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Bumpsteer Kit Install - Steady as She GoesFrom the July, 2012 issue of Muscle Mustangs & Fast Fords By Wes Duenkel Photography by The Author
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We didn't used to think about bumpsteer--until our newly lowered Mustang would almost change lanes when hitting a bump. Correcting it involved guesswork and complex tools. That's not so anymore. Bumpsteer is actually a change in the toe caused by the front end going up and down, and the result is a front end that doesn't track in the direction you are commanding. This ill-handling condition can make the car seem unpredictable and unsafe. Maximum Motorsports' bumpsteer kits and handy bumpsteer gauge make correcting bumpsteer relatively easy and straightforward. It's also recommended to correct rear bumpsteer when lowering an independent rear suspension, such as in our '03 Cobra. After setting the front and rear toe settings to zero, we used Maximum Motorsports' bumpsteer gauge to adjust the front and rear bumpsteer curves. This minimized toe changes when driving to maintain directional stability and handling consistency. We were pleased to find the gauge accurate, precise, and intuitive to use, and were rewarded with a Mustang that tracks straight and true--even when the pavement isn't. Definitions
- Bumpsteer: When a tire's toe setting changes during vertical suspension movement, it's referred to as bumpsteer. We generally want to minimize overall bumpsteer, as it can create directional instability when a car traverses bumps (or during a wheels-up launch). However, it can be used in moderation to create certain handling characteristics. For example, a front suspension that toes-out in bump and toes-in in droop can help a car understeer in corners.
- Toe: Toe is the alignment measurement of a wheel relative to the longitudinal axis of a car. Toe-in refers to when the front of the wheel pointing in toward the car's centerline, and toe-out is when the front of the wheel points away from the centerline. Zero toe means the wheels are pointing straight ahead, and are parallel to each other.
- Thrust Angle: If the rear wheels' toe angles aren't symmetric (e.g., one is toe-out and the other is toe-in), or the rear axle is shifted to one side of the car, then the rear wheels will produce a driving force that is not aligned with the centerline of the car. This misalignment is called a thrust angle. Even if the front end is aligned perfectly, the front wheels must be off-center for the car to drive straight. This is also called "dog tracking."
Before we started, we used a string setup to set the front and rear toe to zero, and we made sure the car didn't have a rear thrust angle. You could also have the car professionally aligned, and the front and rear toe set to zero. However you do it, this step is extremely important because improper toe settings will render all later measurements worthless.  1 We measured the current...  1 We measured the current ride height at all four corners before jacking up the car. We used a piece of tape with a mark as a reference point, and measured to the center of the wheelhub.  2 Once the car was on jackstands,...  2 Once the car was on jackstands, we put a level on the steering wheel to ensure it was centered.  3 With the steering wheel...  3 With the steering wheel centered, we locked the steering in place with Vise-Grip pliers on the steering shaft to keep it in position.  4 So we could easily cycle...  4 So we could easily cycle the suspension while measuring bumpsteer, we installed the front strut without a spring.  5 Here's the Maximum Motorsports...  5 Here's the Maximum Motorsports front bumpsteer kit, which replaces the OEM tie-rod end with a tapered stud, a Teflon-lined spherical bearing, and a series of spacers.  6 Before removing the OEM...  6 Before removing the OEM tie-rod ends and installing the Maximum Motorsports bumpsteer kit, we slipped the adjustable tie-rod spherical bearing over the OEM tie-rod shaft, and backed off the jam nut until it was even with the end of the adjustable tie rod. That way we didn't lose our toe setting after installing the Maximum Motorsports tie-rod end.  7 Then we threaded the MM...  7 Then we threaded the MM piece onto the inner tie rod until it contacted the jam nut, installed the supplied tapered stud into the spindle, chose a series of spacers as a starting point, and torqued the tapered stud's nut to 65 lb-ft.  8 To measure bumpsteer, we...  8 To measure bumpsteer, we used Maximum Motorsports' bumpsteer gauge. It makes a complex task straightforward. We began by attaching the reference plate to the front hub with three open lug nuts.  9 The Maximum Motorsports...  9 The Maximum Motorsports bumpsteer kit includes spacers of varying thickness that you mix and match to change the height of the outer tie rod pivot. Rather than use the nylon insert lock nut during measurement, we used a standard jam nut to make changing the spacer stack faster.  10 We jacked up the control...  10 We jacked up the control arm until the hub was at our desired ride height.  11 With our desired spacer...  11 With our desired spacer stack installed, we set the gauge plate in place, secured it with a weight, and leaned it against the reference plate.  12 We adjusted the position...  12 We adjusted the position of the gauge plate until the top edge was parallel to the reference plate.  13 A level on the reference...  13 A level on the reference plate helped us keep it flat during bumpsteer measurement.  14 With the reference plate...  14 With the reference plate level and the suspension at ride height, we adjusted the dial indicator and pointer positions on the gauge plate until they pointed to the zero mark on the reference plate, and zeroed the dial indicator.  We then slowly jacked up the...  We then slowly jacked up the control arm to 2 inches of bump travel, ensured that the reference plate was still level, and recorded the measurement on the dial indicator. The dial indicator measures the amount of toe in or toe out relative to the pointer, in thousandths of an inch. We recorded additional measurements in 1/2-inch increments until 2 1/2 inches of droop. 15 The goal is to find the spacer stack with the least amount of toe change through the suspension's movement, paying particular attention to the first inch of bump travel. Finding the right combination is an iterative process, but using MM's excellent instructions, we homed in on the right spacer stack pretty quickly. We plotted the final bumpsteer curves for each side, using a spreadsheet to verify our findings. Maximum Motorsports recommends you keep bumpsteer to within 0.020 per inch of suspension travel, which we've indicated on the chart with red lines. For reference, we plotted the front rightside bumpsteer curve with the OEM tie-rod end. It's surprisingly close to the best we could muster. We concluded that on this particular car (and perhaps most '96-'04 Mustangs) a front bumpsteer kit wasn't required when modestly lowering the suspension!  16 Once we settled on a spacer...  16 Once we settled on a spacer stack, we removed the jam nut and torqued the nylon insert lock nut to 65 lb-ft.  17 With the front finished,...  17 With the front finished, we moved to the rear. First, we put a mark on the spindle and recorded a reference measurement between the mark and the edge of the inner tie-rod mounting tab on the rear subframe.  18 Then, we removed the outer...  18 Then, we removed the outer tie-rod end's cotter pin and nut. Using a tie-rod separator that we borrowed from a local auto parts store, we removed the tie-rod end's tapered stud from the spindle. To avoid damaging the suspension, we struck along the axis of the tie-rod end. This method damages the tie-rod dust boot, but it's the most effective method we've tried. Besides, we won't be re-using the tie-rod end anyway.  19 We removed the inner tie-rod...  19 We removed the inner tie-rod end from the IRS subframe.  20 The Maximum Motorsports...  20 The Maximum Motorsports tie-rod (bottom) is considerably stiffer than the OEM tie-rod (top). For a greater range of adjustment, Maximum Motorsports includes a series of spacers for the outer and inner tie rods.  21 We found that installing...  21 We found that installing two aluminum spacers along with the OEM steel spacer above the inner tie-rod end got us in the right range of the optimal bumpsteer curve.  22 We installed the tapered...  22 We installed the tapered stud into the spindle. So we could torque the stud to 65 lb-ft, we used the two supplied jam nuts to keep the stud from rotating. Then we unbolted the shock so we could easily cycle the suspension.  23 We chose a spacer stack...  23 We chose a spacer stack combination as a starting point, and installed a standard jam nut to save time when making changes.  24 Before installing the...  24 Before installing the reference plate on the rear hub, we slipped a couple washers over the studs to get clearance between the brake caliper and the back of the reference plate.  25 After setting up the gauge...  25 After setting up the gauge in the same manner as the front, we jacked up the control arm to 2 inches of bump travel, and recorded our measurements at 1/2-inch increments until we reached 2 1/2 inches of droop travel.  26 After experimenting with...  26 After experimenting with different spacer stacks to find the optimal combination, we removed the bumpsteer gauge and torqued the nylon insert lock nut to 65 ft-lb. 27 Here's a plot of our four bumpsteer curves. Maximum Motorsports recommends you keep bumpsteer to within 0.020-inch per inch of suspension travel, which we've indicated on the chart with red lines. According to Maximum Motorsports' Jack Hidley, "While minimizing overall bumpsteer is important, it's also important to get the curves from each side to match as closely as possible. That way the car doesn't change direction when the chassis pitches."
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