Tires

Alright, lets start with TIRES. These are by far the most limiting component to maximum stopping & cornering ability. All the suspension & brake upgrades you can do is worthless if the tires don’t grip. Tires have many different ratings, some are commonly mis- understood. These ratings are located on the tire sidewall, also on the sticker when new. Temperature and traction are rated on a scale of A, B, and C. C being the worst, and A the best. Also there is a newer AA rating for traction . If you live in a hot climate as we do, I can’t recommend, anything less than an A for temp rating. This is the tires ability to handle high temps. , as well as dissipate heat efficiently. At higher speeds, and under aggressive cornering, tire temps increase, causing it to become less stable ( traction to go away) or even self destruct, not what you want at high speed.

 

As for the traction rating, this one can be deceiving. It indicates the tire’s straight line stopping ability in the wet. Basically the treads ability to channel water out, and the rubber compound to grip on a wet surface. It does not have a direct impact on dry traction, both acceleration or braking, nor does it have anything to do with the cornering traction of the tire. This has more to do with the final rating ( treadwear ). This rating has to do with how soft or “sticky” the rubber compound is. It is rated by numbers . The higher the number, the longer the tread life per mile will be, indicating a harder rubber compound & one that’s not as grippy as a lower number. A treadwear rating of 400 is a fairly hard compound, better for life span than grip. A rating of 200 will wear twice as fast per mile, but grip on dry ground considerably better. We feel that a rating of 100 to 200 works well for the street, without real severe tread wear. Below 100, tread wears quite fast, but grips extremely well on dry ground. These are typically used in autocrossing / racing.

 

Some people actually refer to the treadwear # as the compound rating ( saying 50 compound or 100 compound ) , but this is slang as of different manufactures have different rubber compound formulas with equal ratings, but with different characteristics. It should be noted that with lower treadwear #’s, wet traction is decreased, especially when turning, even if rated AA, compared to a tire with a higher #. Also cornering stability, while affected by the compound, is largely affected by the sidewall , and belt construction of the tire. For example a drag radial rated at 100, may have good acceleration (and braking) traction, but be unstable in hard cornering. Conversely a road race tire rated 100 may have very good handling stability, but not be as good at launching, due to sidewall construction. Some tires have a more controllable, progressive break away just past the limit of adhesion than others do. We recommend you do your home work when choosing new tires, looking at comparisons from suppliers like “tire rack” with the understanding there are always compromises to weigh out.

 

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Brakes

Next up, BRAKES. Powerful brakes not only give you that feeling of security, but are essential for your safety. Any of you who have ever put taller tires on a truck have probably noticed a reduction in braking ability. This is because the taller the tire the more mechanical leverage is being placed on the brake components at any given speed, much like when your towing, there is more effective weight for the brakes to stop. There are many different routes to upgrading your brakes. Simply upgrading your brake pad material (or compound) can help a lot . If done in conjunction with slotted and /or drilled rotors can help even more.

 

Next up are Big brake kits, these usually use upgraded pads & drilled/slotted rotors, but the rotors are a larger diameter, locating the brake caliper further away from the rotor centerline, creating more leverage ( mechanical advantage ) giving increased stopping power. These kits either increase the diameter of just the front rotors, or all 4. It should be noted that sometimes larger diameter wheels will be required to clear the larger diam. Rotor/ caliper set up. Finally upgrading the caliper itself can be done. This usually is a upgrade to give you a larger piston size or more pistons in each caliper, increasing the hydraulic clamping force available, proportionate to brake pedal force.

 

As for basic upgrades, there are a variety of different street performance pads available, they are designed to increase friction (which produces heat) as proportionate to pedal effort. Different pads operate in different temperature ranges. Factory pads are designed with a balance in mind, between pad longevity, noise levels, dust levels, stopping ability, and production costs. Cheap replacement pads commonly don’t even meet OEM standards in any of these areas except cost. OEM pads are designed to have good cold bite and operate at relatively low temps. They are subject to easy overheating, and brake fade if used aggressively.

 

Performance street pads tend to produce slightly more dust, a little squeal sometimes, less longevity, but give you higher torque and temperature range. As you progress into more aggressive race pads, operating temperature ranges increase, as well as torque bite, pad wear, dust, noise, and of course cost. While perf. street pads have a relatively flat torque curve, race pads can have a more progressive torque curve that ramps up aggressively with heat, requiring more driver pedal modulation effort. We can offer suggestions depending on your intended usage. We have used entry level race pads on the street with good success, when extreme stopping power is needed. The higher level race pads are not for street use, due to they don’t have good initial cold bite at lower speeds, and actually need some heat to start to work.

 

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Rotors

As for rotors, drilled and or slotted ones offer some good benefits. They can greatly reduce brake fade. There are two main types of brake fade. The most commonly associated one being where under hard/ extreme use, the brake fluid boils, creating steam in the system and the steam compresses causing the pedal to sink to the floor and loss of braking. This can be alleviated by using higher temp fluids, or at least changing your fluid periodically as of it is hydroscopic ( absorbs moisture from the air) and this reduces its boiling point temps. The other kind of FADE is important to understand. It’s when under hard/ extreme usage, like multiple hard stops, or high speed aggressive braking, the pedal stays up and hard but no matter how hard you push the brakes just aren’t slowing you down much or at all. This is caused by a combination of the pads being overheated (outside there designed operating temp range) and a phenomenon called out-gassing. This is when under heavy friction the pad compound actually produces a gas that pushes out from the friction surface and creates a micro thin layer of gas between the rotor and the pad friction surface. This causes the friction surface to be hydraulically pushed away from the rotor it’s trying to slow down. Not good!

 

Cross drilled or slotted rotors can vent this gas away letting the pad stay in contact with the rotor. Cross drilled rotors can also aid in cooling themselves if properly engineered. Some rotors have a lot of holes and some not many. While more holes make for a greater visual impact, it also reduces the available swept surface area, reducing friction amount per rotation, somewhat reducing performance. Of course this can be compensated for with more aggressive compounds. Rotors with less holes may not have the looks, but can perform better with reasonable pads. Slotted rotors do a quite effective job at getting rid of the gas, without reducing much surface area, but do lose the cooling benefit. Rotors can also be cryotreated enabling them to reach much higher temps and resist warping. All professional motor sports teams use cryo treated rotors. For racing applications I recommend them.

 

A point to note, some people feel that cross drilled rotors are dangerous because they can crack at the holes outward. While this can happen, it is considered somewhat normal to some, this can be reduced by using a high quality rotor, having it cryo’d , and if they do get small cracks, it does not usually cause any immediate problems, just keep an eye on them and when they get to big replace the unit. Remember when pushed to the limits, rotors don’t have an endless life span and should be viewed as a wearable, expendable item. If you don’t beat them to bad they will have a long life of good service.

 

On stainless braided brake hoses, while they look cool they don’t add a whole lot of stopping power, but they do give you less “absorption” than the stock rubber lines, and when push comes to shove, that little bit extra can make the difference. Not to mention they are physically stronger. One final point to consider is front to rear brake bias (balance). If you have increased rear tire width , altered weight distribution, you may be able to take advantage of more rear brake, or you may need less. This can be accomplished by recalibrating the proportioning valve, adding an adj. Prop valve, different master cylinders, even different front & rear pad compounds to name a few. While there are some compromises to consider, you almost can’t go wrong if your choosing to upgrade your brake system. For racing strong brakes allow you to drive deeper into the corner, on the brake for less time, and back into the throttle, making you faster in the long run. The safety is always worth the investment. And remember, your brakes can only stop as good as the tires can grip the road.

 

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Handling

Lastly, HANDLING. This can be a widely opinionated area. Who’s car handles better, or which brand of car handles better. Some of this can come down to individual preferences and expectations. We’ve all seen the G- force charts that compare different vehicles. How do some cars have the same specs as another but handle completely different from each other? Ok, it’s important to understand that these specs are calculated on a skid pad, that only tests steady state cornering. The skid pad test tells us nothing about yaw response characteristics during transitional cornering. Yet this is the most important factor contributing to superior handling. We’ve seen cars with the same skid pad numbers do radically different through a slalom course, then maybe even swap places on very high speed curvy roads. This in part due to the yaw response time designed into the suspension.

 

Engineers that design passenger cars factor in ride comfort, longevity of components, tire wear, road surface sensitivity, costs, etc. when calibrating suspensions to be sold to the general public in order to satisfy the mass majority. Cars like the corvette Z06, Z51, WS6 Trans Am, SS Camaro, Mustang Cobra and Viper represent the most the manufacturer is willing to do for the enthusiast. If they can’t sell hundreds of thousands of a particular part over the life of a model run they simply aren’t interested. Their marketing plans rely on volume. At current technology levels , getting smooth , soft low speed ride comfort and superior yaw responses at high cornering forces cannot be accommodated in the same car. The truth is tuning the suspension to work well at high cornering speeds always trades off some low speed ride comfort. We must each decide how much low speed ride comfort should be sacrificed for added high speed cornering capability.

 

While it may seem easy to increase a vehicles cornering power, with say some larger sway bars, this may not net better high speed handling, which is created with the correct balance of both high cornering power and correct yaw response characteristics. As cornering speeds get higher, the suspension system must get stiffer in order to handle the increased energy levels. To produce a car with truly superior high speed handling, it can only be accomplished by the systematic modification of a wide range of suspension components. We need to treat the whole car as an interrelated system. Everything from the front and rear spring rates, stabilizer bar size’s and rate, hardness of the suspension bushings, shock absorber damping & rebound control, to the size and compound of the tires needs to be considered. A total system approach will net a car with an integrated, balanced feel due to all the parts working in harmony.

 

While drag racers are concerned with the vehicles attitude during acceleration and braking, we road race types are more concerned with cornering/ handling in addition to performing well while accelerating & braking, all the while maintaining a satisfactory ride quality. It’s all to easy to turn your daily driver into a stiff race car, uncomfortable, and un- fun for daily use, with the wrong spring choice for instance.

 

Some basic physics we need to examine is the concept of energy, in particular kinetic energy. This energy is present in all moving objects, and the amount in any particular moving object is determined by both the weight and velocity of that object. This relationship is expressed by a basic formula : Energy = ½ weight x velocity squared (to the 2nd power). This tells us the amount of kinetic energy increases in direct proportion to added weight, but in geometric proportion with added velocity. The point to all this is if the weight doubles the kinetic energy doubles, but if the velocity doubles the energy will be 4 times greater! Think of the suspension components as devices to resist, store and control energy. In example a spring with a rate of 300 pounds per inch can store 300 pounds of energy for each inch of compression.

 

As suspension components are modified for higher cornering speeds, it should be noted that the working range becomes narrower. Thus a mildly prepped Trans Am may corner well at .880 g , and start to feel “edgy” at .910 g. A typical race prepped car may corner well at 1.3 g , but come unglued at 1.310 g. High speed cornering ability at the track can help win the race, but on the street could save your life!

 

Controlling body roll is a major key to good handling. As a vehicle corners it’s weight distribution is pitched to the outside of the turn. The central point about which the vehicle body rolls under cornering load is known as the roll center. On any given vehicle the amount of body roll is dependent on the leverage effect between the vehicle’s roll center and its center of gravity (CG) height. The higher the CG and the lower the roll center, the more body roll. Conversely, the higher the roll center and lower the CG , the less body roll. This is because not as much leverage is placed on the roll center by the CG. Because the tires tend to roll with the body, too much body roll results in a loss of tire contact patch.

 

Basically the body roll pulls the tires away from their ideal position - perpendicular to the pavement. The quick solution is to dial in lots of negative static camber ( lean the wheels in at the top) causing the contact patch to be close to flat during body roll. The problem here is it causes accelerated inside tire wear. A more correct approach is to generate negative camber gain under high cornering loads by raising the roll center, and or lowering the CG. Techniques used to achieve this camber gain on a double A- arm suspension include relocating the arms pivot points, shortening the upper arm length and /or installing a taller knuckle. It is possible to go to far also. Too high a roll center will cause excess tire scrub. That’s going backwards, the GM guys put a lot of effort into turning the ‘88 and up vette into a zero scrub design.

 

Engineers use properties like:

 

TRACK WIDTH: which is the distance between the centerline of each front or rear tire.

 

WHEEL RATE: the effective spring rate when measured at the wheel.

 

ROLL COUPLE PERCENTAGE: the effective wheel rates , in roll, of each axle of the vehicle as a ratio of the vehicles total roll rate.

 

UNSPRUNG WEIGHT: parts like tires, wheels, brake parts, spindles, half the control arm’s weight, etc. Parts that the vehicle springs do not support their weight ,but can affect the spring & shocks ability to control.

 

SPRUNG WEIGHT TRANSFER: the weight transferred by only the weight of the vehicle resting on the springs during body roll. ( the sprung weight transfer only depends upon the CG height and track width. Raising roll centers or increasing roll stiffness will decrease body roll, but not decrease sprung weight transfer)

 

JACKING FORCES: they can be thought of as the centripetal force pushing diagonally upward from the tire contact patch into the roll center. The front jacking force is calculated by taking the front unsprung weight times the G-force times the front roll center height divided by the front track width. Got that?

 

Anyway, they use these when setting up spring rates, stabilizer bar rates and shock absorber damping rates to get the desired results they are after.

 

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Conditions and Corrections

Over-steer and under-steer are caused by unequal body roll during cornering. If the rear of the vehicle slides out of a corner first, it is called over-steer. This usually means the rear tires are not carrying the same weight distribution as the front. If the front tires are carrying a smaller balance of the weight , and the front end tends to push or plow out of a turn then this is called under-steer. The more a tire loses cornering traction, the higher the “slip angle” it is said to have. Although we always shoot for neutral-steer (balanced) , if we have to go one way we will settle for a little over-steer any day. It is much more controllable, with throttle and counter steering than under-steer where your front end is unglued. A well set up car can be pushed into oversteer by more throttle, and back toward under-steer by backing off the throttle. You can “steer” a well balanced car by the throttle alone. The last condition you can experience on a balanced car just past the limit is a 4 wheel slide or 4 wheel drift. This is a favorable condition for an advanced driver capable of putting the car into a drifting condition as a means of putting the car where you want it , beyond what is possible under normal traction conditions. This requires the driver to really be in tune with his machine, and for the inexperienced person could have deadly results if executed at the wrong time and place.

 

How about acceleration, does the front end lift or the rear end squat? If so the rear spring rate may not be stiff enough to control the transferred torque. What about braking, does the front end dive under hard braking, and maybe your getting rear wheel lock up or premature ABS actuation ? This can be caused by too much weight pitching forward causing unbalanced weight distribution. One correction would be going with a higher rate front spring, possibly a progressive one.

 

Stiffer springs almost always increase your handling as long as you realize that you should couple them with stiffer shocks with better damping and rebound control to help control the extra energy the springs will be absorbing and exerting. For instance lets say you have an F-body and you add wider, heavier wheels and tires to the rear, like 11's with 315's , it would be wise to consider a stiffer spring and shock combo to help control the heavier unsprung weight you added. Also as you go higher in spring rates to improve your high speed handling, you must also go softer on the tire compound to be able to utilize the higher rate. Otherwise you will find your car sliding all over the place .

 

As for alignment specs. I will address a couple of points, stock settings obviously will net the best tire wear and least amount of road surface “nervousness” . Due to the crown of most roads , camber specs usually call for slightly positive (top of tire leaning out) , from zero (straight up and down). We set up camber at zero to slightly negative (in at top) for street use settings. This usually gives a good compromise between some added high speed cornering stick , tire wear and a livable amount of road surface sensitivity (which means added steering input needed over road surface irregularities ) More neg. camber can be dialed in, for track use, or street use if your willing to deal with the steering nervousness and heavy edge wear that accompanies it. As for caster, it is the imaginary centerline going thru the upper and lower ball joints. Positive caster is when the upper ball joint is further rearward than the lower, creating a positive rake. Stock settings provide you with good low speed steering response. We like to crank in more positive caster for performance street use, as of it gives better steering wheel return, and better high speed steering response and stability, along with added road feel. This can cause a little lack of low speed response feel.

RIDE HEIGHT:Ok we all know that lowering the car lowers the CG, but another thing we look at when prepping a vehicle is the stance. A lot of cars sit way too high in the rear, causing not only the rear to be light and oversteer to easy , but also lack of good weight transfer under hard acceleration, causing traction issues. By simply starting with leveling the frame out, causing the corner weights to be closer, you can pick up cornering and better launching.

 

SUBFRAME CONNECTORS: On unibody vehicles , the frame has 2 halves, with nothing but the sheet-metal floor pan to tie them together. The addition of connectors eliminates all the flex , stops cowl shake, gives the vehicle that solid feel, dramatically enhances cornering and launching, and helps prevent T-top leaks from starting. They speed up chassis reaction time.

 

COIL OVER SHOCK SYSTEM: On cars such as the C4 thru C6 vettes, although they have 4 wheel independent suspensions, they incorporate a single transverse mounted front and rear leaf spring. This set up has one draw back, when for instance in a high G curve, one of the tires hits a bump or surface irregularity, instead of absorbing it alone, leaving the opposite wheel out of the event, the spring transfers some of the energy to the opposite wheel, upsetting its traction as well. This is called “crosstalk” It can be quite unsettling when it occurs, and coil overs eliminate it, creating a true independent set up, leaving the other wheel planted during the event. This one of those things you don’t know what your missing till you’ve felt it.

 

STABILIZER BARS: Both hollow and solid versions are available, I tend to prefer the solid ones, although the tubular versions seem close & definitely keep the weight down. Most of the time going with a huge front bar is fine but it’s definitely possible to over do the rear causing oversteer, unless you have wider rear wheels and wider, softer compound tires.

 

POLY BUSHINGS: Besides stiffening things up, harder bushings can absorb more energy, with less deflection, helping wheels maintain their alignment settings under heavy load. They can help increase chassis reaction time, making yaw response time faster. Lets the suspension do what it was designed to, instead of a lot of energy being absorbed by soft bushings. For example the C4 vette really responds well to having all the rear bushings done in poly or even heim jointed ends, but in my oppinion , unless you are really hard core leave the front alone. Poly in the front is really stiff, and doesn’t seem to net the same level of improvement.

 

STRUT TOWER BRACE: On cars where this is applicable, this part adds support, helping to stabilize camber settings in hard cornering, by greatly reducing flex in the upper strut mounting points. Good bang for the buck.

 

WEIGHT: Ok any weight reduction you can do helps. The less weight there is to transfer in a corner, the more cornering force a car can generate. Also weight distribution is important, any weight you can shift around (i.e. battery relocation) to get the front to rear weight bias as close to 50/50 as possible will help. Lastly reduce unsprung weight. ( i.e. lighter wheels / tires) Less mass in motion lets the suspension react quicker, control the weight easier, and helps keep the tire planted.

 

AERODYNAMIC DOWN FORCE: Various spoilers, air dams, and wings can add down force to different parts of the vehicle proportionate to vehicle speed, and add to directional stability. Both can help you stay planted.

 

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