like the title says.... i know what they are... but what exactly do they do? in pictures they look really thin which leads me to assume they can't be there... at least not effectively, to reduce flex in the chassis.

 

Im not sure how to explain it, but pretty much they stiffen up the frame. Im not sure why they would work though because they bolt to the frame compared to being welded directly. For a street car, you dont need them, just get the cusco 3pc. floor bar.

 

do the floor bars really make a good difference?

 

The fender braces mounts in between the door inner beam to the (fender) front portion. It actually has a weld joint where Honda puts the frame together. The inner fender brace is to reinforce it to reduce flexes and improves turn in response. It's quite a noticeable difference.

The Cusco bar makes a bit difference too but IMO, it is missing a center bracket which makes the bar STRONGER plus it is way too heavy. If you want a similar type bar with better effect (lightweight), you should consider the Carbing aluminum floor bar.