STRUT BARS & Other REINFORCED BODY FRAMES: Purpose & Effects

Last edited by ReDz on Fri Jun 19, 2009 11:50 pm; edited 1 time in total

A STRUT BAR, STRUT BRACE, or STRUT TOWER BRACE (STB) is mostly an aftermarket car suspension accessory usually used to provide extra stiffness between the strut towers.

It is designed to reduce strut tower flex by tying two parallel strut towers together. Resulting from the improved chassis rigidity similar to that gained from a lower tie bar; may be improved steering precision under high load conditions (e.g. cornering and braking). Moreover, it reduces understeer, tire wear and metal fatigue in the strut tower area. Furthermore, it also transmits the load of each strut tower during cornering via tension and compression of the strut bar which shares the load between both towers and reduces Chassis Flex.

CHASSIS FLEX is a bad thing for several reasons. The first reason is that we can't control it. You want cornering forces and energy to be handled by your suspension because the suspension has hopefully been setup to handle it in a very specific way in order to make the car handle well. If the chassis is flexing, we have no control over it's spring rate and it definitely is not getting any sort of damping force. Chassis Flex is uncontrolled motion and controlling motion is whole point of suspension tuning.

Another drawback of Chassis Flex is that it throws off the alignment. Ruined alignment will throw off force transfers and tire contact patches. Also mitigating the amount of flex in the uni-body will reduce metal fatigue that leads to failures such as cracking and distortion.

Although some cars spend most of their lives driving in a straight line. Such cars might experience the strut towers moving together over time. Track cars spend a lot of their time cornering at over 1G. Thus a track car might see it's strut towers spread apart over the years.

In conclusion, a strut tower bar can be under tension OR compression depending on the environment that the car is operated in.

Moreover, strut bars are also essential in correcting OVERSTEER and UNDERSTEER.

As most modern cars go, car manufacturers employ the FF (Front engine, Front wheel drive) setup for improving driver and passenger safety. The natural behaviour of an FF car is to have a slight understeer, due to its heavier front end. Understeer happens when the front wheels lose their traction and won't turn any sharper, even when the steering is being corrected to turn the car more. This will cause the car to go wide instead of following the line. Understeer can be corrected by stiffening the rear end of the vehicle by adding a Rear Strut Bar and a Rear Anti-Roll Bar.

On the otherhand, Oversteer is when the rear tire lose grip and causing the rear end of the vehicle to slide out of a corner. This phenomenon happens particularly to FR (Front engine, Rear wheel drive) or RR (Rear engine, Rear wheel drive) cars with heavier rear ends. Vehicles with In-Car Entertainment Systems that carry a heavier rear load due to the ICE setup will highly benefit from this chassis reinforcement technique. Oversteer can be corrected by stiffening the front end of the vehicle by adding Front Strut Bars and Front Anti-Roll Bars.

Hence, for more information, please refer to the following diagrams which shows the effects of strut bars and other reinforced body frames that are available on the market.

STRUT BAR & LOWER ARM BAR

BEFORE Rolling Eyes