Smooth is Fast Autocross Performance: Grip

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In other categories, the Hankook impresses less. The Ventus V12 Evo2 is laterally soft when loaded up in a corner, and steering inputs are imprecise. On wet surfaces, its favorable progressivism dries up. It also emits tones that penetrate the cabin, with a high-pitched zip as it rolls and loud thumps over imperfections. Its fourth-place position was cemented by this objective performance that placed it in, well, fourth place. Doing so, however, requires focus to toe the limit and patience to delay throttle inputs slightly.

Without that diligence, it becomes easy to overdrive the tire, at which point grip levels fall off rapidly—but not as detrimentally as with the Goodyear—making graceful and quick recovery difficult. The P Zero used feet of pavement to stop from 50 mph in the wet, 14 feet more than the best-in-test Continental. The Pirelli also tied the Goodyear for the lowest lateral grip in the wet at 0.

The Pirelli is on the wrong side of it. Senna at Donington. Hunt in Japan. ExtremeContact Sport in South Bend. The Continental swept all three wet tests with big margins and showed the smallest performance drop-off between dry and wet tests. Chief among its waterproof virtues, the Continental maintains relatively high grip when the tire starts to slide, unlike the Pirellis and Goodyears. The ExtremeContact Sport locked in second place with a solid performance in the dry, although not exactly threatening the Michelin. It delivers sharp steering precision that makes it feel alert and responsive when driven casually, but that quality fades when pushed past the limit in the dry.

Our ears registered louder thwacks compared with the competitors over the same cracks and expansion joints on-road—similar to the almost metallic clank of a bouncing basketball. In driving, speed usually grows as confidence grows, and this Michelin exemplifies that idea. The Pilot Sport 4 S assures the driver with its tenacious grip, stellar lateral stiffness, and progressive at-the-limit behavior. It is easy and rewarding to drive aggressively, and it allows the driver to return to full throttle earlier than any other tire in this test. Out in the real world, the Michelin demonstrated a subtle tendency to follow grooves in the road.

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Otherwise, the Pilot Sport 4 S is as docile in traffic as it is around a racetrack, never hammering down imperfections nor singing on the smooth stuff. As with the Pilot Super Sport, Michelin is likely to be faced with so many automakers eager to fit the 4 S to their sports cars that it will turn customers away. Type keyword s to search. Oftentimes you will want to do the most important adjustments last as the other adjustments may cause a direct change or change the optimal settings needed on a more important setting.

We'll cover these interactions in the respective sections. We put pressures and cambers at the top of the list because they are basically a no compromise setting and should always be set for maximum grip. They are adjustable on virtually every car and are the primary way we control the tire's contact patch. Everything in racing is ultimately about how the tire's contact patch interacts with the track. We'll go over this more in depth in a future article, but essentially these two settings are about balancing the load across the contact patch between the sidewalls and the center of the tire.

Once you have a baseline setup for your car it's a good idea to start paying attention to tire wear patterns with the goal being even wear or a slight bias toward inside tire wear. This is not only easier than taking temperatures using a pyrometer, but will more accurately tell you how the tires are being used. Tire temperatures are typically affected by too many variables in road course racing to be of use for on track testing for much else that finding out if you are in the ballpark. It's popular wisdom that there should be some sort of ideal temperature spread on the face of the tire in the pits, but unfortunately, it's not that simple.

Tire temperatures are really only going to give good data on a road course if you have advanced onboard telemetry with live tire temperatures. Using live temperatures will also show you the massive temperature changes and variations a tire undergoes and why looking for a temperature spread in the pits is generally not a good evaluation method. Tire wear however, mostly occurs during cornering and will more accurately show you how evenly the tire is being used there. It's still not completely objective, but it's generally better than a tire temperature method.

You can just eyeball the wear, but this can take some time before you see any noticeable difference. If you use a tread depth gauge, you can get accurate results faster. If you are noticing more tire wear on one side of the tire than the other, then adjust camber to compensate. Likewise, you can adjust tire pressures if you are noticing the middle is wearing more or less than the sides.

Greater tire pressure will cause the middle to wear faster. Don't confuse tire shoulder wear, as that is more indicative of an excess toe setting or possibly if camber is very far from optimal. Many unmodified street cars in autocross and track days don't have sufficient adjustment in camber to reach the optimum setting and will get excessive shoulder wear as the tire rolls over onto its sidewall. This should only be a stopgap measure however. Increasing camber if possible, stiffening roll resistance through stiffer anti-roll bars, and lowering and stiffening the suspension will all help allow the tire to get within a better range.

Wear based adjusting can produce a very viable setup and is a great bang for your buck technique as it's relatively easy to do and can produce good results. Road course racing is always an exercise in compromises so often finding a reasonable average setting is sufficient.

So although we put camber and pressures at the top of the list, if you are a little bit off from optimal it's not going to make a big lap time difference. If you have the time and resources though, adding objective hard data to your setup program can be a benefit.

The skid pad is the one place you can effectively use a pyrometer to get good results. If you have access to a skid pad, you can quickly set some good cambers and pressures by making adjustments until you have settings that give you an even temperature spread across the face of the outside tires. If you can, you will want to back this up with finding the average vector G achieved by using telemetry.

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This is better than using just lap times around the skidpad as slight line variations of the driver won't matter. Vector G is also better than lateral G as it will record maximum traction achieved rather than being modified by slip angles. Using the pyrometer will be useful in the beginning though because it will save time in getting close to the optimal settings. Once you are close however, you will want to go primarily by average vector G.

It's important to use average as there is too much noise using the maximum G achieved at one singular point around the skidpad and a driver's inputs could cause a momentary unrealistic spike. As you are searching for optimum settings, it's important to realize that adjusting tire pressure and camber will produce a bell curve on the maximum grip a tire can achieve.

The center of this area is what you want to find, as that will give you the highest average grip on track. Unlike oval racing, road courses are often made up of many different corner geometries, elevation changes, and bankings so there is usually no one ideal setting for camber and pressure. Typically, the best you can do is finding a good average. It's also important to understand that pressures and cambers will each have their own bell curves and these curves interact. The tire pressure that achieves the highest grip will vary with camber setting.

Likewise, the optimum camber setting will vary with tire pressure. The goal is to find what combination produces the highest grip. The best way to do this is to use an XY chart to track out how variations in pressures and cambers affect grip. You would have tire pressures on one axis and camber on the other and then you would fill in the chart with grip achieved. It's generally easiest to do a quick sweep of pressures starting at the top of the chart and working your way down by bleeding off air between runs.

Make sure to also track temperatures throughout to make sure the tire is staying in the same temperature range and not getting overheated or cooling off too much between runs. It's also a good idea to go through the sweep more than once to verify results. Once you've done a pressure sweep, make a decently large camber change such as.

You can then do smaller camber changes once you've found the trend and are honing in on the optimal setting at the top of the curve.

This can be a lot of work, but will not only show you where the peak of grip is, but also how sensitive the tire is to changes. If you don't have access to a skid pad you can do this sort of testing on track if it has a long constant radius corner by setting a custom sector for that portion, but it's going to take longer and be harder to get consistent results.

Anti-roll bars belong near the top of this list because they are going to be the primary way that a driver adjusts the car's balance and will be one of the most frequently adjusted settings. Some cars even allow these to be adjusted directly from within the cockpit. As mentioned earlier in the guide, anti-roll bars don't directly add or take away grip; they simply shift how the load is distributed among the tires during cornering.

This causes a balance shift because of a tire's load sensitivity. You can accomplish the same balance shift through spring and roll center changes, but those are harder to modify usually. Understand that any of these changes can also cause the car to handle bumps differently as well as changing the car's overall roll stiffness. This can change the camber angle the tires corner at so any change in anti-roll bars might require a camber adjustment as well. Overall roll stiffness will also cause the car to feel different in transient handling with greater overall roll stiffness causing the car to respond faster.

So if you like the way a car feels and you have good camber settings, make sure you make even adjustments front and rear to keep the overall stiffness the same. If you soften the front, make sure you stiffen the rear proportionately, and vice versa. This allows you to make balance changes without the necessity of making other changes to the car's suspension to compensate.

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We'll explain the more technical and theoretical side in depth in a future article, but for now just understand that whether you adjust the front or rear anti-roll bar, if you move the car closer to neutral balance you are increasing the car's overall grip potential. Any adjustment that moves a car toward greater understeer or oversteer lowers its overall grip potential.

It's also important to pay attention to where you ideally want this more neutral maximum grip handling to be though. Car balance will change due to track variations as well as driver induced changes such as braking or going to the throttle. A driver's car control skill and preference will generally always remain the overriding factor over the desired car balance. A novice driver will typically want a very stable car that understeers readily and gives them confidence to push their limits.

As a driver's skill progresses, they will want to shift the balance toward less understeer as this will increase the maximum grip a car can achieve and allow faster lap times. As a car decelerates, load transfers to the front tires, which improves their grip while decreasing the grip at the rear of the car. All load transfers like this are similar to the effect aerodynamic elements such as wings have on a car. Many times however, adjusting the brake bias to what allows the driver to best control the car at corner entry is more important.

We'll go over some ways to set the theoretical optimum first and then talk about some of the compromises you may decide to make. The easiest way to set the optimum is visually. You will adjust the brake bias until the front and rear start to lock up under braking at the same time. You might want to have a slight forward bias to lock up the fronts just a little bit sooner for stability though. Either this can be done by having a spotter actually watch the car in a braking zone or another method is to attach GoPro type cameras to the car pointing at the tires.

If you have wheel speed sensors, you could also use telemetry to do this. Although it can be a lot of work installing the speed sensors, being able to very quickly dial in and adjust the optimum brake bias is a great benefit. If you have a sensitive and skilled driver, they will be able to set the brake bias simply based on how the car responds under braking and this might be the ideal way to begin setting your bias even for a novice.

When a driver first starts experimenting with trail braking, it would be a good idea to set a more forward bias for extra stability and then slowly work their way rearward as their skills improve. Some drivers will actually set a more rearward bias than is optimal and use advanced techniques like mixing throttle with braking to have more control over the car at corner entry. There is not a lot of time to be gained by the theoretical optimum bias and it can change from corner to corner if there are elevation changes in the brake zone as well as with changing fuel loads, aero effects, tire grip changes, etc Usually focusing on what makes a driver most comfortable under threshold braking, and trail braking will be the overriding factor.

It's a good idea to decide on your ride height early in the setup process, as it often will directly not only affect several other settings, but will also change their optimum settings. Since ride height effects several factors we'll go through them one by one starting again with what is generally the most important. How dependent your car is on aero effects makes your ride height either extremely important or negligible. All cars will have at least some aero effects, although they could be so minimal as to have no influence on your setup considerations.

Only testing will show how important they are. Cars with underbody aerodynamics such as splitters, tunnels, diffusers, etc For certain cars, this will be the number one performance factor and almost everything done with the setup is in service of optimizing these effects. Truly optimizing these factors is outside the scope of this guide as you need tools unavailable to the average racer, but we'll go over some basic testing procedures you can use to get pretty close.

All cars will see at least some change in drag and downforce with ride height and rake changes and there are a few basic tests to see how much of an effect they might have. This does require a skilled driver to do effectively, but is relatively easy. If you have access to a skid pad you can get better consistent results because if the corners have a different banking that will also change your grip levels.

If a rake adjustments is gaining you more grip in the high-speed corner, but not the lower speed one then you might have a clue that your change improved downforce. Be careful with this approach, because as you'll see below rake will also directly affect car balance in the same way as anti-roll bar changes do.

That is why we compare the high to low speed corner. You want to separate the aero effect from a mechanical balance change from rake that could also increase your grip. The more compression, the more downforce. More overall downforce does not always equal performance though as you have to be able to drive the car effectively as well so keeping the aero balance within a useable window is also important.

In general, increasing rake will increase downforce, but also increase drag. Aerodynamics is complicated and can be counterintuitive sometimes so testing provides the only true answer. To test for any changes in drag, the easiest, but least accurate way is to simply track how changes affect your end of straight speed if you have a long straight.

You can make this test more accurate by using telemetry to track the acceleration from the same speed on the straight. This will correct for any changes in how well the driver navigated the previous corner leading to the straight. Make sure you do these tests under the same weather conditions as small changes in drag might be masked by wind or the weather's effect on engine power. The most accurate way to test drag outside of a wind tunnel is a coast down test, but most track event organizer frown on this during a hot session. You have to test to be sure, but most cars, especially street based ones, aren't going to see big aero effects.

So for most cars, the primary ride height tuning factor is going to be The primary ride height consideration for most cars will be lowering the CG as much as possible without bottoming out excessively or running into suspension compliance issues. Lowering the center of gravity CG reduces load transfer and increases grip.

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  8. All else being equal the lower we can get the CG the faster the car will be. At some point, you will start having issues with bottoming out on the track or having issues within the car's suspension however. You might start hitting bump stops or having issues with tires rubbing bodywork, etc This will entirely depend on the individual car, but one way to test is to remove the springs and manually move the suspension throughout its range of motion to test for any interference. You can also use nondrying ink or similar on any suspected areas of contact to see if the ink transfers.

    The ink technique can be especially useful for testing to see if you are hitting the bump stops or have some other suspension interference. Many times sudden snap oversteers can be traced to hitting the bumpstops and it's often hard to tell if this is the reason without direct tests like this. Sometimes trimming bump stops after lowering can be beneficial. You will most likely still hit bump stops going over curbs however, and they are there to prevent suspension damage from springs coil binding so make sure not to trim too much.

    A side effect of changing ride height is that you will change roll centers, which has an effect on overall roll stiffness and balance. Raising one end of a car will act as if you stiffened the suspension at that end. For example, if you lower the front ride height you are lowering the front roll center, which softens the front roll stiffness and makes the car more prone to oversteer.

    In general, these changes are going to be relatively smaller than making an anti-roll bar change, but it's something to keep in mind if the car is handling differently after a ride height change and you can't figure out why. Understand that it is actually not the amount of rake that causes the balance shift though, just simply the change in individual ride height of the front or rear. You can have a have a very steeply raked car that you would think would oversteer, but still make it understeer through other suspension settings.

    In general though, you just want to think of this as a side effect of ride height changes and not a way to tune the car balance. Lowering the CG will generally still be the overriding consideration. The only time you might want to use ride height changes to modify balance is if you are already at the end of your other adjustments and you still wish to have more oversteer or understeer.

    Another consideration with a ride height change is the direct effect it will have on camber. In most cars, as you lower the suspension, the negative camber on the wheels will increase. The amount will vary based on suspension design, but it's almost universal that some camber change will occur.

    This may be beneficial by itself if the car's camber adjustment range is limited and the optimum camber is more negative than the adjustments allow at a higher ride height. If you have already established optimum cambers however, you will need to re-establish those if you change the ride height. This is one reason that establishing ride height early in the process is a good idea.

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    Dampers are yet another adjustment that can be either extremely important or almost negligible depending on the car, track, and driver. Dampers were originally developed to simply keep a car from oscillating bouncing uncontrollably on its springs. In racing however, dampers are now the primary item controlling the transient handling of a vehicle.

    So as a track contains more and more bumps or quick transitions, dampers become increasingly important. The quicker the suspension has to move the more effect dampers will have. This could be from track bumps, quick transitions such as autocross slaloms, or even quick corrections done by the driver. For this reason, off-road racing teams spend considerable amounts of time on damper development because they are a huge part of the performance package. On a smooth track with no quick transitions however, the dampers become much less important.

    While you can do many things with damper tuning that will affect balance in different phases of cornering, in general it is probably best to focus your efforts on using the dampers to improve the tires' road holding grip and tune the transient handling to your personal tastes. If the track is very bumpy or has curbs that will gain you a good bit of time by going over them then tuning the dampers to accommodate these should be your number one priority because you will be increasing grip. Remember grip is our primary goal. To do this properly requires a 7-post rig, but again like many setup adjustments dampers are always a compromise so you can get satisfactory results just going by feel and using telemetry to track cornering grip and speeds.

    In general, to improve road holding over bumps you will want to soften dampers up to the point that you get no more than one oscillation after a big bump. This means that the car goes to full compression during a bump, and then it can go to full extension before finally settling back to its normal ride height. If you get a pogo effect because of a bump then you need to either stiffen the suspension or avoid the bump because it's too big for the suspension to handle.

    If the dampers aren't able to control the suspension and you get big tire load variations as the car is bouncing you will be decreasing grip. The other end of this compromise is that as you soften up dampers to handle bumps and curbs better you are slowing down how quickly load transfers which changes your transient handling by slowing down how quickly the car reacts to inputs.

    Some drivers prefer a slower reacting car and some prefer a quicker reacting car. Theoretically, the quicker a car reacts, the faster it can be as the tires load up and go to maximum grip faster. This is generally a small difference and only if a driver is skilled enough to take advantage of the quicker loading will it actually be faster.

    In addition, this will primarily only be a benefit during track sections where a quick tire loading is required which is usually only in the center of a chicane as a driver goes from one direction to the other quickly. During a normal corner, the slower transitions cause damper settings to make much less of a difference.

    If you have access to an autocross slalom this is a great way to tune as the constant quick changes of direction will cause the dampers to have a more pronounced effect on handling. To shift balance toward oversteer you would do the opposite. Stiffening or softening all dampers together will speed up or slow down the car's reaction. There really is no right or wrong answer although if you can handle the quicker transitions of a stiffer damper it can potentially be faster.

    The differences are going to be fairly minor however as long as the dampers are in a reasonable range, so feel free to experiment. You can tune dampers at any point during the setup process, as they really don't have a direct effect on any other setting. One other factor to keep in mind is how a car reacts when responding to quick driver inputs during a recovery. Some of the fastest suspension movements can be when a driver is trying to recover a car from a big oversteer and this is probably the time you want the biggest understeer safety net.

    So for extra stability, increasing the front damper stiffness and softening the rear more than you might like during controlled cornering might be a benefit especially to a more novice driver who tends to be a little sloppier with their inputs and is making big corrections more often. There are wide varieties of dampers available with the high end ones allowing separate compression, rebound, and high and low speed damping. Using separate adjustments, you can affect balance in different parts of the corner as well as have more individualized control over how the damper handles bumps vs how they respond to driver inputs.

    We plan to have a future article that will look into all this more in depth, but in general it's not worth focusing too much effort on as the time gains are generally very small and you need advanced setup tools to do it properly. Even then, there is usually large compromises to be made. You should be able to get very good road holding and transient handling characteristics out of basic single adjustable dampers as the driver has a huge influence on how the car acts in transients. Unlike with changes in the primary settings that control steady-state handling, a skilled driver would turn very similar lap times on most tracks with a wide variety of damper settings.

    Toe settings almost exclusively fall into the transient handling category and are mostly going to be driver preference. You can cause excessive drag issues if you go too far however, and there are some grip related factors that we'll cover as well, but these are generally fairly negligible for most road course driving. Toe settings are however, some of the most misunderstood and misused setup parameters. We're trying to keep this guide more "nuts 'n bolts" practical, but feel like we should cover toe a little more in depth here because of the general misunderstandings associated.

    These misconceptions are primarily dealing with front toe so we'll look at that first. A primary purpose of adjusting toe is to alter how the vehicle responds to the initial steering input. Let's look specifically at what is happening at the tires as we adjust toe so we can learn more about it. The primary variable that toe will affect is how quickly the car reacts to steering movements right around center. Contrary to popular knowledge, for a given amount of initial steering, toe-in actually causes a car to turn in quicker, not slower. A side effect of steering forces building quicker however is that there will be a greater self-aligning force on the steering wheel, which will feel more stable to a driver.