Miata Mailing List: October 1998, Message #607

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Mike,

Sorry I'm a little slow in responding to this one, but I have a question   
regarding the non measurement of caster....

I know from when I've had my alignment done on a machine that the maximum   
caster acheivable frome one side of the car to the other is vastly   
different. (4.5 deg versus 3.5 deg) I'm not sure if this is because of   
previous crash dammage, worn bushes, or just manufacturing tolerances.

The guys who have aligned my wheels in the past have elected to crank the   
passenger side back to match the maximum acheivable on the drivers   
side...

Is this necessary? How would I go about it?

If I cranked both mine to max, wouldnt that make the car pull to one side   
on a straight, or at least handle differently turning left from turning   
right?

How could others, who want to try your method, but havent had their car   
aligned professionally, know if they were in the same situation?

I've heard there is a way to calculate caster with a camber measuring   
device like the one you describe, but I dont know the details.....Do you   
have any info on that?

Thanks,

Fletch.

>From:        mikem@sr.hp.com
>Subject:         DIY alignment
>Date:         Thu, 1 Oct 1998 15:45:32 +0000
>
>
>It's very easy to do your own 4 wheel miata alignment and you don't need
>lots of expensive tools.  All you need is a bubble level, some string, a
>tape measure, and post-its.
>
>An alignment consists of camber (front & rear), caster (front), and toe
>(front & rear).  This procedure counts on the car being parked in a flat
>location.
>
>Camber is how much each tire differs from being vertical.  You can make   
a
>camber gauge with a bubble level and post-its.  I have stock 14" alloys   
and
>I measure referenced to the rim of the wheel which is 15" in diameter.   
 One
>degree of camber is .261" over 15" (15*sin(1)).  Each .1 degree will be
>another .026 inches.  So if you want 1 degree of negative camber, place   
a
>post-it 15" above the bottom of the level, so that it extends .261"   
toward
>the wheel.  When the level reads vertical, and the bottom of the level &   
the
>post-it touch the wheel you're done.  The center caps of my wheels   
prevent
>the level from contacting the wheel rim.  You can make spacers so your   
level
>sits outside the obstruction - different sized spacers are even better   
than
>using a post-it.
>
>Practicalities: center the steering wheel, and after any adjustment,   
roll
>the car back and forth a bit so there's no tire stress bending the
>suspension, tightening the adjusters sometimes causes changes, so   
re-check.
>
>Caster can't easily be measured, but you want all you can get.  So the   
aft
>set of the front adjusters are set to push the A arm out as far as
>possible - the front adjusters then tweak in the camber.
>
>Toe is set using the method from last month's GRM.  You run a string   
around
>the car 3 inches from the center of each wheel.  You tie the string to   
axle
>stands or antifreeze bottles or...  Then you adjust the rear string   
anchors
>equally so that the string width is the same both in front of and behind   
the
>car.  Then for each wheel, measure how much closer the front of the tire   
is
>to the string versus the rear of the tire.
>
>This is a very easy, quick, and if you're at all careful accurate   
process.
>
>Good luck
>Mike Marzalek
>mikem@sr.hp.com
>'96 red aerodyne
>Sonoma County, Ca.
>