RE: [ihc] Factory Toe-In Spec, Anyone?

[Steven Stegmann <steve.stegmann@xxxxxxxxxxxxx>]

Tom,

The official reference is to measure it by the angle
in degrees.  This can be calculated fairly easily from
the toe in/out and the tire diameter but I didn't
include it because most people don't have any
reasonable way to measure the angle.  This is what
most alignment machines actually do.

I built a jig to measure the angle of a tire with
respect to the centerline of the vehicle.  I did this
when I was having some rear wheel alignment problems
with a front wheel drive car.  I measured the toe
angle of each of the four tires with respect to the
vehicle centerline and then straightened out the
alignment front and back and then drove it for another
10 years without any problems, except chuckholes.

After this exercise I came to the conclusion that
measuring the angle was overkill, (high PITA factor). 
Measuring the toe at the tire surface was plenty good
enough.  I've done alignments this way and had
Michelin tires last 100,000 miles.  That's good enough
for me.

I actually will set the toe at 0.0 inches +- 1/32 of
an inch on rear wheel drive (Scout counts as rear
wheel drive since it is, 98% of the time).  My method
works just fine to do this.  

On front wheel drive I usually set the toe at 1/16 toe
out +- 1/32.  I figure that as the vehicle is driving
down the road, the front wheels will be pulled a bit
forward and will move toward 0.0 toe while under
power.  

The exact value would be a function of how squishy are
the rubber mountings of the front susupension.  Set it
to 0.0 if they've all been converted to urethane for
instance.

Steve

--- Tom Harais <THarais@domain.elided> wrote:

> Aha Steve!
> 
> Good write up.  But, this brings me back to my last
> point:
> 
> A 1/16th inch difference in track width between the
> front and rear of the
> tire tread will vary the toe setting depending on
> the tire's diameter.  Tire
> diameter can vary between 27" or so and 35" or so,
> depending on size used.
> The 1/16" difference on the tread face of a 35" tire
> is going to yield a
> different actual toe in setting than a 1/16th inch
> difference on a 27"
> diameter tire, even more so when using a 15" wheel
> edge as the reference.
> The difference is probably slight (my Trig
> capabilities are now non-existent
> since I never have to use them), but we're talking
> 1/16th in the first
> place, which is a pretty slight measurement itself.
> 
> Tell me I'm wrong?
> 
> The reference point/diameter effect would be the
> same on camber
> measurements, but not on caster.
> 
> So, what is the correct reference?  You say to use
> the face of the tread,
> but what is the "official" reference? Maybe that's
> why alignment shops use
> minutes of angle instead of a distance measurement?
> 
> Tom