iRacing Dirt UMP Modified Setup Matrix

Rev. 5 – April 6, 2023

Symptom Remedies
Loose on Entry
  • Decrease RR Tire Pressure (Tightens car throughout turn.)
  • Decrease LF Spring Rate*
  • Increase RF Spring Rate*
  • Increase RF Wheel Spacing
  • Decrease RR Wheel Spacing
  • Increase Left Trailing Arm (Will loosen car on exit.)
  • Decrease Right Trailing Arm (Will loosen car on exit.)
  • Increase Chassis J-Bar Height
  • Decrease Axle J-Bar Height
    (More J-Bar rake (split) produces more traction and more body roll. Remember, traction creates roll, but roll does not create traction.)

  • Increase Cross Weight / Left Rear Bite (May loosen car in middle and on exit.)
    (The proper method is to increase LF and RR spring perch offset and decrease RF and LR spring perch offset.)

  • 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 RF Wheel Spacing
  • Decrease RR Wheel Spacing
  • Increase Chassis J-Bar Height
  • Decrease Axle J-Bar Height
    (More J-Bar rake (split) produces more traction and more body roll. Remember, traction creates roll, but roll does not create traction.)

  • Decrease Ballast Forward (Increase Rear Weight)
  • Increase Cross Weight / Left Rear Bite
    (The proper method is to increase LF and RR spring perch offset and decrease RF and LR spring perch offset.)

  • Increase Axle Lead (Tightens car throughout turn and higher/lower extremes may destabilize/slow car on longer straights.)
Loose on Exit
  • Decrease RR Tire Pressure (Tightens car throughout turn.)
  • Decrease Rear Stagger
  • Increase LR Spring Rate* (May loosen car on entry.)
  • Decrease RR Spring Rate* (May loosen car on entry.)
  • Decrease All Spring Rates*
  • Decrease LF Wheel Spacing
  • Increase LR Wheel Spacing
  • Decrease Left Trailing Arm (Will loosen car on entry.)
  • Increase Right Trailing Arm (Will loosen car on entry.)
  • Increase Chassis J-Bar Height
  • Decrease Axle J-Bar Height
    (More J-Bar rake (split) produces more traction and more body roll. Remember, traction creates roll, but roll does not create traction.)
  • Decrease Ballast Forward (Increase Rear Weight)
  • Increase Cross Weight / Left Rear Bite
    (The proper method is to increase LF and RR spring perch offset and decrease RF and LR spring perch offset.)
  • Increase Axle Lead (Tightens car throughout turn and higher/lower extremes may destabilize/slow car on longer straights.)
Loose Throughout Turn
  • Decrease RR Tire Pressure
  • Decrease Rear Stagger
  • Decrease RR Wheel Spacing
  • Increase Axle Lead
Tight on Entry
  • Decrease Right Front Tire Pressures
  • Increase RR Tire Pressure (Loosens car throughout turn.)
  • Decrease Toe-In (More Negative)
  • Increase LF Spring Rate*
  • Decrease RF Spring Rate*
  • Decrease LR Spring Rate*
  • Increase RR Spring Rate* (May tighten car on exit.)
  • Decrease RF Wheel Spacing
  • Increase RR Wheel Spacing
  • Decrease Left Trailing Arm (Will tighten car on exit.)
  • Increase Upper Trailing Arm (Will tighten car on exit.)
  • Decrease Chassis J-Bar Height
  • Increase Axle J-Bar Height
  • Decrease Ballast Forward (Increase Rear Weight)
  • Decrease Cross Weight / Left Rear Bite
    (The proper method is to decrease LF and RR spring perch offset and increase RF and LR spring perch offset.)

  • Decrease Axle Lead (Loosens car throughout turn and higher/lower extremes may destabilize/slow car on longer straights.)
Tight in Middle
  • Increase RR Tire Pressure (Loosens car throughout turn.)
  • Increase Rear Stagger
  • Decrease RF or LR Spring Rate*
  • Increase RR Spring Rate*

  • Decrease RF Wheel Spacing
  • Increase RR Wheel Spacing

  • Decrease Chassis J-Bar Height
  • Increase Axle J-Bar Height
  • Decrease Cross Weight / Left Rear Bite (May tighten car on entry and loosen on exit.)
    (The proper method is to decrease LF and RR spring perch offset and increase RF and LR spring perch offset.)

  • Decrease Axle Lead (Loosens car throughout turn and higher/lower extremes may destabilize/slow car on longer straights.)

 

Tight on Exit
  • Increase RR Tire Pressure (Loosens car throughout turn.)
  • Increase Rear Stagger
  • Decrease LR Spring Rate*
  • Increase RR Spring Rate*
  • Increase LF Wheel Spacing
  • Increase RR Wheel Spacing
  • Increase Left Trailing Arm (Will make car tighter on entry.)
  • Decrease Right Trailing Arm (Will make car tighter on entry.)
  • Decrease Chassis J-Bar Height
  • Increase Axle J-Bar Height
  • Increase Ballast Forward (Decrease Rear Weight)
  • Decrease Cross Weight / Left Rear Bite
    (The proper method is to decrease LF and RR spring perch offset and increase RF and LR spring perch offset.)

  • Decrease Axle Lead (Loosens car throughout turn and higher/lower extremes may destabilize/slow car on longer straights.)
Tight Throughout Turn
  • Increase RR Tire Pressure
  • Increase Rear Stagger
  • Increase RR wheel spacing
  • Decrease Axle Lead (Loosens car throughout turn and higher/lower extremes may destabilize/slow car on longer straights.)

* If you adjust the springs, use the spring perch offset adjustment to put the ride height back where it was originally. This is important.

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

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

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

Note: To print the matrix, use Google Chrome and highlight (select) only what you want to print. Right-click and click print. Google Chrome will send only the highlighted selection to the printer by default. Full matrix with footnotes will fit on two pages.