S2000 Autocross Setup FAQ

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This document is a mix of information gleaned from various posts on
this board and personal experience autocrossing S2000s at the national
level for two years. This FAQ covers setup for SCCA Solo 2 Stock class
autocrossing. It does
not cover setup for SCCA autocross classes other than Stock, nor does
it cover setup for track days or performance street driving, although
some information here may be useful for those applications.

Differences in setup between the ’00-’03 cars and the ‘04+ models are noted where applicable.

I’m
going to somewhat arbitrarily divide the allowed changes into three
categories — the essentials, the nice-to-haves, and the personal
preference items. 


The essentials
— tires, a sway bar, and an alignment — are the things
you must have to be competitive.  If you’re on a tight budget or
aren’t too serious, you can end your list of changes here without
feeling like you’re leaving a ton of time on the table; both Tours and
Pros have been won in cars with just these essential changes
made.  If you’ve ever heard of the 80/20 rule (the first 20% of
the cost nets 80% of the benefit, and the last 20% of the benefit is
responsible for 80% of the cost), the essentials constitute that first
80% of benefit.


The nice-to-haves
— brake pads, shocks, wheels, and exhaust — are the
remaining 20%.  These changes are each worth at most a few tenths
on a sixty second course.  That being the case, while there is
benefit to making these changes, they’re not necessities; the
cost-to-benefit ratio for this category is rather worse than that of
the essentials.

Personal preference items — harness and
engine modifications.  A harness may not pay off directly with
faster times, but some people prefer them, and those people may go
faster because of it.  Engine modifications could provide small
time improvements, but the cost-to-benefit tradeoff just doesn’t make
sense.

{mospagebreak title=The Essentials}

Tires

The most significant change that you can make to any street car destined for
autocross use is switching to R-compound tires (aka “race
rubber”).  Race tires are significantly softer and stickier than
even the best street tires, and consequently, driven properly, can net
huge (multiple seconds on a sixty second course) time improvements.

Tire Sizes

Historically,
consensus was that the optimal tire sizes for the ’00-’03 cars were
225/50R16 in front, and 245/45R16 at the rear.  This consensus was
formed before some of the new R-compound tires (most notably the Kumho
ECSTA V710) became available, though, and may therefore need to be
revisited for 2005. 

At the time of writing, there isn’t total consensus on the optimal tire
size combination for the ‘04+ cars, but 245/40R17 front, 275/40R17 rear
was the most popular combination at the 2004 national
championships.  Other options include 225F / 245R and 225F / 275R.

Hoosier A3S04

Every
national-level S2000 win in the latter half of the 2004 season was
taken on Hoosier A3S04s.  The reason for this was simple — the A3S04
was the only top-level R-compound tire available in S2000-appropriate
sizes.  This year, the Kumho ECSTA V710 will become available in
S2000 sizes, so the A3S04’s dominance will be challenged.  Rumor
has it that Hoosier will respond to this challenge by revising the
A3S04 this year.
A3S04s seem to work best at pressures in the low- to mid-40s.

Kumho ECSTA V710

The
Kumho ECSTA
V710
was introduced in a limited number of sizes in 2004, and
very quickly began earning wins.  By the end of the 2004 season,
the prevailing feeling was that the V710 was noticeably faster than
Hoosier’s A3S04, but this was of little use to the S2000 community
since the V710 was not available in suitable sizes.  It will be
available in sizes appropriate to the S2000 in 2005, however, and while
there isn’t yet any S2000-specific test data, there’s no indication
that the V710 won’t be as successful on the S2000 as it’s been on other
cars.
Optimal V710 tire pressures for the S2000 have yet to be determined.

Kumho Victoracer V700

The
first SCCA national championship won in an S2000 (Gary Thomason in
2000) was won on Victoracers
Time and tire technology have marched on, however, and the Victoracer
is no longer competitive in top-level autocross.  It’s still an
inexpensive, durable, and reasonably sticky tire, though, making it a
great choice for local events or racers on a budget.
Victoracers work best with pressures in the low- to mid-30s.

Hoosier Radial Wet

Hoosier
introduced a new rain tire, the Radial
Wet
, in 2004.  It quickly proved to be the DOT-legal tire of
choice when there is standing water on course — if you’re serious and
well-funded enough to buy dedicated rain tires, your search should
begin and end with the Radial Wets.

Other tires

I am not
aware of anyone having run the Avon
Tech R
on an S2000, although it is available in sizes that would
work on the ’04-’05 cars.  Miata drivers who have tested the tire
report that the Avon is comparable to, but slightly slower than, the
Hoosier A3S04.  Rumor has it that the Tech R will be revised in
2005, so it may get faster.

Goodyear will allegedly be releasing an R-compound tire line in 2005,
but there isn’t yet any information on how fast the new tires will be.

There are many other R-compound tires available in sizes suitable for
the S2000, including the Michelin Pilot Sport Cup, the Yokohama A032R,
the Hoosier R3S04, and the ever-popular Toyo RA-1.  Unfortunately,
all of these tires are optimized for track use, and are rather slower
than Victoracers or A3S04s until they heat up, which doesn’t happen in
a typical autocross.

High-end street tires (most famously the Bridgestone Potenza S-03) have
been used with good success in rainy conditions, but treaded R-compound
tires will be faster.

Sway Bar

A sway bar is important on
the S2000 for two reasons.  The first is that the S2000 is more
prone to oversteer than pretty much any other mass-produced car
available for purchase in the States.  This makes the stock car a
lot of fun on the street, but throw in rapid transitional maneuvers and
the added grip of R-compound tires, and the results get a little too
exciting.  The tire setups usually used in autocross narrow the
width differential between the front and rear contact patches,
exacerbating this tendency towards oversteer.  A big front sway
bar tames the rear end, making driving the car less of a white knuckle
experience, especially in slaloms.

The second reason for a big front bar is that, with R-compound rubber,
the S2000 rolls enough in corners to lift its inside rear wheel off of
the ground.  The S2000’s limited-slip differential is a Torsen
unit; one characteristic of the Torsen is that when one wheel has no
traction, it acts as an open differential.  What this translates
to in an autocross is wheelspin, and lots of it.  A bigger front
sway bar reduces body roll and plants the rear end, allowing you to
power out of corners instead of spinning the inside rear wheel
helplessly.

The demands of autocross and the fact that spring changes are not
allowed in Stock dictate the use a stiffer front sway bar than is
optimal for performance street or even track use.  There are a
number of front sway bars (e.g. Mugen, Muz, etc.) available for the
S2000, but bars not specifically designed for autocrossing aren’t stiff
enough for Solo competition.  This remains true for the ‘04+ cars,
although the newer cars do appear to work well with slightly softer bar
settings. 

The three sway bars that are designed with autocross in mind are built
by Comptech, Saner Performance Fabrication, and Small Fortune Racing
(aka “Gendron”).  Each has its own pros and cons:

Comptech

The Comptech has an unusual design.  I started writing a
description of the mechanics of its operation, but a few paragraphs
later, decided that they’re beyond the scope of this FAQ. 
🙂  Suffice it to say that, unlike a conventional sway bar, the
Comptech is adjusted by moving a bolt between a series of holes in the
bar’s center section, thus varying its stiffness. The process
for making adjustments
on the Comptech bar is rather more
involved than that for a conventional bar.  The Comptech’s real
drawback, though, is its price — in the vicinity of $700.  What
you get for your money is a broad range of adjustment (from 62% to 178%
stiffer than stock) and a beautiful set of anodized aluminum mounting
brackets.
(A note on sway bar stiffness figures — the numbers in this document
are quoted directly from vendor sales literature.  What’s not
clear is whether these numbers are relative to the ’00-’01 bar or the
softer ’02+ bar, and thus it’s not clear whether they can be compared
between bars.)

Be aware that there have been two generations of the Comptech
bar.  The first generation bar had an unfortunate tendency to snap
in two.
The second generation bar shares the same basic design, but was
redesigned to be more durable.  To my knowledge there have been no
reports of failures of the second generation bar, although it should
also be noted that relatively few people use it now that cheaper
alternatives are available.  The bottom line is buyer beware when
buying a used Comptech bar, although since the first generation bar has
not been produced in years, the risk of finding one on the used market
is slim.

Saner Performance Fabrication

The Saner bar is a more conventional 1.25″ solid three-way adjustable
sway bar.  Its great benefit is that, at $185, it’s significantly
less expensive than the other two options.  The Saner bar’s range
of adjustment is rather narrower than the Comptech’s, and its stiffest
setting is arguably still not stiff enough for maximum performance; it
can be adjusted from 91% to 150% stiffer than the stock bar.

The Saner bar has its share of problems as well.  There are
spacers between the bar and the endlinks to ensure sufficient endlink
articulation, but those provided with earlier bars deformed
quickly.  Newer bars come with thicker spacers, but it’s not yet
known if these fix the deformation problem.  The Saner is also
prone to making harmless but annoying clicks and clunks.  Because
of the use of endlink spacers, it has clearance issues with aftermarket
shocks with larger-than-stock bodies — the endlinks may scrape against
the shocks, but this can usually be alleviated by careful alignment of
the bar.  Lastly, but perhaps most importantly, availability of
the Saner bar is extremely variable, subject to the whims of its
manufacturer; several people have endured months-long waits for their
bars.  Plan your order timing accordingly.

The Saner bar can be ordered directly from the manufacturer
(although it’s not listed on the website).

Small Fortune Racing / Gendron

The Gendron bar is a NASCAR-style adjustable sway bar which, like the
Saner, is adjusted by varying the point where the endlink attaches to
the bar arm.  It has a fairly broad adjustment range via six
endlink mounting holes spanning a few inches of the arm.  Because
it’s a modular bar (the arms bolt to a tubular center section), its
stiffness can also be changed by substituting a different center
section — Gendron sells a 1.25″ solid center and two 1.25″ hollow ones
with different wall thicknesses.  As far as I’m aware, no one has
done the math on how stiff a Gendron bar is, but suffice it to say that
the solid bar is very stiff: comparable in maximum stiffness and range
of adjustment to the Comptech bar.  Gendron recommends using the
stiffer hollow bar for the S2000, but experience shows that for the
’00-’03 cars, the solid bar is a better choice.  ‘04+ owners may
want to consider using the stiffer of the two hollow bars.
The drawback of the Gendron bar is that the bar ends are rather thick,
which, like the Saner, can lead to interference between the endlinks
and the shock bodies.  This can be addressed by machining some
material off of the arms to make them narrower and/or using lower
profile endlinks
(the ones linked here also require drilling out
the adjustment holes to accommodate their larger stud diameter).
The Gendron bar was used by Andy McKee (s2k2fast4me) and Jason Saini
(Jason Saini) in their Nationals-winning drives in 2002, 2003, and
2004.  (Trivia: Gary Thomason, the 2000 winner, used a custom
blade-type adjustable bar of which only one example exists.)

The Gendron bar is available only through Small Fortune Racing, another
small shop, run by autocrosser Bill Gendron.  The bar costs around
$500; additional center sections are (if I recall correctly) $150
apiece.  Gendron has been slow to warm to the whole Internet fad,
but can be reached at 413.267.0904.

Alignment

A proper
alignment is important for autocrossing, and compared to the other
changes you’ll be making, a bargain at less than $100.  Individual
alignments vary, but for the ’00-’03 cars, the general consensus falls
in the following ranges:

  • Front toe – 0″ to 1/8″ toe out
  • Front camber – -1.5 to -1.75 degrees
  • Rear toe – 1/4″ to 3/8″ toe in
  • Rear camber – -2.0 to -2.25 degrees

If you want it straight from the horses’ mouths, here are
alignment settings posted by the top three finishers at the 2003
Nationals:

  • Jason Saini (Jason Saini) (Moton shocks)
  • Andy
    McKee
    (s2k2fast4me) (scroll to near the bottom of the first post)
    (Penske shocks) (this post is from the 2002 Nationals)
  • Ian Stewart (Mrsideways) (Koni shocks) (Ian’s alignment is
    notable because he uses zero toe in the rear, perhaps contributing to
    his handle “Mrsideways”)

Each driver’s shock choice is noted since cars on stock shocks
tend to be rather more twitchy than cars on aftermarket units. 
Drivers with stock shocks may want to consider more conservative
settings (e.g. more rear toe-in or less front camber).  Likewise,
alignment settings should be adjusted for cars not running a 1.25″
solid front sway bar and 225F/245R tires.
The ‘04+ cars seem less prone to oversteer to their predecessors, and
may benefit from more aggressive alignments – consider slightly
decreasing the rear toe-in.

{mospagebreak title=Nice-to-have}

BRAKE PADS

The S2000’s stock brake pads have difficulty getting the most out of
R-compound tires, especially on concrete surfaces.  For this
reason, most people run grabbier, more fade-resistant brake pads. 
See [URL=https://www.s2ki.com/forums/index.php?showtopic=236533]this
thread[/URL] and
[URL=https://www.s2ki.com/forums/index.php?showtopic=225883]this
thread[/URL] for discussion of brands and models which have been used
successfully.
Note that you should avoiding using full-race brake pads like
Porterfield R-4s or Hawk Blues on an autocross car.  Race pads
need a few laps to come up to working temperature before they stop
well; you’ll never have that opportunity at an autocross

SHOCKS

There’s only one off-the-shelf performance shock available for the
S2000 — the Koni Sport (also known as the Koni Yellow).  There’s
some debate over whether the Konis are an improvement over the stock
shocks.  They’re somewhat softer than the stock shocks; some feel
this makes the car easier to drive at the limit, while others believe
it slows the car’s reflexes, but the differences are fairly subtle
either way.  One indisputable benefit of the Konis is that they’re
adjustable at all four corners, which gives you some options for fixing
handling problems.  Unlike some other Koni fitments, the rears can
be adjusted with the car on the ground.  Konis run a bit over $600
for a set.
The S2000 benefits significantly from high-end shocks; properly
configured, they make the car much more controllable at the
limit.  At the risk of making a somewhat controversial assertion,
this is primarily due to the custom valving that goes into them rather
than any fundamental advantage inherent to their construction; S2000
shocks custom valved for autocross tend to be significantly stiffer
than either the stock units or the Koni Yellows.  With that in
mind, when shopping for high-end shocks, be sure to go to a vendor with
S2000-specific autocross knowledge.  Some vendors with this
experience include
[URL=http://www.kingmotorsports.com/category.asp?brand=Moton_Suspension&category=Suspension]King
Motorsports[/URL] in Illinois (who supplied the Motons on Jason Saini’s
2003 / 2004 championship-winning car),
[URL=http://www.ankenyracing.com/suspensionparts.htm]Ankeny Racing
Enterprises[/URL] in California (who valved the Penskes on Andy McKee’s
2002 championship-winning car), and
[URL=http://fordahlmotorsports.com/]Fordahl Motorsports[/URL] in
Washington (who provided the JRZs on my car, which never did win
anything :), and who do Motons as well).  Expect to pay out the
nose for custom-valved high-end shocks; prices range from $2000-$4000
for a set.  If shopping for high-end shocks, keep in mind that the
SCCA Stock rules only allow two external adjustments.

WHEELS

The only Stock-legal, (somewhat) off-the-shelf lightweight wheel
options for the ’00-’03 cars are the six-spoke forged BBS wheels
(pictured [URL=http://over6racing.com/photos/Paddock_2.jpg]here[/URL]
on Jason Saini’s car) that were available as a factory option in
Japan.  Four of these shave off about nineteen pounds of rotating
weight.  Unfortunately, the JDM (Japanese domestic market)
six-spoke wheels are hard to come by in North America — used wheels
occasionally appear on s2ki.com’s For Sale and Wanted forum or on eBay,
and quickly sell in the $1000-$1500 range.  Some stores
specializing in JDM products
[URL=https://www.s2ki.com/forums/index.php?showtopic=102403&st=6]may
be able to get them[/URL], but expect to pay $2000+ and wait several
months for the privilege.
The Tire Rack now carries
[URL=http://www.tirerack.com/servlet/CallJsp?target=wheelSearchCloseUp&wheelIndex=21&sizeIndex=0&showRear=yes&setIndex=4&filterSize=&filterFinish=&filterSpecial=]SSR
GT7[/URL] in Stock-legal sizes.  The GT7s are lighter than the OEM
wheels, but only by about nine pounds per set. 
The S2000’s wheels have very large offsets, and in addition, the front
brake clearance is very tight; as a consequence, until recently, no
custom race wheel manufacturer (e.g. Fikse, Complete Custom Wheel) has
been able to manufacture a Stock-legal front wheel. 
[URL=http://kodiakracingwheels.com/]Kodiak Racing Wheels[/URL] now
believe that they can do so, but need someone to
[URL=https://www.s2ki.com/forums/index.php?showtopic=265207]submit
accurate measurements[/URL] before they can confirm.

The ’00-’03 stock sizes are 16″ x 6.5″ +55 mm front, 16″ x 7.5″ +65 mm
rear.  The ’04-’05 stock sizes are 17” x 7” +55 mm front, 17” x
8.5” +65 mm rear.

EXHAUST

The S2000’s stock exhaust is very efficient, so power gains from
aftermarket exhausts are at best incremental — the only justification
for getting an aftermarket exhaust for an autocross car is weight
savings.  The stock exhaust weighs over fifty pounds; relatively
inexpensive single exhausts like those from Spoon, Speed, or JIC save
over thirty pounds off of the back of the car, and extremely
lightweight titanium exhausts like the Amuse single can shave over
forty pounds.  Bring earplugs, though — lightweight single
exhausts are deafeningly loud without silencers, and using a silencer
noticeably reduces high-end power.

{mospagebreak title=Personal Preference}

HARNESS

Some people prefer to be fastened tightly to their seat when
autocrossing.  If you’re one of these people, you may want to
consider a harness, but be aware that SCCA rules prohibit the use of
full harnesses in convertibles not equipped with roll bars.  As
such, if you want a harness, make sure you get a roll bar as well, or
alternately, get just a lap harness belt.

The
[URL=http://www.gofastlab.com//s2ki/product.php?productid=255&cat=33&page=1]CG-Lock[/URL]
is an inexpensive and easy-to-install alternative to a lap harness.

ENGINE MODIFICATIONS

SCCA Stock class rules permit very minimal internal engine
modifications — effectively just rebuilding the engine to stock specs,
except for the use of the manufacturer’s first standard overbore, not
to exceed 0.020″.  Given the tiny potential gains and large cost
of rebuilding the engine (Grassroots Motorsports on their Project
Celica: “Our $3500 rebuild has netted us 4 horsepower”), not to mention
the extreme length of this FAQ, it’s not really worth discussing here.

No one has measured power gains from aftermarket air filters exceeding
a dyno’s range of error, so only install one if you feel like making a
change for change’s sake.

—–

[b][SIZE=3]3.  WHAT’S THE BEST YEAR S2000 TO BUY FOR AUTOCROSS?[/SIZE][/b]

In 2005, both generations of S2000 are classed in A Stock.

There are subtle differences between the ’00-’01 cars and the ’02-’03
cars.  The ’02-‘03 S2000s have a reworked suspension with stiffer
springs, and an ECU revision which independent dyno testing has shown
to result in 5-10 hp gains.  Both of these changes should
theoretically work in the ’02-’03 cars’ favor, but in practice, the
differences are subtle enough that no ’00-’01 national-level
competitors have bothered to upgrade to the later models.

The ’04-’05 S2000s received extensive changes to the suspension, motor,
gearing, and wheels.  The benefits of these changes, and whether
the ‘04-’05 cars are faster than the ’00-’03 cars, have been
[URL=https://www.s2ki.com/forums/index.php?showtopic=149753]debated at
great length[/URL] on these forums.  Relatively few people have
run the ‘04-’05 cars at the national level to date, so there is not yet
enough data to draw any firm conclusions on which generation ultimately
has more performance potential.  It is my opinion that the later
cars will ultimately prove faster.

{mospagebreak title=Recommended Reading}

SCCA 2005 Solo Rules – The SCCA Solo rulebook is available
online for the first time this year at http://scca.com/_filelibrary/File/2005SoloRules.pdf


s2k2fast4me’s 2002 Year in Review
– s2k2fast4me won Nationals in
a Boxster in 2001, then bought an S2000, built it up over the course of
the 2002 season, then drove it to a second national championship at the
end of the year.  His detailed
account
of his car development process is informative for anyone
considering doing the same. 

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