Topic: Autocross preparations

[DeepBlueGXP]

This was written by Mikes before he left Tirerack.com.  He totaled his 06 Z0k on a curb that bent the frame rail.  He has since bought a Mazda RX8

How to prep your Solstice/Sky for Stock Class Autocrossing

First you'll need a car. If you go with the Base Sol/Sky or Z0K Solstice you'll be classed in C Stock (CS). If you get the GXP or Redline you'll be classed in A Stock (AS).

Prep for these classes should be the same.

Whether you want to have fun and run a few autocrosses but mainly keep your car a daily driver or plan on having a trailer queen car strictly for racing these are the changes I would make.

1st- ALIGNMENT!!

The alignment from the factory is OK but there are huge dividends to be had with small tweaks here. Out of the box our cars handle well but have too much under steer for auto x. The easiest way to cure this is a good alignment. When you have the alignment done have the car as close as possible to how you plan to run the car, this includes you sitting in the driver seat. If you do nothing else, DO THIS!!!!

There are 4 major parts to an alignment: Camber, Caster, Toe and Thrust Angle.

Camber

The camber angle identifies how far the tire slants away from vertical when viewed directly from the front or back of the vehicle. Camber is expressed in degrees, and is said to be negative when the top of the tire tilts inward toward the center of the vehicle and positive when the top leans away from the center of the vehicle.

Luckily our cars are very adjustable and can have as much as 2.5-3 degrees of camber in the front. If you want your car to be streetable though I wouldn't go this far. To make the car more responsive, tossable, but streetable I would go with 1.5-1.75 degrees in the front and 0.70-1 degree in the rear. For autox only max that camber out!! The more the better. The top CS cars at Nationals last year were running 2.5+ in the front with 1.5 in the rear.

Caster

The caster angle identifies the forward or backward slope of a line drawn through the upper and lower steering pivot points when viewed directly from the side of the vehicle. Caster is expressed in degrees and is measured by comparing a line running through the steering system's upper and lower pivot points (typically the upper and lower ball joints of an A-arm or wishbone suspension design, or the lower ball joint and the strut tower mount of a McPherson strut design) to a line drawn perpendicular to the ground. Caster is said to be positive if the line slopes towards the rear of the vehicle at the top, and negative if the line slopes towards the front.

Caster is another thing that our car is blessed with. You want as much positive caster as possible without throwing off the other settings. Why? Because positive caster gives you more negative camber as you turn the wheel. Just like camber, the more caster you have the better. Each car will be different so just tell the tech you want max caster, mine ended up just under 8 degrees.

Toe

The toe angle identifies the exact direction the tires are pointed compared to the centerline of the vehicle when viewed from directly above. Toe is expressed in either degrees or fractions-of-an-inch, and an axle is said to have positive toe-in when imaginary lines running through the centerlines of the tires intersect in front of the vehicle and have negative toe-out when they diverge. The toe setting is typically used to help compensate for the suspension bushings compliance to enhance tire wear. Toe can also be used to adjust vehicle handling.

As long as you leave the toe within factory specs (-0.05 - 0.15 front and -010 - 0.30 rear) you wont get excessive tire wear on the inside shoulder during normal driving even though you are running extra negative camber. I have mine set to -0.01 Total Toe. If you are looking for the best possible handling and don't drive on the street a littel toe out can help.

Thrust Angle

The thrust angle is an imaginary line drawn perpendicular to the rear axle's centerline. It compares the direction that the rear axle is aimed with the centerline of the vehicle. It also confirms if the rear axle is parallel to its front axle and that the wheelbase on both sides of the vehicle is the same.

You want this as close to 0.00 as possible for obvious reasons.

Something to watchout for is Cross-Camber and Cross-Caster

Most street car alignments call for the front camber and caster settings to be adjusted to slightly different specifications on the right side of the vehicle compared to the left side. These slight side-to-side differences are called cross-camber and cross-caster.

For vehicles set up to drive on the "right" side of the road, the right side is aligned with a little more negative camber (about 1/4-degree) and a little more positive caster (again, about 1/4-degree) to help the vehicle resist the influence of crowned roads that would cause it to drift "downhill" to the right gutter. Since most roads are crowned, cross-camber and cross-caster are helpful the majority of the time, however they will cause a vehicle to drift to the left on a perfectly flat road or a road that leans to the left.

The use of cross-camber and cross-caster is not necessary and I wouldn't recommend it for cars for autox. Tell your tech you want the settings left to right as close as possible. My cross-camber is 0.01 Front and 0.02 Rear and cross-caster 0.10 Front.

Street/Autocross Settings:

Camber: 1.5-1.75 degrees Front and .75-1.00 degree Rear
Caster: 7.5-8.5 degrees Front
Toe: -0.05 - 0.15 Front and -0.1 to 0.30 Rear
Thrust Angle: as close to 0.00 as possible

Full Race Settings:

Camber: 2.25-3.00+ degrees Front and 1.50-2.00+ degrees Rear
Caster: 7.5-8.5 degrees Front
Toe: 0.15 - 0.25 Front and -0.1 to 0.30 Rear
Thrust Angle: as close to 0.00 as possible

2nd - Tires and Wheels

This is possibly the biggest difference you can make with your car. With an alignment and a set of wheels and tires, your car will be within 95% of any the top cars out there.

For Stock Class autocrossing you can run what is called a DOT-legal race slick. The most popular ones for our cars are the Hoosier A6 285/30R18 and Kumho Ecsta V710 245/35R18. Since these are legal you won't be competitive without them. In 2006 both the Hoosier and Kumho won big National events.

Hoosier A6 285/30R18 (does not need heat cycling)
Kumho Ecsta V710 245/35R18 (needs heat cycling)

Wheels are more limited for Stock Classes. To be legal you have to have the same width and diameter as stock and the offset has to be within 1/4" of stock. This means 6mm either way. The stock wheel is an 18"x8" with a 55mm offset so Stock Legal specs would be 18"x8" with an offset between 49 and 61mm.

Wheels that make a big difference are the OZ Ultraleggera and the SSR Type C-RS. These are the only 2 readily available lightweight Stock Legal wheels for the Sol/Sky and both won National events last year.

The OZ and the SSR both weigh 18.4lbs, about 5lbs less than stock, which makes a huge difference in acceleration as well as response and initial turn-in.

The SSR is a 2-piece Forged wheel. They use a fully forged barrel and have a patented process called Semi-Solid-Forging (SSF) that they use for the center once the center is forrmed and finished it is welded to the barrel. The OZ Racing Ultraleggera on the other hand is a 1 piece Cast wheel. Since this is a simpler, older technology the OZ is significantly cheaper than the SSR.

Once you have wheels tires and a good alignment you are almost all the way there. If you're the average weekend autocrosser that wants to be competitive but not obsessive you can easily stop right here. Just to be thorough I'll go over what else you CAN do to the car and stay stock legal.

[DeepBlueGXP]

Part 2

Exhaust
Exhaust is unlimited after the cat in Stock classes as long as it exits behind the driver. Some of us have simply hacked off the stock muffler and put a new mount in to support the OE 2.5" pipe. Others have created one-off super-lightweight cat-back exhausts that end just before the differential. It's up to you what you want to do but I would definetly do something. The stock exhaust is terribly restrictive, especially on the GXP/Redline.

Air Filter Element
You can't replace the air box, but you can replace the filter element. K&N makes a drop in filter and it's reasonably priced. Get it.

Brakes
You can change out the brake pads for higher performance ones if you like. Since the pad on our car was all new last year no one had aftermarket pads at Nationals. Since then Hawk has stepped up and made the HPS and HP+ for our cars. I would at least get a set of the HPS pads. Still very streetable and rotor friendly but will have a significant impact on how quickly and effectively you can stop the car. Rotors can be replaced as well so long as they are identical to the OE rotors, (i.e. no slotted or drilled rotors allowed for our cars).

Shocks
If you have a base car just getting the Z0K shocks should be enough but there are some other options out there. So far Koni has made their Double Adjustable Shocks ($$$) for the Sol already and their single adjustable Sport Shock should be out soon, (it's much more affordable). Another guy is researching a revalve for the OE Bilsteins so once that is sorted out there should be multiple options available by spring.

Front Sway Bar
Arguably the Z0K bar is as thick as you need but you can also get the slightly stiffer GMPP bar or the soon to be available Eibach bar. Just don't change the rear. You have to use the stock rear bar, no exceptions.

Do all this and go race! It'll be fun, especially with those tires!!!!

[snaponbob]

Even as I type this, there is the potential it will sound like "one-upsmanship", and it is NOT. But having spent more than two full seasons autocrossing my Redline in A/Stock and making a lot of changes the whole time there is some input that can be shared.

DeepBlue is certainly correct about the classes for the two Sols (2.4 and 2.0).

EXHAUST -- On the 2.4 engine stay with the 2.5" exhaust size. The 3.0" system will actually negatively impact midrange performance. On the 2.0 the 3" system appears to be the way to go. There are a bunch of systems available for both engines from supporting vendors. Running a "straight pipe" exhaust IS legal in Stock. However, it can REALLY be annoying on the 2.4 in everyday driving because the only muffling is from the cat. It is not so bad on the 2.0 as the cat WITH the turbo do a good job in noise reduction. Still noisy, but totally manageable in daily driving. I strongly recommend having the 2.0 exhaust exit through the rear valance as it is WAY HOT. (Do NOT ask!!!!!)
AIR INTAKE --NOTHING can be changed except the filter. No mods, no nothing.
SHOCKS -- Owning Konis, I can share a bit of history. Before the single adjustables were made available in August 2007 (I actually had the first retail set in the States) there were some custom made double adjustables. A set of Konis SA Sport shocks can be had for about $525-$550 and they are wonderful. Set at 1/2 turn firm all the way around they are nicer (subjective, of course) than the Bilsteins, and adjustable (Bilsteins for the Kappas are not). Koni does not stock DA's so the SA's can be converted, but you will have about $2000 invested for the shocks and conversion. Not bad, but than other options start to present themselves. Adjusting the shocks REALLY can make a difference in the way the car handles.
BRAKES -- I ran 2007 and 2008 Solo Nationals with Hawk HPS pads and 2008 with stock front and Hawk Plus pads (better brake balance and stronger braking). There are other vendors for brake pads, and besides the brake fluid the pads are the only change that can be made in Stock class.
SWAY BARS the Stock rules are VERY liberal about the front bar, but NO rear bar changes can be made. If you put a heavier bar on the front it WILL increase understeer. Tuning the rebound on the Konis can offset that somewhat. On the 2.4 Sol the ENTIRE Z0K suspension package can legally installed IF, and ONLY IF, the car has an LSD and ABS, as the rules allow a COMPLETE option package to be substituted. (ALL other optional items on a Non Z0K 2.4 are acceptable under the Comfort and Convenience rule.)
ALIGNMENT -- If the Thrust Angle is not ZERO, the car is incorrectly aligned or damaged - PERIOD.  Accept nothing less. Camber is as stated, REALLY adjustable. Even in street use 1.5 deg negative front and .75-1.0 negative rear will REALLY wake up the handling of the car, and will have VERY little effect on tire wear. Up to a point the more negative camber, the better. That said, after MANY alignments, I have found that more than 1.8 deg negative rear camber is actually counter productive. Street, maybe 1.0, and Solo 1.5 - 1.8 will work best. Front camber can really be aggressive with 1.5 for street and 2.4 - 2.8 front negative being a good range. Camber needs will be different on the 2.4 and 2.0, and bars, springs, and shocks can be determining factors as well. Caster is adjustable, but without a special (and expensive) tool the rear caster can't be measured. A good tech can align the rear without any negative impact on the handling of the car. Rear caster is factory set at 4 degrees. Front caster is checked with any four wheel aligner, and is set at 8 degrees at the factory. Up to about 2 degrees you'll be able to maintain 8 degrees caster. Once camber goes beyond 2 degrees caster will be lost, and at 3 degrees neg camber the most you'll have is about 6.5 of caster. The important issue is to have EQUAL caster left and right or you will feel some steering "pull". Toe in/out is a variable that can "tune" corner turn in and rear "stick", but if you are not ready to play with the adjustment at an event set the front at "tolerance" toe out, and the rear at half the front setting but use that number as toe IN rear on a GXP/RL and ZERO rear toe on a 2.4. It's subtle, but effective. I do the adjustment at events at about 3/16" out front and 1/16" in on the rear.
WHEELS AND TIRES   As Deep wrote, DOT "legal" R-Comps are THE way to go if you want to have ANY chance of being "competitive". The sizes he referred to are right for C/S, but the only tire to run on the 2.0 is the 295/30X18 (for a lot of reasons). Tire Rack used to sell the SSRs (about $500 each) and still sells the OZ's (about $300). Both are a tad over 18 pounds vs. 26 pounds for the OEM rims. (The picture of my car is with OZ's. Silver, black, and gray are available.)

Wanna do a tune and get more aggressive with some power and handling mods? Well, then the 2.4s go to C/Street Prepared and the 20 to B/SP (a change from 2007 and 2008). Then there are ALL SORTS of games to play with. That's my plan for 2009 and I have a shopping list!! Can't wait.

Questions? Fire away. The Kappa platform really is an amazingly adjustable system, and they REALLY respond to changes. The more work you can do yourself the more fun you can have tweaking the car.

[CPB]

thanks for all the great info. have auotcrossed a C Prepard car for years but this year will be running my 2008 GXP in stock class. Big diffence in cars so I need all the set up help I can get.

[DeepBlueGXP]

Keep us up to date on your racing.  I'd love to hear about it!!!

[snaponbob]

thanks for all the great info. have auotcrossed a C Prepard car for years but this year will be running my 2008 GXP in stock class. Big diffence in cars so I need all the set up help I can get.

Oh lord, you won't know how to act !!!!!!!!!!! Jumping out of a great thundering Mustang or Camaro with 12" wide slicks that never fully warm up, and then into a nimble sports car is going to be a challenge. Guess what? When you get the Kappa sorted out and adjust to it you may find your times may actually be QUICKER than the C/P car. (Disclaimer: all said in the finest sprit of Solo bench racing    :wink:) Welcome to the club. Any detail questions feel free to ask. Obviously what may work for one guy may be different for another, but having a good baseline is a big jump without all the stumbling around. BTW, the first expenses should be a Curt hitch, Harbor Freight trailer (w/12" wheels), a set of OZ's and 295 Hoosier A6s, and put aside money for a second set of A6s during the season. After about 50-60 they will fall off.

[CPB]

76 Cmaro with 450HP 4:11 gearset with 4speed just had to put right foot down LOL will now have to learn to drive a car and carry some speed. and yes I am sure some times will be faster most times could not come close to using all the power in cp car.

[snaponbob]

76 Cmaro with 450HP 4:11 gearset with 4speed just had to put right foot down LOL will now have to learn to drive a car and carry some speed. and yes I am sure some times will be faster most times could not come close to using all the power in cp car.

HA !!!!!!!!!!!!! KNEW IT. Why do the CP guys build road race monsters for CP? It seem that if the these are such nice E/SP cars, why not just take the SP build a little further out instead rock crushers? They all seem too wide, too stiff, and just sort of too harsh. Of course, since you are coming out of a VERY wide car the Kaapa will not feel too wide, and it is Corvette wide. Carrying speed" is always helpful, but try to imagine a compromise between "speed maintainence" (C/Stock Sols and Miatas) and "point and shoot" (your Camaro). Do you plan on any shocks or R-comps?

[CPB]

very wide and very long wheelbase but you can not beat the feeling of 450hp pushing you back in the seat. Will do alignment first and run stock tires. Had back surgery so had to give up hard ridding CP car. going to try a couple events first before buying tires etc. see if back will take the stress.

[snaponbob]

very wide and very long wheelbase but you can not beat the feeling of 450hp pushing you back in the seat. Will do alignment first and run stock tires. Had back surgery so had to give up hard ridding CP car. going to try a couple events first before buying tires etc. see if back will take the stress.

With stock tires, 2 deg neg front camber, 1.5 neg camber rear, 45psi front and 40 psi rear. (BTW, that's not a bad alignment on the street.)  Be forewarned, the wild bouncing will NOT be something wrong with the shocks but it's the tires acting as their own undamped springs. I took two runs at an Evolution School in March with the stock goodies and I thought I had blown my front Konis. Switched to my Hoosiers and all was right with the world. It will just be different than ANY C/P car. You'll fell like you are a couch by comparison !!!!!!!!!!!!!

[Critterman]

Why that high of a tire pressure with stock tires"?

[snaponbob]

Why that high of a tire pressure with stock tires"?

A couple reasons. 1) The higher aspect ratio of the stock tires mean less stiff sidewalls, thus roller over if he really gets hooked up. Depends on his alignment. 2) Tires act like springs. (That is why NASCAR teams play with pressures during the race, as it effectively makes minor overall spring rates as the car sees it.) Higher pressure means higher spring rate on the part of the tires. When I ran mine on stock tires at an Evo School even the instructor agreed that it was bouncing like a hobby horse on meth!!!! I tried more pressue, which DID help, but swapped to my Hoosiers as it still was, ummmmm, "unpleasant". CPB probably knows what I mean.

[RUTurbo]

For any interested parties, SSR wheel's Bob was referring to can now be found at 25% off on a couple sites, a great deal IMHO.

[snaponbob]

For any interested parties, SSR wheel's Bob was referring to can now be found at 25% off on a couple sites, a great deal IMHO.

Good point and would have been my choice BUT ................... Tire Rack is selling the Solstice/Sky fitment SSR's because they are (apparently) being discontinued. At the time I bought my OZ'z, the SSR was ~$500 each vs. OZ's at ~$300 each. The OZ's are about as light as one can get in an 18X8 wheel at 18.5 pounds. And Tire Rack really supports the SCCA and is a very good vendor.

[RUTurbo]

Yeah TR is great. Purchased my SSR's last month because of the inventory close out. I couldn't pass on a 2 piece wheel for ~325. Only thing that may be seen as a negative for some is there is only one color option, while the OZ has several. Both are great and offer real value for the money.

[snaponbob]

Yeah TR is great. Purchased my SSR's last month because of the inventory close out. I couldn't pass on a 2 piece wheel for ~325. Only thing that may be seen as a negative for some is there is only one color option, while the OZ has several. Both are great and offer real value for the money.

You may want to buy a fifth wheel, as you may need to replace a damaged one and one will not be available!!!! Better to be prepared than to be  pissed!!!!!!!

[CPB]

you are right about higher tire pressures. we had to use some stock street tires in the rain once on the CP car and had to get a lot more pressure to keep them from rolling onto side walls. Thanks for all the great tip snaponbob now just have to wait for spring to get alignment and first event in April will make sure to let you all know what happens.

[RUTurbo]

You may want to buy a fifth wheel, as you may need to replace a damaged one and one will not be available!!!! Better to be prepared than to be  pissed!!!!!!!

Great advice!! I'd be all for it if I wasn't agressivley saving for a set of Volk's!