Calculating caster is really quite simple. Look here:
<http://www.hunter.com/pub/undercar/2573T/steer.htm>.
Now, after you recover from the coma, just remember this: you can't
measure caster directly! Caster is the angle of the imaginary line that
defines the steering axis.
To arrive at caster, you have to deduce it from other observations. You
do not measure caster directly at 20* steering angle, but that's part of
the process. You deduce caster by measuring camber at two known
locations in the steering travel, then making some simple calculations.
Measure camber at one wheel with the wheel turned first 20* from center
one direction, then 20* past center the other direction (40* total
deviation). You can then mathematically deduce caster. All you do is to
add or subtract the camber measurements and multiply by a constant to
arrive at caster angle. You can use other than 20* of steering input,
but you have to use a different constant (as noted in the Smartcamber
manual). Someone else can prove the trigonometry of how these
measurements arrive at caster - I'll pass.
Now, have you read the Smartcamber manual (waiting... drumming fingers
on desk)? ;-)
Here's an html version someone posted:
<http://www.vfaq.com/BADSM/Tools/SmartCamber/SmartCamber.html>.
That will give you the exact procedure for checking camber at the two
20* measurement points and how to deduce caster from that measurement.
*Basically, you multiply the absolute difference in camber angle
observed at the two 20* measurement points by 1.5 to arrive at caster.*
The real trick is getting the 20* just right and being able to repeat
it, then having the fortitude to make an adjustment and measure again...
until you get it right... very time consuming. I went through this
procedure once, noted the location of the camber/caster plates and never
checked caster again since.
One thing that can help is to use two floor tiles with grease between
them under the wheels. This makes the wheels turn easily with no binding
of the suspension. You can also measure 20* more easily from the edge of
the top tile (it will turn with the wheel) than eyeballing the tire or
wheel against a mark on the floor. The steering angle does make a fairly
significant difference in measured camber, so try to be as precise as
possible.
I've found that using the Smartcamber products (no affiliation, yadda,
yadda), some string, duct tape, a protractor, and a carpenter's level, I
can get alignments as good or better than most professional jobs on
mega-buck equipment. The difference is the time you have to invest in
it. After the first time though, you have a pretty good baseline and
making small adjustments is much less time consuming.
--
Ron Katona
'95 M3 BSP #06 - with $15.35 in BMW *SP LEGAL* (eyes rolling) parts on
order to make whole again (can't wait for the labor bill)
----- Original Message -----
From: "Charles Brown" <brow@bright.net>
> OK I got some digital (angle) alignment equipment, and the camber
seems self
> explanatory, but the caster is supposed to be measured at 20* . Does
this
> 20* give you the same *standard* alignment numbers or is the caster
measured
> in "standard specs" as (total) or 90* same as (kingpin inclination)???
>
> Any insight appriciated
> Race this weekend, and if caster is measured at 20*, there is a long
way to
> go and the alligment shop used some *very* creative writing to express
the
> (after) allignemnt.
>
> Thanks
> CB&EMod-Miata
/// autox@autox.team.net mailing list
///
/// To unsubscribe send a plain text message to majordomo@autox.team.net
/// with nothing in it but
///
/// unsubscribe autox
///
|