Strut tower brace/tie-bar
Strut tower brace/tie-bar
(OP)
Most of you have probably seen the aftermarket steel braces that bolt to the top of the strut towers on import cars. This is supposed to stiffen the chassis for better cornering. A lot of cars come with them now straight from the factory. I was just curious, how much do they really help on a street vehicle? Also, are there any design guidelines as far as what thickness of materials to use and how to calculate the forces acting on the brace?
It doesn't seem like the cheap stamped steel braces will do much to stiffen the chassis when you dive into a corner and put thousands of pounds of force on it.
-Jon
It doesn't seem like the cheap stamped steel braces will do much to stiffen the chassis when you dive into a corner and put thousands of pounds of force on it.
-Jon
RE: Strut tower brace/tie-bar
I've never done this, but would be very interested to see the results.
From work I've seen you'll need about 2 kg of metal in the brace (if it is straight) to make a reasonable difference.
One problem is that the improvements are in a host of driver-feel related things rather than any great /measurable/ improvement.
Cheers
Greg Locock
RE: Strut tower brace/tie-bar
A well designed bar can definitely improve steering response in turn in. Tying the towers together minimises their relative motion which allows the springs shocks and antiroll bar to do their job more precisely.
In many street applications there is a minimal amount of room to properly tie the towers together without major surgery, so compromises are necessary. But as
Greg mentioned above you can do some tests.
You can quantify how flexable a particular vehicle is, with a jack and a tape measure.
Dave
RE: Strut tower brace/tie-bar
In terms of measurable effects, the first time I jacked up the car after installing one, I was quite surprised to find that the other side came up about 1/2" -- sort of irritating since I have to either disconnect it or use jack stands every time I jack the car up now.
RE: Strut tower brace/tie-bar
Cheers
Greg Locock
RE: Strut tower brace/tie-bar
RE: Strut tower brace/tie-bar
In the rear, they are used on hatch vehicles with a high mount strut. Here, a rear tower bar can make a big difference. If the vehicle is a open hatch constrution, it is very hard to control the flex of the tower if the shock is mounted high in the vehicle(near the top of the rear seatback). The bar can make the rear feel more firm during cornering. the strange thing with a rear bar is that most of the time, there is actually very little stress on the bar. We have put a strain gauge on a rear tower bar, and basically no values were produced during handling manuvers, But it makes a big feeling change.
RE: Strut tower brace/tie-bar
RE: Strut tower brace/tie-bar
In production we try to get the same effect by building a horseshoe around the strut caps, back to the firewall and across there.
This is obviously a less efficient use of metal.
Cheers
Greg Locock
RE: Strut tower brace/tie-bar
RE: Strut tower brace/tie-bar
The torsional and bending stiffness are global properties of the body, and bracing the towers makes only a very small contribution to those properties. Therefore when you run your optimisation the 'correct' place to strengthen the shell is not at the towers.
Welded would be better but whoever is servicing the engine might have a few choice words if you use a welded brace at the front.
Cheers
Greg Locock
RE: Strut tower brace/tie-bar
-Jon
RE: Strut tower brace/tie-bar
I picture the young Ahnold Schwarzenegger wearing a set of those novelty reindeer antlers. The main car body >>may<< be as rugged as Ahnold, but the suspension towers are mounted out on the tips of the antlers.
High torsional stiffness is best achieved by a large diameter circular tube. We make cars by squaring the tube, then we add gaping holes in the form of doors, trunks, and upper and lower engine bays, further whacking the torsional stiffness. The stiffness that remains comes from the relatively and absolutely puny contributions from box/tube frame rails and "torque boxes" hidden in the body structure. The body and maybe even windshield contribute to stiffness of cars, even (especially?) ones possessing the widely admired "real frame". I heard Corvette converibles get an X crossmember to try and make up for the missing roof. Studebaker increased their frame thickness about 50% when they added V-8 power, and added an X-member on convertibles and the sliding top wagons.
The importance of the door holes is suggested here.
http://www.gmgoodwrench.com/gmgoodwrenchjsp/gmspo/Ponti...
The stress is high at the corners, suggesting large local strains there, making these areas useful for slight stiffening. Adding REAL stiffening via diagonals would be the logical improvement, but as others have suggested, would meet with consumer objection.