How to corner balance a car
Racer Lingo Explained Part: 3
By Steve Grosekemper
Over the last 2 months we have discussed the language used by Porsche techies. It is a little known language referred to as porshese. It is usually heard at driving events and tech sessions. However, it has recently infiltrated the ranks of everything from concours to tours and rallies. I hope as a result of this series of articles you are able to jump into the conversation and impress the crowd with your new found knowledge of the language.
The term we will discuss this month is "Corner Balance." This is a term which describes the distribution of weight in a car. In its simplest form, corner balance is best illustrated by a 100 pound box being carried by 4 equally sized men. Each man caring 25% (or 25 pounds) of the total load. This would be an equally distributed, or balanced load. If one of the 4 men, lets call him Lew, steps on a stack of bricks his corner (the LR corner or C) of the box will rise. The opposite corner of the box (the RF corner or B) will lower due to the increased load imposed by Lew. The two guys at the remaining corners (A and D) are now taking a free ride and the poor guy at the right front corner (B) is stuck carrying 50% of the load instead of his previous 25%. (See example in figure #1)
Now fortunately, none of our cars are being held up by a clumsy guy named Lew. They are however, held up by springs of one sort or another. In virtually all Porsches these springs are externally adjustable in height on at least one end of the car. When the height is lowered on a particular corner the weight is transferred to the wheels opposite of it and its diagonal corner.
As time goes on, there are many factors that can affect the height and corresponding corner balance of your Porsche. Springs can sag or fail, or there can be a misadjustment of new components. Whenever new springs and/or torsion bars are installed, the corner balance
should always be checked.
The benefit of having the corner balance of your car correct is not always all about high speed cornering performance. If your car is setup like the car in example #2. the left front tire is carrying 200 pounds or 33% more weight than right front tire. This extra weight will cause extra tire wear as well as an unexplained pull in the steering. Unexplained because the camber and caster may be even and you will still have a pull.
Another indication of incorrect corner balance is a car that corners differently from side to side. The car may be set up like the car in figure #2. In this case the car may feel very good in a right turn as the extra stiff spring (LF or A) holds the car flat against the cornering forces. In a left turn however, the weak spring (RF or B) will let the cornering forces push that corner down creating excessive body roll.
To check and then set the corner balance, the car is put on a set of scales that are mounted to a perfectly flat surface. The anti-sway bars are then disconnected to avoid interference. After checking the readings, the individual corner heights are adjusted to give equal diagonal weights while maintaining a level ride height. In the real world, corner weights are not as even as we might think. Porsche states that diagonal weights of their production cars should be within 44 pounds of each other. If you can get the car within 20 pounds or less, you are in an ideal range. A real world corner balance sheet from a finely set up 911 with driver weight included might look something like figure #3 below.
As a rule if your car has not had a corner balance, the chances are about 50% that it is not within the 44lb.- 20 kilogram rule. Some cars that I have checked have been as much as 150 lbs. off on the diagonal weights. Even if only a 30-40 pound adjustment has to be made, an immediate improvement in the cars handling will be felt.
Good LuckSource: www.dietersmotorsports.com