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What is a rear sway bar?
Almost all modern cars are factory
tuned to have understeer at the limit. That means
when you corner really fast, the front tires will begin
to lose grip before the rear, so instead of turning,
your car would "under" steer and tend to go straight.
The MINI is factory tuned very well and there is
inherently very little understeer.
A rear sway bar counteracts this
by reducing traction at the rear wheels (changing the
way weight transfers), so at the limit
the car would understeer less, or even oversteer, where
the rear wheels would lose traction before the front,
and you "fish tail". For most drivers understeer
is safer, all you need to do is reduce throttle input
(slow down) and the front tires will regain trip
eventually, unless you hit the wall in front of you
first. However, for a fun to drive experience, its
best to have a choice between understeer and oversteer,
and this is where the sway bar comes in.
The H&R 18mm
There are many brands and sizes
for aftermarket rear sway bars. From the smallest
18mm H&R dual adjustable to 25mm solid race ones.
The thicker the bar, the stiffer it is, thus you gain
more oversteer with a thicker bar. This H&R 18mm
bar has 2 mounting holes for different stiffness
adjustment. For the record, the stock sway bar in
my MINI Cooper is 16mm. An 18mm bar is 1.6 times
stiffer than the 16mm bar.
Install was relatively simple,
drop the rear sub frame and lower the entire rear
suspension, then simply unbolt the rear sway bar and
take it out. The H&R 18mm bar also includes Teflon
coated bushings that does not require lubrication, this
makes it maintenance free and a lot easier to live with
than bars with polyurethane bushings, which requires
semi-solid lubes to stay squeak free. I can tell
you these bushings work a hell lot better than the
polyurethane ones I had in the Volvo, that thing
squeaked like hell in the winter, and in 20000kms the H&R
never made a sound, not even in the dead of winter here
in Calgary.
Stiff or soft setting?
I installed the bar on the
stiffer setting and it definitely made the handling a
lot more neutral. The MINI would still understeer
at the limit at road legal speeds (below 120km/h) most
of the time, but I could get the tail to step out and
slide by trail braking into a corner or lift off the
throttle slightly mid corner. It has just enough
oversteer to entertain and tighten the line at the
limit, but not so much to be dangerous at normal driving
situations.
However, on snow and ice I find
that the MINI has a tendency to oversteer in corners
unless I'm accelerating. Its fun most of the time,
but it does get a little scary when I drive over icy
spots on the road and the car begins to swing around.
That said, the MINI is still very closed to being
neutral, and its not hard to bring the car back in check
again with some slight steering adjustments.
At super legal speeds, its a
slightly different story. The MINI feels almost
too neutral when cornering at 150km/h or higher, the
rear will step out with very slight provocation and it
is a little hairy when you're going at a quick clip.
Basically I have to keep the throttle on when the car
starts to slide, or it'll want to spin around.
With the sway bar set to soft
setting, you could still oversteer but you have to be
totally asking for it (for example, enter a corner
extremely fast, then in the middle of the corner start
braking) The soft setting is a pretty safe setting, you
can feel that the front tires are scrubbing less than
with the stock sway bar, but it isn't enough to make the
rear slide.
Tires make a difference in
sway bar performance
I've had 3 sets of tires on the
MINI so far, the 175/65/15 Continental all season (good
for nothing) tires, 205/50/15 Kumho V710 slicks,
195/55/15 Kumho 712 Supra. I also have a set of
185/65/15 winter tires but I haven't driven with them
yet.
The tires do make an appreciable
difference in the car's cornering balance. The Conti all
seasons didn't grip enough as they wore out. Below 50%
tread left, the Conti would always allow the car to
understeer and scrub the front tires, the suspension
does not load up enough to "activate" the rear sway bar,
thus I've almost never felt any oversteer once the
Contis were starting to wear out. This is even at the
stiff setting of the sway bar.
On the other hand, the V710
racing slicks had more than ample grip to fully load up
the suspension, the car's handling is extremely fun and
tossable. On throttle there was a hint of understeer,
and as you lift just slightly off the throttle, it'll
start to oversteer, very controllable.
The Kumho 712 summer tires were
more of the same as the V710, except for generally less
grip at the limit, it was enough to make the car very
tossable and neutral. My point is, if your tires don't
grip the road enough, you might not get much benefit
from the rear sway bar mod.
I do not recommend a really thick
rear sway bar. For some people, they want to feel the
car being neutral or slight oversteer when they drive at
8/10th, but when you're really pushing the car hard
right up to the limit, then the car will be quite
twitchy. That said, I'm sure there are a lot more
experienced drivers out there than I am, so YMMY.
Cost: $150 CDN
Installation: did it myself
Performance: 10/10 - I have all the oversteer I need,
and most of the time the car will safely understeer
slightly, perfect
Overall: 10/10
No downsides, no maintenance required, just the right
size for the MINI Cooper to bring better cornering
balance and agility.
23/09/06
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