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ST5/TT5 Suspension Mod Factor question


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I sent this question in via email to Greg a couple times and never got a reply. Thought I would try here too-

My question relates to a "quick steer and roll center correction kit" for the BMW E46 chassis. What is the Mod Factor Penalty for installing this type of product on my vehicle? Depending on how I interpret the rules I think it can be either 1) not allowed at all, 2) a 0.2 penalty, 3) a 0.5 penalty, or 4) a 0.2 & a 0.5 penalty.


Background (long and detailed, sorry)

This is the kit I am planning to install: https://www.turnermotorsport.com/p-589340-quick-steer-roll-center-correction-kit-e46-323i-325i-328i-330i-323ci-325ci-328ci-330ci/

The installation requires removing the OEM ball joint, installing a new ball joint, installing a ball joint-to-strut spacer, and installing steering tie rod bump steer adjustment as well. Note that this kit also relocates the outer steering tie rod attachment for the quicker steering ratio as well.
I feel like I can interpret the Mod Factors a few different ways given the nature of the physical changes. According to the current ST5 rules (https://nasa-assets.s3.amazonaws.com/document/document/20304/ST5-6_Rules_2020--v3.2--2-11-20.pdf) I found the following statements. 
  • Section 6.1.3, subsection 2)1c) - states that "Bump steer kits are permitted"
  • Section 6.1.9, subsection 3) - states that "Relocation of OEM suspension mounting points is not permitted".
  • Section 6.1.9, subsection 4) - states that "Control arms may be modified but a Mod Factor shall be assessed.
  • Section 6.1.9, subsection 6) - states that "non-OEM metallic or spherical design replacement bushings (includes modified or replaced ball joints) shall be assessed a Mod Factor"

Then according to the 6.3.2 'Modification Factors' section, under 'Suspension' it says:

  • Replace, modify, or remove control arms, camber arms/links, toe arms/links = -0.5
    • I am only replacing the ball joint, but the control arm remains unchanged otherwise. I suppose this fits under the "modify" term?
    • The tie rod is partially replaced too. Does that count?
  • Non-OEM metallic and/or spherical design replacement suspension bushing modifications on control/camber/toe arms/links, panhard rods, watts links, and torque arms (includes replaced, modified, adjustable, or altered control arm ball joints) = -0.2
    • But then this section specifically calls out modified ball joints with just a 0.2 penalty???


As you can see there is a bit of ambiguity here and I'd hate to get protested or DQ'd due to different rule interpretations. Please help.

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Spec e46 cars don't apply this, and they are very fast / good to drive, by most accounts.


I'll let the experts weigh in on the legality.  Looks like suspension mounting point relocation to me --> not allowed.

The problem is, the acceptable contents of a "bump steer kit" are not defined.

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  • National Staff

I don’t have any emails from you.  I’ll take a look at this in more depth next week—at the track at an event now.  

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21 minutes ago, Greg G. said:

I don’t have any emails from you.  I’ll take a look at this in more depth next week—at the track at an event now.  

I figured something like that happened. Thank you for looking at it when you get the chance.


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  • National Staff

"By correcting the outer ball joint location with our Roll Center Correction Race Kit"

This appears to be a relocation of suspension mounting points that is not permitted in ST4 and below.

Extension of the ball joint and adjustment of the tie rods are generally what a bump steer kit does, and on most kits will take the -0.2 Mod Factor for metallic or spherical bearings.

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