I will be doing a mild drop on my s2000 later this year with bilstein coilovers. .75 to 1" Drop

Will I need steering rack spacers if I already have Megan racing roll center adjuster ball joints with riser plates installed???

 

You don't need either for a 1" drop.

You also don't need either if you're not going after a specific tuning strategy.

However...if you're using RCA plates, you now need steering rack spacers or you'll have some unknown amount of bump steer. You can't just move 1 peice of geometry without throwing other peices off.

You could just go back to stock ball joints and avoid this headache. The geometry was already set relative to other parts by Honda.

 

I do have the stock ball joints still...

Can you help me understand why I would need the steering rack risers along with the RCA w/ plates?

Because I thought the RCA w/ plates alone was designed to correct the suspension geometry when lowering your car.

 

The arc of the LCA, UCA, and spindle and the arc of the tie rods have to relate to each other in some way for the entire range of suspension travel.

All of those components have different arc lengths and different arc center positions which are all designed to work together within the suspension motion range.

With RCA plates, in respect to all the other components you've moved the start point of of the LCA arc by itself downward. So now the components don't move in the same relationship as they were designed to do so.

There's no merit in "RCA's correct the geometry" as a statement by itself. That's just oversimplified marketing.

The RCA is supposed to adjust roll center...which it does do. However, the side effect is that it changes the amount of bump steer by moving the suspension components out of harmony. Did you get lucky and dial out any factory bump steer? Or did you just add a shitload of it? You'd need to measure.

If undesirable bump steer is found...
A tie rod spacer is a better idea than a rack spacer in order to get the parts back in harmony. However, you would need to continue to measure for bump steer and dial in the correct length of tie rod.

I know all this sounds like word salad.

Try youtubing what causes bump steer, how to measure and fix bump steer and what an instant center is.

You don't need *any* of this stuff for a 1" drop on your street/casual track use car.

The S2000 front suspension has fairly low bump steer. Its not 0, but its also not an issue which absolutely needs solving.

 

Lowered with Bilstein PSS9: install axle spacers, Spoon front and rear bump steer kits and have no issues. Also installed the Spoon rigid collars and rear camber kit to keep everything in stock specs.