A well-handling and dynamically...
A well-handling and dynamically balanced car will gain speed in the middle of the turns and a gain of 2-3 mph is worth more in reduced lap times than if you were to add 100 hp to your powerplant in most cases. A car that isn't dynamically balanced won't handle well. Photo by Mike Horne
After all of the bits and pieces related to chassis setup have been discussed in minute detail and all of the preparation has been completed in the shop, we still have to go to the track and see how all of that worked out. Too many times, we need to make adjustments and just plain fix the handling problems that crop up. Readers have told me recently that it's now time to lay out some basic rules for tuning our race cars-so being a good listener, here you go.
The most basic rule of handling and speed for a race car lies in increasing the speed we can go through the middle of the turn. It has been said before, and rightly so, speed gained in the turns will be carried throughout the lap. This is true for both circle track racing and road racing. A car balanced for handling and dynamics is as fast as it can be.
There are other factors that will make your race car faster, but most of the gains are turn related. Given that we can all agree on the above basic principle, we further break the gain down into three turn segments-entry, mid-corner, and exit. The slowest portion of the lap is spent in the mid-turn segment, so that is where we are most interested in gaining speed.
Granted, increased average speeds in the transitions of entry and exit help reduce lap times, but the gains there pale in comparison to gains we can achieve at mid-turn. Speed gained in the middle of the turn will be carried all of the way around the track.
Remember that you need to...
Remember that you need to take care of all of the basic setup parameters before you go to the track. Items like alignment, toe settings, Ackermann, camber and caster settings, rear suspension link settings for rear steer, and more. We don't want to try to tune the setup when we have basic setup mistakes involved. We have discussed all of these in past articles. Dust off your past issues and re-acquaint yourself with those.
For a track that averages 100 mph per lap, a 2mph gain at mid-turn represents a 3/10 reduction in lap times. I've seen fast cars run up on the slower cars by 5 mph or more, and that is the half- to full-second difference between First Place and Fifteenth. So, we necessarily start out our handling tuning with the mid-turn balance, both handling and dynamic balance.
We start out solving our mid-turn handling problems. We do this because our mid-turn handling affects both entry and exit to a large extent. A car that is tight in the middle will most likely be tight into the turn and tight off. If excessively tight in the middle, the car could be loose off and here's why.
When we turn the steering wheel and cause the front wheels to create and/or increase their angle of attack, or angle differential to the direction of travel of the car relative to the racing surface, we increase the traction of those two tires. The more we turn, the more traction we get, up to a point. If the wheels are turned beyond a certain angle, the tire skids and we loose all front grip. But until then, we gain grip.
Suppose we have more rear grip overall than front grip. When we drive through the turns, with the normal steering angle that follows the radius of the turn, we will notice that the car does not want to follow the radius and instead moves up the track toward the outside of the turn. Instinctively, we will turn the steering wheel more until the car follows the radius of the track. It does that because we are causing the front tires to produce more front grip in reaction to the increased angle of attack of the front tires.
There are three turn segments...
There are three turn segments that we tune for. The place to start is in the mid-turn segment where poor handling and dynamic balance will affect the other two segments. We perfect the mid-turn and then tune the entry and exit portions in a way so as not to affect the mid-turn performance we have gained.
If our car isn't too tight, we will just roll through the turns with a slightly greater steering angle and maybe never know we are tight. But, if we are too tight, we will need to input excessive steering angle and we may just over do the adding of front grip from the increased steering angle and change from a car that is tight to one that is loose. Here is what happens.
We go into the turn and feel the tendency to not turn. We quickly apply more steering input and keep adding until the car responds. But the motion is so quick that we inadvertently over correct and add too much front grip just as we are ready to accelerate. Now with more front grip than rear, the car goes from tight to loose and with the power applied, very loose off. This is a very common occurrence.
To change mid-turn balance, we can do one of the following:
• Raise or lower the rear moment center by moving the Panhard bar or J-bar up or down. For leaf spring cars, we can raise or lower the actual spring, but that is not easy. Metric four-link cars also have a tough time changing the rear moment center height and must rely on other methods for changing the balance.
• Change rear spring rates. Softening the right rear spring, and/or stiffening the left rear spring will increase the rear roll angle and will tighten the car, as will softening both rear springs. The inverse is true, stiffening the RR spring and/or softening the LR spring will loosen the car.