Ross Engineering Motorsport Developments

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Corrections to my previous post
How many times have you thought about building a new race car with ether a Pushrod or Pullrod front suspension or rear suspension with Bellcranks but didn’t because you are not sure how to calculate the Bellcrank ratio or the combined suspension ratio. Well we have a program that does it for you. Let’s say you want to try it on the rear of the car. Example Place a strait edge against the inside edge of one rear tire about3” up from the bottom then place another strait edge against the out side of the other rear tire that is your tread width. Then measure the space between the proposed Bellcrank locations. That’s the only measurements you need to make. The program figures out the rest for you. The front with ether Pushrod or Pullrod is just as easy just 3 measurements by you and the program figures out the rest.

How many times have you thought about building a new race car with ether a Pushrod or Pullrod front suspension or rear suspension with Bellcranks but didn’t because you are not sure how to calculate the Bellcrank ratio or the combined suspension ratio. Well we have a program that does it for you. Let’s say you want to try it on the rear of the car. Example Place a strait edge against the inside edge of one rear tire about3” up from the bottom then place another strait edge against the out side of the rear tire that is your tread width. Then measure the space between the Bellcranks. That’s the only measurements you need to make, the program figures out the rest for you. The front with ether Pushrod or Pullrod is just as easy just 3 measurements by you and the program figures out the rest.

After all of the bits and pieces related to chassis setup have been discussed in minute detail and all of the preparation has been completed in the shop, we still have to go to the track and see how all of that worked out.

Too many times, we need to make adjustments and just plain fix the handling problems that crop up.

Now time to lay out some basic rules for tuning our race cars
The most basic rule of handling and speed for a race car lies in increasing the speed we can go through the middle of the turn. It has been said before, and rightly so, speed gained in the turns will be carried throughout the lap. This is true for both circle track racing and road racing. A car balanced for handling and dynamics is as fast as it can be.
There are other factors that will make your race car faster, but most of the gains are turn related. Given that we can all agree on the above basic principle, we further break the gain down into three turn segments-entry, mid-corner, and exit. The slowest portion of the lap is spent in the mid-turn segment, so that is where we are most interested in gaining speed.
Granted, increased average speeds in the transitions of entry and exit help reduce lap times, but the gains there pale in comparison to gains we can achieve at mid-turn. Speed gained in the middle of the turn will be carried all of the way around the track.
For a track that averages 100 mph per lap, a 2mph gain at mid-turn represents a 3/10 reduction in lap times. I've seen fast cars run up on the slower cars by 5 mph or more, and that is the half- to full-second difference between First Place and Fifteenth. So, we necessarily start out our handling tuning with the mid-turn balance, both handling and dynamic balance.

Mid-Turn
We start out solving our mid-turn handling problems. We do this because our mid-turn handling affects both entry and exit to a large extent. A car that is tight in the middle will most likely be tight into the turn and tight off. If excessively tight in the middle, the car could be loose off and here's why.
When we turn the steering wheel and cause the front wheels to create and/or increase their angle of attack, or angle differential to the direction of travel of the car relative to the racing surface, we increase the traction of those two tires. The more we turn, the more traction we get, up to a point. If the wheels are turned beyond a certain angle, the tire skids and we loose all front grip. But until then, we gain grip.
Suppose we have more rear grip overall than front grip. When we drive through the turns, with the normal steering angle that follows the radius of the turn, we will notice that the car does not want to follow the radius and instead moves out on the track toward the outside of the turn. Instinctively, we will turn the steering wheel more until the car follows the radius of the track. It does that because we are causing the front tires to produce more front grip in reaction to the increased angle of attack of the front tires.
If our car isn't too tight, we will just roll through the turns with a slightly greater steering angle and maybe never know we are tight. But, if we are too tight, we will need to input excessive steering angle and we may just over do the adding of front grip from the increased steering angle and change from a car that is tight to one that is loose. Here is what happens.
We go into the turn and feel the tendency to not turn. We quickly apply more steering input and keep adding until the car responds. But the motion is so quick that we inadvertently over correct and add too much front grip just as we are ready to accelerate. Now with more front grip than rear, the car goes from tight to loose and with the power applied, very loose off. This is a very common occurrence.
To change mid-turn balance, we can do one of the following:
• Raise or lower the rear moment center by moving the Panhard bar or J-bar up or down. For leaf spring cars, we can raise or lower the actual spring, but that is not easy. Metric four-link cars also have a tough time changing the rear moment center height and must rely on other methods for changing the balance.
• Change rear spring rates. Softening the rear spring, will increase the rear roll angle and will tighten the car, as will softening both rear springs. The inverse is true, stiffening the spring and loosen the car.
• Softening the front springs will help the car turn, but to a lesser degree than making rear spring changes. Spring split at the front also has less affect and has more influence on entry characteristics than on mid-turn. More on that later.
• Installing larger or smaller sway bars will have an effect on handling. The stiffer the bar, the less the front will want to turn. So, to help cure a tight car, we can go to a softer sway bar.
• Increase or decrease the cross-weight percent. As we make changes to the cross-weight, we affect the handling of the car and we can easily make the car neutral in handling by making cross-weight changes. But, this is not the ideal method by any means; it's just the easiest.

• The reason this method is not ideal is because for every car and combination of springs and weight distribution, there is an ideal cross-weight that matches up with a dynamically balanced setup and is related to the front-to-rear weight percentage. If we knew this magic number, we could just dial it in and then make spring or moment center changes until the car was neutral and then everything would be just right.
• Increase or decrease stagger? This is never an acceptable way to tune the handling of your race car. For every turn, there is an ideal stagger that will allow the car's rear wheels to roll around the radius and not influence the direction the car travels from following that radius.

Entry Problems
Once we have set up the car to be neutral in both handling and dynamic balance, we need to evaluate the entry handling. If our entry is without issues, meaning it is straight ahead, not tight or loose, and no excess steering input is needed beyond the normal transition from straight to left turn, then we are good to go.
If all of the alignment issues have been sorted out, there should never be entry problems, but there are influences that could affect entry stability and balance. Here are the top ones to consider.
• A. Rear alignment is the number one cause of entry problems Either by misalignment of the rear tires or by rear steering of the rear end, a car can become tight or loose on entry and that can translate to mid-turn problems. The truth is, you should have checked and corrected any rear alignment problems long before you came to the track. Rear alignment and rear steer are not tuning tools.
• B. Shocks affect entry Shock rates that restrict movement of one or more corners of the car can negatively affect entry.
• C. Brake bias changes affect corner entry There is an ideal brake bias that will allow maximum braking of each set of tires based on the loads those tires carry. Different cars with different centers of gravity will require different brake bias. front to rear, rear to front
Tune your brakes so that wheel lockup occurs simultaneously at the two ends of the car under heavy braking. We do not want the brake bias to influence entry handling characteristics. Never try to correct a tight car by increasing the rear brake bias or fix a loose-in car by increasing front brake bias.
To test your bias settings, try this exercise. Try entering the corner with sufficient speed and with a soft application of the brakes and feel the entry balance. If good, proceed to the next step. If not, refer to steps A. through C. above. Once the car is neutral without heavy braking, then enter the corner at speed with the normal brake pressure that would be used in the race or in hot laps and see if the handling changes. If so, tune the brake bias to be neutral.

• Setup changes to solve corner entry problems? We never want to make changes to our spring rates, sway bars, weight distribution, or moment centers to try to solve entry problems. When we do that, we will certainly change our mid-turn handling in a negative way. We should have already tuned the car so that the mid-turn handling was balanced correctly.
There is an exception to the above rule. We can initially plan out our spring selection so that our entry transition is best for the type of track we will be running. For flatter tracks, running even spring rates across the front, or a rate opposed to the rear spring rate, will help the transition into the corner. It is best to make that choice before you go to the track so you won't need to make changes after you tune the mid-turn.
• Throttle modulation on entry can help solve problems with abrupt release of the throttle If we quickly jump off the throttle and into the brakes, we can upset the car to where it affects our entry speed and stability. It can also cause us to slow too quickly and attain a slower speed than is necessary to maintain through the entry portion of the turn.
This is a real phenomenon that occurs with a number of drivers. The practice of early release and later application of the brakes helps with the transition from acceleration to braking. The method is one of the primary tools taught by Mike Loescher in his driving school at Finish Line Racing-and it works. Many entry problems simply go away with an improved entry strategy.
Corner Exit Handling
Most of the time, solving the mid-turn handling will solve corner exit problems. If we were tight in the middle, we would most likely be tight off or tight/loose off. If we were loose through the middle, then we would be, well, loose off, of course.
The process of increasing mid-turn speeds means that we have also increased our exit speeds, or the speed at which we begin to accelerate. This is a big deal and the reason why we spend so much time perfecting the mid-turn balances and trying to increase speed through that portion of the turns.
The ways some tracks are laid out contribute to corner exit problems. A flat track offers less grip than a banked track because the lack of dynamic down-force created by the banking to help provide more overall grip. So, we need to enhance bite in other ways.
Loose Off Condition-Rear Steer
To solve loose off If we know we are good through the middle, then a loose off condition can be solved with the application of rear steer that happens only upon the application of power. Basic rear steer from chassis roll does not help us because it will change our mid-turn handling.
There are ways to utilize the rotation of the rear end, if using a lift arm or pull bar, so that the motion of the rotation of the rear end causes the rear wheels to move fore and aft to create rear steer to the left to tighten the car off the corner.
Think this process out and try to arrange the components on your car to utilize this process. If definitely works. If you must run a solid third link or other type of rear suspension where the rear end can't rotate, then go to the next step.
Shock rates can increase the cross-weight percent on exit to tighten your car off the corners.
Throttle control will allow the rear tires to maintain their grip on the track surface and help to provide better acceleration. Once we lose grip in the rear, we must back off the throttle until we regain grip before we can continue to accelerate. By exercising throttle control, we may feel like we are giving up performance, but in reality, we are providing the most acceleration possible.
Throttle control is defined as the modulation of the gas pedal through a range of motion, never moving quickly from one position to another, in order to keep the tires in contact with the track surface. The rate of change in throttle position must be altered depending on your position on the track and through the corner, so the driver must develop an educated foot.
Many drivers report that they never got past half throttle over the course of an entire race they won. This means that they were working from off throttle to half and many points in between. It is the developing of efficient throttle modulation that is one of the most effective tools you can use to promote bite off the corners.
Conclusion
The above suggestions may at first seem like a bit few compared to all of what we know about chassis setup, but remember that we have supposedly already solved the critical issues facing our race car. We have aligned it, checked the moment center design, checked for binding in the suspension, added adjustable shocks, and done all of the other maintenance things we know we should.
The last thing to do is run the car. If you're just learning these things, take good notes and concentrate on what is happening. And when you do get the car all dialed in, be sure to maintain that good setup
You Might Have A Handling Problem If...
• If you see excessive heat or wear on one tire versus the other tires, you might have a handling problem.
• If you are more than a half second slower than the fastest car on the track, you might...
• If your car starts out the race fast and then trails off, you might...
• If you have to wait longer than your competition to get back into the throttle, you might...
• If you bought that $25,000 cheater crate motor, run illegal fuel, soaked your tires, and installed traction control, and are still getting beat, yes my friend, you might just have a handling problem.
thanks