Difference between a strut bar and a sway bar

What is the difference between a strut bar and a sway bar? What do each of them do?

Perhaps you provide some context to your question, I have seen Honda use some odd names, “compliance bushing” is one that comes to mind.

My 2009 Honda accord has something called a front strut tower bar which is basically a bar under the hood that connects both sides of the front suspension at the tops of the wheelwells. How is this different from a sway bar which connects the suspension of the left and right side at the bottom of the vehicle?

Now that you have provided context, we can give you good responses. The way the question was originally asked would not have answer the question you really wanted answered! Thanks, OldSchool!

The bar on top is sometimes called a “Stay Bar” or a “Tower Brace” - and I am sure there are other terms as well. This bar merely prevents stiffens the where the strut is attached. This provides more precise handling.

The sway bar reduces the difference in travel between the 2 suspensions - ie, it reduces sway.

I would suggest you buy some books on suspension and handling. A good one is “How to Make your Car Handle” by Fred Puhn. It was written quite a few years ago, but the information is timeless!

I understand what you are saying with the sway bar but I’m still not quite sure what is going on with the tower brace. How can a bar attaching the two struts on top on the wheelwells provide any difference in handling of the car? Can you please elaborate, thanks very much.

It works because your car uses uni-body construction, basicly no frame. This type of construction is very cost effective but the body will twist and this bar adds strenght.

As others have said, a ‘strut bar’ or ‘tower brace’ is used to add rigidity to the body when it’s going around a corner. They’re most often seen on cars with McPherson struts (hence, ‘strut bar’) because the McPherson strut puts sideways loads on the body through both the bottom mount and the top mount, which is where the strut bar attaches. By making the body stiffer it improves (to some extent) the steering feel, making turn-in sharper. You’ll also see them used sometimes to connect the rear axle’s shock towers, but that has much less value, because shocks don’t put lateral loads into the body, only vertical loads.

Another term for sway bar is anti roll bar. As you turn the car, because the center of gravity of any car is above the tire’s contact patch, the car tends to roll in the opposite of the turning direction, kinda like kicking a floor lamp at its base. As the car rolls, one wheel goes up into the wheel well and the other falls away from the car.

Some cars with vague response would allow the body to roll first then swings the nose of the car. With this kind of delayed response, you can’t accurately determine how much steering is actually required until the car changes direction. If you can’t accurately determine the required steering input, you’d be constantly making steering corrections thru the turn, which is very unsavory for those looking for a sports car response.

If the car starts to roll as it changes direction, you can accurately determine how much steering you need. That’s the purpose of anti roll bar. It provides some resistance to the opposite motions of the wheels. However, in an off road situation, you want the wheels to freely move in opposite directions so that each wheel may have as much contact with the ground as possible. Also, anti roll bar tends to degrade ride quality; hitting a bump or pothole on one side would rock the body side to side. Too much anti roll stiffness can adversely alter the geometry and contact patch of the tire during a turn, limiting ultimate cornering capability.

Strut bar is a brace. It adds rigidity to parts of the body that aren’t suppose to move, specifically suspension mounting points. Just as the roll of the body causes delayed response, the flexing of the body before the turning of the tire also cause a delayed response. The less the body flexes, the sooner the tires steer. For the general driving public, the delay caused by the flex of the body is so minor that most car manufacturers do no bother installing a brace. But professional race car drivers would notice the difference.

“Strut Bars” or tower braces first appeared when Carol Shelby took a '65 Mustang Fastback and made a GT-350 out of it…He discovered that when equipped with sticky tires and good brakes, the Mustangs Falcon platform was twisting so much the windshields would break and pop out when the cars were cornered hard…By bracing the tops of the spring towers, a more ridged structure was created…He also replaced and re-located the lower control arms to improve the cars track performance…

Strut bat attaches attaches to the top of the strut/shock towers and stiffens the body.

Sway bay is attached to the body and lt & rt suspension. It reduces body sway or lean.

Others have provided definitions, I’ll add personal thoughts.

Unless you’re racing, strut bars (or whatever nomenclatire the manufacturer chose) on stock vehicles are pretty much just “eye candy”.

Sway bars (upgraded ones) can actually make a difference on stock vehicles. They can help a car stay level and handle noticably more stable in curves without significantly degrading the ride. Hotchkiss is probably the most prolific of the manufactureres and offers upgraded sway bars for countless vehicles. Sway bars actually are a bar of spring steel connected to each wheel and secured to the chassis. When the chassis leans, the relative movement of the wheels twists the bar like a spring element. Its effect is as Chunky described, except that I’d argue that it keeps the tires in better relation to the road’s surface making going around curves more stable.

I do agree with Chunky that too much antiaway becomes counterproductive. “understeer”, that feeling that the car is being “pushed”, is generally designed in to provide feedback for the driver that they’re going too fast. Completely removing that “understeer” can result in a driver not reailzing that the vehicle’s limits are being pushed and losing control suddenly and unexpectedly. The old Army jeeps had that problem, and way too many suddenly flipped on the drivers. Some small modern SUVs have suffered from this also.

Inproper use of antisway bars can adversely affect handling also. Putting an upgraded rear bar without also upgrading the front bar can cause the inside wheel to lift prematurely and result in loss of control.

I wanted to mention these because I’m guessing that your query was becasue you were considering adding these items. The strut bar is without danger, but if you add upgraded sway bars be sure to buy a matching front & rear set from a reputable manufacturer.