On 25/6/19 8:03 am, Arlen G. Holder wrote:
> On Mon, 24 Jun 2019 18:31:52 -0000 (UTC), Arlen G. Holder wrote:
>
>> I appreciate the time, effort, and care for accuracy, as very few people
>> would understand my common statement that the main reason most people can't
>> do alignments at home isn't that they can't measure or tweak, but that the
>> math would make most people's head explode.
>
> Hi Xeno,
> BTW, one statement I can't yet wrap my head around is this one, which says
> that the high positive camber on the inside tire on turns is actually a
> NEGATIVE camber with respect to the force vectors.
>
> <https://i.postimg.cc/YqHVb5gY/mount33.jpg>
>
>
> What the heck does _that_ mean?
>
I thought that one would stump you. ;-)

The clue is in the wording - *with respect to the force vectors*.

That diagram you linked to above, I'll use that in an attempt to explain
what is meant.

For a start, dismiss the middle wheel, ignore it.

Now imagine the left hand wheel is on the *outside* of the turn. You can
see the effect of the lateral forces acting on the tread. The arrow
indicates the *force vector* direction.

Lets now deal with the other wheel. Imagine it is the wheel on the other
side of the car and the axle is coming out of the left side rather than
the right. It has positive camber with respect to its position on the
car but, naturally, it is leaning the other way. The lateral forces,
however, are acting in the same direction as the outside wheel but the
effect on the inner wheel is different. *To these forces*, the inside
wheel looks to have negative camber because they aren't referencing the
vehicle as being left or right. The forces see two wheels trying to turn
in the same direction but are leaning in opposite directions.

This picture will assist you in imagining the scenario.

http://www.conceptcarz.com/images/Bu...-10-MH-010.jpg


One wheel, the outer, is showing a positive camber to the lateral force.
The inner, on the other hand, is showing a negative camber lean with
respect to the lateral forces. It will look like this;

https://www.gmforum.com/attachments/...ivecamber1.jpg

The above pic shows what the inner wheel likely looks like on the road
in a sharp turn. Just imagine that red arrow is the turning force at the
contact patch. It is not hitting the outer tread edge *first* like the
opposite wheel is. The outer tread is not touching the road so the force
is acting on the outer half, or less, of the tread. That will cause some
distortion of the sidewalls as the mass of the car tries to pull against
the contact patch and flatten the tread somewhat. But, and it is a big
but, modern radials don't have a lot of ability to flatten the tread,
steel belted radials even less so. Overinflated tyres really aren't
going to mitigate that very much.

The pic really does show what you are up against. Have you looked under
your tyres whilst parked on a flat surface? I think you would be
enlightened.


Whilst on the topic, have a look at this book;
https://manualzz.com/doc/31232614/th...ing-principles

I was browsing through my dead tree library here and came across the
following. Go to page 181, section 3.5.3. If you don't get the meaning
of the text, Fig. 3.50 should make it clear. The kinematics of the
double wishbone suspension (the SLA) make it clear that the KPI (same as
SAI) *angle* alters on bump and rebound due to the different radii in
the arc of each arm. That same angle alteration of KPI angle also
affects camber. It is in the text description of the diagram;
Construction determination of the kingpin inclination alteration
angle on double wishbones which is *equal* to the camber alteration.
The highlight is mine but what that diagram is telling you is that as
you go into *bump*, your KPI increases and your camber moves
commensurately to the negative.

The same applies to McPherson Struts as can be seen in Fig 3.51

This backs up what I was saying with regard to the camber angle change
on an SLA suspension following the SAI/KPI change, and vice versa. If
you alter the camber, you have also altered the SAI/KPI. So, by moving
camber to the negative you are increasing the SAI angle, with all the
possibilities, both negative and positive, that entails.

What does this mean to us when cornering? Well, weight transfer will
force the *outer* wheel into bump and give you a more negative camber on
the *outer* wheel. The problem *for you* is that weight transfer works
best *at speed*. At low speed, the outer wheel is probably retaining
some positive camber. Have a look at your outer wheel when your steering
is at the full lock. I'm guessing it may well still be at a positive
camber angle. Not as much as the inner wheel but it too could be
contributing to the edge wear.


Anyway, the first pic on this thread led me to this article which I
think you will find interesting.

https://www.gmforum.com/buick-172/to...cement-305196/

It relates to him switching from a strut with no camber adjustment
provision to one that did have that provision. If you recall, I said
that a strut suspension, depending on where the adjuster is, can have a
camber adjuster that doesn't affect SAI much, if at all.


In summary, if you want to understand the kinematics and
elastokinematics of suspension systems, this book will do it for you;

https://manualzz.com/doc/31232614/th...ing-principles

I linked to it previously. I have dead tree versions of the first
(English) edition 1996 and the second (English) edition 2001.

I'll respond to your other post shortly. Right now I've done my head in
again cogitating over all this stuff. ;-)


--

Xeno


Nothing astonishes Noddy so much as common sense and plain dealing.
(with apologies to Ralph Waldo Emerson)