- 271
- United States
- The__Ghost__Z
Part 1 - On the nature and purposes of Drifting
Part 2: Precision - More complex factors in drift physics
Part 3: Weapons - Novice Drift Initiation Techniques
Part 4: High Caliber Weapons Advanced Drift Initiation Techniques
Part 5: Mid-Corner Drift Physics - Executing a drift at a speed and angle.
Part 6: Math and Comparative Tuning - Tuning drift cars in relation to eachother
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Compared to my previous entries, this is probably the most important. This is one of the last bits of information, and reveals the most about my technique and knowledge of drifting. I am posting it now because I feel safe to say that I have exhausted all of GT5's drifting potential. Competitions are idiotic, teams are immature and unskilled, normal rooms are no longer challenging, and I achieve more fun doing double contact drifts off of the Chicane at Special Stage route 5 or Monaco in practice mode than simply repeating the same perfect sections, or maximizing my time throughout a course. Quite frankly, I am tired of my tuned 240Z being able to outdrift in both speed and angle all but an S2000 GT1 or RX7 TC. Since there is no more need to keep my secrets... here we go.
THIS IS HOW I TUNE MY CARS. It may not be perfectly correct, but I feel it is as accurate as can be, given that GT5 itself is not a perfect simulator. In some ways, it may be even more precise than GT5, but it produces results. The math might be wrong in some places, I am not a mathematician and it's never been my strong suit, however based on my own knowledge and the research I've done, I *think* it is correct. By all means, feel free to improve on it if you can, as I am certain there are even more clever things that better mathematicians than I can do.
Put simply, this is my attempt at smashing apart any argument saying that drift cars are simply tuned "by feel" and without precision. This is silly, and a truly good drifter should know by mathematics, exactly what is happening to his car at any point in a corner, and learn to look at numbers and adjust his driving style accordingly.
This section is rather math-heavy, but I will keep calculus out of it and stick to basic algebra. This section involves ratios and comparative tuning. If the method here is applied correctly, you should be able to make any drift car drift like any other drift car, by making sure that the "important ratios" I list are the same on both cars. A lot of the calculation is theoretical, so if there are math errors (I use an excel spreadsheet and rather than give you my exact tune, I will just present theoretical numbers) I will attempt to fix them as they are noted, however, this is more so you can understand the equations and use them yourself.
Tuning Weight and Weight Distribution
First off, Static Weight Distribution. The grip a tire has is proportional to the weight being pressed down on this tire. You can take a pencil eraser and slide it across a flat surface easily, but if you press down on it, you get more resistance to sliding. This may seem wrong, since it implies that heavier cars have more grip. However, heavier cars have more lateral G on the tires, meaning that the tires have more grip, but they require more grip to accelerate the higher weight at the same speed laterally. The load transfer of a car increases as the weight and the height of the Center of Mass increases. The greater the load transfer, the less you can approach the maximum grip of the tires. The tires, which have no greater cornering ability when not attached to the car, cannot reach the same peak cornering when attached to a heaver car, or higher center of mass, vehicle. However, because some cars (for example, GT86) have extremely low centers of mass, they may have less load transfer than a lighter car (for example, AE86) which has less weight but a higher center of mass. A car will be drift at a maximum speed higher if it has a lower ratio of its center of mass height to its weight.
This is the important part: Having a lower center of mass, or less load transfer, will make you car drift faster at all angles. For a given angle, the car will corner better and produce higher G numbers.
CH Tires are rated to about .85Gs. Depending on the load transfer and size of the tire's contact patch, (which varies car to car) it may be between .7-.9Gs, but rarely for a street car reach 1G consistently.
You can find the total load transfer of a car, which is the difference in "weight" on the wheels from Static to Cornering speed, by the following:
(Tire G rating) * (Total Weight, KG) * [(Center of Mass Height, MM) / Track Width)]
The Track Width is half of the car's total width, in MM.
The produced number is the amount of weight from the "center" of the car, is pushed to the outside. You can figure out, under normal cornering (no throttle/brake) exactly how much weight is on the tire by dividing that number by the Static front/rear weight ratio (given to you by the Ballast Screen)
Example: A car is 900KG. Assume load transfer is 500KG, with a 60/40 weight distribution. Static weight is:
Front: 900 x .6 = 540KG
Rear: 900 x .4 = 360 KG
And thus,
Front Right Tire: 270KG
Front Left Tire: 270KG
Rear Right Tire: 180KG
Rear Left Tire: 180KG
This means that under corning, "500" KG is moved to the outside of the car, in proportion to how it is under static weight. This is found by this formula, for front (substitute rear percentage for rear):
Load Transfer * %of Front Weight + Tire's current weight
So our front load transfer is 500 * .6 or 300KG. This means that 300 KG will be lifted from the front inside tire, and placed on the outside tire. 200KG will be lifted from the rear inside, and placed on the rear outside.
Result:
Front Inside Tire: -30KG
Front Outside Tire: 570KG
Rear Inside Tire: -20KG
Rear Outside Tire: 380KG
You will notice that some of the tires have lift forces, as in they actually are being lifted as the car pulls to the outside. However, because only the body rolls, and the unsprung weight does not, that unless those numbers highly exceed the unsprung weight AND the weight being pressed down by the suspension, the wheels will not lift off of the ground. A good example is taking the '70 Charger with stock suspension on high grip tires. It will lift a tire off of the ground under cornering and braking, because of the extreme lift force due to a high load transfer and low spring rate.
Next, you can calculate the load transfer under braking.
A car can brake at the same max Deceleration as it can grip in max sideways acceleration. Since braking is load transfer to the front, you can simply use the same load transfer number from before, but instead of applying it inside/outside, apply it front to rear. You can quickly see how a Braking Drift works, and how effective it will be, if you apply both the braking transfer and cornering transfer at the same time. When done so, usually there is lift forces on all but 1 tire. This is astounding, but if your car is not brake drifting properly, you can use these mathematics to figure out exactly how to maximize front-rear weight transfer under braking.
IMPORTANT RATIO #1: A CAR'S PERFORMANCE CAN BE MEASURED BY THE RATIO OF ITS LOAD TRANSFER / TOTAL WEIGHT. A LOWER NUMBER WILL CORNER, AND THUS DRIFT, FASTER However, less weight transfer will make it more difficult to initiate a drift. A highly skilled drifter will be able to drift with minimal weight transfer, but without using the E-brake and suffering its drawbacks as well.
These calculations only give us, however, the change of grip at the tires. They do not tell us the way that the weight shifts around the car above tire level. This is Weight Transfer, and it can be easily measured by the angle that the car's body rolls. Less body roll doesn't mean that the car has higher grip, but it means that the car has less movement to reach its max corning potential, so the load transfer is not as sudden or drastic. This can be adjusted via the spring rates. Alternatively, more body roll on the front VS the rear will cause the load transfer at the front to happen later, and that delay will cause the car to relatively have more grip at the rear during initial cornering, producing understeer. The opposite is true as well, as a proportionally stiffer front will cause the rear to roll and oversteer more. A perfectly neutral car should have its spring rates in the same ratio as its static weight distribution. So a 60/40 car would have its spring rates in a 6/4 F/R ratio to be neutral, causing the whole body to roll as one unit. I, for one, prefer neutral rolling cars. But this is not just a matter of preference, because the ratio of the front roll angle to the rear roll angle tells you, under extreme weight transfer which wheels lose traction first.
So then, to tune your car's weight comparatively:
Calculate the weight transfer, and tune your weight so that the weight transfer / total weight is the same ratio Front/Rear and Left/Right as your "ideal" car.
Tuning Suspension:
Spring rates, as explained earlier, have a drastic effect on how tires lose traction under extreme load transfer. Here, I will explain how to calculate body roll based on your suspension and weight transfer numbers.
Static Support Your car sinks down on its suspension. Spring Rates, for my GT5, are given in KG force /mm. This makes it very easy to calculate static support. What this number is, is how much KGs of upward force the spring exerts per millimeter of compression. To figure out how your car sinks on its springs:
Distance dropped = Static Weight over Wheel / Spring Rate
In our car, Front right weight is 270KG. for a front spring rate of 9 KGf/mm, that means that for every MM of compresion, 9 KG of upward force is given. So that means that 270/9, or 30mm. The reason why a neutral car has the same front/rear ratio for both weight and spring rate is as follows:
Spring Rate = Static Weight over Wheel / Distance Dropped.
So for our rear, at 180KG, to drop 30 MM as well (resulting in a car that is flat when it is just sitting there) 180 / 30 = 6
9 spring rate front and 6 rear is a 60/40 split.
Now, to calculate roll angle, we need to know how much the outside body dips (and inside body lifts) under cornering. Since we already know how much weight is on each wheel during extreme cornering, it is quite easy to apply the same formula:
Distance Dropped = Weight under cornering / Spring Rate
Outside front tire is 570 KG, so it drops 63.33mm. That means that from its normal 30mm drop, it drops an additional 33.33 mm. This makes sense, since the wheel's "weight" is almost doubled, so should its drop. This is where it becomes important to note that if there is not 33.33 mm of distance between the tire and the bottom of the vehicle when it is static, the body of the car will hit the wheel under cornering.
The roll angle can be found like a triangle. From the center of the car to the outside (half of the width, in this case 800mm) being the hypotenuse, the distance dropped (33MM) being the opposite leg.
Roll Angle: Sin(Opposite / Hypotenuse), or here, .0412 radians. Take that times about 57.2957795 to get that in degrees.
IMPORTANT RATIO #2: TOTAL ROLL ANGLE, AND FRONT ROLL ANGLE / REAR ROLL ANGLE To make one car handle similar to another, make the front roll angle of one car the same to the other, and same with the rear. If you want neutral roll, make all of the numbers as close as possible.
This same basic formula can be applied to Front/Rear roll under braking and acceleration.
Camber and Toe
Camber should be no greater than the roll angle. Increasing front camber higher than rear will, assuming front and rear roll is the same, cause additional grip to the front relative to the rear. Increasing rear camber does the opposite. This introduces oversteer and understeer respectively.
Front Toe-In causes tires to resist the change in motion, resulting in a low turning angle for full lock, which can stabilize the front turning in (but reduce its cornering speed). It also produces better stability under braking, and improves braking performance because the contact patch is wider. Rear toe does the same, but it stabilizes the rear. This is especially useful on cars with a high power/rear weight ratio. High rear toe out destabilizes the rear, meaning that the rear will lose traction quicker in the event of sudden change of direction. Front toe-out does the opposite of front toe-in.
Ride Height
Ride Height simply lowers the Center of Mass, or raises it. The number given is in mm. You can create more weight transfer/roll angle by raising the center of mass, or less by lowering it. If it is too low, however, and the body rolls farther than the suspension has room to travel, then it will hit the edge of the car's wheel wells under cornering or braking. Stiffer springs reduce body roll, and thus can counteract this.
Dampers
Dampers do not affect how much body roll your car has. It affects how slowly or quickly you reach that max roll once force is applied. It should also be noted, that dampers affect front/rear roll, so their settings should be proportional to the front/rear roll bias. They are largely a "by feel" scenario.
IMPORTANT RATIO #3: DAMPER SETTINGS / TOTAL ROLL As a car has greater roll, it needs looser dampers to reach that max roll at the same time as another, stiffer car with less roll. The opposite is also true. A car with 2 degrees body roll, if it "feels" comfortable at 6 dampeners, would feel similar in changing the body roll if it had 1 degree body roll and 3 setting dampers.
Earlier I described the "damper" drift. Because you can adjust both how fast dampers extend and how fast they compress, you can do some nifty tricks to initiating a drift. If you have the front dampers compress quickly, and the rear dampers extend quickly, (low settings in proportion to body roll) the body roll to the front under braking is going to be sudden. Loose enough, and it will "shock" the rear tires into suddenly losing traction sooner. This means that under heavy braking, the rear slips quickly. However, if the front extension and rear compression is high, that means once you start accelerating in the corner, the forward roll changes roll less dramatically to a backward roll than it did under braking, giving you a "planted" and smooth corner exit and control during the drift. While you can improve the handling of the car with minor adjustments toward this setting, making it dramatic will allow that shock to make the car simply want to drift under merely normal braking!
Tuning Brake balance
An often overlooked portion of tuning, but for drift tuning I find it to be completely vital. If you have no progressed enough of a drifter to be able to not use ABS, then ignore this. If you feel you are good enough however, this is vital information.
The brake balance on a car is not proportional to its weight distribution or body roll. It is proportional to the lift forces that the ground exerts upward on the car's tires to stop it. Under braking, a car can be said to rotate forward, the rear wanting to flip over the front. It is the weight of the car pressing against the friction of the ground that allows it to slow.
In our car with 900 KG, and 60/40 weight distribution and .85Gs CH tires, braking at .85 Gs (max braking force) means that the load transfer (as we said earlier, assume 500KG) is so that 500KG, 300 of which is going to move to the front tires. This means under braking, our weights are as follows, for one tire:
Front tires: Normal Tire Weight + (Load transfer) + (Front Downforce)
Rear Tires: Normal Tire Weight - (Load Transfer) + (Rear Downforce)
For each individual tire, we divide the load transfer and downforce each by 2.
So for our car with 900 KG, 500KG weight transfer, and no downforce:
Front Right Tire: 520KG
Front Left Tire: 520KG
Rear Right Tire: -70
Rear Left Tire: -70
The overall Braking Forces of the car is going to be the G rating of the tires times its total weight. Here, is it 765kg. We want to know how that braking force is divided front/rear The Lift Forces of the car are going to be:
Front: [(1-%of weight in front)*Total Weight] - Braking Forces * Center of Mass Height/WheelBase]
Rear ^ Above number, subtracted from total Braking Forces
The ratio of this number is the ratio of your brake balance for a neutral car.
If you want the front wheels to lose traction first, you increase the brake pressure of the front beyond that ratio while keeping the rear the same. If you want the rears to brake traction first, you increase the brake pressure of the rear while keeping the front the same
Now you know what ratio to do, but how high the number should be, is up to you. A higher number will mean greater braking forces, but a more sudden and likely wheel lock under braking. A low number will allow you to "floor" the brake pedal with less accuracy and not produce wheel lock as quickly. I prefer extremely high (7-9) front brake pressure, with the rear in the normal ratio, so that I can do my experimental Brake-lock drift.
IMPORTANT RATIO #4: BRAKE FRONT/REAR BALANCE Self-explanatory. To make to cars brake similarly, this ratio should be the same. Note however, if a particular car's brakes are significantly worse in the front or the rear compared to the other car you are taking your information from, you may need to adjust for this. Likewise, more powerful brakes overall will require lower brake settings in general to achieve the same results if they came from a car with stronger brakes.
Tuning Power/Transmission Ratios
Power is not necessary to drift. It may be necessary to do some types of drifts, but not all cars need power to drift. What we are concerned with is the power ratio to the grip of the wheels. This is the most simple, and least intensive type of tuning done to a drift car.
A car's power to the wheels is determined by the gear ratio of the current gear, times the final gear, times the gear ratio of the tire. Because GT5's tire diameters are not given (as far as I know) I will omit this. You can adjust by feel for cars of varying tire diameters, but on most drift cars they vary by relatively little and cannot be adjusted anyway, so there's no sense in telling you how to tune them.
IMPORTANT RATIO #5: TORQUE/REAR WEIGHT + DOWNFORCE
To find rear torque:
Torque at Given RPM * Current Gear Ratio * Final Gear Ratio
What we want is for a car that you already feel comfortable in, to have the same ratio of Torque/Rear Weight at a given speed for the entire length of the powerband.
This means that when you accelerate between gears, you will produce the same "power" and tire spin in both cars and shift at similar points. There is a problem however, the tighter the gears are, the more torque is produced and the smaller the power band. Generally, cars with little engine torque want to have "short" gears so they receive maximum rear wheel torque. This means that their powerband is smaller, which can be advantageous.
However, extremely powerful cars will require "longer" gears, so they produce the same torque at the wheels as the less powerful car. This means that they have a wider powerband. So we cannot tune for just peak torque, or torque at horsepower peak. We have to tune for the length of the power band, otherwise when tuning a more powerful car to drift like a less powerful car, it does not drop out of its powerband (and suddenly allow the rear wheels to stick!) when shifting up.
Therefore, the more "peak" is in the torque band of the car, the worse it will be at drifting, because it requires a tighter powerband to maintain a relatively average torque across the duration of a gear. This is why the Nismo Z-Tune Z33, with his highly peaked turbocharged torque curve, is much more difficult to handle than the Nismo S-Tune Z33, which can be supercharged with a nice, flat torque curve.
The general numbers to consider are the Torque at your HP peak (where you will spend most of your time), the Torque 1K over, 1K under, and 2K under your peak. Take those numbers, and divide them by the weight over the rear wheels:
(Torque 1K over at engine * "X" Gear ratio * Final Gear) / Weight of car at Rear + Downforce
Do the same for At HP peak, 1K under, and 2K under. You may need to go 3K under if you are shifting with very long gears, or do not plan on revving above the HP peak. Because GT does not give you these numbers, estimate given the dyno graph it provides.
Those numbers for your car you tuning, should be as close as possible to the numbers of the car you are already familiar with.
How you can tune this: Add weight to the rear (be sure to readjust every other setting, from suspension to braking too) reduce power, or adjust the gears, or add downforce.
If you need tighter gear ratios to stay in a flat torque curve, reduce the power and keep the gears tight. If your torque curve is very flat, then you can keep the power high and lengthen the gears. If you cannot do either, add rear downforce. If, once downforce is added (or cannot be added) it still is not close to the desired numbers, add weight. Adding weight should be a last resort.
Determining Center of Mass
A while ago I asked this board if you could find the height of the center of Mass on GT5. This is vital information for determining body roll. I was initially told it was not present, however, I figured out a way. It requires working backwards from known formulas.
Since we know how to figure out total body roll based on load transfer, which is dependent on the Center of Mass height, and the suspension tuning, if you can measure body roll knowing all other variables, you can figure out center of mass height.
So to do this, give arbitrary but neutral suspension settings (same spring rate ratio as your front/rear static weight bias) and put tires with known G-force ratings, and then do a skidpad test and record the replay. Go into photo mode and place yourself directly in front of the turning vehicle. Record the G force (from the replay data at that second) and take a protractor to the screen and measure the body roll from the centermost front of the car to the outside in degrees, and convert to radians.
Then, use this formula:
Roll in Radians = SIN(MM drop from static)/Half Width of Car)
Or A=SIN(B/C)
B = Total Cornering Drop (D) - Static Drop (E)
Or B = D-E, or A=SIN([D-E]/C)
We'll assume Front measurements of angle and spring rates, although if the car is neutral, it should work for rear as well as long as you adjust the weight values and spring rates accordingly.
D = Corning Outside Wheel KG (F) / Front Spring Rate (G), E = Static Wheel KG (H) / Front Spring Rate (G)
Or D = F/G, and E = H/G, so we get A=Sin([F/G-H/G]/C
F = Load Transfer (I) * Front Percent of Weight (J) + Static Wheel KG (H)
or, F= I*J + H, so we get A=Sin ([[I*J+H]/G-H/G]/C)
I = Tire G Rating (K) * Total Weight (L) * Center of Mass Height (M) / Half of the Car's Width (C)
or, I= K*L*(M/C), so we get: A=Sin([[[K*L*(M/C)*J]+H]/G-H/G]/C)
A = .0523 Radians (about 3 degrees measured on TV, lets assume)
G rating: (K) = .85
Total Weight (L) = 900 kg
Center of Mass Height is what we want to find.
Half of Width (C) = 800mm
Front Percent of Weight (J) = .6
Static Front Wheel KG (H) = 270KG (60% of 900, divided by 2)
Front Spring Rate (G) = 9 kg/mm
So we get: .0523 = SIN([[[.85*900*(M/800)*.6] +270/9] - 270/9] / 800)
.0523 = SIN ([[[459*(M/800)] + 30] - 30]/800
.0523 = SIN (0.0007171875M)
Inverse SIN on both sides:
0.052323872 = 0.0007171875M
M = about 72.9. This means that, if we are observing 3 degrees of body roll with those given settings, then the center of mass must be about 73mm from the ground. This is likely not true, so our "guess" at 3 degrees of body roll is conservative, and the observed amount is likely higher if you try it for yourself on your own drift cars.
IMPORTANT RATIO #6: Less of a ratio, but the CENTER OF MASS height is vital to the similarity of a car, as it affects Ratio #s 2, 3, and 4.
So to recap, when you have a drift car you "like", and want to pick a different one (because of innate ability or personal preference) you want to tune for the following, to be as close as possible between the two cars:
1. Load transfer / Total Weight
2. Total Roll Angle, and the ratio of the Front/Rear Roll Angles
3. Damper Stiffness / Total Roll
4. Front/Rear Brake Balance, and overall brake balance to the lift forces.
5. Torque / Rear Weight+Rear Downfroce
6. Height of the Center of Mass
With this, you should be able to take a drift car you currently can drive well, and make almost any other FR car drive like it as well. There are more specifics (such as the length/width ratio, size of the wheelbase, and other things) that affect how it turns, but most of those are things you cannot tune so I did not include them. Hopefully this wakes up some of the "drift tuners" on this board to a more precise and controlled manner of tuning. It will, unfortunately, also give away my largest advantage over most drifters, leaving me to just out-drift them on experience alone.
We are nearly ending this series. I plan to do one more installment, covering more broadly how all of this mathematics translates to driving style and giving overall tips to make who (if someone has followed this thread so far) is a good drifter, into a phenomenal drifter.
I may also release my Excel spreadsheet that I use to tune. It is one column per car, with about 200 rows of data and calculation afterwards, a good portion of which is covered here.
Part 2: Precision - More complex factors in drift physics
Part 3: Weapons - Novice Drift Initiation Techniques
Part 4: High Caliber Weapons Advanced Drift Initiation Techniques
Part 5: Mid-Corner Drift Physics - Executing a drift at a speed and angle.
Part 6: Math and Comparative Tuning - Tuning drift cars in relation to eachother
=====================
Compared to my previous entries, this is probably the most important. This is one of the last bits of information, and reveals the most about my technique and knowledge of drifting. I am posting it now because I feel safe to say that I have exhausted all of GT5's drifting potential. Competitions are idiotic, teams are immature and unskilled, normal rooms are no longer challenging, and I achieve more fun doing double contact drifts off of the Chicane at Special Stage route 5 or Monaco in practice mode than simply repeating the same perfect sections, or maximizing my time throughout a course. Quite frankly, I am tired of my tuned 240Z being able to outdrift in both speed and angle all but an S2000 GT1 or RX7 TC. Since there is no more need to keep my secrets... here we go.
THIS IS HOW I TUNE MY CARS. It may not be perfectly correct, but I feel it is as accurate as can be, given that GT5 itself is not a perfect simulator. In some ways, it may be even more precise than GT5, but it produces results. The math might be wrong in some places, I am not a mathematician and it's never been my strong suit, however based on my own knowledge and the research I've done, I *think* it is correct. By all means, feel free to improve on it if you can, as I am certain there are even more clever things that better mathematicians than I can do.
Put simply, this is my attempt at smashing apart any argument saying that drift cars are simply tuned "by feel" and without precision. This is silly, and a truly good drifter should know by mathematics, exactly what is happening to his car at any point in a corner, and learn to look at numbers and adjust his driving style accordingly.
This section is rather math-heavy, but I will keep calculus out of it and stick to basic algebra. This section involves ratios and comparative tuning. If the method here is applied correctly, you should be able to make any drift car drift like any other drift car, by making sure that the "important ratios" I list are the same on both cars. A lot of the calculation is theoretical, so if there are math errors (I use an excel spreadsheet and rather than give you my exact tune, I will just present theoretical numbers) I will attempt to fix them as they are noted, however, this is more so you can understand the equations and use them yourself.
Tuning Weight and Weight Distribution
First off, Static Weight Distribution. The grip a tire has is proportional to the weight being pressed down on this tire. You can take a pencil eraser and slide it across a flat surface easily, but if you press down on it, you get more resistance to sliding. This may seem wrong, since it implies that heavier cars have more grip. However, heavier cars have more lateral G on the tires, meaning that the tires have more grip, but they require more grip to accelerate the higher weight at the same speed laterally. The load transfer of a car increases as the weight and the height of the Center of Mass increases. The greater the load transfer, the less you can approach the maximum grip of the tires. The tires, which have no greater cornering ability when not attached to the car, cannot reach the same peak cornering when attached to a heaver car, or higher center of mass, vehicle. However, because some cars (for example, GT86) have extremely low centers of mass, they may have less load transfer than a lighter car (for example, AE86) which has less weight but a higher center of mass. A car will be drift at a maximum speed higher if it has a lower ratio of its center of mass height to its weight.
This is the important part: Having a lower center of mass, or less load transfer, will make you car drift faster at all angles. For a given angle, the car will corner better and produce higher G numbers.
CH Tires are rated to about .85Gs. Depending on the load transfer and size of the tire's contact patch, (which varies car to car) it may be between .7-.9Gs, but rarely for a street car reach 1G consistently.
You can find the total load transfer of a car, which is the difference in "weight" on the wheels from Static to Cornering speed, by the following:
(Tire G rating) * (Total Weight, KG) * [(Center of Mass Height, MM) / Track Width)]
The Track Width is half of the car's total width, in MM.
The produced number is the amount of weight from the "center" of the car, is pushed to the outside. You can figure out, under normal cornering (no throttle/brake) exactly how much weight is on the tire by dividing that number by the Static front/rear weight ratio (given to you by the Ballast Screen)
Example: A car is 900KG. Assume load transfer is 500KG, with a 60/40 weight distribution. Static weight is:
Front: 900 x .6 = 540KG
Rear: 900 x .4 = 360 KG
And thus,
Front Right Tire: 270KG
Front Left Tire: 270KG
Rear Right Tire: 180KG
Rear Left Tire: 180KG
This means that under corning, "500" KG is moved to the outside of the car, in proportion to how it is under static weight. This is found by this formula, for front (substitute rear percentage for rear):
Load Transfer * %of Front Weight + Tire's current weight
So our front load transfer is 500 * .6 or 300KG. This means that 300 KG will be lifted from the front inside tire, and placed on the outside tire. 200KG will be lifted from the rear inside, and placed on the rear outside.
Result:
Front Inside Tire: -30KG
Front Outside Tire: 570KG
Rear Inside Tire: -20KG
Rear Outside Tire: 380KG
You will notice that some of the tires have lift forces, as in they actually are being lifted as the car pulls to the outside. However, because only the body rolls, and the unsprung weight does not, that unless those numbers highly exceed the unsprung weight AND the weight being pressed down by the suspension, the wheels will not lift off of the ground. A good example is taking the '70 Charger with stock suspension on high grip tires. It will lift a tire off of the ground under cornering and braking, because of the extreme lift force due to a high load transfer and low spring rate.
Next, you can calculate the load transfer under braking.
A car can brake at the same max Deceleration as it can grip in max sideways acceleration. Since braking is load transfer to the front, you can simply use the same load transfer number from before, but instead of applying it inside/outside, apply it front to rear. You can quickly see how a Braking Drift works, and how effective it will be, if you apply both the braking transfer and cornering transfer at the same time. When done so, usually there is lift forces on all but 1 tire. This is astounding, but if your car is not brake drifting properly, you can use these mathematics to figure out exactly how to maximize front-rear weight transfer under braking.
IMPORTANT RATIO #1: A CAR'S PERFORMANCE CAN BE MEASURED BY THE RATIO OF ITS LOAD TRANSFER / TOTAL WEIGHT. A LOWER NUMBER WILL CORNER, AND THUS DRIFT, FASTER However, less weight transfer will make it more difficult to initiate a drift. A highly skilled drifter will be able to drift with minimal weight transfer, but without using the E-brake and suffering its drawbacks as well.
These calculations only give us, however, the change of grip at the tires. They do not tell us the way that the weight shifts around the car above tire level. This is Weight Transfer, and it can be easily measured by the angle that the car's body rolls. Less body roll doesn't mean that the car has higher grip, but it means that the car has less movement to reach its max corning potential, so the load transfer is not as sudden or drastic. This can be adjusted via the spring rates. Alternatively, more body roll on the front VS the rear will cause the load transfer at the front to happen later, and that delay will cause the car to relatively have more grip at the rear during initial cornering, producing understeer. The opposite is true as well, as a proportionally stiffer front will cause the rear to roll and oversteer more. A perfectly neutral car should have its spring rates in the same ratio as its static weight distribution. So a 60/40 car would have its spring rates in a 6/4 F/R ratio to be neutral, causing the whole body to roll as one unit. I, for one, prefer neutral rolling cars. But this is not just a matter of preference, because the ratio of the front roll angle to the rear roll angle tells you, under extreme weight transfer which wheels lose traction first.
So then, to tune your car's weight comparatively:
Calculate the weight transfer, and tune your weight so that the weight transfer / total weight is the same ratio Front/Rear and Left/Right as your "ideal" car.
Tuning Suspension:
Spring rates, as explained earlier, have a drastic effect on how tires lose traction under extreme load transfer. Here, I will explain how to calculate body roll based on your suspension and weight transfer numbers.
Static Support Your car sinks down on its suspension. Spring Rates, for my GT5, are given in KG force /mm. This makes it very easy to calculate static support. What this number is, is how much KGs of upward force the spring exerts per millimeter of compression. To figure out how your car sinks on its springs:
Distance dropped = Static Weight over Wheel / Spring Rate
In our car, Front right weight is 270KG. for a front spring rate of 9 KGf/mm, that means that for every MM of compresion, 9 KG of upward force is given. So that means that 270/9, or 30mm. The reason why a neutral car has the same front/rear ratio for both weight and spring rate is as follows:
Spring Rate = Static Weight over Wheel / Distance Dropped.
So for our rear, at 180KG, to drop 30 MM as well (resulting in a car that is flat when it is just sitting there) 180 / 30 = 6
9 spring rate front and 6 rear is a 60/40 split.
Now, to calculate roll angle, we need to know how much the outside body dips (and inside body lifts) under cornering. Since we already know how much weight is on each wheel during extreme cornering, it is quite easy to apply the same formula:
Distance Dropped = Weight under cornering / Spring Rate
Outside front tire is 570 KG, so it drops 63.33mm. That means that from its normal 30mm drop, it drops an additional 33.33 mm. This makes sense, since the wheel's "weight" is almost doubled, so should its drop. This is where it becomes important to note that if there is not 33.33 mm of distance between the tire and the bottom of the vehicle when it is static, the body of the car will hit the wheel under cornering.
The roll angle can be found like a triangle. From the center of the car to the outside (half of the width, in this case 800mm) being the hypotenuse, the distance dropped (33MM) being the opposite leg.
Roll Angle: Sin(Opposite / Hypotenuse), or here, .0412 radians. Take that times about 57.2957795 to get that in degrees.
IMPORTANT RATIO #2: TOTAL ROLL ANGLE, AND FRONT ROLL ANGLE / REAR ROLL ANGLE To make one car handle similar to another, make the front roll angle of one car the same to the other, and same with the rear. If you want neutral roll, make all of the numbers as close as possible.
This same basic formula can be applied to Front/Rear roll under braking and acceleration.
Camber and Toe
Camber should be no greater than the roll angle. Increasing front camber higher than rear will, assuming front and rear roll is the same, cause additional grip to the front relative to the rear. Increasing rear camber does the opposite. This introduces oversteer and understeer respectively.
Front Toe-In causes tires to resist the change in motion, resulting in a low turning angle for full lock, which can stabilize the front turning in (but reduce its cornering speed). It also produces better stability under braking, and improves braking performance because the contact patch is wider. Rear toe does the same, but it stabilizes the rear. This is especially useful on cars with a high power/rear weight ratio. High rear toe out destabilizes the rear, meaning that the rear will lose traction quicker in the event of sudden change of direction. Front toe-out does the opposite of front toe-in.
Ride Height
Ride Height simply lowers the Center of Mass, or raises it. The number given is in mm. You can create more weight transfer/roll angle by raising the center of mass, or less by lowering it. If it is too low, however, and the body rolls farther than the suspension has room to travel, then it will hit the edge of the car's wheel wells under cornering or braking. Stiffer springs reduce body roll, and thus can counteract this.
Dampers
Dampers do not affect how much body roll your car has. It affects how slowly or quickly you reach that max roll once force is applied. It should also be noted, that dampers affect front/rear roll, so their settings should be proportional to the front/rear roll bias. They are largely a "by feel" scenario.
IMPORTANT RATIO #3: DAMPER SETTINGS / TOTAL ROLL As a car has greater roll, it needs looser dampers to reach that max roll at the same time as another, stiffer car with less roll. The opposite is also true. A car with 2 degrees body roll, if it "feels" comfortable at 6 dampeners, would feel similar in changing the body roll if it had 1 degree body roll and 3 setting dampers.
Earlier I described the "damper" drift. Because you can adjust both how fast dampers extend and how fast they compress, you can do some nifty tricks to initiating a drift. If you have the front dampers compress quickly, and the rear dampers extend quickly, (low settings in proportion to body roll) the body roll to the front under braking is going to be sudden. Loose enough, and it will "shock" the rear tires into suddenly losing traction sooner. This means that under heavy braking, the rear slips quickly. However, if the front extension and rear compression is high, that means once you start accelerating in the corner, the forward roll changes roll less dramatically to a backward roll than it did under braking, giving you a "planted" and smooth corner exit and control during the drift. While you can improve the handling of the car with minor adjustments toward this setting, making it dramatic will allow that shock to make the car simply want to drift under merely normal braking!
Tuning Brake balance
An often overlooked portion of tuning, but for drift tuning I find it to be completely vital. If you have no progressed enough of a drifter to be able to not use ABS, then ignore this. If you feel you are good enough however, this is vital information.
The brake balance on a car is not proportional to its weight distribution or body roll. It is proportional to the lift forces that the ground exerts upward on the car's tires to stop it. Under braking, a car can be said to rotate forward, the rear wanting to flip over the front. It is the weight of the car pressing against the friction of the ground that allows it to slow.
In our car with 900 KG, and 60/40 weight distribution and .85Gs CH tires, braking at .85 Gs (max braking force) means that the load transfer (as we said earlier, assume 500KG) is so that 500KG, 300 of which is going to move to the front tires. This means under braking, our weights are as follows, for one tire:
Front tires: Normal Tire Weight + (Load transfer) + (Front Downforce)
Rear Tires: Normal Tire Weight - (Load Transfer) + (Rear Downforce)
For each individual tire, we divide the load transfer and downforce each by 2.
So for our car with 900 KG, 500KG weight transfer, and no downforce:
Front Right Tire: 520KG
Front Left Tire: 520KG
Rear Right Tire: -70
Rear Left Tire: -70
The overall Braking Forces of the car is going to be the G rating of the tires times its total weight. Here, is it 765kg. We want to know how that braking force is divided front/rear The Lift Forces of the car are going to be:
Front: [(1-%of weight in front)*Total Weight] - Braking Forces * Center of Mass Height/WheelBase]
Rear ^ Above number, subtracted from total Braking Forces
The ratio of this number is the ratio of your brake balance for a neutral car.
If you want the front wheels to lose traction first, you increase the brake pressure of the front beyond that ratio while keeping the rear the same. If you want the rears to brake traction first, you increase the brake pressure of the rear while keeping the front the same
Now you know what ratio to do, but how high the number should be, is up to you. A higher number will mean greater braking forces, but a more sudden and likely wheel lock under braking. A low number will allow you to "floor" the brake pedal with less accuracy and not produce wheel lock as quickly. I prefer extremely high (7-9) front brake pressure, with the rear in the normal ratio, so that I can do my experimental Brake-lock drift.
IMPORTANT RATIO #4: BRAKE FRONT/REAR BALANCE Self-explanatory. To make to cars brake similarly, this ratio should be the same. Note however, if a particular car's brakes are significantly worse in the front or the rear compared to the other car you are taking your information from, you may need to adjust for this. Likewise, more powerful brakes overall will require lower brake settings in general to achieve the same results if they came from a car with stronger brakes.
Tuning Power/Transmission Ratios
Power is not necessary to drift. It may be necessary to do some types of drifts, but not all cars need power to drift. What we are concerned with is the power ratio to the grip of the wheels. This is the most simple, and least intensive type of tuning done to a drift car.
A car's power to the wheels is determined by the gear ratio of the current gear, times the final gear, times the gear ratio of the tire. Because GT5's tire diameters are not given (as far as I know) I will omit this. You can adjust by feel for cars of varying tire diameters, but on most drift cars they vary by relatively little and cannot be adjusted anyway, so there's no sense in telling you how to tune them.
IMPORTANT RATIO #5: TORQUE/REAR WEIGHT + DOWNFORCE
To find rear torque:
Torque at Given RPM * Current Gear Ratio * Final Gear Ratio
What we want is for a car that you already feel comfortable in, to have the same ratio of Torque/Rear Weight at a given speed for the entire length of the powerband.
This means that when you accelerate between gears, you will produce the same "power" and tire spin in both cars and shift at similar points. There is a problem however, the tighter the gears are, the more torque is produced and the smaller the power band. Generally, cars with little engine torque want to have "short" gears so they receive maximum rear wheel torque. This means that their powerband is smaller, which can be advantageous.
However, extremely powerful cars will require "longer" gears, so they produce the same torque at the wheels as the less powerful car. This means that they have a wider powerband. So we cannot tune for just peak torque, or torque at horsepower peak. We have to tune for the length of the power band, otherwise when tuning a more powerful car to drift like a less powerful car, it does not drop out of its powerband (and suddenly allow the rear wheels to stick!) when shifting up.
Therefore, the more "peak" is in the torque band of the car, the worse it will be at drifting, because it requires a tighter powerband to maintain a relatively average torque across the duration of a gear. This is why the Nismo Z-Tune Z33, with his highly peaked turbocharged torque curve, is much more difficult to handle than the Nismo S-Tune Z33, which can be supercharged with a nice, flat torque curve.
The general numbers to consider are the Torque at your HP peak (where you will spend most of your time), the Torque 1K over, 1K under, and 2K under your peak. Take those numbers, and divide them by the weight over the rear wheels:
(Torque 1K over at engine * "X" Gear ratio * Final Gear) / Weight of car at Rear + Downforce
Do the same for At HP peak, 1K under, and 2K under. You may need to go 3K under if you are shifting with very long gears, or do not plan on revving above the HP peak. Because GT does not give you these numbers, estimate given the dyno graph it provides.
Those numbers for your car you tuning, should be as close as possible to the numbers of the car you are already familiar with.
How you can tune this: Add weight to the rear (be sure to readjust every other setting, from suspension to braking too) reduce power, or adjust the gears, or add downforce.
If you need tighter gear ratios to stay in a flat torque curve, reduce the power and keep the gears tight. If your torque curve is very flat, then you can keep the power high and lengthen the gears. If you cannot do either, add rear downforce. If, once downforce is added (or cannot be added) it still is not close to the desired numbers, add weight. Adding weight should be a last resort.
Determining Center of Mass
A while ago I asked this board if you could find the height of the center of Mass on GT5. This is vital information for determining body roll. I was initially told it was not present, however, I figured out a way. It requires working backwards from known formulas.
Since we know how to figure out total body roll based on load transfer, which is dependent on the Center of Mass height, and the suspension tuning, if you can measure body roll knowing all other variables, you can figure out center of mass height.
So to do this, give arbitrary but neutral suspension settings (same spring rate ratio as your front/rear static weight bias) and put tires with known G-force ratings, and then do a skidpad test and record the replay. Go into photo mode and place yourself directly in front of the turning vehicle. Record the G force (from the replay data at that second) and take a protractor to the screen and measure the body roll from the centermost front of the car to the outside in degrees, and convert to radians.
Then, use this formula:
Roll in Radians = SIN(MM drop from static)/Half Width of Car)
Or A=SIN(B/C)
B = Total Cornering Drop (D) - Static Drop (E)
Or B = D-E, or A=SIN([D-E]/C)
We'll assume Front measurements of angle and spring rates, although if the car is neutral, it should work for rear as well as long as you adjust the weight values and spring rates accordingly.
D = Corning Outside Wheel KG (F) / Front Spring Rate (G), E = Static Wheel KG (H) / Front Spring Rate (G)
Or D = F/G, and E = H/G, so we get A=Sin([F/G-H/G]/C
F = Load Transfer (I) * Front Percent of Weight (J) + Static Wheel KG (H)
or, F= I*J + H, so we get A=Sin ([[I*J+H]/G-H/G]/C)
I = Tire G Rating (K) * Total Weight (L) * Center of Mass Height (M) / Half of the Car's Width (C)
or, I= K*L*(M/C), so we get: A=Sin([[[K*L*(M/C)*J]+H]/G-H/G]/C)
A = .0523 Radians (about 3 degrees measured on TV, lets assume)
G rating: (K) = .85
Total Weight (L) = 900 kg
Center of Mass Height is what we want to find.
Half of Width (C) = 800mm
Front Percent of Weight (J) = .6
Static Front Wheel KG (H) = 270KG (60% of 900, divided by 2)
Front Spring Rate (G) = 9 kg/mm
So we get: .0523 = SIN([[[.85*900*(M/800)*.6] +270/9] - 270/9] / 800)
.0523 = SIN ([[[459*(M/800)] + 30] - 30]/800
.0523 = SIN (0.0007171875M)
Inverse SIN on both sides:
0.052323872 = 0.0007171875M
M = about 72.9. This means that, if we are observing 3 degrees of body roll with those given settings, then the center of mass must be about 73mm from the ground. This is likely not true, so our "guess" at 3 degrees of body roll is conservative, and the observed amount is likely higher if you try it for yourself on your own drift cars.
IMPORTANT RATIO #6: Less of a ratio, but the CENTER OF MASS height is vital to the similarity of a car, as it affects Ratio #s 2, 3, and 4.
So to recap, when you have a drift car you "like", and want to pick a different one (because of innate ability or personal preference) you want to tune for the following, to be as close as possible between the two cars:
1. Load transfer / Total Weight
2. Total Roll Angle, and the ratio of the Front/Rear Roll Angles
3. Damper Stiffness / Total Roll
4. Front/Rear Brake Balance, and overall brake balance to the lift forces.
5. Torque / Rear Weight+Rear Downfroce
6. Height of the Center of Mass
With this, you should be able to take a drift car you currently can drive well, and make almost any other FR car drive like it as well. There are more specifics (such as the length/width ratio, size of the wheelbase, and other things) that affect how it turns, but most of those are things you cannot tune so I did not include them. Hopefully this wakes up some of the "drift tuners" on this board to a more precise and controlled manner of tuning. It will, unfortunately, also give away my largest advantage over most drifters, leaving me to just out-drift them on experience alone.
We are nearly ending this series. I plan to do one more installment, covering more broadly how all of this mathematics translates to driving style and giving overall tips to make who (if someone has followed this thread so far) is a good drifter, into a phenomenal drifter.
I may also release my Excel spreadsheet that I use to tune. It is one column per car, with about 200 rows of data and calculation afterwards, a good portion of which is covered here.
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