On 15/6/19 2:55 am, Arlen G. Holder wrote:
On Fri, 14 Jun 2019 12:58:31 +1000, Xeno wrote:

Use the term Steering Axis Inclination (SAI) as your vehicle likely does
not have kingpins.

Hi Xeno,
I typed up a super detailed response, after viewing every second of those
three videos, where the first and last seem to have the same graphics, and
the middle (whiteboard) one was a bit different - and where that wheelcam
shot of the tire literally bending away from the rim - and the temperature
methods of determining footprint on hard cornering were illuminating.

Yes, I learnt a couple of points from those videos too so it seems you
can teach old dogs new tricks. I have found, in order to gain a better
appreciation of steering geometry and suspension systems, one needs to
look at those places that are extreme. In this case, it's in motor racing.

I hate losing data, but I lost it when the PC rebooted, so suffice to say I
appreciate the videos, from which I learned good stuff, particularly about
that "scrub radius".

I didn't find a lot on the net about "camber scrub", and those videos

You won't. Information on it is scarce since it is an undesired effect.
However, if you look at what the wheel is doing vis a vis camber during
high angle (note - not high speed) cornering, then you can visualise the
issue. Note too that tread blocks have a limited degree of flexibility
and, as such, are likely to exceed that during high angle cornering
resulting in tread scrubbing.

didn't cover specific tire wear on the slow speed (less than 40mph)
constantly lock-to-lock turns we perform on the mountain, where the goal
is how to modify the set up for the vehicle in a compromise to minimize
that 'camber scrub' on FWD and RWD vehicles without adversely affecting
straight-line handling.

The reality is that you are faced with a *compromise* and there are many
such in steering and suspension geometry. Any gain in the tyre wear
scenario will negatively affect high speed. If you happen to see a
Porsche Cayenne in a parking lot with its wheels turned at a high angle,
the camber angle displayed will amaze you. I know it amazed me. Of
course, when you realise that vehicle's suspension is *optimised* for
high speed and high power operation in a very narrow band either side of
straight ahead, it all makes sense.

Yes, that is basically all the small service station had next door to
where I did my apprenticeship. You have missed the primary requisite
however - a guaranteed dead flat and level garage floor. Also a lock to
lock the steering wheel to the desired centre position;
https://i.ebayimg.com/images/g/sJIAA...58p/s-l225.jpg


Everyone says you need a perfectly flat garage floor, which, as far as I
know, mine is pretty flat based on putting a level on it - but I don't
really know how flat is flat enough.

A level will only give you a localised point. You need something that
can verify any point in the garage floor against a common datum point.
These can be used for that purpose and aren't expensive;
https://www.bosch-do-it.com/au/en/di...898-199931.jsp
Or you could hire one for a day just to verify your garage floor. A
professional one of these should have been used when the floor was
poured and leveled anyway.

Given that a millimeter or two of height adjustment in any one corner might
be necessary for most garages, I guess your suggestion above adds two
nice-to-have tools to the home DIY alignment check mix...
o Steering wheel centering lock
o Some kind of way to put the 4 wheels on a wormscrew-adjusted plate

Googling found the first, but the second was in the thousand dollar range.

Are there good redneck solutions for leveling the four tires?

Most wheel aligners that I have used come with ramps that have the added
benefit of raising the vehicle a couple of feet off the floor. Ramps,
even without the aligner heads, provide a relatively easy means of
leveling the required work area. They don't even need to be raised more
than an inch or two. If the floor area is really out of whack, two or
four ramps made of wood of varying thicknesses might suffice. You can
even check the level easily these days with laser levels as I mentioned
above. My brother has one of the professional units since he is a
concreter but cheaper DIY versions, like the one in the link, should
suffice for this purpose.

--

Xeno


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