This article is one in a series that have been released in conjunction with Wayne's new book, 101 Performance Projects for Your BMW 3 Series. The book contains 272 pages of full color projects detailing everything from performance mods to timing the camshafts. With more than 650+ full-color glossy photos accompanying extensive step-by-step procedures, this book is required reading in any 3 Series owner's collection. The book was released in August 2006, and is available for ordering now. See The Official Book Website for more details.
The BMW 3 Series cars are well known for their agility and superb handling. However, because of the chassis design, there is a weakness in the 3 Series cars. The front shock towers are not well supported in the 3 Series chassis. In fact, they are somewhat isolated and unsupported. As a result, the towers can bend and flex under heavy cornering. This flexing can cause detrimental changes in the handling of your car, because, in general, the stiffer the chassis, the better the handling of the car. Camber strut braces are designed to maintain the distance between the shocks under heavy cornering. A bar linking the top of the shock towers ensures the towers do not bend when the chassis is flexing.
Well, that's what the marketers say when selling these bars. The strut bars are yet another controversial product that many people feel the need to install on their BMWs. On some cars (the early Porsche 911s, for example), the installation of the strut bar is an important chassis stiffening device. Because of the Porsches' rear-engine design, the front chassis can be decidedly weak, particularly when rust has started to affect chassis stiffness. But the BMW chassis is different. It's supported by a much more rigid frame that includes a very strong engine mount bar that runs the width of the car under the engine.
Which strut bars are most effective? I have little faith in the aluminum strut bars. Aluminum is not a very strong metal--you can often bend aluminum pipes with your hands. Add the fact that most strut bars are angled to fit neatly around the engine and under the hood, since there's no straight shot across the engine bay. This combination creates a very weak support when you consider the forces you're trying to counteract. In my opinion, an aluminum strut brace is merely window dressing for the engine compartment.
I'm also not fond of bars with hinges built into the strut mounts. If they move at all, the shock towers are likely to see movement that would place the strut brace under compression and tension. A stiff connection between the strut towers is vital to proper strut bar operation. Any time you place a fastener in the assembly, you introduce backlash and slop in at least one direction (compression or tension). Thus, the bar becomes ineffective in at least one direction (compression or tension).
The best strut tower braces are one-piece units manufactured out of thick, welded steel pipe. These braces offer the best protection against chassis flex when installed between the two strut towers. The strut braces manufactured by Ireland Engineering for the E30 cars fit this description perfectly. Their strut bars are some of the beefiest designs on the market.
If you ask die-hard racers who drive their 3 Series cars on the track, most of them don't run with a strut brace and can't feel the difference even when pulling significant side loads (1.4 g's) out of the corners. For dedicated track cars, the strut towers are often reinforced with steel pipe welded diagonally across the engine, connected to the front of the firewall.
The bottom line? If you believe a strut bar will benefit you, or you are looking to spruce up the engine compartment, adding one to your car is a relatively simply task-simply bolt it on top of your strut towers. If your goal is increased performance, I recommend the bar only for a very stiffly sprung, dedicated track car. Make sure it's a high-quality unit that's designed properly: close-fitting on the struts, manufactured out of steel, a minimal amount of angles in the bar itself, and no hinges. A better upgrade, and one that should be installed first, is the BMW E36 convertible lower X-brace that stiffens the lower part of the chassis (see Project 66).
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I bought this strut brace from a major manufacturer and was very disappointed when it arrived. The camber strut brace attaches to the top of the shock towers with the three nuts that also hold the top shock mount. This polished aluminum model is made to fit the 318is. I do not recommend this type of strut bar as a performance improvement. Aluminum is not very strong, the mounts on the top of the strut allow for too much slop, and the angle of the bar makes it look like I could bend it with my own two hands. I consider bars like these mostly for show.
Shown on this M3 is a strut tower brace from Dinan. This beautiful product has carbon-fiber inlays and anodized caps for the top of the strut towers and really spruces up the engine compartment. However, I question how much structural support it actually provides, considering its relatively thin aluminum construction.
Although not as attractive, this brace is probably the most effective. The thick, large-diameter steel pipe directly reinforces the shock towers and requires significant forces to deflect and bend. Despite the two rather large angles in the brace, the strength of the steel pipe should compensate for the reduced rigidity. This is the type of bar I'd recommend if you want to install one in your car.