Miata Mailing List: September 1998, Message #65

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Great post, Doc! Hardly seen such informational posts these days. My DEL
key on the keyboard is definitely more dirty then other keys. :-(

I wish I had recorded the numerical alignment data every time I did an
alignment change, too. IIRC, I have also had about 8 alignment changes
up-to-date (in 3 years time of ownership). The 1st 3 changes were made
within a month's time period, after I put in the springs/shocks/sways mods
and before the car's 1st autoX season began. 

With alignment #1 in Feb '96, I recall I went with -1.2 deg front camber,
-1.0 rear camber, about 3 deg caster, 10 minute front and rear toe-in
(didn't know Miq's spec until quite a bit later). That is on a 1.25"
lowered ride height. The reason for more front camber than rear was that I
got used to the -2 front and 0 rear (live axle) setting of my previous car
-- '85 RWD Toyota Corolla GTS. The result was not satisfactory. The stiff
sways/shocks were able to make the turn-in response almost as great as a
formula car, but the front camber was still not enough to take the quick
weight shift.

So I went with alignment #2 about a week later. That was to increase front
camber to -1.8, rear camber to -1.5, castor was increased a bit, toe
unchanged. You must have thought by now that -1.8 front camber should be
even worse than -1.2. This is where I want to answer John Freas' original
question. There's not a be-all-end-all alignment setup for a miata of any
springs/shocks/sways that will work perfect on all autoX/road
courses. That's because different kinds of corner needs different
alignment setup to work with different springs/shocks/sways setup. For
example, my car with ST springs/sways works well in medium to large G
circles with my current -1.1 front and -1.6 rear camber setup, but not as
good with my old -1.8 front and -1.5 rear setup. However, with the
Illuminas cranked up to full stiff on tight autoX courses, the old -1.8
front camber definitely allows more tossing of the car than the current
-1.1 front.

Alignment #3 was done shortly after to reduce rear camber from -1.5 to
-1.2. To complement the great steering response of the front suspension
setup, "on/off" throttle was sometimes possible exiting tight corners. To
prevent inside rear wheel loses power (I don't have an LSD), rear camber
was reduced. This was done also because I stiffened the rear sway for
better tossibility. The 1st closed club autoX event with a tight course
showed the shocks/sways/alignment settings worked really well. People were
amazed by the way the car could go thru' a set of tight slalom. The
defending regional champ in another miata couldn't do it as clean as I
did. In the 1st regional race shortly after, it clearly showed from the
video that I was able to brake later than most other cars into a u-turn,
managed to get the inside rear wheel off the ground, and was able to
applied full-throttle much earlier than most other cars. That resulted in
a 1-second ahead of the defending champ if I didn't hit the cone which was
not advantageous to me anyway. 
 
Later on in regional races, course design has generally been changing
towards smooth and fast. In the next two or three alignment changes in one
and a half years, there were only minor changes each time to see what
different toe/camber/castor works out. I won the championship the 1st year
in my miata and got a 2nd place in the following year.

Around mid season this year, I was getting more serious on alignment
setting because I was (and still is) facing tough battles using my
no-more-than 130hp normally aspirated 1.6L against a Sebring 1.6L with
suspension mods like the US National champ Guy Ankeny's CSP miata (Penske
shocks, 245 Hoosier tires, etc.) In the 1st battle, I was able to lag
behind not more than .5 second behind Guy Ankeny (helping the owner to
tune-in the car). And I was able to beat the car owner who had been able
to beat CSS (US CSP) times in his then stock 1.6. I knew that once the
owner got use to everything, his times would be greatly improved. 

So I decided to start everything from scratch. I started with stiffest
front sway and middle rear sway settings with the old alignment setup. The
less-oversteer setup (from middle front, middle rear sway settings) is
necessary for the new parking lot (with smooth/fast course setup) we are
using this year. Once the sways settings was changed, I definitely noticed
a change in alignment setting was necessary. Since the less-oversteer
setup doesn't allow as much tossing of the car, front camber has to be
reduced from -1.8. To complement the front camber setting, rear camber had
to be increased from -1.3. Using G-circles for tuning, I found out after 2
to 3 alignment changes that the current -1.1 front and -1.6 rear camber
settings gives the most balanced setup with the current sways settings. 
Toe in setting remains unchanged at less than 5 minute both front and rear
(more on toe setting in a later post).

With this setup, the car is not able to take as much tossing at stiffest
shock settings as before and probably just a bit slower in tight chicanes
and slaloms. But it is easier to drive in fast and smooth-flow courses
with medium or medium stiff shocks settings. Adding to the equation, I
replaced the 185/60/13 Hankook R compound (lighter and more tossable) with
the fat sticky 215/50/13 BFG R1 (heavier and much stickier than Hankook). 
So far both of us have won 2 races and the championship points is very
very close. That means who wins the last race wins the championship. We'll
see on Sept 20th.

So back to John's original question, if you, John, find out your front
tires are scrubbing significantly on the outer-most edge even with great
front camber, it's quite likely as most people say that soft tire sidewall
is the cause. But it could also result from a "tossing" driving style on a
tight course with stiff compress-stroke front shocks settings. You may
probably need to change your driving style a bit or shocks/sways settings
a bit.

So John, regarding tire wear, I found it interesting to notice that my
-1.8 front/-1.3 rear camber settings gives more tire wear on the inner
tread blocks of the rear tires than the front, although both front and
rear tires wear more on the inside than the outside. Note that I'm talking
about my street tires which have never been used on an autoX course. OTOH,
my brother Terence's -1/-1.5 camber settings on his '90 clearly shows the
front street tires wear more on the outside and the rear wear a bit more
on the inside. The interesing thing is that the wear "ratio" between
outer/inner edge on the rear tires seems to be worse with my -1.3 rear
camber than his -1.5!

OTOH, my 1st and 2nd set of Hankook race tires (the 1st set went to my
brother after 1/2 season when I got my 2nd set of sponsored race tires
which went thru' 2 full seasons of about 80 autoX runs and 2 track days)
wore out quite evenly at the rear and just a bit more wear on the inside
of the front ones.

Doc, I have 

On Fri, 28 Aug 1998, Doc Wynne wrote:

> On Thu, 27 Aug 1998 22:28:18 +0000, "John Freas"
> <jfreas@earthlink.net> wrote:
> 
> >While we're on the subject of alignments and tire wear, here's a question
> >for those who know:
> >
> >So, my question is; is the Miata able to accept more aggressive camber
> >than the Miq alignment provides, and at what cost to handling?  Obviously
> >straight line tire wear will suffer, but my intention is to balance out
> >the wear as an average, with cornering taking out what straight line
> >driving misses.  What kind of numbers are we talking wrt camber angles? 
> >Do the folks who actually /race/ the car use this kind of aggressive
> >alignment?  Merv?
> 
> [snip] --------8<-----------
> 
>  It seems that *for most cars* more caster is a "good thing", as
> it adds negative camber to the outside wheel/tire during a
> corner. This helps to negate any camber lost by body roll caused
> by weight transfer. This also has a slight down side as well, in
> that the greater the caster, the greater the corner weight also
> changes (corner weight would not change on a car with zero
> caster). On a relatively softly sprung car with relatively soft
> sway bars, this is fine as the rest of the suspension seems to
> "absorb" the differences and since the suspension is relatively
> soft, the camber lost to body roll is canceled by the additional
> camber.
> 
>  With modified suspension, however, things are a bit different.
> If you changed springs and sways, you now have less body roll and
> somewhat stiffer suspension, so you need less additional camber
> added for good tire adhesion...hence you need less caster. You
> can also do without the greater corner weighting change caused by
> the large caster angle. (As an example, look at an off-road truck
> with it's huge caster settings - more than +10 deg. on some - and
> with the truck stationary, cut the wheel from lock to lock.
> You'll notice the "outside" corner of the truck will actually
> "rise" from the caster.)
> 

Haven't tried that but IIRC, trucks and SUVs at full steering lock usually
give 10+ deg +ve camber for the inside wheel and a few deg +ve camber for
the outside wheel. That's because of their kingpin geometry. Their knuckle
(upright) rotating axis leans too much towards the centreline of the car
(in a direction similar to the -ve camber of the front wheels). This
geometry creates more front +ve camber when turning either way, compared
to the high caster angle (actually kingpin inclination) which creates -ve
camber for the inside wheel and +ve camber for the outside wheel. With the
high kingpin inclination for the miata and most RWD sportscars, the
outside wheel should actually lift and inside wheel lower. That means the
outside corner should drop instead of what you say, Doc, right? 

Just another $0.02... Canadian. :-(

--
Chris Chu and Shirotora
'90 Crystal White
http://infomatch.com/~cchu/
--