Lotus Wheel Alignment (Flyin’ Miata)

So… with the ride height and corner weights set and a preliminary set of alignment values I set about switching out the wheels for the Flyin’ Miata hub stands. While the hub stands have some big advantages (as we’ll see in a moment) setting ride height and corner weights on the stands would require some sort of “conversion” to account for the height of the stands and “rolling radius” of the tires (it’s not 1/2 the diameter and depends on tire pressure). Fortunately the combination of a scissors lift and wheel stands makes switching over to the hub stands quick and easy. The image below shows the Toe Bars on the hub stands with Carl’s thrust angle string system installed.

The first order of business is re-calibrating all four Toe Bars from the wheel hubs…

Then setting up to measure toe using tape measures between the hub stands underneath the car, and thrust angle using the strings.

The first round of hub stand Toe and thrust angle measurements agreed reasonably well with the values recorded from the ART laser toe gauge. In fact the measurements from the rear were nearly exactly the same (Toe IN: .062”) while the front showed a larger Toe OUT condition (.25” vs .20”). While I can not explain exactly why this occurred at least it showed the the error in the same direction… just a little more of it.

The image below shows the Flyin’ Miata hub stand system in place on the front right corner of the Lotus Exige.

By moving around the car a few times taking Toe angle measurements from the hub stands… I made sure the measurements repeated nicely. I then decided to bust out a set of wrenches to adjust the front tie rod ends and bring the front wheels into alignment.

Having the thrust angle strings right there in front of you while making adjustments to the tie rods is very nice. The fact that you can reach down and check the tape measurements anytime as well makes this process fast, intuitive, and confidence inspiring. With the car at waist level and wheels of the way the task is almost too easy. A couple of trips from side to side and about 3/4 of a turn with the wrenches brought the front wheels into alignment.

With the rear wheels consistently measuring Toe IN: 1.5mm I decided to leave them alone and moved on to removing the hub stands and putting the wheels back on the car for one last measurement with the ART Laser Toe Angle Gauge.

The results…

• Front: Toe OUT: .5mm (2 minutes)
• Rear: Toe IN: 1.5mm (12 minutes)

Or…

FM Hub Stands… Thrust Angle?

After the long involved posting earlier it seems appropriate to spend a few minutes talking about thrust angle and how it relates to the Flyin’ Miata hub stands. The good folks at Flyin’ Miata used to offer the thrust angle gage pictured below. It was meant to be aligned to the centerline of the vehicle chassis and referenced while measuring toe with the hub stands. They recently discontinued selling it because it was not easy to use accurately. The image on the right shows the FM hub stands “enhanced” to facilitate thrust angle measurements.

 

Fortunately Carl Schulhof's string method for measuring thrust angle is easily adapted to the FM hub stands. The diagram below shows the details of Carl’s system with the equal length spacers supporting the strings at the “outboard” ends of the wheels and the measurement points in between.

The image here shows Carl’s thrust Angle string setup implemented on the Flyin’ Miata hub stands. The steel ruler at the far left hand side takes the place of one “spacer” while the ruler on the right is the measurement point for the front wheel. The rulers are aligned with the measurement points on the toe bars that we calibrated earlier. We set the string the same distance from the measurement point at all four corners and simply read the numbers on the (measurement point) rulers at the right.

As seen here… reading the strings on the rulers works very well.

All of the elements of this system are fastened directly to the hub stands which makes removal of the system no more complicated that unbolting the hub stands and setting everything aside. Furthermore when the system goes back on the car it stays remarkably well calibrated.

FM Toe Bar Calibration

The Flyin’ Miata hub stands facilitate toe measurements using a tape measure underneath the suspension components and body parts. The tape is stretched between the bars on opposite sides of the vehicle. First you have to “calibrate” the bars…

With the hub plate attached to the axle you pivot the bar using the adjusting knobs to make it parallel to the wheels (as shown below) . Flyin’ Miata recommends using a laser pointer held against the face of the wheel hub as a reference.

After quite a few “fits and starts” I’ve developed a calibration routine that works well for me. Instead of reviewing all my failed efforts I’ll just jump ahead the successful one here. The calibration of the FM toe bar required making a set of “spacers” to clamp between the hub plates and hubs to create a large stable base for the laser line level. Purchasing a high quality Bosch line and point laser made a huge difference as well!

Clamping a set of hook rulers to the toe bar measurement points and using the “trailing edge” of the laser line results in the high visibility and repeatable results shown in the images below. Especially important is fact that this “evolved” system allows the user to operate in a nearly “hands free” manner while adjusting the bar.

With the toe bars calibrated it is on to measuring toe!