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Put That Power Down - Tech

Horsepower’s for Closers But It Means Nothing If You Can’t Put It Down Effectively. Set Up Your Chassis Right and You Could Become a Track God.

Super Street Archives
Feb 1, 2012
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Basic physics tell us that quicker lap times and winning the traffic light drag races are more about grip and balance than outright power. Masters of the art of chassis tuning such as Lotus recognized this decades ago, and their range of perfectly matched sports cars are the pinnacle of this philosophy proving that any Elise can kill most cars through the twisty stuff…

But what can the humble driveway tuner learn from these chassis setup gods? Sure, at the most extreme levels, tuning a chassis is about heavy calculations, mathematical equations and the interaction of materials in complex ways that have caused heated debates as long as the automobile has been used in anger, and enough books have been written to fill entire libraries. You see, everything on your car is inter-related—suspension, brakes, steering, tires and weight distribution. These are just a few of the factors to consider when getting that balance just right.

Luckily for us, many of these calculations have been done for us and the arguments already had by the manufacturers of the finest aftermarket parts and it’s a question of mixing and matching components to transfer power to the street—but as everything is connected, where on Earth do you begin?

To begin, understanding the principle that in any form of performance driving the bottom line always comes down to the contact patch of the tires in relation to the road surface is key. Too many people spend bucket loads of cash on power upgrades, when in reality some of the wisest ways of spending your hard earned dollars are through modifications and upgrades to the parts than actually transfer put that power down and make it stick.

The other important notion to get your head around is that making an adjustment in one area can drastically affect the balance elsewhere—quite often messing it up massively—and sometimes just identifying a poor handling issue can prove, let’s say, tricky.

Is My Car Poor Handling Then?
No, not necessarily. Manufacturers spend billions of R&D dollars on making their ranges handle well out of the box, and who are we to dare to argue? In actuality, it’s all about compromise.

Very few of us spend our entire lives on the track, and the same said manufacturers have to build cars for everybody and every situation—a tough job. But to sweeten up your handling to gain those vital extra tenths of a second, we have to identify what those compromises are and eliminate them—the only way to do this properly is through serious seat time to identify the weaknesses.

Once you have it’s about making modifications in an incremental fashion to identify what works and what doesn’t. I know I’ve said this before, but I really can’t stress this enough—one alteration can hold the key to everything else, but in the same way, one extra turn of a spanner or 5mm difference here or there can be counter-productive to the point of turning your car into a pig. In this respect probably the best tools in a chassis tuner’s box are a pencil and a pad—noting what works and what doesn’t one at a time will unlock those magic mods that allow you to enjoy your valuable track time (or drive home from work) to the fullest.

Looking closely at chassis tuning offers a range of benefits to both you and I, including: 1) A well-setup chassis can make an average driver look a lot more like a track god as if your car’s easier to handle at speed you’ll set quicker times; 2) Your tires will last longer under extreme torture; 3) Your car will stay in one piece longer as you’ll stand a much greater chance of avoiding the barriers.

Now, for a short disclaimer: This guide is in no way a quick fix to all of your ride’s handling issues. But what it will do is explain what’s what under the skin of your car, how it affects the behavior of your car in certain ways and in certain situations and what you can do about it…

How Low Can I Go?
Any car has two roll centers (generated by the front and rear suspension); they move as the car corners, brakes, accelerates and any combination of the former, and to get your car handling sweetly, the roll centers must be matched correctly (although not necessarily at the same height).

With McPherson struts—none of that live axle nonsense—the front roll center is about a third of the distance between the lower control arm’s pivot point and the ground. As you lower the car, the roll centers will change and the further the difference between the two, the more the car will roll. This affects handling and stability.

On track you want the car as low as possible without the tires scrubbing and vital components grounding out or inducing the dreaded bumpsteer (see jargon buster). On the road, this isn’t practical due to potholes, drain covers, small animals and the like, but getting the center of gravity as low as possible will increase stability and reduce body roll, of course optimizing it in relation to the rest of the suspension components.

Rock and Roll
Every time you turn that wheel in the cockpit, the attack angle of the tires to the tarmac changes and this causes the car to pitch in and the body to roll towards the outside of the corner. Doing this reduces the contact patch, and therefore grip, so minimizing and controlling body roll is one of the first places to start.

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Most modern imports use independent suspension, so the front and rear deal with their share of the body shell’s inherent roll separately. As most cars also use a monocoque chassis, all the stressed members are incorporated into the body, thus exerting fairly extreme forces under acceleration, braking and hard cornering that alters the suspension geometry and alignment.

Increasing rigidity is achieved simply in the first instance by tying those independent suspension components together. So, rather than the flexing of individual parts working against each other, they work in harmony and forces are transferred more evenly.

If you want to see chassis flex in action, check out the way a car’s wheel cocks itself up under extreme cornering loads – logic now surely suggests that your car’s available traction is reduced by 25%. This looks cool, but it really isn’t a good scenario for quick, controlled cornering bracing!

Keep It Tight, A’ight
Ultimately, any of the modifications that follow must be made from the onset in relation to your overall plan for the car. For example, if you plan to go all-out track mental, then a cage will be an essential, and fitting it will determine the subsequent route you take with other chassis alternatives as the rigidity will change the overall bias and weight transfer. This is because what once worked well on a chassis with a certain amount of torsional flex won’t work the same once the structure is stiffer.

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With this in mind, some simple first steps for tying the chassis together start with the addition of strut braces. These can be had for as little as $150 these days—cars like the RX-8, 350Z, and Subaru STI come with them already—and are one of the easiest ways of creating that physical link between the tops of the suspension towers to control independent flex. The more you spend, the better materials and more adjustability you get, but ultimately a more rigid chassis will keep the car flatter and more stable and give a more direct steering response—all good stuff.

Next up we can start fine-tuning, a good move now is up-rated (either thicker or stiffer material) anti-roll (or anti-sway) bars. Just as we’ve already linked the tops of the suspension struts, these will link the bottom joints and likewise balance any motion from one side of the car to the other. As most cars are biased towards understeer from the factory—it’s safer that way, being harder to generate wild throttle oversteer—a larger rear bar tunes out the tendency to plough on its corners and give sharper turn-in. We would always suggest upgrading front and rear together however, as, for example, by placing a larger front bar on a RWD car will just compound the problem creating a more nervous chassis—be careful as you go significantly larger at either end though so as not to upset the chassis too much. Again, incremental changes are the way forward. For around $200 front or rear—a host of top manufacturers make these, Cusco, H&R, Eibach, Tanabe, ST—this is a perfect complement to the strut brace.

For ultimate stiffness, a rollcage not only protects you in case it all goes horribly tits-up but is precisely triangulated to fix to key structural and suspension points on the chassis. Cages come in two flavors, bolt-in or weld-in, and the more expensive motorsport-oriented cages will offer multiple fixing points and effectively act as one giant strut brace for the entire car’s cockpit. Undercar braces also increase torsional rigidity by further fixing the suspension and structural shell points together—top JDM makers like Carbing/Okuyama and YR-Advance make nice stuff, and again, expect to pay anywhere from $400-2000 depending on the level of bracing (front, rear or full brace) and the materials used. Bear in mind where it is and make sure anything bolted the underside of your ride is corrosion resistant!

It’s great to see that manufacturers are cottoning on the appeal of track days as well—rumors have it that the interior of the upcoming FR-S from Scion has been designed in such a way as to allow the future installation of a cage! All this fits with Toyota boss Akiro Toyoda’s claim of producing a car designed for ‘the true enthusiast’ and to ‘transfer the thrill of the race track to our vehicles.’

Weight Balance and Distribution
Balancing your car’s weight evenly across the front and rear axles is the key to maintaining maximum grip. Too much weight over either axle compared to the opposite end of the car will lead to undesirable over—or understeer characteristics and screw with the car’s balance under heavy acceleration or braking.

Starting from the top down, re-proportioning the car’s sprung weight is the first DIY mod that most of us can do (and have done) at home on our driveway. An afternoon’s work can demonstrate real benefits by doing things like removing rear seats, stripping sound deadening and carpeting throughout the car. Another way is to replace panels with lighter weight glass or carbon-fiber panels—something we all love as it gives us the motorsport feel and look while delivering a genuine performance benefit as well.

For track applications, you ideally want your ride to stay flat and well-balanced under braking (for example, on the approach to a turn), but possibly to shift slightly rearward as you gas it out of the turn. The purpose of anti-lift/dive settings are to control the weight transfer longtitudinally as uprated anti-roll/sway bars control it laterally. Altering the suspension geometry through the relocation of the pivot points of the lower control arms adjusts the lift/dive by adding positive caster to the front wheels, so less force is diverted through the car’s springs. Instead it is transferred to the rest of the chassis as whole, giving greater grip and directional stability; on the street the benefits are reduced ‘tramlining’ or wandering on uneven surfaces. Anti-lift kits (or ALK for those who like to talk the talk) are another relatively inexpensive modification at $250-300 from firms like Whiteline and Perrin, that include both the relocation bracket and stiffer than OEM bushes that will give a more solid link to the control arm.

Uprated drop links, between the anti-roll bars and control arms, again help optimize the chassis components around them and ensure you get most out of your anti roll bar. Drop links start at around $150-200 and are great for neutralizing preload on the sway bar if it’s adjustable.

Unbalancing the weight distribution on purpose can also be very useful, in drag racing for example where you see the top teams launching hard with the nose pitched down. Contrary to popular belief, if you see these high-horsepower monsters wheeling off the line, chances are the geometry is not aligned in an optimal fashion as lifting the front wheels is giving you less overall grip—going upward usually means you’re not going forward!

Glossary of Terms
Understeer: At the limit of traction, the front slides before the rear and the car ploughs straight on. OEM cars are set up this way to make them more predictable.
Oversteer: Conversely, at the limit of traction the rear slides first and the car spins tail first—more difficult to control if it all goes wrong…
Bumpsteer: Poor suspension geometry (and often over-lowering) can cause your car to decide its own course when encountering a bump. In more general terms, unless on pool table-smooth surfaces the steering will need constant inputs to hold a true line.

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The inward or outward tilt of the wheel at the top of the tire affects handling—and looks—massively. Positive camber tips the top of the wheel outwards, negative tips it in. While we all dig the insane stance of some show cars (note: hardparkers) with the tops of the tires tucked under the arches with the tarmac side sticking out by six inches, this is never a good way to run a road or track car. It will kill the rest of the car’s chassis components much quicker, but it also gives an uneven contact patch making the car handle like a pig.

Under cornering conditions, body roll naturally tips the top of the tire toward the apex, so the addition of negative camber helps maintain the maximum contact patch. Getting the best out of your tires in terms of grip for ultimate cornering speeds and longevity for tire wear can all be affected by camber adjustments. Slight adjustments are the key again as too much negative camber can cause handling trade-offs that include nervousness under braking and acceleration and, at the extreme, a loss of braking force—far from good.

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The pros will adjust camber settings on a circuit-by-circuit basis in relation to the banking of the curves and whether there is an abundance of either left or right hand bends, and the length of the curves. To drop another example in, clockwise oval racing will almost certainly favor negative camber adjustments to the left front and a more positive setting on the right front to induce pull to the right. The more aggressive the settings, the greater the tendency to pull—check out NASCAR to see some of this science in action. Positive camber adjustment would almost certainly be unnecessary (and even unwise) for your regular commute, but can be useful as you consider ride height drops as lowering your car into the weeds will introduce negative camber as the geometry changes and the wheels are pulled in.

Either way, adjustment (or correction) kits usually involve the replacement of upper control arm (on-double wishbone cars)—a bar with a pivot at either end. Your car will have several of these, including the upper and lower control arms that attach suspension members to the chassis and help synchronize the motion of the wheels in relation to the body. Nine times out of ten, OEM control arms are fixed and can wear very quickly under punishing driving conditions. And, as we all know now that the chassis components all work in harmony, worn arms (and their bushes) will give you a shitty wallowing ride and loosening the dynamics of the chassis as a whole. Uprated items (typically billet aluminum with polyurethane bushings) resist twisting and bending further, can be adjusted depending on your preference and reduce the weight by anywhere up to 40%. Pay anywhere upwards from $350 per pair for a quality set companies like Agency Power or Skunk2, to name but a few.

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Given the fact that almost all modern cars now have power steering across the range, most cars come from the production line set up with positive caster—the angle to which the steering pivot axis is tilted from vertical—but as you approach a zero degree setting the steering behavior changes. With positive caster settings, when you let go of the steering wheel the car will pull itself straight.

Adjusting the caster can dramatically affect the amount of steering effort required, increase the sharpness of the turn-in and ‘feel’ given back through the wheel and allow your car to track a decent, steady line.

More positive camber—i.e. with the pivot axis tilted backward so the top pivot is further rearward then the bottom pivot—tends to straighten the wheel when you pushing on, thus increasing stability in a straight line. Negative camber adjustment will give quicker steering for better changes of direction—for example, top drifters will use a -2% of adjustment—the downside being twitchiness and tendency to pick up each and every imperfection in the road surface.

Lower ranges of adjustment are more common on heavier cars to keep the steering effort reasonable and still sharp. Again it’s all a compromise between one factor and another.

Toe-in and toe-out describes the position of the leading edge of paired wheels in relation to each other. Toe-in indicates the leading edges are pointed towards each other; toe-out is when the leading edges face away from each other. This is measured on either degrees of difference from a parallel alignment or, increasingly, in millimeters. Toe-in promotes stability in a straight line at the expense of steering response, while pro racers will make the trade-off between twitchy steering for the sharper-in and good corner entry speeds at the expense of mid-corner and corner exit feel from a more toe-out setting.

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Excessive adjustment either way causes uneven wear on either the inside (too much toe-out) or outside (too much toe-in) edges. Adjustments need to be made equally with front and rear, with rear-drive more likely benefitting from increased toe-in for stability (toe-out can make the ass end oversteer-prone when on the gas) with front-drive vehicles set with toe-out to counteract the chassis’ natural tendency to understeer when pushed hard into a bend.

Probably the most important component in any vehicle is the driver. Consistency from your hands and feet on the controls are the keys to going faster, along with precise adjustment of anything we’ve talked about to get the best out of your car.

So, to make real progress and turn your car into a serious performance tool, you need to compare like with like. In the real world, this means if you’re entering a tight right-hander hard on the brakes and the front end feels unstable, don’t make an adjustment and then take a different line at a different speed. This won’t tell you whether it was your new line that made the difference (or made the situation worse) or the adjustment itself.

You have to be self-critical as well. Too many drivers blame a poor setup for slow lap times, and therefore don’t ever get any faster. If you make a change and it doesn’t work, always have additional solutions in mind; if you don’t you start making blind setup changes, not knowing why you’ve done what you’ve done.

That way madness lies…

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