09/25/01 by notyper
Many of you have probably heard the recent discussions about the
twitchiness of the S2K's rear end, and in particular it's tendency to snap
oversteer in certain situations. I spent about an hour in an S2K today on some
semi-deserted curvy roads that I know quite well. I won't name the roads, but
JES98GSR will know some of them (Portuguese is the word).
I had a chance to work the car hard through cambered, off-camber, flat, uphill
and downhill turns with increasing, decreasing and constant radius profiles.
Most corners were in the 35-65mph range, so I didn't have a chance to get anywhere
close to a high speed problem (which is good).
The car was completely stock, with the exception of a Mugen header (Jeff has
driven this car too). About 6000 miles on the original tires and 1/2-3/4 tank of
gas. Runs were made with and without a passenger. Here's my assessment, followed
by some comments on setup.
First of all, the S2K can get very loose if you are injudicious with the
steering wheel. It does not like to be pitched into corners, nor does it seem
too happy with trail braking. Thanks to a nearly 50/50 weight distribution with
driver and a big rear sway bar, removing weight from the tail while turning can
be problematic. At low speeds it can be useful to rotate the tail through tight
corners, but at higher speeds it can be a bit scary for the average enthusiast.
The car doesn't seem to have any bad habits in unusual corners. Usually, the
biggest problems tend to occur in off-camber and decreasing radius corners. The
inherent balance of the S2K was unaffected by off-camber turns (there was just
less grip), and the car did not seem fazed by decreasing radius turns, provided
you don't lift the throttle (much). Just ease and turn in a little more.
Experimenting with cornering techniques and lines, the car seems
to prefer a traditional cornering line. If you prefer to trail brake, you'll
need to alter your line a bit to take advantage of the rotation (you can
essentially take a tighter line). In terms of technique, I tried both a fast
entry and a slow entry to the corner. On a fast entry, the tail wants to come
out much easier, thanks to the need to trail brake a bit and/or turn in more
rapidly. This can cause you to lose momentum and botch your line. OTOH, if you
take a bit of a slower line into the corner, the rear end is much more
trustworthy. Tuan recently autocrossed his S2000 for the first time recently and
he reports that the fastest lines were using "slow in, fast out".
Preferring this approach for it's lower pucker factor, I then experimented with
getting through the corner. At first, I tried a traditional steady throttle line
through the corner. This results in a touch of understeer at the limit. If you
are forced to lift, this is where the tail can get away from you (more on that
in a minute). It also means you can't get on the gas quite as quickly. However,
I did find that you can set up a slight drift angle with the rear tires which
allows you to carry much more speed and get a much better exit. It also feels
much safer, believe it or not. In fact, the drift angle is so slight that you
may have difficulty noting it until you unwind the wheel coming out of the
corner and floor the throttle. You'll perceive a bit of tire spin as the rears
hook up. The best indicator with this particular car was a slight howling of the
rear tires when you got the drift going.
What I liked about this approach was that the rear was already
sliding, even if it was just a bit. This meant that any additional oversteer
wasn't going to be surprising. In other words, it wasn't going to snap on me.
Additionally, I could get traction back just by modulating the throttle instead
of lifting, counter-steering, etc. In fact, I didn't find myself needing to
correct the drift with the steering wheel at all. This is ideal IMO because I
want progressive breakaway of traction which gives me time to correct.
Now, obviously, in high speed corners, it will be much harder, if not
impossible, to drift the rear end with the throttle. Hence, you're setting
yourself up for more of the dreaded snap oversteer. I had a chance to experience
this on a wide, deserted industrial road doing some 50-60 mph slaloming (no
cones, just swerving back and forth). What happens is that as you approach the
limit, you're trying to stay steady on the gas. If you pick up a bit too much
speed, you're forced to turn in a bit harder and the tail will eventually want
to begin breaking away. That first slide is relatively easy to catch, what with
the quick steering of the S2K. It's what comes next, when you regain traction,
that kills you. You're sliding, you correct, the rear end regains grip and snaps
hard back the other way. I did this three times on purpose, at relatively low
speeds, and could only catch the snap back once. The other situation, which I
was privy to at Willow Springs, is coming in a bit off line at high speeds,
getting a bit of understeer, lifting and having the same thing happen (I was
riding in the car when this occurred).
Everyone knows you shouldn't lift at the limits in a corner, but what do you do
about oversteer not caused by lifting or excess throttle? Well, if you're going
to leave the stock alignment and tires alone, your best bet may be to stay on
the gas. Not full throttle necessarily, but enough to keep weight on the rear
tires and to keep some slip going so you don't get the snap.
Delving deeper, I think there are some quick and easy (relatively inexpensive)
solutions to reducing or eliminating this problem.
1. Swaybar change - a smaller rear bar or bigger front bar would have the same
effect, creating a little more understeer at the limit. In low speed turns this
could easily be balanced by more throttle, at high speeds it would be more
comfortable for the non-race car drivers among us. Many auto-x S2K drivers have
told me it is very difficult to put lots of power down coming out of tight
corners because the very stiff rear bar wants to lift the inside rear tire.
Unfortunately, stock class auto-x only allows you to change front sway bars, so
they're stuck with that approach. A smaller rear bar would reduce oversteer and
probably improve rear traction on corner exit.
Stock front anti-sway bar.
Stock rear anti-sway bar.
2. Alignment - I need to talk to some experts, but the stock S2K
uses the following camber specs stock:
Camber (F/R) -0.5/-1.5
Toe (F/R) 0 / - 1/8" (I believe, but the rear is definitely toed in).
Obviously, from these specs, Honda engineers are trying to keep the rear
planted. I'm not sure alignment changes will cure the snap, but it may reduce
the chances you'll experience it. First, the front. I'm not sure any changes are
needed here, but if we're going to add grip at the rear, we may want to add a
touch of toe-out in the front to improve turn-in characteristics without giving
up the understeer we're dialing in with more rear grip. At the rear, we might
choose more toe-in as well as more negative camber. The toe really depends on
what happens to toe during bump movements. If the rear gains toe-in under
compression, then we might be able to cure a lot of the snap with more rear
toe-in because when the rear tire slips and releases, it'll provide more force
to keep the rear end in line. With a single driver in the car, we might even
want to consider asymmetric toe settings at the rear (probably a little more
static toe on the passenger side). If toe remains constant during bump, I don't
know that characteristics will change, just the limits. More negative camber
probably just moves the limits too, but again, I really need to speak with an
3. Tires - Look closely at the SO-2's on the S2K. The fronts, while smaller,
also have a more rounded cross section. The rears OTOH, are very flat across the
tread. What does this mean? Well, the rounded cross section in front provides a
little less traction than a squarer tire, but it is probably less camber
sensitive and will have more progressive breakaway characteristics. The flat
rear tire profile will provide lots of grip, provided camber is set right.
However, when it breaks away, it will be more abrupt. A tire with a more rounded
profile might just help a little back there. Emphasis on might. In the
short term, running a little more rear tire pressure might be able to
approximate this. OTOH, it could stiffen the sidewall enough that any deflection
you're getting as warning could be diminished. Only experimentation will tell.
Smaller, rounded shoulder of the front 205-55-16 tire.
Broad, square shoulders of the rear 225-50-16 tire.
Any other experts out there with opinions, please post them.
Also, keep in mind that these are 10/10ths considerations. At 9/10ths the car is
a beautiful handler and at 10/10ths is still racecar sharp. It just requires a
more deft touch than many will have. This is the sharpest handling production
car I've ever driven, especially among (front-engine, rear wheel drive (FR)
cars (some MR cars may be better). However, that comes with the price of being
sensitive to mistakes at the limit. Personally, I like it, but a little
understeer is more comforting for us FWD guys.