In the case of the Challenger, bump steer is both a good news and a bad news situation. Starting with the good news; Dodge (as do all manufacturers) does its best to eliminate bump steer within the stock factory location. At stock ride height and suspension settings, an OEM Challenger should measure in around 0.0625 (1/16) inches of bump steer. This is very close to zero (obviously) and thus Dodge has done a good job, especially when considering the Challengers of yore (going back to the 60s and 70s) had bump steer measurements of around 0.75 inches!
The bad news regarding Challengers and bump steer is that they become susceptible to it when lowering the ride height or swapping in some coil overs. Under these conditions, the steering arc will change from that of the suspension travel and lead to bump steer.
The exact science of bump steer, tie rod, and suspension geometry is as such. Draw one line from the upper ball joint directly to the lower ball joint (let’s call it line A). Draw a second line that joins the upper control arm pivot point to the lower control arm pivot point (line B). The outer tie rod must fall somewhere on line A and the inner must fall somewhere on line B. Furthermore, the center of the tie rod must align with the center of the control arms, which can be depicted by extending a parallel line and seeing where they intersect (with each respective control arm).
Now, for a more simplistic approach.
In order to achieve zero bump steer, the tie rod must travel along the same arc (between the lower and upper control arm) that the suspension does when displaced. This means the length and angles of the tie rods play a critical role in maintaining this careful tangential relationship and lowering the ride height via springs or coil overs is sure to disrupt the OEM calculations. Thus, bump steer will rear its ugly head and something will need to be done about it.