Brake Balance Adjustment

Balanced stopping is as important as a balanced set up. To win, you need all 4 calipers doing their share of the work. Ensuring that your braking system shares the load proportionately will create a fast and stable car on corner entry. Your brake manufacturer can utilize past experience to help your team to select the correct components for your car weight, tires, horsepower, track size and banking. When I was young, my Dad taught me that 4 tires work better than 3 when it came to chassis set ups. The same holds true for braking. Getting all the tires to share the load results in faster lap times and improves consistency.

Once you have installed the correct brake system components, a brake balance bar is one of the few adjustment tools the driver can utilize right from the seat. For your brake balance bar adjuster to work properly, it is vital that you set up your pedal balance bar per the instructions provided with the hardware. For trouble free operation the pedal balance bar must be parallel to the frame rails when the pedal is full depressed. Often, teams set the balance bar parallel to the frame in the static position – this will cause binding and problematic performance. Installing the pedal balance bar parallel to the frame in the depressed position allows the front brakes to come on first promoting a stable corner entry.

After you have verified that your parts are installed correctly, you can begin choosing a brake balance bar adjuster that meets your needs. A quality brake balance cockpit adjuster will give your driver a tool that can be used during racing action.

This Brake Balance Adjuster is lightweight and mounts without dis-assembly. The steel braided flex hose is reinforced with Nylon tubing on the interior nearly eliminating the chance of binding.

Understanding how the brake balance performs will help you to get the most out of your brakes and your driver accessible adjustments. By cranking on the adjuster you are changing the percentage of leverage force to each master cylinder. Adding front brake changes the angle of the pedal balance bar assembly. In a given amount of pedal travel – adding front brake reduces the travel distance of the rear master cylinder piston. Reduced travel equal less total braking force.

Adjusting the brakes with a brake balance bar comes with compromise. Today’s brake systems are very advanced. The small reduction in overall braking force is often a good trade off as gaining the adjustment ability can be the difference between winning and losing. At tracks that work the brake system to extremes, it is important to consider that overall braking force is reduced. If you run at the same track every week you may want to explore different brake components verses relying on the adjustment method. If you find yourself dialing to all front or all rear every week then replacing components may be a choice that allows your brake balance adjuster to be more effective.

Changing the leverage percentage to favor the front brakes promotes a solid corner entry. Getting your car into the corner in a stable fashion is mandatory for drivability and builds driving comfort. If you go too far with the front percentage then your car can exert too much force to the front tires and the car can begin to pick up the dreaded middle push. Adding front braking percentage is a great choice if the car is twitchy or uncomfortable at corner entry.

Conversely, if your car has a pushing condition then dialing more rear brake can help to set the car into the turn via the rear brake assist. More rear brake percentage can be a great tool that helps a car to turn. Use caution as going too far can create rear brake lock up should the driver need to smash the brakes to avoid an accident.

Caliper mounted Brake Pressure Gauges allow you to check the pressure at each caliper. Regular use can help you to identify brake system issues. If you see a reading that is outside your norm you should inspect your brake system to find the root of the problem

At tracks that create bright red glowing rotors your goal should be to work towards having the rear brakes do as much of the stopping work as possible. Identifying the point where too much rear brake causes unstable corner entry provides a record of the setting to avoid. Once the maximum rear brake bias leverage point is established a few turns to the front for stability will help to minimize the potential for an unstable entry. Achieving the maximum from the rear brakes takes load off the front. At heavy braking tracks, obtaining maximum safe force out of the rear calipers can prevent overworking the front brakes.

There are many brake balance bar adjuster systems on the market. Be sure to mount your version properly. Utilizing a robust flex connecter at your pedal assembly prevents unwanted binding. Steel braided versions have a rigid Teflon interior that resists binding – a guide support and a straight shot into the pedal assembly promote smooth operation.

 If your brake balance adjuster system is a speedometer cable style, be sure to have a straight connection point and provide a cable guide support near the pedal assembly. Speedometer cable style units can flip into a loop rendering your adjuster useless at exactly the wrong time. Proper installation will prevent the cable from flipping into a knot. The rubberlike coating on the speedometer style cable can melt with heat. Often, the melting happens with a new car when the rubber cable sleeve is strapped to close to sources of heat. Route away from heat sources or insulate the rubberlike coated cable versions to prevent the outer coating from melting onto the cable.

Driver brake adjustment, used properly, can be the final touch to get the last ounce of speed from a good handling racecar. Further, cockpit brake adjustment can help drivers to adjust to changing track conditions or wearing tires.

Gain can come with pain. Over use of the brake adjuster can cause teams to chase their car handling characteristics. If you think of the brake balance adjuster as a fine tuning tool you will rely on chassis adjustments to balance corner handling – keeping the balance adjuster in the center of the range when the green flag drops provides the maximum adjustment ability during the race. Starting the race with the pedal balance bar perfectly parallel to the frame in the depressed position puts your brake system in the center of the range and provides maximum braking force.

Brake Balance Adjusters with a measuring scale make recording your setting an easy task. You should record your brake balance setting as a routine part of your set up process.

Recording your brake balance adjustment should be a weekly routine. You can measure the setting with a cockpit adjuster system that utilizes a scale to indicate balance position. Another option is to track the amount of turns front or rear “off of center”. If you count turns you simply record the number of adjustment turns with center being the pedal balance bar being parallel to the frame when depressed. For more accuracy, you can use calipers to measure the pedal balance bar location by measuring the master cylinder rods before and after each race.

Dash mounted Brake Pressure Gauges give you a quick reference to witness the line pressure difference created with just one turn on the Brake Balance Adjuster. Dash mounted gauges can give you an early warning to braking system leaks or problems.

You can utilize brake bias pressure gauges to witness the affect of turning the brake balance adjuster. Just one turn can make a significant change on the bias gauges. Understanding your bias gauge readings can help you to establish a baseline for your brake set up. Keep in mind, that pressure is just one element in your braking system. Variables such as piston size, quantity and master cylinder size must be taken into consideration. A brake bias gauge set provides an easily viewable baseline helping you to leave the shop ready to go – or should I say stop?

As with any adjustment, it is only good if you can repeat the change in a consistent and predictable fashion. With the proper hardware, your team can eliminate problems and orchestrate a bias towards winning.

Go Forward – Move Ahead

Jeff Butcher

04/1/12

Instant Center Adjustment

Why do we care about the Instant Center in the front suspension? We know our car builder spent plenty of time engineering the proper roll center. Instant Center of the Left and Right side front suspension are a piece in the puzzle that creates Roll Center.

Since I am opposed to over engineering at the track, I prefer to focus on Instant Centers and adjust them with the same freedom that is applied to adjusting the rear roll center. “Just try it” is my philosophy when it comes to adjusting the Instant Center at the track.

Before you start moving parts around it does pay to understand the geometry that creates instant centers. I like to explain mechanical design by using words like “stuff” or “things” instead of complicating simple topics with big phrases such as “dynamic roll propagated via G-Force induced dynamic wheel loading”. Really, we can explain stuff by simply understanding that there is more front end travel at a high speed high banked track than you would find if you set up some orange cones in a parking lot.

Timing your suspension travel by balancing spring rate, roll bars and shocks with the leverage created by Instant Centers can maximize your Big Bar set up. For that matter - any set up is benefited by experimenting with Instant Center locations.

Instant Centers are easy to visualize. You find the little spot the same way on both sides of the front of the car. For this review we will take a snap shot of the RF suspension. Your A-Arm is bolted to the frame via an ear that is welded to the frame horn. Your lower control arm bolts onto the cross member. You have a spindle pin and the tire size sets the height of the wheel center off the ground. Your A-Arm is about 7” to 12” long and your lower control arm is probably around 16” to 18” long for your typical late model that has a 63.0” track width. Basically, if you have a stock car, the parts that create the Instant Center are similar regardless of your brand of car.

My goal is here is to eliminate the fear that can be associated with the big pile of details that create the magical Roll Center. Really, roll center is often found at about 1.5” off the ground to 2.5” off the ground for most cars – give or take an inch. The left to right location moves all over the place depending A-Arm length. Of course, as soon as you run the suspension through travel the roll center moves about. With a huge roll bar, the rules have changed and once the car has been pulled down to the ground with your insanely stiff rebound shocks, the roll center and instant centers move around much less as compared to when we had a pair of 350’s on the coilovers and an 1-1/8” bar.

Big Bars require new thinking. Since planting the nose piece to the ground is the new norm, then it would seem that the suspension layout is less important – or is it? With the nose piece held to the ground by huge rebound numbers and a sway bar that nearly eliminates body roll, then why do we care about roll centers and instant centers at all?

While the movements are less, they are still there. We still have dive, roll and plenty of bumps. But, all of those movements happen faster and the distance traveled, once the nose pieces is sucked down, is less. With this “new” information how can we make an effective adjustment utilizing Instant Centers along with shocks and springs?

It pays to think about the mechanical leverage of the Instant Center. Adjusting the Instant Center can be the subtle adjustment that compensates for the reduced actual center of the corner travel induced by giant sway bars. Since the Instant Center is 2 simple lines per side we can visualize it easily. The first line is drawn through the center of the upper ball joint and extending through the inner pivot. Be sure to find the true center of the ball joint provided by your ball joint manufacturer. The second line extends from the lower ball joint through the inner pivot on the lower control arm. Extend both lines until they intersect. Boom – the Instant Center is created. Through suspension travel the intersect point moves based on the length, angle and connection point of the upper A-Arm and the lower control arm. See the accompanying photo for the visual and you will see that Instant Centers are pretty simple to understand.

The Instant Center is easy to visualize right at the track. Simply follow the lines of the upper and lower arms until they meet. Be sure to utilize the actual ball joint center provided by your ball joint manufacturer.

Now examine the RF Instant Center and how we can use mechanical leverage to our advantage. Let’s assume our track width is 63.0”.  If the hypothetical RF Instant Center is 4 inches off the ground and 3 feet left of the vehicle centerline we end up with about 49.5” (close enough) of leverage. If we make the RF A-Arm Longer and keep the same connection point on the frame ear pivot we move the RF Instant Center more to the left. The longer A-Arm gets flatter and it takes the imaginary line longer to run into the line from the lower control arm. The change lowers the RF Instant Center as well. So, hypothetically, let say we moved the RF Instant Center to left about a foot and down 2” (Since we are starting from a known baseline all we care about is the direction of the adjustment – we can repeat the change by tracking the slugs we use).

 A-Arm length and mounting height have a dramatic effect on Instant Center Location. Carrying an inventory of A-Arm lengths gives you more Instant Center Adjustment choices right at the track.

The longer lever arm created by the adjustment scenario in the prior paragraph compresses the RF spring more than it would have in our baseline set up. The car speed and banking provide the same amount of force, but the longer lever creates more travel at the RF. Really – it is like running a softer RF spring when the chassis rolls. Lowering the RF Instant Center promotes more roll. The longer lever from the Center of Gravity gives an additional boost to roll.

Bolt on tube sections make quick work out of changing A-arm length. Moving Instant Centers at the track is an adjustment you should try more often. The bolt on tube section is a rigid advantage on snouts where the A-Arm wraps around the frame.

Here is where the fun starts – let’s keep it simple. You can draw your suspension and do the actual math and record it for future reference. For now – let’s just think about the concept. Moving the RF Instant Center to the Left effectively softens the RF spring through chassis roll. But, if you want a softer RF spring, why not just put one in? Well, this is where you need to think about the corner entry, when the car is relatively traveling in a straight line, and the corner middle where the car is in full roll. If you balance the Instant Centers, and consider all of the compromises that come with race car set ups, you can make subtle adjustments by manipulating the timing of suspension compression (corner entry) and suspension roll (corner middle).

When your car is going perfectly straight, the giant sway bar is doing about zero. If the car is going straight and you smash the brakes then the ultra soft springs you have up there may not hold the car for a stable entry. You can fix the problem by adding stiffer springs for straight line (entry) braking, but then the middle may suffer due to the stiffer springs you thought you needed? From your baseline, adding front spring to get some help with corner entry stability coupled with moving Instant Center to the left creates a lever to help the car roll – now you get help under braking without suffering more spring rate during roll. The game is in balancing the Instant Center with the entry “dive” and the mid-corner “roll”.

Your car builder has the baseline figured out when it comes to Instant Center and Roll Center. But, track conditions change and driver styles vary. Maybe you can utilize Instant Center changes just like you use the Panhard bar? Try it and see if “Mikey likes it”.

The adjustment idea I like best for Instant Center manipulation is to use the same length A-Arm but simply move the upper frame pivot point up and down to get your desired result. I prefer moving the pivot point of the upper A-Arm for subtle adjustments. The benefit of moving the upper pivot point is that hardware is available to make it easy, you can make subtle changes, you avoid messing up the bump steer and the camber curves stay in line. Your car builder spent a mountain of time and testing on your baseline front end design so it pays to make adjustments that are subtle verses stretching the design parameters to extremes.

Using a slotted ear and slugs makes adjustments easy. You can move the pivot point in small increments by carrying a slug kit. You can raise and lower the Instant Center right at the track. If you want more roll, but don’t feel like you can run softer springs, you can simply change a slug and raise the RF A-Arm Pivot point. Raising the pivot point will move the RF Instant Center farther left and lower. The subtle adjustment gives you some turning help without decreasing braking stability. The RF gives you easy adjustment and you can “feel” the affect of the change just like when you move the panhard bar. You do have to readjust camber – easy deal.

Slugs that are marked give you an easy way to record Instant Center changes. A 1/4" slug makes a profound difference. Draw it out when you have time. At the track, just bolt in a pair!

A slotted A-Arm frame tab works perfectly with the slug system allowing for quick and precise adjustments.

The LF Instant Center is important too. You can use the LF to raise or lower the roll center. You can also use the LF to move the roll center left or right. You can accomplish the same thing with the RF, but this article is trying to provide simple examples to help your team see the concept and give you the confidence to try what may be a new adjustment for your team. You can certainly draw it all out, but for today just think about what happens when you move the Instant Center with simple A-Arm slugs.

When you run a Shorter RF A-Arm you generally move the roll center to the right. The shorter RF A-Arm has more angle and intersects with the lower control arm line faster – that is easy to understand, right? If the Roll Center is closer to the right it speeds the rate of travel and the car reacts quicker. Go too far and you will blast through the travel before the full force of the center of the corner arrives. When this situation occurs, the “soft push” is usually the result. So, this is a magazine article and you have a race car going around a real track. Reading is fun and accepting the limitations within this article will help you to just try adjustments. There are a ton of variables and the goal of this lesson is to simply discuss one element as if Instant Centers were not connected to anything else – of course they are! But, if by forgetting about all of the other “stuff” we can learn how to manipulate Instant Center adjustments to overcome a problem then we have learned something new.

Changing A-Arm length requires the camber to be reset. A billet nut plate speeds changes when time is short. An accurate billet caster camber gauge is a must for any race team.

Since your car builder spent the time to build your car with a proven Roll Center location we want to be careful to not adjust so much that we erase the years of testing and knowledge that our car gives you when you buy a frame. So, from a prior article Roll Center is explained here:

Roll Center Explained:

To simplify the Front Roll Center thought process it helps to understand the creation of the so called magical point.  Front Roll Center is a calculated point verses a physical place. To find it you must first locate the Instant Center both left and right.

The RF Instant Center is found by drawing a line through the center of the RF upper A-Arm ball joint extended out though the center of the A-Arm inner pivot point on the frame. Another line is drawn from the RF lower outer ball joint center though the lower control arm frame pivot. The RF lower control arm line is extended out until it meets the RF upper control arm line. Where these lines intersect is called the Instant Center. The LF Instant Center is found in the same way.

After both Instant Centers are located you can now find the Roll Center. From the RF Instant Center you draw a line back to the RF contact patch center. From the LF Instant Center you draw a line back to the LF contact patch center. Where these two imaginary lines, running from the contact patches to the corresponding Instant Center intersect, is the Roll Center. Remember – the Roll Center moves as the suspension goes through travel.

Spend time to learn about Roll Center when you are in the shop. At the track - trial and error is still common, even for Cup teams with full time engineers. 

Note:

Since the “Roll Center” location is a moving point is space it gets complicated – carrying graph paper at the track is not feasible, I prefer to spend time thinking about roll center during the design stage of building a chassis – and much thought is placed into Roll Center when designing any suspension.

 At the track, it is easy to visualize Instant Centers and difficult to think out roll center. By simplifying, I can adjust Instant Center locations right at the track as I can easily see how the upper A-Arm line passes through the lower control arm line. With simple visual estimation, I can have another adjustment method at the track and I carry slugs to make repeatable changes just like I would move the Panhard bar or change a spring.

If you use a RF A-Arm frame mounting plate that is slotted for height adjustment you can use slugs to ensure you have repeatable and documentable changes. For the Front Instant Center adjustment you can simply record that you moved the RF inner A-arm mounting point up a1/8th inch with a slug. Changing a slug is pretty easy.  If the driver doesn’t like the adjustment you can simply bolt the original slug back in.

Instant Center adjustments at the track can be used to create the feel of stiffer front springs under braking yet have the front springs feel softer in the center of the turn due to the longer lever that is created by the Instant Center length change. Many variables come into play and the teams that get the variables closest wins.

At the track – I usually focus on Instant Center adjustments by moving slugs on the upper A-Arms. You can move the lower points too, but you bring in rack location issues and bump steer corrections. The upper adjustment is easy to understand especially when track time is limited.

Lowering the RF A-Arm inner pivot raises the Front Roll Center and moves it to the right. Negative Camber is added and may need to be reset.

Raising the RF A-Arm inner pivot lowers the Front Roll Center and moves it to the left. Negative camber is reduced and may need to be reset.

Lowering the LF A-Arm inner pivot raises the Front Roll Center and moves it to the left. Positive camber is reduced and may need to be reset.

Raising the LF A-Arm inner pivot lowers the Front Roll Center and moves it to the right. Positive camber is added and may need to be reset.

The reality is that Front Roll Center is simply a derivative of the Instant Center locations.  Instant Centers are simple even through dynamic roll. Why complicate your trackside thought process with imaginary lines? Keep it simple at the track and use slugs to maintain records and repeatability. You can engineer at will after the race and study the Roll Center changes you accomplished and measure the affects of bolting in a few simple slugs.

Engineering becomes more important in racing every day. When time is short, educated experimenting is equally as valuable.

Go Forward – Move Ahead

Jeff Butcher

06/08/12