PedalFaster

S2000 STOCK CLASS AUTOCROSS SETUP FAQ, v2.03
Last updated: August 17, 2010

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TABLE OF CONTENTS

1. INTRODUCTION AND SCCA CLASSIFICATIONS

2. STOCK-LEGAL MODIFICATIONS

2.1 Essential setup items

2.1.1 TIRES
2.1.1.1 Tire sizes
2.1.1.2 Hoosier A6
2.1.1.3 Kumho ECSTA V710
2.1.1.4 Hoosier Radial Wet
2.1.1.5 Other tires

2.1.2 SWAY BAR
2.1.2.1 Small Fortune Racing / Gendron
2.1.2.2 Saner Performance Fabrication
2.1.2.3 Ankeny Racing Enterprises
2.1.2.4 Comptech

2.1.3 ALIGNMENT

2.2 Nice-to-have setup items

2.2.1 BRAKE PADS

2.2.2 SHOCKS

2.2.3 WHEELS

2.2.4 EXHAUST

2.3 Personal preference setup items

2.3.1 HARNESS

2.3.2 ENGINE MODIFICATIONS

3. WHAT'S THE BEST YEAR S2000 TO BUY FOR AUTOCROSS?

4. RECOMMENDED READING


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1. INTRODUCTION AND SCCA CLASSIFICATIONS

Having seen a bunch of threads like this one go by on the Racing and Competition forum, I figured it was high time that someone wrote an autocross setup FAQ to get the commonly-asked stuff out of the way. Since I was bored, I wrote it myself.

This document is a mix of personal experience autocrossing S2000s at the national level for two years, ongoing correspondence with people still running S2000s nationally, and information gleaned from various posts on this board.

This FAQ covers setup for SCCA Solo 2 Stock class autocrossing. The S2000 is eligible for the following classes in SCCA national-level competition:

• A Stock
• B Street Prepared
• F Prepared
• D Modified (AP1 motor)
• E Modified (AP2 motor)
• Street Modified 2
• Street Touring R (provisional class in 2010)

This FAQ 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 AP1 ('00 - '03), AP2 ('04 - '08), and CR models are noted where applicable.


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2. STOCK-LEGAL MODIFICATIONS

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 not concerned about the last couple of tenths, 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.

Last and least as well are the 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.


2.1 Essential setup items


2.1.1 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.


2.1.1.1 Tire sizes

There are two approaches to tire sizing on the S2000 -- staggered and equally-sized (or "square").

Historical consensus was to run a staggered setup: 225 front / 245 or 265 rear for the AP1 cars, or 245 front / 275 rear for the AP2 cars. All but one of the national championships won in S2000s have been won with staggered tire setups.

Having said that, the current preferred setup is to run an extremely stiff front sway bar to reduce wheelspin, which in turn requires running equally-sized tires front and rear to maintain handling balance. The preferred square tire sizes are 245 all-around for AP1 cars, and 245 or 275 all-around for AP2s. Note that non-CR AP2s may experience tire rubbing on the front fender liners if 275s are used.


2.1.1.2 Hoosier A6

The vast majority of top national-level Stock-class autocrossers use Hoosier A6 tires. The A6's advantages over its primary competitor, the Kumho V710, are its more precise feel, its lighter weight, and the availability of a 245/45R16 size for AP1 cars.

Optimal A6 tire pressures are in the mid- to high-30 psi range.


2.1.1.3 Kumho ECSTA V710

The Kumho ECSTA V710 is a less expensive alternative to the Hoosier A6. Consensus is that the Hoosier is a slightly faster tire for most applications, but the Kumho is still capable of winning - the 2009 A Stock national champion drove a Corvette on V710s. V710s will also last longer than A6s, although they tend to "fall off" (lose grip) after 40 - 50 runs.

Optimal V710 tire pressures are in the low-30 psi range.


2.1.1.4 Hoosier Radial Wet

The Hoosier Radial Wet is 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.


2.1.1.5 Other tires

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 R6, and the ever-popular Toyo RA-1. Unfortunately, all of these tires are optimized for track use, take longer to warm up than the Hoosier A6 or Kumho V710, and are less grippy than the aforementioned tires even after they're up to temperature.

High-end street tires have been used with good success in rainy conditions, but treaded R-compound tires will be faster.


2.1.2 SWAY BAR

A sway bar is important on the S2000 for two reasons. The first 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 second reason for a big front bar is that the S2000, particularly the AP1, is more prone to oversteer than pretty much any other recent mass-produced car. 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 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.

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


2.1.2.1 Small Fortune Racing / Gendron

The Gendron bar is a NASCAR-style adjustable sway bar which 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 hollow 1.375" center sections as well as solid and hollow 1.25" center sections. The 1.375" bar is generally necessary to control wheelspin on non-CR cars; the 1.25" bars are sufficient for CRs.

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 is available only through Small Fortune Racing, a small shop run by autocrosser Bill Gendron. The bar costs around $900.


2.1.2.2 Saner Performance Fabrication

The Saner bar is a conventional 1.25" solid three-way adjustable sway bar. Its great benefit is that, at $275, it's significantly less expensive than the other options. The Saner bar's range of adjustment is narrower than either the Comptech's or the Gendron's, though; its stiffest setting isn't stiff enough for maximum performance on non-CR cars.

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 these deform quickly. 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 Performance website is http://www.sanerperformance.com. Saner's phone number is (772) 324-1339.


2.1.2.3 Ankeny Racing Enterprises

Ankeny Racing Enterprises ("ARE") has begun producing 1.5" blade-adjustable sway bars for the S2000. These haven't seen widespread use at the national level yet, but their specifications suggest that they should be a good, easily-adjusted alternative to the Gendron and Saner bars.

The ARE bar costs around $900 with one adjustable blade, with a second adjustable blades costing an additional $125.

The Ankeny Racing Enterprises website is ankenyracingenterprises.com. ARE's phone number is (805) 527-1137.


2.1.2.4 Comptech

Comptech used to produce an autocross-specific sway bar for the S2000. Comptech went bankrupt in 2007 and was reconstituted as a race and engine-only shop; it no longer builds S2000 sway bars. Comptech bars still appear for sale occasionally, though.

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 (click here for an image of the bar and holes). 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 -- just under $1000. What you get for your money is a broad range of adjustment and a beautiful set of anodized aluminum mounting brackets.

Be aware that there have been two generations of the Comptech bar. The first generation bar had an unfortunate tendency to snap in two (for the visually-minded, there's a picture here). 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 have used it. 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.


2.1.3 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 the general consensus falls in the following ranges:

• Front toe - 0" to 1/8" total toe out
  
• Front camber - maximum available (generally between -1.5 to -1.8 degrees)
  
• Rear toe - 1/16" to 1/4" total toe in
  
• Rear camber - -0.2 to -0.5 degrees more than the front camber

Drivers with stock shocks or sway bars smaller than 1.375" may want to consider more conservative settings (e.g. more rear toe-in or less front camber).


2.2 Nice-to-have setup items


2.2.1 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 this thread and this thread for discussion of brands and models which have been used successfully.

Note that you should avoiding using full-race brake pads like 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.


2.2.2 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. The Konis have stiffer rebound damping but softer compression damping 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.

Non-CR S2000s benefit significantly from shocks with autocross-specific valving, which make the car much more controllable at the limit. Koni Yellows can now be revalved to autocross-specific specs by Koni North America; see this thread for more information.

Before Koni began offering autocross-specific valving, many national-level competitors used custom high-end shocks (Moton, Penske, JRZ, etc.). These are still an option for people willing to pay out the nose (expect to pay $2000 - $5000 for a set) for shocks that can be custom-valved to the driver's specifications, and which may perform incrementally better as a result. When shopping for high-end shocks, be sure to work with a vendor with S2000-specific autocross knowledge.


2.2.3 WHEELS

The only Stock-legal, (somewhat) off-the-shelf lightweight wheel options for the AP1 cars are the six-spoke forged BBS wheels 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 may be able to get them, but expect to pay $2000+ and wait several months for the privilege.

The Tire Rack generally carries at least one lightweight wheel model appropriate for the AP2, but the specific manufacturer and model varies, so check their website for details.

The S2000's wheels have very large offsets, and in addition, the front brake clearance is very tight; as a consequence, most custom race wheel manufacturers (e.g. Fikse, Complete Custom Wheel) have difficulty fabricating Stock-legal front wheels.

The '00-'03 stock sizes are 16" x 6.5" +55 mm front, 16" x 7.5" +65 mm rear. The '04-'08 stock sizes are 17" x 7" +55 mm front, 17" x 8.5" +65 mm rear.


2.2.4 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. Autocrossers on a budget can also fabricate their own lightweight single exhaust by sawing off the stock mufflers and welding in a lightweight universal race canister. Either way, bring earplugs -- lightweight single exhausts are deafeningly loud without silencers, and using a silencer noticeably reduces high-end power.


2.3 Personal preference setup items


2.3.1 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 CG-Lock is an inexpensive and easy-to-install alternative to a lap harness, but can wear seatbelts prematurely.


2.3.2 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.


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3. WHAT'S THE BEST YEAR S2000 TO BUY FOR AUTOCROSS?

Short answer: it's still not clear. Although there are significant differences in suspension, wheel and tire size, powerband, and gearing between the various years and variants of the S2000, examples of each generation and variant have been campaigned with success at the national level. Buy the car that suits your budget and personal preferences.

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4. RECOMMENDED READING

SCCA 2010 National Solo Rules - The SCCA Solo rulebook is available online at http://scca.com/documents/Solo_Rules/2010_..._solo_rules.pdf.

A-arm bracket thread - The brackets attaching the front upper A-arms to the chassis on AP1 cars tend to crack and pull away from the frame under heavy use. See this thread for more information. The brackets were strengthened in the AP2 update, and there have been no reports of them failing on AP2s.

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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VERSION HISTORY

v1.0 - FAQ created - 04.01.01
v1.01 - Added Recommended Reading section, table of contents, and section numbering; performed general cleanup but probably introduced several jet-lag induced errors as well - 04.01.15
v1.1 - Added '04+-specific commentary where appropriate, revised Tires section to reflect the 2004 season's tire choices, added the "What's the best year?" section, and made numerous minor content and formatting revisions - 04.09.06
v1.2 - Incorporated lessons learned during the 2004 season and feedback received from other members; added information on the 2005 R-compound tire choices - 05.02.05
v1.3 - Updates to reflect new tire options, AP2 setup, and new setup trends from the 2005 and 2006 seasons - 07.02.11
v1.31 - Added note about 245/45R17 Kumho V710 rubbing on the front fenderwell - 07.09.03
v1.32 - Fixed broken link to Jason Saini's alignment - 08.08.19
v1.33 - Changed title from "S2000 autocross setup FAQ" to "S2000 Stock class autocross setup FAQ" and added link to 2009 rulebook - 09.03.14
v1.34 - Updated the URL for the Saner website - 09.03.16
v2.0 - First major update in two and a half years; updated every section to reflect the current state of the art - 09.09.13
v2.01 - Corrected the prices of the Gendron and ARE sway bars and noted that one national championship has been won on a square tire setup - 09.09.16
v2.02 - Fixed some characters that weren't rendering correctly that were introduced in the v2.0 update - 09.12.06
v2.03 - Updated SCCA Solo rule book link to point to the 2010 rule book and removed the white space from the version history section - 10.08.17

Doug Hayashi

Nice FAQ, lots of good info there.

Only point that I would question is the $100 alignment. A true race shop doing alignment, corner balancing, and a nut/bolt check on your suspension parts will probably be more like $250-300 bucks, since it will take them 3-5 hours to do it right. But if all you want is a quickie alignment, you can probably get the no-frills one for 100 bucks.

-Doug

CoralDoc

Excelent Summary! This is a valuable resource.

I'll add that the Comptech swaybar has non-trivial weight benefits compared to a Saner or Gendron bar. As measured on my bathroom scale, the stock swaybar weighs 6 lbs, the Comptech Gen II bar weighs 16 lbs and I've read that the 1.25" solid bars weigh more than twice as much. Can anyone provide real data on this?

As one of the people that broke the Comptech Gen I bar, I can say that the Gen II bar is a vast improvement. I broke (cracked at the bolt hole on the inner bar) the first bar after only a few events, wereas the Gen II bar has laster over 15 autocross events and 8 track events. I recently inspected it and there is no sign of fatigue.

With the Gen II bar set at full stiff, my car would work very well on concrete and would understeer on asphalt when using Kumho V700 tires.

PedalFaster

[QUOTE]Originally posted by Doug Hayashi
Only point that I would question is the $100 alignment.

Gregg Lee

I agree this is an excellent compilation.

Since Shocks are so expensive, both in price and time to set up, perhaps you will excuse a little more clarification.

Koni Sportshocks. These are rebound adjustable only, one rate. At full firm, both front and rear rebound are significantly firmer than stock, enough so to back off rate in slick conditions. Front bump rate is at least as firm as stock. Rear bump rate is indeed softer than stock and this is a good thing since it greatly reduces rear skitter out on irregular surfaces. (I have a set.)

Moton, etc. It is important to note that these are multi adjustable, with separate bump and rebound rates and separate high and low speed adjustments, at least on bump. (They still meet the two adjustment rule because only two rates are externally adjustable - the rest require disassembly). So for example, the rear bump rate can be set stiff on low speed to delay lean in transitions, acting a bit like a stiffer swaybar, while the high speed bump rate is set soft to allow the wheels to track over irregularities and not skitter out like the stock shocks.

This my give a clue why they are so expensive, and why getting the settings right takes both time and experience. (I don't have these but have discussed with some who do.)


Gregg


[QUOTE]Originally posted by PedalFaster
S2000 AUTOCROSS SETUP FAQ, v1.0
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INTRODUCTION

SHOCKS

There's only one off-the-shelf performance shock available for the S2000 -- the Koni Sport (also known as the Koni Yellow).

PedalFaster

Hmm -- one of us needs a new scale. I just weighed my stock bar at 10.1 lbs., and the NASCAR / Gendron-type 1.25" solid bar I was running for most of last year at 20.2 lbs. I don't know if the Gendron's arms are aluminum or steel; if they're the former, then it should be a couple of pounds lighter than my steel-armed bar.

I would be surprised if the weight difference between the Gendron and the Comptech was huge (more than a few pounds); if you set the Comptech bar to full stiff while only using one bolt, then most of the inner section is just dead weight.

[QUOTE]Originally posted by Gregg Lee
Koni Sportshocks [...] front and rear rebound are significantly firmer than stock, enough so to back off rate in slick conditions.

PedalFaster

The Muz bar is actually mentioned:

I agree with Ian's assessment -- you did well at Nationals (and kicked my ass!) because of your awesome driving, and probably could have done even better with a big front bar.

Having said that, everyone's car setup preferences vary; some people like their cars loose, some like them pushy...

Steve

PedalFaster

Minor update:
The changes don't merit rereading the FAQ if you've already been through it once.

Steve

PedalFaster

Made some mostly '04-centric updates:

[QUOTE=PedalFaster,Jan 1 2004, 02:41 AM][SIZE=1]v1.1

PedalFaster

Actually, the Tire Rack apparently has SSRs in Stock-legal sizes: https://www.s2ki.com/forums/index.php?showt...0&#entry4487953

Adding this information to the FAQ is on my list of things to do...

Steve