Sway bars are what hold your car as flat as possible in a turn, and as such, are pretty critical components when it comes to building a car that can take a corner respectably. Make no mistake, the BK is a heavy car, and must be treated as such when you do your build. Now don't go home and cry because you made a poor choice buying a 3000lb+ car to build for having fun with; that's not the point here. The point is that with the proper upgrade parts, the fact that this is a fat car will matter less/not at all when it comes to apexing corners if you build it right.
Sway bars are one of the most important suspension modifications you can do to your car, and arguably offers the most noticable different in handling vs. stock against any other individual aftermarket upgrade when added to the car on it's own. So, obviously, you need sway bars.
Adjustable Strength Bars
Some bars are 'adjustable' - meaning they will have multiple boltholes at which to attach the bar to the strut's end-link. Typically the closer inward on the bar the hole is, the 'stiffer' the bar is going to be, because you are giving the bar less material to bear the load on, and thus less opportunity for flex during operation. Beware of low-cost, cheap un-branded EBay adjustable sway bars, as they will almost undoubtedly be a one-size-fits-all bar that someone is welding end-tabs onto in a shack somewhere. A good sway bar HAS ABSOLUTELY NO WELDS ANYWHERE.
A sway bar should be one continuous bar that was cold-formed into that specific shape which fits your car. This means the metal structure will evenly bear load across the bar; when metal is welded a heat-affected zone is created at the point where the metal was heated during the process, and the weld fillet is not integral to the structure; it was added to it. Therefore, do not cheap out on sway bars.
A broken sway bar that is clanking around under your car is not going to kill you or cause handling problems; it will just make you look and feel like a spanner.
Front & Rear, or just Rear?
Depending on what you do with your car, you may wish to simply purchase & install a rear sway bar only. This is because, if for example - you are going for drift specifically - you will want your front to be as loose as possible in terms of roll (this allows the front tires to stay in contact as long as possible during lateral push) and you will want your rear to be easily kick-able at will. The stiffer a sway bar is on one set of wheels, the more 'weight' (momentary inertia) gets loaded more immediately by that set of wheels in a turn.
Example: You enter a left hand turn, and hammer the car hard left. The weight load shifts to your aft passenger side wheel. The softer the suspension is, the more the car body will 'roll' and sustain a portion of the load (soften the blow to the tire on the pavement) before the tire gets hit with the load.
Same scenario, your suspension is tight as a virgin after Sunday School with no give at all - the firm suspension does not allow the body to roll very much at all, and as such the load gets sent directly to the tire's contact patch on the pavement; voila, SLIIIIIIDE!
Install front & rear sways as an upgrade if you are road-racing and/or you don't want to make the car anymore ass-happy than it already is, in a nutshell.
2012 BKI / 2013 BKII End-Link Compatibility Problems
Before purchasing a sway-bar kit for your car, call the manufacturer and/or the reseller to verify it fits your year or read their info to verify fitment. Hyundai revised the car's forward end-links to not suck so much for the 2012 model year, and I understand they are at it again with the BKII end links. Some manufacturers have been known to include a pair of OEM end links upon request to fit your 2012 or BKII, some simply advise you to order a set from your local dealership; honestly the parts are not expensive, but check first before you are under your car with your entire suspension removed; a grown man crying isn't a pretty sigh.
Greasable Bushings
Your aftermarket sway bar will include larger, firmer, ribbed-for-her-pleasure bushings as a necessity for mounting the bar. These bushings will of course need to be greased on assembly and they will need to be re-greased over time as the car is driven.
If you know the diameter of your sway bar, there are almost always aftermarket bushings available - sometimes right off the shelf of your local Autozone/O'Reillys etc under the brand name Energy Bushings - which have Zerk fittings. These are little nipples with an attached cover/cap. These bushings allow you to simply jack up the car, pull the caps off, use your grease gun with it's Zerk nozzle (fits right onto the nipple), pump a bit of lube in there nice and cleanly, re-attach nipple cap, drive.
This allows you to rapidly lubricate (and who doesn't enjoy rapid lubrication?) the bushings without taking anything apart. This is good. These bushings are typically very inexpensive as well... to the tune of twenty dollars usually.
Products Available
Bear in mind no one of these sway bar kits will really "outperform the other"; some are a little stiffer, some are adjustable, some are not. Adjustability is of no consequence to 99.9% of drivers. Once again, shop with the reseller of your choice and remember to call/check for fitment on your 2012 BKI or BKII.
Whiteline - [Adjustable] These guys are well-known in motorsports and well respected by communites such as Evos and STis. They sell their bars individually (front/rear) and in two different flavors - stiff and invincible. Their 27mm rear and 30mm front is a little on the hard side for some folks, so if you don't like the idea of getting thrown left - right in your seat through almost any turn, get the softer, smaller diameter ones. If you're doing a race build that includes some sturdy and secure racing seats, this is the kit you need to buy, it's value for price is unbeatable. Also they use polyurethane bushings which are far more durable and stiff than the rubber bushings other brands use.
Eibach - [Adjustable] These guys are pretty much the first name that comes to mind when a guy falls out of bed in the morning and says "Sway bars". Equal to Whiteline in quality and accoutrements; these are adjustable as well, include quality polyurethane bushings, however per Eibach's usual strategy - they are one-size-fits-all with 29mm bars front and rear as the only option. Nutshell: Invincible flavor only. Really not a bad thing when you think about it.
Stillen -[Adjustable] Very high-quality sway kit which is adjustable, basically equivalent to Eibach. But wait there's more! Stillen includes high quality polyurethane bushings with greasable Zerk fittings included! (at least according to their product photo) This is super duper cool! Also Steve Millen is way less of an asshole than his brother!
ST - No idea who these guys are, never heard of them, however their product is built properly, includes quality polyurethane bushings and is priced fairly. At 22mm their rear bar is on the soft side so this may not be for you if you're a balls-out hooligan. Also they are baby puke green. But still completely fine and good to blow your money on!
Tanabe - Overpriced. Reasonable quality, but for the same/less money, you can do better. Also, their R&D process is more fucked up than the path that kid in the Family Circus takes home from school everyday.
Cusco - With a single bar costing more than most pairs of sway bars, rather than giving Cusco any of your money - I recommend instead re-gifting them any hard-as-brick Christmas fruitcakes you get in the mail this year to tell them how you feel about their pricing. Their bars are no different than anyone elses. This kit even includes rubber bushings along with it's premium price. AMAZING.
Progress - [Adjustable] About the only good thing here is they are affordable. Their end tabs are welded onto the sway bar. This is a bad thing; when really pushed, this tab will fail and you'll look like a tool. You'll probably lose too.
