Hobbies Cars & Motorcycles Four Wheel Alignment Explained Thrust Angle, Included Angle and Steering Axis Inclination Share PINTEREST Email Print Cars & Motorcycles Cars How Tos Buying & Selling Basics Reviews Tools & Products Classic Cars Exotic Cars Corvettes Mustangs Tires & Wheels Motorcycles Used Cars SUVs Trucks ATVs & Off Road Public Transportation By Matthew Wright Matthew Wright has been a freelance writer and editor for over 10 years and an automotive repair professional for three decades specializing in European vintage vehicles. our editorial process Matthew Wright Updated May 08, 2018 If you hit a serious bump you might need to get an alignment. Alignments are not usually expensive and include adjustments of suspension like camber, caster, toe in, toe out, thrust, and 4-wheel alignment. Let us show you definitions of what all of these things mean to you and the health of your car or truck. 01 of 03 Thrust Angle The angle between the thrust line and centerline. If the thrust line is to the right of the centerline, the angle is said to be positive. If the thrust line is to the left of center, the angle is negative. It is caused by rear wheel or axle misalignment and causes the steering to pull or lead to one side or the other. It is the primary cause of an off-center or crooked steering wheel. Correcting rear axle or toe alignment is necessary to eliminate the thrust angle. If that is not possible, using the thrust angle as a reference line for aligning front toe can restore center steering. 02 of 03 Included Angle The sum of the camber and SAI angles in a front suspension. This angle is measured indirectly and is used primarily to diagnose bent suspension parts such as spindles and struts. 03 of 03 Steering Axis Inclination (SAI) The angle formed by a line that runs through the upper and lower steering pivots with respect to vertical. On an SLA suspension, the line runs through the upper and lower ball joints. On a MacPherson strut suspension, the line runs through the lower ball joint and upper strut mount or bearing plate. Viewed from the front, SAI is also the inward tilt of the steering axis. Like caster, it provides directional stability. But it also reduces steering effort by reducing the scrub radius. SAI is a built-in nonadjustable angle and is used with camber and the included angle to diagnose bent spindles, struts and mislocated crossmembers.