SAI vs CASTER?
ChrisCoaster
in my Subject.
One centers the wheels and returns from turns via the vehicle's
weight, and the other uses trail created by tilting the steering axis
back to achieve the same effect.
My current car and my last traded - somewhat - more caster for less
SAI.
Specifically, my 2005 Chevy Malibu had 2.5 ~ 3.5 deg. pos Caster and
12.5 ~ 13.5 deg. SAI.
My current, 2008 Kia Optima has 3.5 ~ 4.5(!) deg. pos Caster and only
11.5 ~
12.5 deg SAI.
Both cars acc to spec.
I do like driving the Optima better(conventional power steering) even
though more of it's weight is on the front wheels than was on the
Malibu's. Better steering feel and fewer annoying corrections. The
only thing I didn't have in the Malibu that I have with the Optima is
noticeable bump-steer(probably due to the greater Caster angle).
My question is: Which alignment spec is more critical to keeping the
car straight? I notice that most passenger sedans have between 2 ~ 4
degrees of caster but 12 ~ 14 deg of SAI. I also know that too much
positive caster becomes very "negative" in reverse, making backing up
tricky.
Would I be correct, in designing a chassis, to go even more
aggressive
on SAI(15, 16 deg) and less aggressive on Caster(2, 3 deg max)?
I like that "riding on rails" feeling and I don't believe one should
have to spend much more than $20,000 for a new car to get it. It's
all design and marketing, so theoretically couldn't ANY car possess
tight steering manners over 20-30mph and just have stronger power
steering assist kick in at lower(Parking) speeds? I also realize
that
something called "dampening" in the p.s. system has a role in all this
along with stiffer
poly bushings, but I like to look at alignment specs first - on a
design level.
thanks for your thoughts,
-ChrisCoaster
"Bizarro" @ Six Flags New England
ALWAYS Superman:Ride Of Steel 4 Me!