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Making your car go faster, Part 3.1: Tuning the rig

Ok, it's a sailing analogy, I admit it. We now return you to our
regularly scheduled car conversation.

In our last epistle we talked about different modifications you can do
to your suspension and how they affect weight transfer: both side to
side and front to rear. To summarize a very long piece of mail ("Why
didn't he just send the summary, Marge?"):

1. Side to side weight transfer is "bad" and we want to minimize it
during cornering.
2. We can control front to rear weight transfer with individual
suspension component selection/adjustment.

In this saga, we'll explore why we might not necessarily want a car to
be neutral and why there's no perfect setup.

A given that most people understand, and that is widely and frequently
quoted, is that understeer is better than oversteer. Is that true, and
if so, why? 

The short answer is that understeering cars are less likely to spin than
oversteering cars. A more detailed answer requires us to examine human
nature.

If you find yourself going into a corner too hot, whether on the street
or track, what's your natural reaction? Your mind screams: TOO FAST and
your right foot, which controls the speed of your car, immediately
reacts by lifting. If that same foot is completely unenlightened, it
might even step on the brake (hey, that's how you slow down, right?).

Bad call.

Lifting causes your car to decelerate, and deceleration causes weight
transfer from rear to front. And that means the rear end is lighter.
Lighter means the tires have less lateral adhesion available, so the
rear end is more likely to break away as a result of turning forces. A
fraction of a second later your view ahead is out the side window. This
is not a good situation to be in. THIS IS AGGRAVATED IN A CAR THAT
OVERSTEERS. By aggravated I mean that the car is more likely to do this,
and with less effort to initiate it, than an understeering car. That's
why Porsche 911s are for advanced drivers: follow your instincts in your
911 and the next sound you'll hear is your local body shop's cash
register.

So almost all street cars are setup at the factory to avoid such a
calamity. An understeering car will, UP TO A POINT, just plow the front
end off at a tangent to the intended line should you be so foolish as to
lift in a hot turn. Of course, even an understeering car can be made to
spin (remember the Dukes of Hazard?). Classic American cars are famous
for this, since 60-70 percent of the weight was over the front wheels
and the cars had no ABS. Get on the brakes hard and whammo, the rear
wheels lock and it's spin city. That's how the Dukes did all those
lovely bootlegger turns. But that's at the extreme. Typically, if you're
Joe Driver, you're in a little faster than you like so you lift. Nothing
bad happens. 

Of course, this is a terrible way to get around a race track. Let's look
at two examples: a Club Ford and an F1 car. 

The Club Ford has low horsepower, light weight, and skinny hard tires.
Watch any CF race and you'll notice right away that the fast guys slide
the cars through all the turns. Since the cars are not capable of
generating high levels of lateral adhesion, the fast way through a turn
is to oversteer the car through the first half of the turn, then power
out. A typical CF turn, broken down, looks something like this:

1. Brake late
2. While still traveling too fast to make the turn, ease off the brakes
slightly and crank the wheel
3. With the rear end severly lightened, it will oversteer dramatically,
rotating the car quickly
4. Immediately get back on the throttle, while straightening out the
steering
5. Weight transfer from front to rear, causing the rear to reduce the
amount it's sliding
6. The lightened front end begins to slide as well
7. Now the car is pointed toward the apex, but aligned with the exit of
the turn. If the car went straight ahead it would drive over the apex
towards the corner workers. 
8. However, the car ain't going in a straight line. It's moving forward
and sideways at the same time. This is the classic, rarely performed by
people who say they have in their street cars, four wheel drift. It is a
thing of beauty to witness. 
9. The car drifts out to the exit of the turn, by which point it has
lost sideways momentum and is going where it's pointed again: down the
track.

This is the secret to winning CF and FF and FV and such-like classes.
Just watch a race and you'll see it. The guys in the weeds are the ones
still learning how.

Now let's look at a F1 car. This car has high-horsepower, is light, and
has wide, soft, sticky tires. It also has significant aerodynamic aids
to create downforce when cornering.

Frankly I haven't a clue how to setup an F1 car. But my guess is that
the drivers like them pretty neutral, with maybe a tiny bit of
understeer. The cars are so fast that a loose car could get away from a
driver before he could react. If you watch the in-car from F1 races,
you'll see them cranking in opposite lock all the time though chicanes.
That's not ideal, they're compensating for something that's wrong. The
more you turn the wheel, the slower you go. Driving an F1 car sideways
is not the fast way around the track. Those cars are in a very different
league, because of aerodymanics. Those wings are designed to create
downforce, which (because it increases loading) makes the tires stick
better. (See? "Road hugging weight" isn't a total fiction, just a
mis-statement.) As a matter of fact, 3Gs laterally is common. When the
car has that much lateral acceleration, to have the tire let go means
things will get ugly instantly. Only the truly great can drive such a
car, and one of the reasons is from an old Carly Simon song. 

Stayed tuned for Part 3.2...
John Browne
BMW CCA
BMW ACA Puget Sound Region
M3 LTW (PeeKay)
Suburban 2500 (Godzilla)
326 iX (Spunky the brave little car)

copyright (c) John Browne; all rights reserved