Alignment questions

[HoosierDaddy]

I'm going to get an alignment after installing BMR CB005 and Steeda alignment sleeves.

Below is the alignment specs before doing that. I can't feel any difference in alignment but likely something is changed now due to the more random way the cradle was installed by Ford. Am I wrong in thinking nothing else but toe would be changed when aligning the cradle?

Am planning to use BMR's recommended specs which really aren't much different than I had from the factory other than my factory settings having more rear camber than BMR (or Ford) recommends.

I welcome any comments on my base settings or BMR's

I've seen lots of alignment sheets from other member posts but none were from whatever software was used to print mine. If that means a particular alignment system that someone is familiar with any pros or cons?

All the specs I've seen show toe in degrees, my specs show toe in inches. Is there a standard conversion from inches to degrees or is it car dependent? And what is SAI?

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[Norm Peterson]

SAI is Steering Axis Inclination - a line drawn through the ball joint pivot at the bottom and the strut shaft where it attaches to the strut mount. When you steer the car, the front wheels turn about this inclined axis, not about a vertical axis like you might first think.

Toe in inches is the linear difference between toe measurements at the front and at the back of the tire. For a 27" diameter tire, the trig for 1/16" is arcsin(0.0625/27), which works out to about 0.13°.


Norm

 

[HoosierDaddy]

SAI is Steering Axis Inclination - a line drawn through the ball joint pivot at the bottom and the strut shaft where it attaches to the strut mount. When you steer the car, the front wheels turn about this inclined axis, not about a vertical axis like you might first think.

Toe in inches is the linear difference between toe measurements at the front and at the back of the tire. For a 27" diameter tire, the trig for 1/16" is arcsin(0.0625/27), which works out to about 0.13°.

Thanks.

Since Ford, BMR, etc. use degrees, I'm thinking they are using some not so common system. And using inches seems like an invitation to problems. For instance, the green/red/black colors are based on a specific model car (see bottom of sheet). That means it could be wrong (regarding color) if an owner changed wheels/tires whereas the optimum degrees would stay the same regardless of wheel/tire. which is likely why Ford, BMR, etc specify degrees and not inches. I doubt the shop actually measured my tires or recalculated the optimum inches if they were different than stock.

In my experience being different than the norm (no pun intended) is more likely to be a red flag than comforting. Makes me nervous they display in inches.

I did a search on Visualiner Pro32 (upper left of sheet) and it seems to be for a Snap-on John-Bean system. Anyone here familiar with those? Pros and cons?

I want to use this shop because they did my alignments before/after track days 20 years ago and were great. Same owner, same manager (I'm taking his word - don't remember). I'm guessing the equipment has changed over the years.

 

[Norm Peterson]

FWIW, here in the USA, toe always used to be measured in fractional-inches. Going to angular measure for toe is relatively recent.

While it's true that changing tire diameter would change a toe angle based on matching a fractional inch spec, there usually isn't enough diameter change involved to make much difference. 1/16" (0.133° to 3 digits) for a 27" diameter tire becomes 0.138° for a 25.9" tall tire, basically a meaningless change.


Norm

 

[Norm Peterson]

As to the colors, green has always meant "within spec" and red was "out of spec". All that was needed for the fractional inch system to work on later year cars is for somebody to set up a little conversion based on the stock tire size.

Or look through the mfr's shop manual because sometimes manuals have provided both inch and angle specs. The shop manual for the WRX in my sig provides three sets of toe specs - fractional-inch, degrees, and mm.


Norm

 

[NightmareMoon]

As Norm says, inches isn’t an uncommon unit of measurement. Its an old report format, the machine is measuring the same thing, the same way.

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