derBayerische May/June 2022 - 28

An E30 M3 driver
lifting BOTH inside wheels
at NCC's October HPDE.
Now THAT'S a stiff suspension.
Photo by FormerInstants.com
Thoughts from an HPDE Suspension Clinic
(What you need to know, whether a novice or an experienced driver.)
By Jack Raymond | Photos by Alan Olson and as credited
A
t NCC's October HPDE event,
I had the pleasure and privilege
of participating in a suspension
clinic with guest stars
Dr. Tommy Ivic of Tier Car Care and
Austin Via of BimmerWorld.
Questions and answers from the
event follow.
Q: My buddies have made a bunch
of suggestions for suspension
mods, but I don't understand any of
it. Should I just go with their flow?
A: Before you make any changes, you
should understand how your car is
behaving, how you want it to behave
differently, and how to achieve that.
Q: Ok. Are there any constraints on
what I'm allowed to change?
A: It depends on whether or not
you're signing up for a Club Race, a
Time Trials, autocross, or any other
kind of competition, in which case
you'll need to know what the rules
are for the car class you want to be
28
in. You also need to consider
whether the car is still going to be
used as a street car or as a pure
track car or something in between:
* Pure street car
* Modified street (usually power
mods)
* A street car that's track-able
* A track car that's still street-able
(and street legal)
* Purpose-built track car
Be honest with yourself - if you say
" it's a track car " and you get a really
stiff suspension, you might not be
happy when you actually continue to
use the vehicle as a daily driver and
family car.
Q: Is there anything I can do to
improve track handling without
modifying the car?
A: Tire pressure, tire size, and
alignment. When you come off the
track, check your hot tire pressures.
Don't exceed 39 psi hot. If they're
over 39 psi, let some air out to get
down to 39 psi. Once the tires are
completely cold, check the pressures
again. That'll be your cold tire
pressure for this car on this track.
Note: some driver's prefer lower
target pressures. Experiment to see
what works best for you.
Also, chalk the edges of your
tires so you can see how much
they're rolling over during a session.
If they roll over onto the sidewall,
then your tire pressures may
be too low. (If your tires " roll over "
no matter how high you run the
pressure, then your alignment
doesn't have enough camber, or
your suspension is too soft.
Keep reading.)
If your car understeers and the
front tires are narrower than the rear
tires, then try " squaring up " the
tires, i.e., use the same size tire in
the front as in the rear. Even though
BMW factory wheels are often
narrower in front than in the rear,
you'll be surprised to see that a tire
up to 30mm wider than stock can be
mounted on those front wheels,
though the tire may be a bit pinched.
For example, the stock tire sizes for
my E46 M3 are 225/40-19 front and
255/35-19 rear, however, I run
255/35-19 tires front and rear on the
track, using the stock wheels (and a
wheel spacer on the front so the tires
don't rub against the suspension).
Squaring up the tires means that the
contact patch (i.e., the footprint) on
the front is more-or-less the same as
the rear, which goes a long way to
reducing understeer, since understeer
is caused by insufficient grip
by the front tires.
In regard to alignment, I like a
little toe out in front because it helps
the car turn in. Try 0.1 degrees per
wheel. In the rear, set a little toe in to
keep the car stable, 0.1 degrees per
wheel. Also, set as much negative
wheel camber as you can get in the
front (at least 2 degrees, but not
more than 3 or 4 degrees) and then
match that in the rear.
Q: What is toe? And what is negative
camber? And why do I care?
derBayerische
https://www.nccbmwcca.org/driving-events/high-performance-driving-schools/
derBayerische May/June 2022

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