I've posted a few times about the differences, strengths/weaknesses of the early and late C4 front suspensions and now I'd like to offer a thought and see what the general reaction is.

So I think it's established that the early design is superior from a performance and driving feel standpoint. The late version has a 17 degree (or thereabouts) SAI and a ton of anti-dive and we don't really want that, do we?

The early version has more traditional numbers but its one drawback is that it also has almost 3" of positive scrub radius, which is way over the recommended number, which I often see as around 1/2".

So here's my thought:

What about creating longer versions of the early style arms that push the knuckles/spindles about 2.5" outboard and then using wheels with an additional 2.5" positive offset (for about 3.75" total) to maintain the same overall wheel footprint but with only about 1/2" positive scrub?

What are the possible drawbacks, geometry-wise? If you used the stock knuckle, then it would alter the suspension geometry a bit by reducing the arc between the upper and lower arms in front view and thus pushing the Instant Center a little farther out. How much this would affect the handling, I have no idea. But you could (maybe?) use small spacers at top and bottom of the knuckle to increase its height and thus retain the stock geometry.

Pushing the steering arms farther out would affect the ackerman. If the stock lines intersected at the rear axle centerline, then this mod would push that point farther back. I don't know where it actually lands on the C4 in stock form, though, and I'm guessing it's not designed for full ackerman. So maybe this wouldn't matter that much? Seems like the 'Vette is known for playing fast and loose with ackerman.

The steering tie rods would need to be lengthened but if the knuckle spacers were used, then I don't think there would be any bumpsteer induced, right?

I think this would also change the mechanical ratio of the springs and shocks but at least that's a relatively easy matter to address with parts selection.

For reference, here's a pic I posted previously illustrating the scrub radius on the early IFS:

 

That’s basically a late model lower control arm… you would need longer uppers (SPC for example).

84 has smaller brake caliper mount if that matters.

will need a late swaybar and relocate the sway bar a little bit forward I think

 

Good call, AZSP33D! That's fairly convenient. I've spent my Friday evening working up a diagram in CAD to illustrate this idea. Seems like it may have some legs.

This is the same early C4 IFS as shown above but with 15" long late C4 lower a-arms ( early are 13.25") swapped in and longer custom uppers installed. Using the stock mounting points on the early C4 subframe and makign the lowers horizontal, it came out with a roll center 2" above ground so I dropped the upper mounts 1/2" and gained almost 1" of roll center height. I think it's still a little lower than the stock roll center but it's easy to adjust.

It's also noteworthy that this would require 17" wheels minimum, I think. Neither of the C4 suspension iterations place the upper ball joint within the wheel like this does so wheel diameter isn't an issue in stock form but it is here.

True to my mental conceptualization, pushing the spindle out and using much more positive offset on the wheels did yield a reduction of the scrub radius to a respectable number. However, it did take using 11" wide wheels to get there. Sticking with 9.5" wheels 2.75" positive offset, there's still 1-3/8" scrub radius. Better than stock but still too much. At least for this exercise.

The trick is making everything else work. For instance, the steering rack is the primary matter of concern, as it would probably need to be adjusted in at least one way. Height, width--these are question marks. Then again, I didn't change the spindle height at all here with spacers like I previously mentioned so perhaps doing that would obviate the need for steering rack changes as well as the upper a-arm mounting points. I guess I have another drawing to do.

EDIT: The small differences in geometry involved with spacing the spindle slightly are finer than the resolution of my inexact drawing so I'm abandoning that graphical pursuit. One thing I realized when attempting, however, is that the spacing wouldn't necessarily be uniform top and bottom; the crucial point is that the steering arm pivot would need to travel precisely along its predetermined line from the far Instant Center. The spacers required would be somewhere around 1/8" so I don't know if that's even a thing.

 

Interesting idea, but the road feel of the early cars is likely due to the large scrub radius. Unless you're worried about steering wheel kickback during asymmetric braking (under ABS control on test track surfaces) or running a diagonal split brake system you might want to leave it alone.

 

We're never going to get to the moon with that attitude.

Here's another thought. What about using C6 or C7 spindles with this arrangement? If there's a way to get C6 or even C7 hubs in there, that'd be a material improvement beyond the suspension geometry. Also, the lesser depth of those hubs would require less positive offset on the wheels--maybe to the point that you could find some wheel off the shelf.

 

Use a taller lower BJ to raise RC, there's plenty of room. Lots of people say front RC between 0" and 3" and I prefer 3-3.5" range, and another benefit to the shorter roll couple is I don't need to run a big front sway bar (which couples the front suspension so it's not so independent) and additionally a lower rear RC as the rear could really use more grip, RC axis very level or tilted down in he back even like some hill climb monsters. Trans Am cars have been lowering the RRC and raising the FRC more and more in recent years. Outside of that, Porsche has done this to the extreme for many decades.

 

Here's a follow-up to the C6 spindle idea. Using non-exact and non-official dimensions gleaned from internet research, I've approximated the C6 spindle in my drawing and it seems to work really well. It did exactly what I was hoping: reduce the required positive wheel offset and offer better hubs. I know there's a matter of incompatibility with the ABS stuff at play here but at least mechanically it should be possible to get the prized C7 hubs mounted up in there. Unless anyone can offer insight to the contrary?

The one thing I'm unsure of is the steering arm location on the C6 spindle so I don't know what kind of mismatch with the C4 rack location is happening there. It looks close in the drawing so my hope is that either small steering arm spacers or a minor rack reposition could take care of it.

 

I think the C6 spindle has the upper outboard BJ/pivot on the bottom, but there are so many aftermarket modular units that you can probably do whatever you want.