There are many teams still today who struggle throughout the season with their cars handling. Many times, the problem lies somewhere simple where a slight adjustment or a small tuning procedure could make the car much better.
If your team took a day or two in the shop and looked in the right areas, you might be able to finish the season on a high note and finally get some success. We’re here to help you do that. We’ve seen and heard about a lot of race car problems, after the fact. Let’s get ahead of the curve.
We are going to try to help you find your problem by focusing on the symptoms. We’ll go through the entry, middle turn, and exit segments and name some common problems and offer some possible solutions. We need to keep in mind that some handling problems have multiple sources.
Before you undertake this analysis, please make sure your team has already completed the tasks of proper alignment of the rear end, checked and set the correct toe in the front wheels, checked and eliminated bump steer and checked and reduced the Ackermann to a minimum.
We should also assume that team has evaluated their front geometry and re-designed it as necessary for a more efficient front end dynamic. If not, please go back and read our numerous articles on those subjects. If so, and any one of these were out of whack, then maybe those were some of the problem. If everything checked out, then let’s continue.
Corner Entry
Entry problems involve a car that is loose or tight and this may differ from what the car does in the middle. A loose-in car can change to a car that is tight in the middle.
If the problem was the same on entry as it was in the middle and maybe off the corner too, then we just have a loose or tight setup in the car. When they are different or the middle is fine, but the entry is off, we need to look at what affects the entry handling. What we don’t want to do is make changes that will ruin our middle segment performance.
There are three major causes of loose in. One is brake bias. Too much rear brake percent can cause a loose car only when braking and to the extent you are braking. A track that requires heavy braking on entry is one where brake bias becomes more critical.
If you brake lightly or more briefly, then your problem might be somewhere else. That’s not to say brakes couldn’t be part of the problem, but those kinds of tracks usually see more straight ahead braking lasting a shorter amount of time than at a track with tight turns and heavy braking lasting well into the turn-in phase.
The second primary reason for loose-in is a left rear shock that has too much rebound resistance. For most stock cars, we never need more rebound in the left rear shock than is needed to control that spring rate. For a 175 lb/in to 225 lb/in spring rate, a shock rate equivalent to a 3 shock, or 75 to 100 lb of force at 10.0 inches per second is sufficient. It is never a good idea to free up a car that is tight-in by increasing the rebound in the LR shock.
Next on the list for loose-in is rear alignment which includes both static alignment and rear steer. Your rear suspension system could be steering both to the right and left through the motion of the right rear during entry. Let’s look at how that happens.
As the car enters the corner and begins to turn in, the RR will compress moving towards where it will end up at mid-turn. For most three, and even some four, link suspensions, the initial movement will push the RR wheel back causing rear steer to the right.
Once the motion has progressed, the chassis mount for the link should move the link through level and then start to pull the RR forward as it moves downward to end up either with zero net rear steer, or a slight rear steer to the left. This of course all depends on the angle of the link at ride height and the amount of travel.
This motion is usually quick enough so that the car never really goes loose from the momentary rear steer to the right. But, if the RR shock has a lot of compression and/or the RR spring is stiff and slows or restricts that movement, then the time where the car is steered right is prolonged and the car could start to go loose.
The only rear shock that should have a higher than normal compression is the LR and that is to provide better bite off the corner, but more on that later. So, think about these three conditions and sort out why you are loose-in by focusing on those areas.
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