Supposedly the ultimate step in suspension tuning and set up, it is my belief that corner weighting is often quite misunderstood and the actual act of doing it, very over rated.
Here is why… Corner weighting doesn’t change (or at least not in any meaningful way), front to back weight distribution, or improve left side versus right side balance. You probably already knew that. The only meaningful thing that corner weighting a car can do, is improve side to side balance. I.E. if a car tends more towards understeer when turning one direction, and tends more towards oversteer when turning the other, there is a very good chance that adjusting the corner weights can make the car handle more consistently, no matter which direction is being turned.
A new season of racing has begun, and corner weighting has been coming up in conversation quite a bit amongst fellow racers. Any magazine article that I have ever read, talks about cross-weight (the combined total of the left rear and right front weights), and if you are driving an autox or a road course, they all make a cross-weight of 50% of the total vehicle weight, the final goal of corner weighting.
Circle track set up guys call the cross-weight “wedge”. If a car has a cross-weight of 50% it is said to have zero wedge. With more than 50%, it has positive wedge, less than 50% it has negative wedge. On a circle track, wedge is used to tighten the car up (i.e. it makes the outside front do more work, and the outside rear do less), de-wedging makes the car looser. Guys who turn left however, realize that cross-weights alone, are arbitrary, and the ideal cross-weight for a circle track car (usually much higher than 50%) will depend on a number of different things: stagger, alignment… left to right weight balance and more.
An autox car or road racer is typically as symmetrical as possible… but left to right weight balance is almost never perfect, and that dampens the value of a magical 50% cross-weight.
As we already noted, the simple act of corner weighting cannot change front to rear weight distraction, and it cannot change the total weight on either side of the car. That means, it cannot change the total cornering power a car has when turning one direction. The only thing corner weighting can do, is adjust the difference in front to rear weight distribution on either side of the car.
I call it the lateral weight balance.
Adding wedge, increases the forward weight balance on the right side of the car, while simultaneously increases the REAR weight balance on the left side of the car. Ideally, (1) our right side weight total would equal the left side weight total, and (2) the left side F/R weight distribution would equal the right side F/R weight distribution. If those two things were true, we’d have zero wedge, or a 50% cross-weight.
However, as soon as we have a lop sided car (i.e. with a 7’ tall driver on the left side, or one that was primarily designed to be RHD and thus has major components like the battery, or the gas tank, or the turbocharger on the left side of the vehicle… or ALL OF THE ABOVE) that 50% cross-weight becomes an entirely arbitrary measurement.
If the goal of corner weighting is to get the car to handle the same way in left and right turns, then targeting a 50% cross-weight is like measuring strut angle inclination to get camber. The two are related, but not equivalent.
The closer the two side weight totals of the car are to each other, the closer a 50% cross-weight will be to getting you to an equivalent lateral weight balance. If the car has very different total weights side to side, and a 50% cross-weight, then it’s going to handle very differently when turning left vs right. We can always adjust the corner weights for a 50% cross-weight, and we can always adjust the corner weights for an equivalent lateral weight balance, but since the cross-weight doesn’t ALWAYS give us the result we are looking for, why not look instead at lateral weight balance?
But wait… it’s not that simple… lets think of some other things that affect the way our car handles: alignment, roll couple, total weight transfer, driver inputs, differential set up and on… and on. All of these things can effect what corner weights give the best feel/performance. Maybe as a driver you always turn in harder to the left and thus feel like the car understeers when going left. Is it worth removing some cross-weight? You could. What if the car has an open diff and always blows up the drivers rear tire on corner exit? Is it worth adding some cross-weight to help put the power down? Maybe. And there is more we can think about than even that (i.e. tire physics and the decrease in tires operating coefficient of friction as the weight on it increases, or the rate at which lateral load transfer takes place) but things start to get quite complicated. Ultimately, I’ve always been happy adjusting corner weights at the track, without a scale based on what I want the car to do. I suppose that would require having some sense of feel for the car, which is 93% of the fun here anyways. If you are missing that, then I guess you should just copy the fastest guys set up and hope for the best.
DISCLAIMER: my opinion, my methods, my failure or success. Discussion welcome.