Transfer

The F1, much like the SB is heavily dependent on weight transfer and the ability to feel this aspect of the car. As you slow down, G-forces push forward, moving to the opposite side of the car than the direction of turn when you roll into a corner. Forward G transitions to lateral G and you must maintain an appropriate G-loading (which corresponds with tire loading) not to break loose a tire through excess braking force, excess throttle application, or sliding of the tire when it cannot maintain the level of grip you are requesting. When discussing grip or traction levels, a “traction circle,” should be mentioned. The traction circle is a theoretical concept in which the grip level of the car (or directional G-force put on the car) is shown as the circumference of the circle. When we accelerate, the weight is put on the rear of the car (bottom of the circle). When we slow down, the weight is on the front (top of the circle). Left and right turns appear on the opposite side of the circle such that an evenly distributed left turn would appear as a marking on the right side of the circle (which is what you would expect given the driver feels G-forces on the right side of the car when turning left). Using telemetry, you can see that the traction circle is never perfectly circular, but is a function of available power, braking, and tire grip (Figure 1). 

Figure 1. G-Forces


When weight is distributed evenly as the car is sitting in the pits or at a stable speed with neutral forces acting upon it, the neutral condition is the central part of the traction circle. As you transfer weight entering a corner and the weight transitions to one side, the feel of the car changes. If you are on a circular skid pad (Centripetal Circuit) in a left turn at constant speed, when you release the throttle to slow down, the weight transfers to the right-front. As this occurs, the right-front of the car is now generating more force than any other part of the car and the front end will turn left. Leaving this unattended, the car will spin-out due to oversteer commanded unless the rear has enough grip to maintain control of the car. If you add throttle to catch the car before it spins, you will notice that you can transfer weight back to the rear of the car creating a more neutral condition. If you add too much, it would then be an understeer condition as you have more weight on the rear of the car. This is only true to a point. Since the F1 has such tremendous torque, it is easy to break the rear tires loose with the throttle. This wheelspin reduces traction, though small amounts can be used to move the rear of the car around to point the car in a specific direction. There can be times when on-throttle oversteer is faster. Mastery of this is tricky, but important to the proficiency of the driver. To truly maximize grip throughout a corner, the driver must find the right combination of dynamic corner weights and input those at precisely the right time. In the case of the centripetal Circuit, in a left turn, try to load the front-right and hold the car at its optimal slip-angle range (which is found by both listening to tire-scrub and noting sector times). This is achieved through slight oversteer and catching the proper angle with an appropriate level of throttle. During deceleration phases it is found through either trail-braking or throttle modulation (yes...you can slow down and still be on-throttle!). Use the weight transfer of the car, along with other driver inputs, to maximize traction around any circuit as you find the best/minimum cornering radius or the fastest cornering times through living on the edge of available grip with weight transfer.

Turn-in

 I can’t just turn the wheel hard. I can over-turn the wheel, under-turn the wheel, use the throttle or brake to turn the car, use the camber of the road, or specific curbing grip areas to maximize grip. At the turn-in, turn the wheel enough to load the front end to the loading required to generate sufficient entry grip. When turning the wheel, there is a sweet spot for each corner. Realize that the tire turns and is neither perpendicular (the tire rolls over onto it's side a bit) nor parallel (the tire is being turned by the wheel at an angle to the surface) to the road surface. The tire is turned slightly more than is needed for the intended path. This develops a “slip angle,” which is defined as the angular difference between the amount required for the intended path and the actual angle of the wheel/tires. This amount is usually a range dependent on tire and surface conditions. When this initial phase is accomplished, if no trail-braking is required, get right back to the throttle and modulate the throttle throughout the corner for best sector times. As you transition toward the apex, a variety of forces act upon the car to make perfect cornering quite difficult. Bumps in the road, aero-push from cars in front, and car balance all contribute to overall grip achieved, but the perfect racing line is generally unchanged. Work the car toward the apex recognizing that any variance in balance causing understeer or oversteer must be corrected precisely with the throttle (and in some cases the brake). Simply easing off the throttle provides significant loading on the front and oversteer in the direction of turn. If you enter the corner too fast, there may not be oversteer available to make the apex without spinning out or demanding too much out of the rear tires, resulting in rear wheel slip beyond traction limits. This is correctable, to a point, but the line will suffer and the driver will have to compensate with a loss of exit speed, variance in line, or an off-track situation. Slower entry and faster exit typically is a more conservative approach that requires a lesser degree of precision with minimal loss in sector times. A fast-in, slow out typically loses time and is subject to a greater level of required precision.

Accelerating out of a Corner

Switching from braking and corner entry to middle and exit discussions, weight transfer and slip angles are now magnified on the rear of the car. Acceleration moves the G-forces rearward with cornering forces moving it to the loaded side. The G-loading must be smooth as was the case in the braking/entry discussion. The F1 can be set up to achieve understeer or oversteer based on driver preference, though oversteer is preferred and generally results in more speed overall through a corner. With higher aero-downforce, the F1 may struggle for front-end grip from the driver's perspective, but in reality the G available is slightly higher and is being used. The F1 can, and should, be turned with the rear a bit. As the driver hits the apex, hopefully the throttle is active and the brake is no longer needed. Any throttle position (1% to 100%) is better than coasting or braking. Try to attain a minimal throttle setting  as opposed to coasting in the corners. The battle for cornering speed is solved by manipulating the throttle to attain optimal grip levels while maintaining the perfect racing line. This may require very little throttle inputs that allow the nose to track with the wheel turned to maintain the aforementioned slip angle or grip range. Exiting the corner, ensure your eyes are securely focused on the exit point and smoothly accelerate out, compensating for oversteer with the racing line as required to push the car to the very edge of available racing track. There may be situations where a line-shift from optimal exit point to optimal entry points is warranted. If the next turn is tight, there may be reason to not take the exit to the track limits, but rather reduce the turn radius to achieve an entry point with a specified weight transfer. 

Weight transfers can be “snappy” at times, so be careful to transition side-to-side movements appropriately to allow the weight time to shift. Too quick of a transfer may send too much instantaneous loading to the opposite side resulting in the front or rear bearing the majority of an over-bearing force. If that happens, it will understeer or oversteer respectively.  Over-corrections are common for new drivers as they learn how and where the weight transfers happen. An over-correction is simply turning the wheel due to oversteer to the point where the rear load shifts abruptly and is often unable to reverse. If you are sliding the rear, a turn in the direction of the slide will “catch” the car, but if a correction is made in this manner, the correction must be returned to normal before the weight transfer is completed such that the rear of the car realigns itself with the desired slip angle. Some of these transitions can be manipulated by driving technique and others through the car setup.