Setup The Race Car III

Setting Up The Race Car Part 3

Roll couple distribution:

Roll couple distribution, which can be termed roll stiffness, is a major factor for oversteer and understeer. Increasing the roll stiffness at one end of the car will produce a greater tire slip angle on that outside tire. So if a car is oversteering, it can be brought into control by increasing the roll stiffness at the front end, there by increasing the tire slip angles.

What this means is, install a stiffer front anti-roll bar or stiffer RF spring to increase the front roll stiffness. For understeer the reverse is true.

Roll couple is adjusted with springs and anti-roll bar rates. The stiffer end of the car will lose traction first (because of the greater slip angle). If the cars front suspension is stiffer than the rear, the roll couple distribution will produce Understeer because the front end is handling more weight transfer.

Center of gravity height:

The centre of gravity is the geometric center of weight location. The CGH is the point above the ground where this exists. All forces of acceleration, lateral acceleration and deceleration act on the entire car through the CGH. The height of the CGH is a very important consideration for cornering ability. The lower the CGH, the better the cornering. We can lower the CGH by adjusting the ride height.

Roll center:

Every vehicle has a front and rear roll centers and they are completely independent of each other. The roll centre is a theoretical point – determined by the pivot locations and angles of the suspension linkages – about which the particular end of the vehicle rolls.

The front and rear roll centers are joined together by a straight line running through the center of the car called a roll axis (again, theoretical). During cornering, a car will roll about this roll axis.

The relationship between the CGH and the roll axis is what determines the amount of body roll that takes place during cornering. The greater the distance between the CGH and the roll axis, the greater the body roll angle for a given lateral acceleration force. Hence, the less distance, the less body roll, which is precisely what we are looking for.

As a guideline generally the front roll center will lie between 1 and 3 inches above the ground and the rear roll centre falling between 8 and 12 inches above the ground.

Front weight bias:

The front weight bias can be adjusted by clicking the weight bias tab on the garage screen. Front weight bias is the amount of weight on the front of the chassis as compared to the rear of the chassis. Sliding this weight forward gives you more front weight or bias. This is primarily used to set the static cornering performance of the car.

Increasing the front bias tends to tighten while decreasing loosens the chassis, especially at mid-turn and through the exit.

Front weight bias were allowed adjust from a range from 45.8% (1650 lbs.) to 54.2% (1950 lbs.). How much weight should we move to the front? A better way to look at this is how much weight should be placed at the rear of the car and the rule of thumb should be “the more the better”.

We need more weight on the rear to be able to accelerate faster coming off a corner. For a given amount of acceleration, the cornering force available on the inside tire increases tremendously when there is heavy rear weight bias. Braking ability is also enhanced with rear bias. The best braking is achieved with a cars weight distribution is as close to 50/50 as possible.

The more front bias you run the tighter the chassis, especially at mid turn and beyond. Less front bias, the looser the chassis gets. A front bias of 48% to 50% would be a good starting point and work from there. Anything below 48% or higher than 51% isn’t realistic in a real cup car, but can still be effective given different spring rates and frame heights.

Experimentation once again with all these variables will be the only way to correctly determine the proper front weight bias given the various circumstances.

Generally speaking, the flatter the track, the more front bias required. The higher the banking the less front bias required, because of less braking and less weight being transferred to the front. More rear bias would be preferred at tracks like Daytona and Talladega.

A slower track that require shorter gear ratios, will also require less front bias. This is due to the problem of wheel spin that can occur during acceleration. You would rather have less front bias or more rear bias to help transfer weight to the rear quicker to avoid wheel spin.

Another factor that must be considered when dealing with front bias is fuel. As fuel is burned, your rear weight distribution is lowered. You will lose approximately 1% of rear weight per every 5 gallons burned. This means that by the end of a full fuel run you’ll lose over 4% rear weight. With less fuel and less rear weight, the car will have a tendency to tighten up as fuel diminishes.

Although your not directly changing your front bias, you will be effecting the amount of weight that is being transferred as fuel is burned. This will result in an ever changing car as fuel dissipates.

How Front Weight Bias effects the handling of the chassis:

More front weight bias tightens the chassis.

Less front weight bias will loosen the chassis.

Left weight bias:

Left weight bias is pretty straight forward, it moves the center of mass of the car left or right of center, which helps even out the weight transfer when the car is turning. We are allowed left bias adjustments from 54.2% (1950 lbs.) left side weight, to 45.8% (1650 lbs.). For ovals, always set the Left Bias at 54.2%

A road course is the only reason you would ever want to adjust the left side bias. The reason is you have to deal with both left and right hand turns. If the right and left hand turns are about equal, then you would want to set the bias to 50%. At tracks where there are more right turns than left, you want to consider moving more weight to the right side of the car.

This allows you to get through those right hand turns a little quicker, but at sacrificing losing speed going through the left hand turns. The effect is more subtle, but if your trying to tweak the last couple of tenths out of your lap times, it may help.

Ride height:

The chassis ride height is simply the distance measured in inches from the bottom of the frame rails to the ground. This measurement is taken at all 4 corners of the car where the frame rails are lowest to the ground. NASCAR has limits as to the minimum ground clearance allowed. Ideally you would want to run your chassis as low as possible. When you lower your ride height, you lower the centre of gravity. With a lower centre of gravity, less weight transfer will occur while cornering.

A number of criteria must be considered when adjusting ride height. Those include chassis clearance, camber change, front and rear roll centers and roll couple. The front roll centre and rear steer isn’t an option for us to adjust. They are built into the chassis itself. Rear roll centre can be taken care of by adjusting the track bar, which also effects roll couple distribution.

Camber will have to be readjusted after making a ride height change, because your camber angles and the contact patch of the front tires change as your car is raised or lowered, due to the roll couple change. Check your tire temperature for proper camber angles.

An important factor we must consider is chassis clearance. If the ride height is set to low the car may bottom out on the track. This is more likely to occur at high speed, high banked tracks where the centrifugal forces are higher. To cure a car that bottoms out you can do one of two things. Raise the ride height or run stiffer springs. On paper, the softer the springs and lower the car, the better off you should be, so experimentation is the only real answer.

We are allowed to adjust the ride height on the LF, LR, & RR. The RF is fixed at 6.00″ and is grayed out. The LF we are allowed to change the ride height from 4.50″ to 6.00″. The LF is always the lowest point of the car and should always be set at 4.50″.

The LR we are allowed 4.50″ to 6.50″, which is a half an inch higher than the LF. Finally, the RR is always the highest point of the chassis and again we are allowed from 6.00″ to 7.50″. Adjusting ride height effects the way weight is transferred while cornering. Running a higher LR then the RR, puts more weight on the RR.

This will cause a loose condition entering the corner. Just the opposite is true when running the higher RR then the LR, will create a tight condition upon entry into a corner. Adjusting the split between the LR & RR you will get different degrees of oversteer and understeer.

Another thing to consider when raising the ride height in the rear of the car, is how it effects the aerodynamics of the car. Raising both LR & RR ride heights raises the entire back of the car pushing that big spoiler running into the air. This will create more drag and downforce, because it is catching more wind and will slow your straightaway speed. One good feature of this allows the back of the car to stick better in the corners. Running a higher ride height may allow a lower spoiler setting. Trail and error will prove worthy here.

Also remember your springs will play an important role in determining your overall ride height. In general, the lower the car, the faster your car should be.

Wedge:

The word “wedge” originates from the historical days of auto racing when wedge-shaped blocks were used under transverse leaf springs to jack weight from one corner of the car to the diagonally opposed corner. When the RF weight jacking screw is screwed down, the chassis is moved up on the spring and weight is transferred to the LR corner.

This is called adding wedge to the chassis. Because the total vehicle weight must still remain the same, the LF and RR corners of the chassis get light as more wedge is jacked in.

Jacking wedge into a chassis is a crutch that has been used for years because of the lack of knowledge about spring selection and other various methods of chassis tuning. If the rear end is loose (oversteering), the RR spring should be changed to a softer rate or the RF spring should be changed to a stiffer rate. Wedge should not be added. Only when the chassis has been sorted out to near perfection as possible should one or two rounds of wedge be added if it is necessary.

To set wedge, take the average tire temperatures of the RF and LR tires, compared to the average of the two front tires, then to the average of the two right side tires. The diagonal average should be 5 to 10 degrees cooler than both the front and right side averages. If its hotter, you have too much cross weight. Cooler you need more wedge.

Wedge should only be used to keep the back of the car tight entering a corner while also adding bite exiting a corner during a race.

Spoiler:

The spoiler itself is a wide piece of rigid aluminum located on the rear deck lid that spans the length of the trunk. The purpose of a spoiler is to increase the downforce to the rear of the car. This is accomplished by how the air is passed over the back of the trunk lid as it hits the spoiler. The rear spoiler catches air pushing down on the back of the car allowing for better traction through the corners.

How much air catches the spoiler is determined by the angle the spoiler is placed at. We are allowed a range of adjustment from 45 degrees to 70 degrees. The lower the number the lower the angle of the spoiler and less downforce at the rear of the car. A higher number the greater the angle of the spoiler and more downforce is applied to the back of the car. An increase in downforce allows the car to corner faster, brake or accelerate harder than without it.

Spoilers have the added benefit of adding very little mass in exchange for large amounts of downforce. However, the increase in downforce is not free. The price is aerodynamic drag and higher tire temperatures.

A spoiler depends on speed to work. The faster a car travels the more downforce is created. At speeds below 40 MPH, the increase in downforce is negligible.

You may think a setting of 70 would be the best for cornering and it might very well be depending on the track. At superspeedways the disadvantage to running a higher spoiler angle is that it increases drag slowing you down on a straightaway. At the high banked, high speed tracks of Daytona and Talladega, minimize spoiler angle, since downforce isn’t as critical. The high speed tracks naturally creates downforce on the car.

Generally, you want more downforce on the rear at short tracks and one mile ovals.

Decrease spoiler angle as you go to longer and faster tracks.

Another point to remember, the higher the spoiler angle the tighter the rear will be. The lower the angle the looser the rear will be.

Fuel levels:

Winston Cup cars are required to run with a 22 gallon fuel cell. Your allowed to adjust the fuels levels from 1 gallon to 22 gallons for practice sessions only. All races as well as qualifying must begin with a full 22 gallons in the tank.

We are now faced with 5 options. Take on a splash of fuel as well as 1/2, 1, 1 1/2, or 2 cans.

A splash of fuel will give you 2-3 gallons.

1/2 can gives you 5-6 gallons.

1 can equals 11-12 gallons.

1 1/2 cans will give you 17-18 gallons.

2 cans will fill your tank with 22 gallons.

The less fuel your carrying the faster your car should be. This of course depends on tire condition.

The important thing to understand about fuel, is how it effects the handling of your car as it is burned. 1 gallon of fuel weighs 6.17 pounds. Multiply that times 22 gallons and you have an extra 135.74 pounds your carrying in the back of the car behind the rear axle during qualifying and at the beginning of a race.

As fuel is burned, your rear weight distribution is lowered. You will lose approximately 1% of rear weight per every 5 gallons burned. This means that by the end of a full fuel run you’ll lose over 4% rear weight. With less fuel and less rear weight, the car will have a tendency to tighten up as fuel diminishes. This is important to remember when taking on less fuel late in a race.

If your setting your chassis based on using a full 22 gallons, you may think that by taking less fuel that you will be quicker. Depending on your setup that might not be the case.

The best solution is to practice your setup with different fuel levels to see how it performs. It’s also possible to make a wedge or track bar adjustment in the pits to compensate for how your chassis will react with less fuel.

Grill tape:

Grill tape is nothing more than duct tape that is applied to the front of the car, covering the openings for air flow to the various components that are cooled through the force of air. These components include the radiator, oil/transmission coolers and brakes. The only component were interested here, is the radiator.

We can run as little as 0% tape all the way up to 100% which covers every opening in the front grill. The amount of tape that can be added, is done in 5% increments. The more tape you apply the hotter your engine will run. Keep an eye on your water & oil temperature gauges and warning lights on your dash board. Running excessive amounts of tape for a long period of time will result in engine failure.

Why put any tape at all on the front end?

Taping off the openings in the front of the car reduce drag and increases speed. Instead of air going through the car, air is being forced around the car. This places more downforce on the front end. More downforce will make the front of the car turn into the corner quicker. Excessive amounts of tape can cause too much downforce making the rear of the car light, creating a loose condition.

The secret here is to find the best trade off between speed and handling. Try to get away with as much tape as possible on superspeedways without causing excessive water & oil temperatures. More tape will increase lap times. If you discover you can get away with running more tape, but become to loose, try to adjust for the looseness elsewhere.

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