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iRacing Dirt Late Model Setup Matrix

April 5, 2019: After doing a lot of testing, I have found that shock adjustments affect the car much differently than expected. I'll leave it at that. I have updated the matrix to reflect those findings.

Rev. 6 - April 5, 2019
Symptom Remedies
Loose on Entry
  • Increase Toe-In
  • Increase Brake Pressure Bias
  • Increase LF Spring Rate*
  • Increase RF Spring Rate*

  • Increase Left Upper Trailing Arm (Will loosen car on exit.)
  • Decrease Right Upper Trailing Arm (Will loosen car on exit.)
  • Increase Chassis J-Bar Height
  • Decrease Axle J-Bar Height
  • Decrease J-Bar Height at Both Ends
  • Increase Ballast Forward (Decrease Rear Weight)(May loosen car on exit.)
  • Decrease Cross Weight / Left Rear Bite (May loosen car in middle and on exit.)
  • Increase Axle Lead (Tightens car throughout turn and may destabilize/slow car on straights.)
Loose in Middle
  • Decrease RR Tire Pressure (Tightens car significantly throughout turn.)
  • Decrease Rear Stagger
  • Decrease RR Spring Rate*
  • Increase LR Spring Rate*
  • Increase Chassis J-Bar Height
  • Decrease Axle J-Bar Height
  • Decrease J-Bar Height at Both Ends
  • Decrease Ballast Forward (Increase Rear Weight)
  • Increase Cross Weight / Left Rear Bite (May loosen car on entry and tighten on exit.)
  • Increase Axle Lead (Tightens car throughout turn and may destabilize/slow car on straights.)
Loose on Exit
  • Decrease RR Tire Pressure (Tightens car throughout turn.)
  • Decrease Rear Stagger
  • Increase RF Spring Rate* (May tighten car on entry.)
  • Increase LR Spring Rate* (May loosen car on entry.)
  • Decrease RR Spring Rate* (May loosen car on entry.)
  • Decrease All Spring Rates*
  • Decrease Left Upper Trailing Arm (Will loosen car on entry.)
  • Increase Right Upper Trailing Arm (Will loosen car on entry.)
  • Increase Chassis J-Bar Height
  • Decrease Axle J-Bar Height
  • Decrease J-Bar Height at Both Ends
  • Decrease Ballast Forward (Increase Rear Weight)
  • Increase Cross Weight / Left Rear Bite (Will loosen car on entry.)
  • Increase Axle Lead (Tightens car throughout turn and may destabilize/slow car on straights.)
Loose Throughout Turn
  • Decrease RR Tire Pressure
  • Increase Chassis J-Bar Height
  • Decrease Axle J-Bar Height
  • Decrease J-Bar Height at Both Ends
  • Increase Axle Lead (Tightens car throughout turn and may destabilize/slow car on straights.)
Tight on Entry
  • Decrease Both Front Tire Pressures
  • Increase RR Tire Pressure (Loosens car throughout turn.)
  • Decrease Toe-In
  • Decrease Brake Pressure Bias
  • Decrease LF Spring Rate*
  • Decrease RF Spring Rate*
  • Increase LR Spring Rate*
  • Decrease RR Spring Rate* (May tighten car on exit.)
  • Decrease Left Upper Trailing Arm (Will tighten car on exit.)
  • Increase Right Upper Trailing Arm (Will tighten car on exit.)
  • Decrease Chassis J-Bar Height
  • Increase Axle J-Bar Height
  • Increase J-Bar Height at Both Ends
  • Decrease Ballast Forward (Increase Rear Weight)(May tighten car on exit.)
  • Increase Cross Weight / Left Rear Bite (May tighten car in middle and on exit.)
  • Decrease Axle Lead (Loosens car throughout turn and may destabilize/slow car on straights.)
Tight in Middle
  • Increase RR Tire Pressure (Loosens car throughout turn.)
  • Increase Front and Rear Stagger
  • Decrease RF or LR Spring Rate*
  • Increase RR Spring Rate*
  • Decrease Chassis J-Bar Height
  • Increase Axle J-Bar Height
  • Increase J-Bar Height at Both Ends
  • Increase Ballast Forward (Decrease Rear Weight)(May loosen car on exit.)
  • Decrease Cross Weight / Left Rear Bite (May tighten car on entry and loosen on exit.)
  • Decrease Axle Lead (Loosens car throughout turn and may destabilize/slow car on straights.)

 

Tight on Exit
  • Increase RR Tire Pressure (Loosens car throughout turn.)
  • Increase Rear Stagger
  • Decrease RF Spring Rate*
  • Decrease LR Spring Rate*
  • Increase RR Spring Rate*
  • Increase Left Upper Trailing Arm (Will make car tighter on entry.)
  • Decrease Right Upper Trailing Arm (Will make car tighter on entry.)
  • Decrease Chassis J-Bar Height
  • Increase Axle J-Bar Height
  • Increase J-Bar Height at Both Ends
  • Increase Ballast Forward (Decrease Rear Weight)(May loosen car on exit.)
  • Decrease Cross Weight / Left Rear Bite (May tighten car on entry.)
  • Decrease Axle Lead (Loosens car throughout turn.)
Tight Throughout Turn
  • Increase RR Tire Pressure
  • Decrease Chassis J-Bar Height
  • Increase Axle J-Bar Height
  • Increase J-Bar Height at Both Ends
  • Decrease Axle Lead

Bold face remedies are the go-to fixes for each symptom. You might try those remedies first.

Tip: Don't stack adjustments. Make one adjustment at a time and test it.

* iRacing Dirt Late Model Spring Adjustments:

If you adjust the springs, use the spring perch offset adjustment to put the ride height back where it was originally, or at least try to adjust the ride heights so that you get the left rear bite back where it was originally. If you adjust the springs and don't return the ride heights to their original values, you are inherently stacking adjustments and you should always avoid that.

iRacing Dirt Late Model J-Bar Adjustments:

  • Raising the j-bar on the chassis and lowering the j-bar on the axle is known as increasing the rake. It will generally tighten the car. If you do the opposite, it will generally loosen the car. In the real world, TOO MUCH rake (aka j-bar split) may actually loosen the car through the center of the turn.
  • In general, changing the j-bar on the axle is a bigger adjustment than changing it on the chassis. You could use the axle end as a coarse adjustment and the chassis end to fine tune. Try to stick to adjusting the bar on the chassis end and changing the rake. If you feel the need to adjust on the axle end, adjust .5 inch at a time only.
  • Moving both ends of the j-bar up or down raises or lowers the rear center of gravity of the car. You are moving the roll center in relation to the center of gravity. Moving the entire bar UP evenly LOWERS the center of gravity, and vice versa.
  • As a general rule of thumb, raise the entire bar for a fast track and vice versa. Most of the tracks initially released on iRacing would be considered fast.

iRacing Dirt Late Model Axle Lead Adjustments:

Try to keep axle lead as close to zero as possible, especially on bigger, faster tracks. It's a good way to tighten or loosen the car quickly for different track conditions. If you're in the process of building a setup, I recommend keeping it close to zero for more stability and straight line speed.

If you see any errors or have any questions, I can usually be found in Discord.

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