On 25/6/19 4:31 am, Arlen G. Holder wrote:
> On Mon, 24 Jun 2019 15:44:03 +1000, Xeno wrote:
>
>> Sorry about the delay in this response; I have been giving the issue
>> lots of thought. Far more thought than I have ever previously been
>> required to put into it. I understand the specific phenomenon, up to a
>> point. A lot of the heavy maths involved are beyond my pay grade. ;-)
>
> Hi Xeno,
>
> 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.
>
> As you and Clare are well aware, it's a LOT more than just trig!
> o Suspension geometry inter-relationships are engineeringly complex!
It is when you get into elastokinematics without which many suspension
designs wouldn't work. It isn't just for *insulation* that rubber bushes
are used. Some designs wouldn't work without that bit of give that the
bushings provide.
>
>> Yes, start with caster setting reductions as they are the safest to dick
>> with.
>
> Thanks for confirming that the first step (whether or not I choose to go by
> airing up the tires), is to lower positive caster to the lowest angle
> within spec.
As I mentioned in a previous post, airing up the tyres will put more
pressure on the *centre* of the tread and reduce the tyre's ability to
conform to the road surface under lateral deflection.
Camber and the reduction thereof, on the other hand, has to reduce the
effect given that it is *one* of the causes, albeit not a major one.
>
>> Also, tolerances can be leveraged as well. For instance, if you
>> have a caster range of 1-3 degrees positive with a half degree
>> tolerance, you could arguably drop the caster to half a degree positive.
>
> I agree with the tactic of using the tolerances, inevitable in any
> suspension geometry result, which is why the spec is always a range.
>
> The good news is that it's possible to measure with sufficient accuracy, I
> believe, at home, using the home measuring equipment we've already stated,
> all of which, as always with tools, end up being free:
Are you using *free* meaning the tools pay for themselves in the long,
or short, term.
> 1. Camber bubble gauge & wheel clamp jig
> 2. Toe plates (usually an extension to the camber wheel clamp jig)
> 3. Tape measure and trigonometric calculator
>
> In addition, we've discussed these "niceties" in terms of free tools
> 4. Steering wheel lock (which can be rednecked)
> 5. Turn plates (which can be rednecked)
>
> Since the home alignment tools are free, the problem is simply that the
> math involved makes most people's head explode; which is why I very much
> appreciate your astute step-by-step advice.
>
>> You will have reduced steering return but SAI and pneumatic trail should
>> still work for you as designed. Steering will be lighter, that is one
>> benefit, but may be a little less stable at higher road speeds. It's a
>> case of trying it out and seeing the effect on the highway.
>
> I agree with all your statements that I need to realize alignment spec
> ranges are a mix of compromises, where, luckily, I drive like a little old
> lady on the highway, so "at speed" isn't more than about 75mph or 80mph at
> most, even on Highway 5 which has a 70mph speed limit, as I recall.
>
>>> Here's a shot from today with the vehicle parked at one of the curves.
>>> o Passenger tire at (static) steering-wheel lock, heading uphill:
>>> <https://i.postimg.cc/T1HkcsX5/mount31.jpg>
>>
>> That's quite a bit of positive camber there.
>
> I thank you for cluing me in to LOOK for the high positive camber at
> steering wheel lock, which is, in reality, the REASON for the contact patch
> unidirectional feathering on ONLY the outside edge of the INSIDE tire!
> <https://i.postimg.cc/hGvsXBjK/mount34.jpg>
>
> Given that front tire is clearly worn ONLY on the outside edge, that
> positive caster of the inside front tire at steering wheel lock says it
> (almost) all, does it not?
Pretty much.
>
>>> o Driver side tire at that same wheel lock situation:
>>> <https://i.postimg.cc/KYXHVC3n/mount32.jpg>
>>
>> Man, does that ever look quite negatively cambered. I'd have expected it
>> to be closer to vertical. It could of course be camera angles. Have you
>> tried dropping a plumb bob next to the tyre to get an idea of what the
>> camber angle actually is on both wheels?
>
> Thanks for pointing out that this outside tire, at static steering wheel
> lock, shows what appears to be negative camber, but where the tire, which
> has a few thousand miles on it, is STILL worn more on the outside edge,
> with the unidirectional feathering easily felt when running my hand over
> the tire in both directions.
Don't forget, you turn left *and* right. For 50% of the time each wheel
has an inside running to a high camber turn.
>
> My main plan for measurement is to obtain the camber gauge and wheel jig
> first, and then I can check all sorts of things for a DIY alignment
> o Camber at tires pointed straight ahead
> o Camber with tires at plus and minus 15 degrees (to calculate caster)
> o Camber at full steering wheel lock (to assess effects of camber scrub)
> etc.
You really are keen on this, aren't you?
>
>>> It's not easy to tell, but that inner tire (which is the one wearing the
>>> most in these slow speed lock-to-lock turns) should be taking on a more
>>> positive camber, while the outer tire should be taking on a more negative
>>> camber.
>> Yes but, due to the direction of forces at the contact patch, the one
>> with positive camber is getting the same force direction as the outer
>> negatively cambered tyre.
>
> Aurrgh. This suspension stuff is so confusing it makes my head explode! 
You were warned! ;-)
>
> I "thought" that the outside front tire in a slow speed tight turn downhill
> carries most of the weight, but, that outside tire has a flatter contact
> patch due to the effect of decreasing positive camber, so it's the inside
> front tire that wears most because, while it's not carrying most of the
> weight in the steep tight turn, it's far more tilted onto it's outside
> edge, such that the weight it does carry is disproportionate carried by a
> small portion of the outside tread of that inside tire.
Yes, you have the hang of it.
>
>> That's an important point which your link
>> makes clear and, I must say, is the only place I have ever seen that *in
>> print*. I had already deduced that much from observation but it is nice
>> to see that others see it too.
>
> Hmmmm... I'm confused so can you clarify which link you're referring to?
>
> Since it's an important point that both of us know better than almost
> anyone on this thread, which is that what we're seeking to explain is not
> "in print" on the net in very many places, if any - is _this_ the link?
> <https://i.postimg.cc/YqHVb5gY/mount33.jpg>
That's the very one. I did *attempt* to explain it in my other post. I
hope I was successful in that little endeavour.
>
> If so, that came from this link, for reference purposes:
> <https://www.quora.com/When-turning-I-see-there-is-a-plus-camber-in-a-vehicle-Why>
>
> Which, I quote here for reference:
> "The combination of these various angles affects the wheel camber when
> steered. The inner wheel in a turn takes on positive camber because the
> steering pivot is angled. By the same token, the outer wheel takes on more
> negative camber.
>
> But actually both of these things are desirable. The purpose of negative
> camber is to increase grip in a turn. As a car turns, the tyre has to
> resist the force which is causing the car to turn. The outer wheel does
> most of the work, but without negative camber, the tyre would tend to roll
> away under the wheel and reduce contact with the road. The camber
> counteracts this effect so that the tendency of the tyre to roll under
> actually increases the contact, and hence grip, just when it¢s needed. But
> think about the inner wheel in the same turn. While it carries less of the
> turning force, what appears to be positive camber is actually negative
> camber with respect to the turning force. So that tyre is also gripping
> harder than it would do without camber.
>
> *So it only looks like positive camber - in fact it¢s really negative*
> *camber, because it¢s the inner edge of the wheel that is leading in a*
> *turn*"
>
> Aurrgh. This constantly changing camber stuff is making my head explode!
It takes time, and patience, lots and lots of patience.
>
> For example, I've re-read this sentence a hundred times, and I still can't
> make any sense out of the camber mechanism ... can you?
Yes, I can, but I have been working at it - a lot!
> "But think about the inner wheel in the same turn. While it carries less
> of the turning force, what appears to be positive camber is actually
> negative camber with respect ot the turning force"
> <https://www.quora.com/When-turning-I-see-there-is-a-plus-camber-in-a-vehicle-Why>
>
> What does _that_ mean?
When you look at a vehicle, you only see camber as it is with respect to
the vehicle centreline, not with respect to the forces acting on it.
Positive camber is the wheel leaning out at the top, *away from* the
vehicle centreline. That locks you into a specific way of thinking.
I was fortunate that I have worked on all sorts of equipment in my time.
There have been times where I have had to think *differently*. Like when
I was working on these;
https://encrypted-tbn0.gstatic.com/i...GhEgjwO8f0jPWg
Not a lot different to your car really, isn't it? Note that camber gain
on that inside turning wheel.
But graders have more force vectors to worry about than just cornering
forces. The blade hanging underneath creates a whole different set of
force vectors and the *steering* needs to be able to cope with that. To
that end, grader steering has a few tricks up its sleeve. The one that
concerns us however is this;
https://cdn.forconstructionpros.com/...e2c6fd4f. jpg
In the case above, we now do not have camber angles referencing the
grader centreline. Instead we have the camber angles referencing the
*load*. In this case the load is the *reaction force* from the grader
blade trying to push the grader to our right *as we view it*. That
reaction force is being resisted by the forces at the contact patch of
those wheels which is in the opposite direction - to our left. The
wheels now are presenting themselves as *negative camber* to the ground
force. The extreme angle allows the tyres to bite in to the ground and
increase the grip.
This is precisely what your front tyres are doing, though much less
exaggerated, not the result of a hydraulic system and the force is
inertial because of cornering. The fundamentals are there however.
>
> How can positive camber be negative camber at the same time?
> (I realize force vector diagrams are involved - but it's hard to fathom.)
I hope my *grader* makes it more clear. Forget the vehicle centreline
and focus on tyre angles with respect to the lateral forces and you'll
see it all.
>
>> By making the tyre stiffer with increased pressure, you may be reducing
>> tread squirm. A little bit of *tyre* flex to help the tread blocks
>> maintain contact as they pass through the contact patch would, I
>> suspect, be a good thing. I wouldn't make overpressuring the tyres the
>> first stage.
>
> Interesting ... ok, so reducing positive caster to the low end of spec can
> be the first step. Thanks for that advice.
It is the way I would go.
>
>>
>>> 2. Second, potentially decrease positive caster (to the low end of spec)
>>> (where the goal is to change how SAI affects the camber angle under turns)
>>
>> Note my point re tolerances.
>
> Yup. It can actually be below spec, if I could measure to better than
> tolerance, given the spec includes worst case tolerance already.
>
> Thanks for that observation.
>
>>> 3. Third, possibly (increase?) static negative camber (within spec)
>>> (although increasing negative static camber "may" also decrease the SAI)
>>
>> Increasing negative camber will *increase* SAI. Remember, camber and SAI
>> (inclination) are locked together because of design and the proof is in
>> the *included angle*. Let's establish a few reference points here; Study
>> the following diagram;
>> https://encrypted-tbn0.gstatic.com/i...sn-_-So5HKf2GM
>> The salient point; SAI + Camber = Included Angle.
>
> That's a nice diagram that shows the relationship between
> o Steering axis inclination
> o Camber
> Resulting in
> o Included angle
Yes, we are all visual thinkers.
>
>> Note that the included angle is designed into the steering knuckle and
>> cannot be changed. That means the relationship between the camber angle
>> and the steering axis *inclination* is fixed.
>>
>> Now observe this one;
>> https://slideplayer.com/slide/463401...suspension.jpg
>
> It looks the same to me.
> o Steering axis inclination
> o Camber
> Resulting in
> o Included angle
Fundamentally it is but the difference is that SAI change is a lot more
difficult because the two pivot points are far apart.
>
>> It's the same thing with an SLA suspension. This one is more relevant to
>> us. A little aside here. If I want to change the camber to the negative,
>> I would have to move the upper ball joint inwards. That is usually done
>> with shims at the upper control arm inner pivot. If the adjustment is at
>> the inner end of the lower control arm, I'd have to move the lower ball
>> joint outwards to get camber more negative. In this case the adjustment
>> likely would be eccentric plates or bolts on the lower control arm inner
>> pivots. Since I cannot alter the *included angle* as it is designed in
>> to the steering knuckle, what do you think is happening to the tilt of
>> that pivot axis (line between ball joint centres) as I move the upper
>> ball joint inwards while the lower ball joint remains where it is? You
>> have to be making the steering axis tilt *away* from the vertical reference
>>
>> Try to imagine you're confronted with a vehicle where the static camber
>> setting is 0 and the included angle is, say, 10 degrees.
>> Given this; SAI + Camber = Included Angle - therefore 0 + 10 = 10. If I
>> now want to change my camber's current 0 degree setting to the negative,
>> say, by 2 degrees, and given my included angle is currently 10, my
>> camber change has to increase the inclination of the steering axis by 2
>> degrees. It will be leaning further inwards at the top ball joint by 2
>> degrees from its original 10. It will now be inclined by 12 degrees with
>> respect to the vertical reference point.
>
> As always, you're way ahead of me, so I'm reading (and re-reading what you
> wrote), where it all makes sense while I read it, but I have to ABSORB it
> to make sure it makes sense intuitively to me (sort of like how I have to
> constantly shift my mind when thinking of gravity as a curvature in
> spacetime as opposed to a simple force).
>
>> We know the prime cause of the camber gain on the inside wheel of a turn
>> is because of the SAI angle.
>
> This is the key point, I think, is it not?
That is indeed key.
>
>> We also know that positive caster merely
>> worsens the effect.
>
> Yup. This need to lessen positive caster is something you've finally worked
> into my brain so that it's now "intuitive", much like how I'm trying to
> work the fact that there are, in reality, something like 10 dimensions to
> the universe, which takes a while before it becomes intuitive.
Universe dimensions, I never grasped that bit of intuition. Have enough
hassles dealing with real world issues, like suspension kinematics.
>
>> So, by moving the camber by any degree to the
>> negative will worsen our SAI status by the same amount.
>
> Ah. This is important!
It is indeed a salient point. The other point, which I made in my other
post, is that body roll will, on SLA suspensions, increase negative
camber on the outer wheel which will also increase the SAI angle. By
going beyond spec with the static negative camber, you could go beyond
optimal negative camber on that outer wheel during hard cornering and
adversely affect the size and/or shape of the contact patch. That could
impact slip angles. Remember, because of weight transfer, the outside
front wheel carries way more than its fair share of vehicle mass. You
really don't want to do anything that will impact that wheel's grip on
the road. A negative camber change could easily alter (reduce) the slip
angle at that front wheel and turn your car into an oversteerer.
>
> It means I don't want any more negative camber than the spec (plus
> tolerance) allows for, most likely (at least for this one purpose).
At this point in time, yes.
>
>> This is the
>> conundrum, one of many, that face the suspension designer. The increased
>> SAI, in and of itself, will increase camber gain - worsening the very
>> problem we are trying to solve. The manufacturer believes, with the
>> current settings they specify, that they have the middle ground covered.
>> The difficulty is that your situation is at the extreme boundary of that
>> middle ground.
>
> Yup. Luckily I don't care much for high speed stability, if they define
> high speed as over about 80mph, which I almost never go.
High speed is *highway speed* which is generally 60mph+
>
> I care about tire wear on the outside edge of the front tires mostly.
>
>> Have a look under the car in question and see what the camber adjustment
>> actually does. If it changes the relative *lateral* location of one ball
>> joint to the other, you are effectively screwed. That means the included
>> angle cannot be changed without some bending or a different steering
>> knuckle with the appropriate included angle.
>
> Each vehicle is different, where my bimmer sedan, for example, only has
> camber adjustments in the rear, and where aftermarket camber plates are
> needed on the front struts, which is going too far, IMHO >
> I'll stick to the low end of spec, within tolerances, as you suggested.
>
>>
>>> 4. Set toe to spec last.
>>> [If I got anything wrong, please let me know as it's confusing!]
>>
>> You are definitely getting there. As I said, it really does one's head
>> in trying to visualise all these steering kinematics.
>
> Yup. Of the half dozen jobs I want to do that most people NEVER do in their
> entire lives, the alignment is singularly different not because it's hard
> to measure at home (it's not), nor because it's hard to adjust (that's
> easy) - but - because the knowledge needed is of an amount that makes most
> people's brains explode.
You got it.
With minimal knowledge of steering and suspension, I can have you doing
wheel alignments in no time. You just need to understand the
fundamentals of SAI, caster, camber, toe, toe out on turns and a few
others and you can do the job. The trick though is diagnosis and that's
where a much greater depth of knowledge is required.
>
> I think the MAIN takeaway is to reduce caster to the low end of spec.
>
>> It gets a bit more messy with MacPherson struts, especially when you
>> move to superstruts. Given the distance between the two pivot points on
>> the steering axis, getting any decent degree of camber and caster change
>> is rendered more difficult. That said, depending on the manufacturer's
>> method of attaching the steering knuckle to the strut, there are ways to
>> adjust camber without *adversely* affecting SAI. For that purpose you
>> use what are known in the trade as camber bolts. These are eccentric
>> bolts that allow about ~1.5 degrees of camber adjustment. You can get
>> camber kits that *extend* the limited factory adjustment as this video
>> shows;
>> https://www.youtube.com/watch?v=Qe9AS99o3o8
>
> Some, but not all, the vehicles I'm seeking to align at home have no front
> camber adjustment anyway, where I've made a conscious decision to stay
> within OEM specs.
Wise. I remember one chap who wanted *more* steering lock so he dicked
with the lock stops (they were external and on the steering arm). It all
went well for him until one day, whilst engaged in a bit of *spirited
driving*, including some opposite locking, his steering box jammed at
the end of its travel. It didn't end well for him. Those lock stops had
a *specification* for a very good reason, a hard lesson he learnt well.
>
>> There may be some SAI effect depending on the system used but, compared
>> to the *limited* options (bending, replacement knuckle) available to you
>> on SLA suspensions, there is hope. Note, I think that camber kit as
>> shown in the video will have some effect on SAI but not as much, in
>> terms of degree change, as it has on the camber itself.
>>
>> Confused now?
>
> Yup.
> I think I have my battle plan though, although no battle plan survives
> intact after contact with the enemy...
Consider it a learning exercise, the outcome of which will influence
your next *strategy*.
>
>> Steering and suspension design is one huge mass of compromises.
> Yup.
>
> One thing is whether we can accurately measure camber "well enough" with a
> cellphone, where I use a $100 level but a cellphone "might" be accurate
> enough by now... do you think?
>
You can but try it. A straight edge against the rim and the phone on
that. You would need to check wheel bearings and ball joints for play as
that will influence your readings.
Ball joints, ah, there is another misunderstood item in the car
industry. But let's not go there.
BTW, you are not alone;
http://www.peachparts.com/shopforum/...tire-wear.html
Apart from him getting neg and pos caster mixed up, there are a few
points made in this brief forum discussion that you might want to take
note of.
Also, not all the pros understand the camber scrub issue.
A perfect example here;
http://www.mcgrathauto.com.au/tyre-wear-2/
They say it's cornering on roundabouts that does damage and only to the
passenger side. *but* the scrubbing can be on *both sides* depending on
the direction you are turning. Roundabouts, because you always travel
the same way, would give you a bias to one side. Camber scrub should
occur on the driver's side if the roundabout is *tight* and a lot here
are.
But, when you think about it, leaving roundabouts aside, a turn to the
passenger side on any *intersection* crossroad will always be *sharper*
than a turn to the drivers side.
In your case, LHD, when you turn right from the RHS side of the road,
you turn *tight* in order to keep on the RHS of the exit road after you
complete your turn. On the other hand, when you turn left, you enter the
intersection from the RHS of the road, you swing *wide* so you exit the
intersection on the RHS of the exit road. Right turn is a *small* arc,
left turn is a *large* arc and, as we know, it's the small arc turns
that do the damage and, in this case, it's the passenger side tyre that
suffers.
For us here in Australia, the reverse is true since we are RHD.
In summary, the inside of your tightest turns will be when you turn to
the passenger side. Since that tyre is the inside runner on the tightest
turns, there is likely to be greater camber scrub on the passenger side.
In your case, you have tight turns *both ways*. Is there a bias in the
wear pattern however?
FWD cars have a greater issue with camber scrub since they generally
have high SAI angles, not to mention a greater forward weight bias. The
general consensus is that the passenger side will wear more on the
outside of the tread than the driver's side. There are a great number of
reasons given for this, including the *camber of the road* but, when you
sit down and think deeply about it, you wonder if camber scrub is
playing a devilish little role here also.
Have I messed with your mind again?? ;-)
--
Xeno
Nothing astonishes Noddy so much as common sense and plain dealing.
(with apologies to Ralph Waldo Emerson)