What Does an Upper or Lower Tie Bar Do?by Chris Stevenson
Tie bars come in upper and lower designs for most cars that have unibody and independent suspension. They are primarily aftermarket parts, with the exception of vehicles like the Honda Integra and the Civic Type-R models, where they come as standard component applications. Tie bars are made by several manufacturers, available for front upper and lower and rear upper and lower applications. Each model vehicle has particular mounting instructions, but in all cases the tie bars connect the same main suspension or frame components for the purposes of reducing flex and stretch of the chassis body.
Tie Bar Construction
Tie bars have straight or curved billet steel tube construction, with welds and connection flanges at each end. Some lower tie bars have rectangular tubes, hollow in design and lightweight. Depending on the model, tie bars can have single or double bends, or possess additional brace bars between their end points. They have no bushings or flex joints and are designed to remain rigid under heavy load and torque conditions.
Lower Front Tie Bars
Lower front tie bars come in the straight bar designs, or braced frame configurations, depending upon the model. Each end of the tie bar bolts to the main lower control arm mount, usually the front, which connects the two load-bearing control arms. The lower front tie bars strengthens both sides of the chassis, disallowing flex between the body and suspension parts. They also keep the front end in alignment during very hard cornering and high speeds, where the caster and camber angles can momentarily flex or deviate from specifications.
Upper Front Tie Bars
Upper front tie bars are usually constructed of a one-piece tubular, steel support rod. They come in hook or angle mounting configurations, depending upon the model. They connect both shock towers via tower mounting bolts on both sides and assist in keeping the upper body frame rigid during hard turns under rapid acceleration or hard braking. They also help to reduce the odds of rollover, but this depends on the vehicle's profile height from model to model and its tendency to roll or sway more or less.
Lower Rear Tie Bars
Lower rear tie bars come in configurations similar to front lower tie bars but might have an extra brace that connects to a main frame support. They are designed to keep the rear end from unnecessary sway and flex during hard turns at high speed, or hard braking turns. They assist in keeping camber and caster angles in check for vehicles that have rear suspension alignment features.
Upper Rear Tie Bars
Upper rear tie bars have similar design construction to upper front tie bars and mount to the shock towers, either in the rear compartment of SUVs, in the trunk of conventional cars or under the chassis at the top of the strut tower. They are designed to keep the upper rear body from flexing during high speed turns and assist in decreasing rollover. Rollover characteristics can differ from model to model, according to vehicle height and center of gravity.
Tie Bar Applications
The proponents of tie bars claim the true benefits apply primarily to high performance and racing applications, where heavier-than-normal loads and speeds are common. Track racing and off-road vehicles are cited as getting the most use from tie bars. Although conventional cars and trucks can be equipped with tie bars, the benefits can be negligible to slight, depending upon driving conditions and performance characteristics.
A more significant improvement on chassis rigidity could be realized with the installation of tie bars on older unibody vehicles that have undergone metal fatigue, resulting from repeated stress and flex. Tie bars on older vehicles could strengthen a weak frame, improve handling characteristics and lessen or eliminate annoying chassis squeaks and groans.
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