The 2G Turn Harder Page

The Left Front Suspension
The Left Front Suspension

This page will help you get the best handling out of your 2G DSM, both on the street, on the racetrack and the autocross course. Note that many of these modifications will take you out of Stock class in SCCA racing, so decide which class you want to run in, and for how long. Mods 1-6 are legal in stock class, within limits. This is an evolving page, mostly generic information for now, but I'll be adding 2G specific information as we learn more about how the 2G DSM handles.

For a description of camber change during cornering see: Body Roll 101

A discussion of weight transfer, body roll, spring rates, and swaybars: Weight Transfer 502

In SCCA Solo racing, the 2G Turbos run in G-Stock, E-Street Prepared, C-Prepared, and E-Modified. The 2G non-turbos run in E-Stock, C-Street Prepared, E-Prepared, and D-Modified.
 

1. Driver
 

"Oh, he can drive…he can drive beyond the limits of the tires, the engine, the car, anything!" Harry Hogg, Days of Thunder


  The driver is the most important part of the handling system of the car. If you don't know how to handle the car, all the following mods won't do you near as much good. Get some seat time with your local SCCA, BMW Club, Porsche Club, Corvette Club or whatever. Autocross/Solo II is a good way to get seat time nearby, safely, and cheaply.

Aside from the larger, more famous, and more expensive driving schools such as Skip Barber and Bonderant, many aforementioned clubs offer driver's schools sometime during the year, and McKamey Driving School travels around the country to various SCCA regions and has very good instruction for the money.
 

2. Tires and wheels
 

"Tires is what wins a race" - Harry Hogg, Days of Thunder
  (Any DOT-approved tire is legal in Stock and Street Prepared classes. Any wheel is allowed in Street Prepared, but only wheels of stock width and diameter are allowed in Stock class. Also, in Stock class, the offset of the wheel must be within .25" of stock. Some local clubs may have a 'street tire' class for cars with tires meeting a minimum treadwear rating.)
 

The tire allows the rest of the suspension to do what it is supposed to. It is the final link in the chain of events from the driver to the road surface. Provided you give it the correct inputs, the tires must be able to produce the desired output. The standard 100,000-mile passenger tires from Walmart may last you the life of the car, but are not going to produce the kind of handling you're looking for. The wheel also has a large effect on handling, particularly in how well it matches the chosen tire.

First, decide on a tire size. Anything wider than a 225 is going to stick out beyond the fenders a little. 245's will fit without rubbing with the proper wheel. Anything wider than that will require some stiff springs to keep the tire from contacting the fender, or you'll have to have the fender flared. In reality, the stock bumpstops in front will prevent wider tires from rubbing on the fender, since there isn't much travel up front, but more on that later.

Width:

As they say, wider is better. Wider means more contact patch, and better traction, as long as you run an appropriate wheel. A too-narrow wheel will cause the tread to become round instead of flat, and you lose contact patch. A narrow wheel will also allow the sidewall to flex more and lose more contact patch under cornering. The wheel, at a minimum, should be at least 70% of the tire width. The stock 215/55-16 are actually too wide for the stock 16x6 wheels! The only time you would want to break this rule is for competing in stock class. The BFG R1 has a super stiff sidewall, and works acceptably on narrower rims. Unfortunately, they have been discontinued, and it appears that their replacement won't be as forgiving.

The wider the wheel you get, the better the response of the tire is going to be. For a 225mm tire, get a wheel that is 7 to 8 inches wide. For a 235mm tire, 7.5 to 8.5 inches, and for a 245, 8 to 9 inches. The wider wheel will be better at keeping the tire positioned under the wheel, and not deforming under cornering loads.

Height and Aspect Ratio:

A smaller diameter tire will give you a shorter gear ratio, and may improve acceleration in the FWD cars. The AWD transmissions are already geared lower, and a smaller diameter will mean you can't hold any given gear as long (shifting more costs you time), so isn't as much of a benefit. Getting a tire nearly the same diameter as stock means you won't have to recalibrate the speedometer. To compute the approximate tire height, multiply the width in millimeters by the aspect ratio, divide by 12.7 and add the wheel diameter in inches.

The Aspect Ratio (a.k.a. Series) is the '45' in 235/45-17. It means the sidewall height is 45% of the section width (235mm in this example). A lower offset ratio (shorter sidewall) will mean a harsher ride and less compliance. A more compliant tire (higher sidewall) will take hold slower and easier, which means it is more forgiving of sharp driver input. However, a shorter sidewall will keep the tire from rolling and riding on the sidewall under hard cornering. There's seems to be a happy medium somewhere around 45 to 50 series.

Street Use:

Factor in your local climate. If you're going to be driving on snow or ice, consider a all-weather high performance tire, such as the Dunlop SP4000, BFG VR4, and the Yokohama AVS S4-Z. In climates that rarely get snow, or if you plan to have a set of snow tires on for winter, get a set of ultra high-performance tires like the Dunlop SP8000 or Bridgestone RE71. For maximum handling, some people have been known to run DOT-approved road-race rain tires (such as the Yokohama A032) on the street, but they are noisy and might not be optimal in the rain, nor do they last as long. Never run pure autocross or road-race slicks on the street, unless you want to do a Nancy Kerrigan impersonation the first time it rains. To and from events is ok, as long as you watch the weather. For our somewhat traction-deprived FWD drivers, the tall sidewall will be a big advantage in absorbing the shock of acceleration and helping keep the tires hooked up.

Autocross/Road-racing:

Consider getting second set of rims to mount your autox tires on, no matter what kind of tire you put on them. The inevitable flat-spotting and tread chunkin that occurs in autocrossing (particularly if you don't have ABS) will make street driving very annoying. For the ultimate in autox grip, consider a set of autocross- or roadrace-compound tires.

  • The BFG R1 is discontinued, but was probably the best tire around for Stock class cars due to it's built-in negative camber and ultra-stiff sidewall. The new g-force tire that replaces the R1 does not have the build-in camber and is molded at 3/32" tread depth, unlike the 6/32" R1, so they probably will not last as long.  However, they are supposed to be a more predictable, compliant tire.  They may end up being more Hoosier-like.
  • The Hoosier tires tend to wear quickly, especially if your camber is off, but are the ultimate in DOT-approved stickiness. The Hoosier Autocrosser bias-ply tires are actually too soft for our heavy cars, especially in hot weather, and they damage easily.  The Hoosier Radial comes in 2 tread compounds, A for autocross, and R for roadracing. The A compound is quite soft, and may not work well on very hot days, nor is it suitable for dual track/autox duty. The new tread compound that Hoosier has come out for 1998 with is supposed to last longer and and be more forgiving of insufficient negative camber.
  • The Yokohama A008RS & RSII were also a good tire, and lasted longer than either the Hoosier or the BFG, but at some cost in grip. Unfortunately, the A008RS and A008RSII have been discontinued and Yokohama hasn't come out with a replacement yet, except for the A032.  The A032 is more like a road-racing rain tire, and would be a good choice for a street/autox tire.  They are loud, however.
  • The Kuhmo V700 tire appears to be every bit as good as the R1. In fact, I've found it to be a little more predictable at the limit. They have a distinct "howl" at the limit, unlike most tires that squeal. Good audible feedback to know when you are at the limit. It also lasts over 100 60sec autox runs. They are molded at 6/32nds tread depth, and are available shaved to 3/32nds, but this doesn't seem to be necessary and seems to shorten tire life. I'll most likely be running V700's for the 1999 season.
  • Toyo also make a suitable tire, the RA1, and should be very similar to the Kuhmo.
    •


    For Stock class cars, get the widest tire you can fit on the rim. For most 2G's, this is a 225/50-16. I'd stick with the BFG R1's for this size, as the extra-stiff sidewall works well with too-narrow stock 16x6 rims. For '97+ AWDs, I've heard you can put 235/45-17's on. For the Street Prepared and beyond, a 225/45-16 on a 16x8 or 235/45-17 on a 17x8 or 8.5 is probably a good start, but 17" tires are rather more expensive. If you have very stiff rear springs (stiffer than say the Eibach Pro-Kit or H&R springs), you CAN put 245/45-16's on a 16x8 +35mm offset rim. 16x9's with Hoosiers would be best for this setup but would be expensive. Note that the fronts, even at full bump, will not rub the fender. There isn't that much suspension travel. The rear 245's WILL rub at full bump, but the stiff springs should prevent that.

    The larger the diameter, the lower aspect ratio of the tire required to keep the diameter close to the same, and as mentioned under 'Tires'. The shorter sidewall is less compliant, in that it's transition from gripping to sliding is less predictable. The shorter sidewall also means the rim has less protection from potholes and bumps, so you can damage the rim easier. As I mentioned under 'Street', the taller sidewall is a big help at keeping the FWD cars hooked up by absorbing the shock of acceleration, particularly when dumping the clutch. A 14" or 15" wheel with a 50-series sidewall might be an advantage here.

    (see the Wheel Offset FAQ).

    3. Alignment
     

    (Legal to change in SCCA Stock Class within stock limits of adjustment. For DSM's, that means no camber or caster adjustment. In Street Prepared class you may use eccentric bushings to adjust camber)

    Toe is the relative angle between the front or rear tires. If the tires point in towards each other (pigeon-toed), that's toe-in. If they point out, that's toe-out. Front toe-out will improve turn in and shorten the turn radius by making the inside tire turn more than the outside. However, too much and the car will wander under braking. Some people have recommended about 1/8" to 1/4" for autocross. On the street, this will severely increase tire wear, so keep the toe at zero. If you're swapping tires for competition, front toe is easy to change with a pair of 22mm wrenches (or even better a 22mm and a 7/8" Flare-end). Mark the two settings with dots or lines of paint on the tie-rod to make changing them easier. I'm not sure how much this helps the 2G cars, as our suspension already goes toe-out under compression. Try and see what works best for you.

    Camber is the angle of the wheels from vertical. If the tops of the tires are closer together than the bottom, that's negative camber. Negative camber is will keep more tread in contact with the road under hard cornering, and lessen outside shoulder wear during racing. As the car rolls in the turn, the suspension angle tips the wheel to the outside of the turn, causing the inside shoulder to lift up from the road surface, reducing traction. By adding negative camber, the tire will gain more contact as it rolls over, increasing traction. Too much will also increase tire wear under street driving, and make the car more darty, prone to bump-steer and tracking with grooves in the road. Fortunately, the 2G suspension gains negative camber under cornering, so they can get by with less static negative camber. Note that lowering the car will also induce negative camber.

    Camber should be tuned using a tire pyrometer and a skidpad, or lacking a skid pad, an autox course. Something long enough to get the tires good and hot. Measure the temperature immediately, before they cool, at 3 points across the tread:
     

    4. Brake Pads


      (Unlimited in Stock and Street Prepared classes)
     

    Upgrading the brake pads will allow you to brake harder, and thus carry more speed later into corners. More importantly, better pads withstand higher temperatures, so they won't fade as easily when you're using the brakes a lot. There's nothing worse than going hard into a corner and putting the pedal to the firewall, finding out you've overheated the brakes. The performance pads are more prone to squeal, and often produce more brake dust. Some metal pads are extremely hard on the rotors. MetalMasters, Performance Friction, and Hawk Autox compound all seem to be good.
     

    5. Shocks
     

    (Legal in Stock Class as long as the spring perch is the same height as stock. Unlimited in Street Prepared Class)
     

    Shocks control the rate at which weight is transferred from one side of the car to the other as you enter a corner. Despite the name, all shock absorbers really do is provide increasing resistance to movement with increasing velocity, and dampen the action of the springs. This is why the rest of the english-speaking world refers to them as "dampeners". Stiffer shocks will provide better response and, most importantly for autox, increased transient handling. By using different shock stiffness at the front and rear of the car, you can fine-tune the oversteer/understeer characteristics of the car, although not as effectively as springs and swaybars.

    For autocross and roadracing, a set of adjustable shocks important for tuning the suspension, as well as maintaining a livable ride on the street. The stock 2G shocks are fairly weak, so this makes a huge difference. The biggest difference you will notice is in transitional maneuvers like slaloms, where you are loading and unloading the suspension rapidly. If you're going to do springs in the future, wait and do both together and avoid doing the same work twice. For the ultimate in adjustable suspensions, get a set of adjustable 'coil-overs', threaded shock bodies with an adjustable spring perch that allows you to easily adjust ride height and balance the corner weights, as well as choose from a variety of spring rates.

    The three available shocks are the Koni's, Tokicos, and the GAB's. The 2G Koni's, unlike the 1G version, are adjustable without removing the shocks. The current Konis available are only adjustable in rebound. The Tokico's and GAB's are adjustable from the top, and adjust both compression and rebound at the same time. On their softest setting, the ride of the Koni's isn't noticibly different from the stock shocks. Even on the softest setting, however, the GAB's are quite stiff. Consequently, the GAB's are stiffer than the Koni's at the hardest setting. If you're mainly concerned with street driving, get the Koni's. If you're the competitive type, get the GAB or Tokico for the front shocks. I have had 2 rear GAB shocks begin to leak on me, while the stock shocks in the same location have lasted all winter with the coilover springs! There may be a quality control problem with them.
     

    6. Harness and Seat
     

    (Harness is legal in Stock Category. Both are legal in Street Prepared)
     

    Now that you are braking and cornering harder, you'll find yourself sliding around in the seat. The natural reaction is to brace yourself in by pressing against the steering wheel, which reduces your feel for how the car is behaving. Keep yourself steady with a 4-, 5-, or 6-point racing harness. A 2" 4-point is fine for autox, and more comfortable, but may not meet the requirements for other types of racing. A good seat that provides more side support than the stock seats helps. Schroth makes a good 4-point harness that is street legal, with 2" wide straps that seem to be more comfortable than the usual 3" ones.
     

    7. Springs
     

    (Spring changes are prohibited in Stock class. Legal in Street Prepared)
     

    Springs absorb shock and control suspension movement. Stiffer springs will reduce body roll, brake dive, and acceleration squat. As we learned in the Alignment section, body roll will result in positive camber, reduced contact patch, and loss of traction. For an advanced discusion, see Weight Transfer 502.

    At first, this might seem like a good first mod. Springs are fairly cheap (<$250), and lower the center of gravity of the car. If your goal is looks, fine. If your goal is handling, do the shocks at the same time. The 2G's shocks are somewhat weak, and without the stiffer shocks, the suspension will be underdamped and bouncy, resulting in lots of airdam scraping. Body roll will feel reduced, but the car will actually handle worse in some circumstances due to the lack of dampening, particularly in transitional maneuvers like slaloms. Springs can be used to change the understeer of the car by increasing or decreasing the spring rate at one end. Too stiff, however, and the car won't absorb bumps.

    Front Suspension:

    Even stock, the 2G does not have much travel in bump. With the stock springs, the top of the shock sits about 1" from the bottom of the bumpstop! The bumpstop itself will probably compress an additional inch or so, resulting in a rise in spring rate, becoming stiffer as the bumpstop compresses. This is why, especially with stiffer shocks, the 2G DSM handles slaloms great, but pushes heavily in sustained cornering. In addition, you may hit the bumpstops under braking, resulting in a dramatic increase in front spring rate and weight transfer to the front tires. Lowering springs will only make this problem worse! Even the stiff springs available with the coilover kit do not entirely stop this without some consideration as to ride height.

    Now, for the coilover springs…The ride, with 450lb/in springs in front and 300lb/in in back, is NO WORSE than with the H&R springs! In fact, the ride is somewhat improved! The 1.3" drop provided by most aftermarket springs pretty much just sits the car down on the front bumpstops, making for a rough ride. With the coilover kit, body roll is almost completely gone, and tire wear during competition is much more even, rather than mostly on the outside shoulder. I would HIGHLY recommend that you go ahead and spend the extra money and get the coilover kit rather than the standard street springs, even if you don't autocross. For some pictures comparing the H&R springs to the coilover kit, see autocross.html.

    Conventional wisdom for a RWD car says you should use the softest spring in the rear that keeps the suspension from bottoming out. Thus the soft rate helps tame oversteer while keeping it from hitting the stops and producing that sudden rise in rate that will cause snap oversteer. This applies in reverse to our AWD and FWD cars. The softer spring in front will help the front hook up while keeping it off the stops will prevent it from 'washing out' of the turn. Front springs in the range of 450-550lb/in seem to work well. I think the 450's will do fine with the addition of a front swaybar, but the FWD tuners may forgo the front bar and just get the stiffer front springs (see Anti-sway bars, below). In addition, to lower the car without sacrificing bump travel, I suggest getting or making upper spring perches that will move the shock rod, and thus the bumpstop up. This will keep the car off the bumpstop and improve cornering in tight, sustained turns. Ground Control makes a rather nice set to go with the coilover kit.

    Rear Suspension:

    AWD: Well, now, conventional wisdom says that to reduce understeer we should stiffen the rear suspension up. But, our 2G rear suspension has alot of toe change during suspension travel. What this means is that, under acceleration, when the car rocks back on the rear suspension, the outside rear tire will toe out, point away from the turn, and bring the rear end around. It also means that the rear suspension toes in under braking, which increases stability, but also increases understeer under braking. If you are a trail-braker, using the brakes in the corner to swing the back end around, a stiffer rear suspension will help this. Turns taken at constant speed would also benefit from a stiffer rear suspension, but this could be accomplished with a larger rear swaybar. For this season, I will be experimenting with the softer rear suspension to generate trailing throttle oversteer. Stay tuned for further updates!

    FWD: Stiff. The stiffer, the better. 400lb/in or more, and a big rear swaybar. Even try putting narrower tires on the back than on the front. Really, I'm serious! If you FWD guys find a good setup that takes most of the understeer out of the car, let me know. I'm sure it's possible, just takes a little more work. 

    8. Strut Tower Braces

    (Not allowed in Stock category. Allowed in Street Prepared, but must only connect top or bottom of the suspension only, so it cannot be triangulated to the firewall.)
     

    Now that you've stiffened the suspension your cornering forces will increase. This will cause the body itself to flex in response to cornering and bump forces (it already did this before, it was just less noticeable). A strut tower bar keeps the strut towers from flexing. This also has the added benefit of reducing the creaks and rattles of the car. There are front and rear upper bars and front lower bars available. Note that while an adjustable bar may be more convienent to put on, the adjustability is additional flex in the bar. Consider having the pivot points welded after installation.
     

    9. Anti-Sway bars
     

    (Stock category: The front anti-sway bar may be removed or replaced. Street Prepared: Unrestricted)

    Take a look underneath your 2G. You'll notice a linkage going under the car, connecting the lower control arms. It's free to rotate up and down, held in place by the end links and a pair of bushings connected to the frame. There is one front and one rear. These are your stock anti-sway bars! Fortunately, Chryslebishi provided us with some pretty hefty swaybars on the front, and the AWD cars have a pretty good one on the back, too. The front bar is 19mm and the AWD rear bar is 18mm. Compare this with the 8-10mm bar off a 3000GT SL!

    Also known as swaybars or anti-roll bars, these are a good way to tune the car's cornering response. Swaybars work by linking the left and right suspension together. Swaybars act like springs, but only when the wheels move relative to each other. If you hit a speed bump with both wheels, the swaybar has no effect. This is good for ride comfort, since many road irregularities hit both wheels at the same time. When you corner, however, the suspension on the outside of the turn compresses while the inside suspension expands. This is where the swaybar comes in by providing additional spring rate under cornering, reducing body roll and improving traction. As the suspension on the outside of the corner begins to compress, it pushes up on the swaybar link on that side, causing the swaybar to act against the inside suspension.

    Swaybar stiffness increases with the 4th power of the radius, so a 20mm bar is 52% stiffer than a 18mm bar. Stiffness is also directly proportional to the length of the end arm where it attaches to the lower control arm. By having some sort of adjustability at the end of the arm, you can tune the stiffness slightly, but it's difficult to get much adjustment on a production car, particularly ours. The alloy of steel that the bar is made of makes little difference in the stiffness, as the Sheer Modulus of Elasticity does not vary much between different steels.

    Stiffening the swaybar at one end will improve weight transfer to the other end, resulting in improved traction on the end opposite the stiffer swaybar. For DSM's, that means the rear sway bar should be stiffened reduce understeer. You could slightly stiffer swaybar in front will help control body roll, depending on the front springs, and a significantly larger rear bar to eliminate the understeer. The bars must be proportional to the spring rate, so a 1" rear bar will not work well with stock springs…in fact it will cause the inside tire to lift of the ground in a corner. Lifting the rear tire might not be a bad thing on FWD cars, since it's only there to hold the back end off the ground anyway. However, a large enough front bar may lift the inside front tire off, or at least reduce the weight on it, and worsen wheel spin coming out of corners. If any FWD driver gets a chance to try out front swaybar setups, let me know how this is affects wheel spin.

    If you're in Stock class, you can change the front bar ONLY. Now, as I said, stiffening the front bar will improve weight transfer in the rear, getting more traction back there, but will also reduce front body roll and keep the tires more vertical, improving front traction as well.

    Addco and Suspension Techniques have both promised swaybars in the near future. A company called RM Racing has also put out a set that is 13/16" (20.6mm) both front and rear, and the set is supposed to work well with the stock springs. With the coilover kit, I'm not sure a stiffer front bar is necessary, but would help keep the car off the bumpstops in corners. Ideally, I'd like to have a set of rear bars in 20mm, 22mm, and 24mm to be able to tune the car for various track conditions. Stay tuned for a review of the RM Racing swaybars!
     

    11. The Big Brakes
     

    (You're on your own. Bigger brakes will have little affect on the street. For autox, even just cross-drilled rotors will put you in Prepared, unless you are upgrading a FWD to AWD brakes)
     

    If your aim is roadracing, you'll probably want to upgrade the brakes at some point. Larger diameter rotors will provide more braking power and reduce brake fade. Larger brake calipers with more pistons will also increase braking power. There's some debate about crossdrilled vs. slotted vs. solid rotors. Crossdrilling and slotting are supposed to help hard braking somewhat. Crossdrilling, however, tends to cause stress cracks at the holes, where as slotting doesn't. Slotting is also easier to do. Of course, crossdrilling looks cool, too.

    A couple of notes on the stock brakes: The 2G AWD cars come with 2-piston front calipers stock and considerably larger rotors than the FWD cars. Some of the early '95 cars also had vented rear discs. Consider these as potential upgrades to save cost, as well as being a Street Prepared legal modification.
     

    12. Roll Bar/Roll Cage
     

    (Roll bars are legal in Stock and Street Prepared and are required for Solo I events and some track events. Roll bars may be welded. Roll Cages must be bolted in Stock and Street Prepared)
     

    The roll cage must not only be designed to protect the occupant (that's you) in a roll-over, but should also be designed to add chassis stiffness, even if it's bolted in. Make sure it meets all the requirements of your racing organization.
     

    13. Bushings
     

    (Shock Absorber bushings are legal to change in Stock Class. All suspension bushings may be changed in Street Prepared, provided metal proportions remain the same.)
     

    Well, it looks like Suspension Techniques will have suspension bushings available soon, if not already. For now, the universal swaybar bushing set #9-5122 fits the 18mm rear bar on the AWD, and the #9-5123 may fit the front 19mm bar after bending the bracket.

    Bushings will reduce the compliance of the suspension, preventing it from flexing under loads applied during suspension movement. In short, the suspension will react faster to inputs, improving turn in and keeping better control of the movement of the suspension. It will also increase transmission of vibration to the car, however.
     

     Some Suspension Tuning books:

    Tune to Win, by Carroll Smith

    Performance Handling, by Don Alexander

    How to Make Your Car Handle, by Fred Puhn