If you drive aggressive you need stiff. If you're a cruiser medium or soft. And teins aren't bad...just not good compared to the other coils most people have. There's a reason why people sell them a year after they buy them.

 

You need to change suspension.

Search your new springs by spring rates: around 550lb/in + front and 450lb/in +/- rear.

Notice that Tien, competitvely priced, avoids this important performance information in their specs and leans more on the predicted drop height to make a sale.

 

Tein Basis are labeled with 500lb/in in both front and rear. So they should be just fine... right? Sorry but I've had these ordered for a decent amount of time and have been waiting for them to come in stock (Got a good price) and I need to know asap if I should cancel the order.

 

...Dude; I suggest that you double check (Q&A) with your supplier on a couple of specs and how those specs will change handling asap to verify what you and your sedan should expect.
Even ask them to explain, if they know of rumors as to why some Basics kits get launch off their cars in short order for something different.

1) Most important is that the Basics are "linear" springs.

So many buyer remorse testimonials must have some truth.
I've never had Tein Basics (entry level/ designs) but maybe the folks dumping them after a short term install for some better coilovers or springs really don't understand what went wrong buying Basics.

Coilover kits spring rates do vary by model "year" and quotes should state that the spring type and rate is "linear" or "progressive".

Linear spring handling/ stiffness is predictable and my choice.
I want constant tension to be loading my suspension regardless of spring travel during normal or hard driving. For street driving in all seasons I want under-steer.

Progressive rates are "variable" in an unspecified range of travel determined by Tein engineers. For most "cosmetically dropped" cars the suspension allows soft tension at first spring compression/ travel then leading on to increasing stiffness at higher compression / travel depending on a variety driving conditions.

2) You think you have 500lb/in fronts and rears.
Usually street kits linear front springs are 25-40% stiffer than rear to keep under-steer cornering and body roll in check for daily driving.
Equal (like you think) or greater spring rates at rear suspension compared to front approach's over-steer which is a racetrack oriented cornering choice.

Tein Basic rears are 448, I think per Tein and could be "progressive" type.
OK for sedan rear stiffness & better than my 390, if they are linear.
But your Basic fronts are 504,I think per Tein; much stiffer than OEM but slightly soft in my experience and only if they are linear type spring.

I'm driving 560 linear springs up front which give me comfort ride, tight steering and on target stiffness for dropped sedan.