Wheel alignment Specs Question

Pulled this up at random: http://workshop-manuals.com/mazda/mp...ons/alignment/ Align specs for a 2002 Mazda MPV.

This vehicle calls for only 2deg of positive Caster, and ZERO degrees SAI(kingpin).

Question: When very conservative or no angle is built in to the alignment, what other methods can be used to keep the vehicle straight, and to self-center the steering wheel from a turn?

wrote:
> Pulled this up at random:
> http://workshop-manuals.com/mazda/mp...ons/alignment/
> Align specs for a 2002 Mazda MPV.
>
> This vehicle calls for only 2deg of positive Caster, and ZERO degrees
> SAI(kingpin).
>
> Question: When very conservative or no angle is built in to the
> alignment, what other methods can be used to keep the vehicle
> straight, and to self-center the steering wheel from a turn?

Depends on the system, some use a self centering steering rack or have
valving in the steering box to assist.
On FWD vehicles the engine torque to the wheels also helps as the
differential tries to even the tractive effort.
Doesn't take much caster when any of the above are used.

--
Steve W.

Steve W. wrote: "4:35 AMSteve W.
- show quoted text -
Depends on the system, some use a self centering steering rack or have
valving in the steering box to assist.
On FWD vehicles the engine torque to the wheels also helps as the
differential tries to even the tractive effort.
Doesn't take much caster when any of the above are used.

--
Steve W. "


I see. Electro-mechanical means of straightening her out.

Personally I'd rather rely on good old gravity and geometry to straighten the steering out of turns. Ton of caster or king-pin, plus just enough power assist for parallel parking. Keep simple - fewer systems to break down.

On Wed, 12 Nov 2014 16:06:03 -0800 (PST),
wrote:

>Pulled this up at random: http://workshop-manuals.com/mazda/mp...ons/alignment/ Align specs for a 2002 Mazda MPV.
>
> This vehicle calls for only 2deg of positive Caster, and ZERO degrees SAI(kingpin).
>
>Question: When very conservative or no angle is built in to the alignment, what other methods can be used to keep the vehicle straight, and to self-center the steering wheel from a turn?

Are you saying you can't adjust it to have some SAI? If it's
adjustable just dial a little bit in. It's your car.

On Friday, November 14, 2014 at 3:59:19 AM UTC+8, wrote:
>
>
> I see. Electro-mechanical means of straightening her out.
>
I thought you needed small scrub radius with electric power steering
as less power is available than hydraulic. Of course you could use
electohydraulic servo valve, but that would get expensive.

Ashton Crusher wrote: "Are you saying you can't adjust it to
have some SAI? If it's adjustable just dial a little bit in. It's
your car. "


Perhaps I didn't phrase my question clearly enough. I was
asking that, if Mazda speced 0deg SAI(kingpin angle), and
only +2deg caster for that particular model, what else might
they be using to assist steering return and straight-ahead
stability on it?

On Mon, 16 Feb 2015 10:13:53 -0800 (PST),
wrote:

>Ashton Crusher wrote: "Are you saying you can't adjust it to
>have some SAI? If it's adjustable just dial a little bit in. It's
>your car. "
>
>
>Perhaps I didn't phrase my question clearly enough. I was
>asking that, if Mazda speced 0deg SAI(kingpin angle), and
>only +2deg caster for that particular model, what else might
>they be using to assist steering return and straight-ahead
>stability on it?

Camber, caster, and kingpin inclination are the three factors.
However, although toe has nothing to do with wheel return, it can make
the car walk around when trying to go straight. Some cars - and
drivers - are sensitive to even smallish changes in toe. If you are
constantly correcting in both directions it might be toe. I missed the
beginning of this thread, though, so I have no idea what your main
concern was.

On Mon, 16 Feb 2015 11:10:31 -0800, Bill Vanek >
wrote:

>On Mon, 16 Feb 2015 10:13:53 -0800 (PST),
>wrote:
>
>>Ashton Crusher wrote: "Are you saying you can't adjust it to
>>have some SAI? If it's adjustable just dial a little bit in. It's
>>your car. "
>>
>>
>>Perhaps I didn't phrase my question clearly enough. I was
>>asking that, if Mazda speced 0deg SAI(kingpin angle), and
>>only +2deg caster for that particular model, what else might
>>they be using to assist steering return and straight-ahead
>>stability on it?
>
>Camber, caster, and kingpin inclination are the three factors.
>However, although toe has nothing to do with wheel return, it can make
>the car walk around when trying to go straight. Some cars - and
>drivers - are sensitive to even smallish changes in toe. If you are
>constantly correcting in both directions it might be toe. I missed the
>beginning of this thread, though, so I have no idea what your main
>concern was.

now that everything is computer controlled there is no reason they
can't be reading sensors for steering rack position, wheel angle,
whether the wheel angle is changing or being held constant, the angle
of the car centerline, etc,etc and using any or all of them to control
what the steering box is doing. A lateral accelerometer can sense if
the car is moving sideways and that signal could be compared to
whether the driver has turned the steering wheel to cause it. If the
steering wheel was not turned the system could make the steering box
counter steer to stop the lateral movement of the car. Once this
stuff gets computerized and senorized there's just a ton of stuff it's
possible to do.

Ashton Crusher wrote: "now that everything is computer controlled there is no reason they
can't be reading sensors for steering rack position, wheel angle,
whether the wheel angle is changing or being held constant, the angle
of the car centerline, etc,etc and using any or all of them to control "

Which leads me back to my original premise: Why can't all this be
done simply with more aggressive doses of the directional
alignment cues: SAI, Caster, Camber. Save the computer stuff
for ESC(electronic stability control), but keep good old fashion
physics in charge.

And someone here mentioned the relationship between scrub radius
and electric power steering, perhaps that's why my first experience with
electric(2005 Chev Malibu) was less than satisfying. Icrave road feel,
being able to sense the differences in road surface composition, and
being able to feel weight build up when I'm turning the steering away
from center.

So again, in the Mazda MPV example, is it possible that electro-
mechanical means are beiing used, in conjunction with conservative
doses of caster, etc, to center the steering from turns?

On Tue, 17 Feb 2015 06:05:26 -0800 (PST),
wrote:

>Ashton Crusher wrote: "now that everything is computer controlled there is no reason they
>can't be reading sensors for steering rack position, wheel angle,
>whether the wheel angle is changing or being held constant, the angle
>of the car centerline, etc,etc and using any or all of them to control "
>
>Which leads me back to my original premise: Why can't all this be
>done simply with more aggressive doses of the directional
>alignment cues: SAI, Caster, Camber. Save the computer stuff
>for ESC(electronic stability control), but keep good old fashion
>physics in charge.
>
>And someone here mentioned the relationship between scrub radius
>and electric power steering, perhaps that's why my first experience with
>electric(2005 Chev Malibu) was less than satisfying. Icrave road feel,
>being able to sense the differences in road surface composition, and
>being able to feel weight build up when I'm turning the steering away
>from center.
>
>So again, in the Mazda MPV example, is it possible that electro-
>mechanical means are beiing used, in conjunction with conservative
>doses of caster, etc, to center the steering from turns?


To your most recent question my guess is that the more aggressive
doses of directional stability result in greater rolling resistance
and consequently lower gas mileage. Years ago I would have thought
the notion that they would deign a car with "tricks" to gain some
trivially small amount of reduced "drag" to be just absurd... why
would you worry about the added expense and complexity of "active
radiator shutters" to gain 0.0x more mpg. Yet they are looking at all
those tiny things hoping to coax another 1% greater fuel economy from
the NEW car. So my guess is letting the steering system ACTIVELY work
at keeping the car stable creates less drag then making the car
inherently stable. That's not to say that the car is unstable if the
system "goes out" but they think its worth doing the "hard way", i.e
actively/electronically to get the extra mpg then doing it the easy
(old) way where the car is just naturally stable.

As an anecdote from a friend of mine who was working on sound
issues... he was talking with someone at GM and they said they monitor
the wind noise generated by the air over the top of the cab and they
can tell when the dies that stamp out the cab tops are worn out
because of the increase in noise from the no longer perfectly
correct/most aerodynamic shape that they are supposed to be stamped
to.