Register And Remove These Ads
That's a super hard question to answer. Depends on so many things. You can't really put a number on it, but a good suspension setup with proper spring rates for your tires, proper alignment, proper valving, etc. is worth a pretty significant difference on most cars over stock. I should add that even good quality coilovers that are setup improperly or not matched well with the rest of your setup can sometimes be even worse than stock suspension. Over lowering without modifying the roll center, too stiff/soft spring rates, not enough/too much dampening for the spring rates, etc. are all commonly made mistakes. So long story short, coilovers are an excellent idea if you know how to use them.