Page 20 - PCA Metro NY Region POST | 2019-April-eMag
P. 20

(Track Ramblings, Continued from page 16)
What we have accomplished in this manner is to go through the turn with the largest possible radius, which has given us the potential for the highest speed in the turn since the highest ra- dius allows the greatest speed without exceed- ing the tire’s g-force capacity.
You will attend classroom sessions during your track days, and the importance of the line will be explained and emphasized.
Vehicle dynamics is the behavior of the car as it is moving. It is influenced by many factors, and as you spend more time on the track, attend more track classroom sessions, and perhaps read more on the subject, you will understand more of these factors. Here are a few of them, but if you want, you can skip to the bottom to get to the action item rather than read some theory:
Understeer and oversteer: these are conditions which occur as tires approach their limit of grip. In understeer, the front tires’ loss of grip ex- ceeds that of the rear tires, and the car swings wider than the angle directed by the steering wheel; conversely, in oversteer, the rear of the car ‘steps out’. It is often said that understeer is when the nose of the car hits the guard rail, while oversteer is when the rear hits the guard- rail.
Weight transfer:
As you accelerate, you put more weight on the rear tires and less on the front. That is why the nose rises when you step on the gas, and the tail rises when you press on the brakes. When you go through a corner, the car leans, with the outside (the right side in a left turn) going down, since weight is being transferred to the outside.
You may wonder what difference this weight transfer makes. The answer is that the extra weight placed on the front tires under braking increases their grip potential, while correspond- ingly the reduced weight on the rear tires at
that moment reduces their grip; and in corner- ing there are similar effects. As your speed in- creases relative to a corner’s maximum value, these weight transfer effects can be significant, which leads to a very important effect: trailing throttle oversteer, or ‘TTO.’
TTO can occur when you are in a corner and you abruptly let off the gas (you ‘trail the throt- tle’). This causes weight transfer to the front, giving the front tires more grip than they had a moment earlier, and at the same time there is weight transfer away from the rear tires, given them less grip. The nose pulls in toward the apex, while the rear goes outward towards the outside of the track. This can result in an in- stant spin, which you don’t want. Modern cars with stability control moderate or even eliminate this effect but even so, track drivers should be careful not to get into a TTO situation.
FUN FACT: Stability control works by being able to measure the amount of difference between the direction of the steering wheel and the car’s actual travel (called ‘yaw’). If the steering wheel is calling, say for 15 degrees of direction change but the car has only a 10 degree change, that is an understeering condition. The PSM (‘Porsche- speak’ for Porsche Stability Management’) sys- tem will apply braking to the inside rear wheel, which will force the car to turn more. For an over- steer condition, the outside front wheel would be braked.
The Action item: When you are on track, try your best to be smooth with the controls. This can be difficult to do but it is very important. As you are going through a turn if you are adjust- ing the steering back and forth in an attempt to ‘hit your marks’ (the turn-in, apex and track-out points), you are giving very inconsistent signals to the springs, shocks and tires and they will not perform at their best.
I think that is enough for one column.

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