Chassis Adjustments To Address Handling Issues

First, Identify If The Handling Issue Is Driver Induced or Chassis Induced

Before making any chassis adjustments we first need to identify if the handling issue is driver induced or chassis induced. Here are a few simple rules to help us identify this. We’ve addressed any issues that are driver induced in this video. This content will address any handling issues that we can fix with some adjustments to the chassis.

 

• Is the handling issue inconsistent and varies from corner to corner? – Adjust the driver.
• Does the handling issue only occur at one specific corner? – Adjust the driver.
• Does the handling issue at a specific type of corner, like a carousel, high-speed corner, low-speed 90 degree corner? – Adjust the chassis.
• Does the handling issue occur on left or right turns only? – Adjust the chassis.

 

What Should I Adjust First?

In the chart shown below we’ve sorted the major chassis areas to adjust sorted from the more difficult to make displayed on top, to the easier to make on the bottom. When we are in the shop preparing the car we will typically start from the top and work our way down. At the track we will start from the bottom and work our way up.

 

A downloadable version of this is available here: Download File.

 

 

If we are at the track and we’ve discovered some chassis issues, or maybe we are just trying to find more speed we can use this chart to give us a place to start.

 

Starting from the bottom and working our way up:

 

Brake Bias

This will typically be seen on corner entry when the driver is on the brakes. If we have a brake bias valve this is a simple, easy adjustment to make at the track. If we don’t have a brake bias valve we can tune the brakes by experimenting with different brake pad compounds (i.e. a less torquey or more torquey brake pad). An easy change to make at the track. Or you can experiment with diameter of brake lines producing either a more progressive or more linear brake feel. This will typically be done back in the shop however.

 

Understeer:

• Add brake bias to the rear. Meaning, more brake torque to the rear, or less torque front.

Oversteer:

• Add brake bias to the front. More torque up front, or less torque to the rear.

 

Tire pressure

Many teams don’t have a brake bias valve and changing brake pads at the track may be a bit time consuming. Tire pressure is really one of the more simple changes we can make when we are at the track. If your chassis is already pretty close this is typically where you may spend the most time tuning the chassis on a track weekend.

 

Understeer – Corner Entry to Mid-Corner:

• Decrease front tire pressure.

Oversteer – Mid-Corner to Exit:

• Decrease rear tire pressure.

 

Shocks/Dampers

Another simple area to tweak at the track is shock and damper settings if your chassis is already pretty close.

 

Understeer:

• Single Adjustable shocks:
  • Consider a more firm/stiffer front shock rebound (shock responds slower, keeping weight on the front), and/or less firm rear shock rebound (shock responds sooner, moving weight from the rear to the front).  Think about it. Under brakes on entry, the fronts go into compression, and the rear goes into rebound. You want to move that weight to the front quickly. Then as you begin to release the brakes and begin turn in (fronts go into rebound) you want to keep vertical load on the front tires for a longer period of time, giving us grip.
• Double  Adjustable shocks:
  • Consider a less firm front low-speed shock compression (vertical load to the front sooner), or more firm rear low-speed shock compression (as we apply throttle we want load to the rear slower to help fix mid-corner understeer).

Oversteer:

• Single Adjustable shocks:
  • Consider a less firm front shock rebound (you want the fronts to come out of rebound sooner placing vertical load to the rear) , or more firm rear shock rebound (you want the rears to come out of rebound slower keeping vertical load on the rear).
• Double  Adjustable shocks:
  • Consider a more firm front low-speed shock compression (you want the fronts to compress slower keeping vertical load to the rear), or less firm rear low-speed shock compression (you want the rears to compress sooner placing vertical load to the rear).

 

Alignment

 

Understeer:

• Adding front toe-out can help keep heat in the front tires and also help turn-in. Too much front toe-out though may make the car hard to drive on the straights as the car may get “darty”.

Oversteer:

• If oversteer occurs after initial throttle application consider running less negative rear camber. This provides for a larger tire contact patch.

 

Sway Bars

 

Understeer:

• Soften front sway bar and/or stiffen rear sway bar.

Oversteer:

• Stiffen front sway bar and/or soften rear sway bar.

 

Sway bars affect the amount of load transfer you experience. You have  a physical connection from the inside tire to the outside tire. A stiffer bar results in more load transfer to the outside tire mid-corner. This takes load off the inside tire resulting in less overall grip for that axle. Stiffer bar on the front, relative to the rear, will tend to more understeer. A stiffer bar on the rear, relative to the front,  will tend towards oversteer. Softer front sway bar relative to the rear will tend to give you more rotation as you enter a corner.

 

Ride Height / Rake

 

Understeer:

• Decrease front ride height or increase rear.

Oversteer:

• Increase front ride height, decrease rear.

 

Springs

 

Understeer:

• Soften front spring rates and/or stiffen rear springs.

Oversteer:

• Stiffen front spring rates and/or soften rear springs.

 

We hope these provide you some guidance on what to modify and which direction. Don’t try small changes (the change won’t be large enough to sense on track), yet also don’t make them too large. For tire pressure try a couple pounds. If you saw improvement, try a couple more pounds until things get worse. Then back off to the previous setting. For shocks try two-clicks or a 1/4 turn. Obviously there are many variables to consider. At the grassroots level the driver will gain confidence as the day goes on. Track and ambient temperature also matter. These change. It helps to keep a good log book showing the settings you are using and the weather and track conditions. “There is no free lunch” as Carroll Smith says.

 

 

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