While I do love using take-off circle track parts because of their incredible value, they do present some unique challenges.  When using OE parts, it is generally safe to assume that things will fit.  After all, they did when the car was delivered.  If you start mixing and matching OE components from different vehicles or model years, you can run into problems, but even then you have an OE setup that is a known working configuration and can be used as a target point.

No such target exists with race parts unless you buy complete assemblies, which are hard to find used and much more difficult to put together.  There is no factory service manual and exploded parts diagrams with part number call-outs for most of the race stuff.  Certainly not for add-on parts like brakes to hubs.

I found this out with brake rotor to spindle clearances.  The spindle uses a bolt-on steering arm assembly that also incorporates the lower ball joint taper.  There are two settings, high and low, and was previously covered in the front suspension design blogs, the lower hole is what I needed to use.  The problem was that the rotor to hat mounting bolts would hit the heads of the bolts that attach the steering arm.

I believe that the reason this happens is because I am using the 8 on 7″ bolt pattern rotor.  This is the most common, and therefore cheapest one on the market.  The 8 on 7″ pattern is used by Wide-5 hubs (about which I have written before) that don’t use a hat, but have an integral rotor mounting system.  More importantly, it is also the bolt pattern used by my rear hubs which also have an integral mounting system, so in order to be have just one rotor configuration that fits all four corners, I would need to stay with this design.

When I got the spindles, they came with some bolts that had been cut in a way I didn’t like.  So I ordered some replacements.

Little did I know at the time that I would find out why these bolts had been trimmed in this way.

The new bolt, front, is from ARP and made especially for this purpose.  A ¾” fine thread bolt could probably hold up a bridge, and when it comes from ARP, it is likely going to be able to do anything you ask of it without complaint.  The head of the ARP bolt is smaller than the originals, but not quite enough.  I still had to trim them.

Here you can see the problem.  The rotor mounting bolts would touch the spindle bolt head were it not ground down.  I forgot to take pictures before the bolts were ground down; probably because I was so frustrated at the time.  Even with the heads trimmed, you can likely see where the clearance problem would have occurred.  I once wondered why there would be both 8 on 7″ and 8 on 7.625″ mounting patterns for rotors.  Answer above.

So, I took my nice, new bolt and did to them exactly what the previous owner of the spindles had done to his steering arm mounting bolts: I ground the heads down.

As you might imagine, these ARP bolts aren’t the easiest things in the world to cut.  Each pair of bolts consumed a 4″ cutoff wheel.  I wouldn’t even think of using a saw.

All’s well that ends well.  There are no clearance problem now and I have new bolts holding things together.  I am sure the previous owner of the spindles would chuckle were he to read this as he likely went through the same thing and for the same reasons.  Wish I’d have known.

Previous installments:
Part I – Getting Started
Part II – Picking Calipers and Rotors
Part III – Staying Flexible
Part IV – Handling the Hydraulics
Attached – V8Mongrel Brake Calculation Worksheet
Part V – Making the Match
Part VI – Better Brake Balance
Part VII – Computing Brake Bias

Final Thoughts
Having gone through all the calculations, I think that the basics of how I design an upgraded brake system should be quite clear. Here are a collection of random thoughts that didn’t really fit in well in previous entries.

Mounting Ears
One important thing to check is whether or not there is enough room for the caliper mounting ears. The one liability of the Wilwood Superlite caliper I have repeatedly referenced as a benchmark is the 3½” mounting ear spacing. This can often interfere with the OE mounting ears. Also, it is best to try and have the ears on the spindle and the ears on the caliper on the same plane. That way, a flat bracket can be used to mount. No fancy machining. If there is a small offset, go to Essex Parts and order Caliper Mounting Shim Kit Part No. 19 04 137. This kit is under $10 (at the time I write this) and includes fourteen 7/16″ inside diameter round shims ranging from 0.010″ to 0.120″ thick. They allow for perfect caliper alignment.

Add Mass
When building for speed, lightweight is the way to go. But when it comes to brakes, mass is key. When in doubt, go bigger and heavier. While cutting weight in a car is always a good way to go faster, when it comes to brakes, more mass means a greater safety net. This isn’t to say that you need pizza dish rotors and calipers larger than a loaf of bread. Rather, that if you are undecided on two options, my opinion is that picking the larger of the two is a good idea.

Duct It
Brake mass is key in fighting fade, but you can never out mass the atmosphere. Short of driving your car into the ocean, chances are the best heat sink to be found is the air around us. Get it to your brakes. Air to the center of the rotor is key, but don”t forget about the calipers. There are a number of ways to do brake ducting, but the best ones bring the air right to the brake parts and take it from the very front of the car. How the rest is done is pretty much immaterial in my experience.

Tune Bias with Pads
Once the hard parts of a brake system is set, the performance of the system can still be tuned. If you have not plumbed in a bias knob, front to rear balance can be tuned using pad coefficient of friction. Running a more aggressive (higher mu) pad in the rear will shift the bias in that way. The main liability in this approach is that the change in coefficient of friction is rarely the only thing that changes. Often, a more aggressive pad will take longer to bring up to temperature. When one axle is in its optimum operating zone and the other is not, braking can be less than ideal. This is why on any car without ABS that I put on track, I like to fit a bias knob.

Experiment with Pads
If you can convince like minded car owners to run the same caliper as you, it opens up a great opportunity to try different compounds of brake pads. Even if the cars are different, switching pads for a session on track is a great way to try something new. The catalog descriptions of brake pads read a lot like the descriptions on a wine list. I have found the only way to really know how a pad will perform is to run it. Obviously, if you have to buy all the pads, it can get expensive. Sharing pads is a great way to try with minimal risk.

Plumbing
I use high quality, Teflon® lined, stainless steel lines whenever motion is needed. I have found that most circle track race shops such as Lefthander Chassis and Speedway Motors have, in stock, pre-made and tested lines in varying lengths. These are priced competitively with doing it yourself and offer far greater peace-of-mind since they are tested. Add an adapter the caliper end and one for the chassis end, and it is easy to get the lines you need.

Thanks and Credits
Todd Cook at TCE Performance Products for being willing to talk, teach and accommodate odd-ball requests.
Andy Crawford for trusting me to help him design his 240SX brake upgrade.
Wilwood for providing the best tech info of any brake part manufacturer.
High-Performance Brake Systems: Design, Selection, and Installation by James Walker, Jr.
Multiple articles published by Grassroots Motorsports.

This series of entries has been a lot of fun for me to write.  Having done more than one brake upgrade project, I thought it might be interesting for others to read my process.  I intend to take these entries, rework them and make them into one file.  Andy Crawford has volunteered to be the illustrator for that project.  Just remember, this is not a how-to guide, this is information only.  What you do is up to you, and you must take full responsibility for it.

Previous installments:
Part I – Getting Started
Part II – Picking Calipers and Rotors
Part III – Staying Flexible
Part IV – Handling the Hydraulics
Attached – V8Mongrel Brake Calculation Worksheet
Part V – Making the Match
Part VI – Better Brake Balance

Computing Bias
This is where things finally come together! No more piecemeal, we can finally look at the brake system in its entirety and get the results of our hard work. I think that the best way to do this is take the spreadsheet line by line, explaining each input and each result. V8Mongrel Brake Calculation Worksheet

5-Leg
This is the pressure exerted by your leg when you press on the pedal. Measured in pounds. I use 100 because it is easy. If anyone knows a better number from testing, please post it in the comments section.

6 – Pedal Ratio
This is the force multiplication from the pedal. To figure your own pedal ratio, measure from the center of the pivot to the center of the pedal. Then, from the center of the pivot to the point where the master cylinder attaches. This is your raw ratio. Divide both numbers by the distance from the pivot to the master cylinder to convert it to X:1 format.

7 – Master Diam
The diameter of the master cylinder in inches.

8 – Master Area
A computed value based on what is input on line 7. Is square inches.

9 – System Force
A computed value. The leg force multiplied by the pedal ratio, divide by the area of the master cylinder. This is the amount of force that the master cylinder sends out to the calipers.

12 – Piston 1 Diam
Note that this is just one side of the caliper, opposite of what was done previously. There is no need to double for a slider here as for bias, as long as you are consistent, it doesn’t matter. This is the diameter of one piston in the caliper. If you have four piston calipers, you must enter a value in line 14 as well. Six piston, enter in line 16.

13 – Piston 1 Area
Computed value of the area of piston 1. If you enter a second and third piston diameter, these will compute in lines 15 and 17 respectively.

18 – Total Area
The computed sum of all piston areas.

21 – Pad mu
The coefficient of friction of the pads. As a rough guideline, use 0.35-0.40 for performance street, 0.40-0.45 for dual purpose pads and 0.45-0.55 for full race pads. Better still, talk to the manufacturer, explain what you are doing, and they will likely give you the right value.

22 – Pad height
It the rotor is mounted at 12 o’clock, how tall the pad is, in inches.

23 – Rotor diameter
The measured outside diameter of the rotor.

24 – Effective radius
A calculated value. This is the distance from the center of the rotor to the center of the pad. This is the lever arm when the pad clamps down and slows the car.

27 – Clamping Force
The computed value that expresses how much force the caliper will exert upon the pads. It is the output force from the master multiplied by the caliper piston area.

28 – Wheel Torque
The calculated value of the clamping force multiplied by the coefficient of friction multiplied by the lever arm (effective radius). This is the your front wheel brake force.

31 – 47
These lines are duplicates of those listed above except for the rear brake system.

50 – Clamping Bias
As stated in Part VI, this is the hydraulic split, expressed as the percent going to the front brakes.

51 – Torque Bias
This is the actual brake bias as will be seen by the wheels. Hopefully you will be very close to the OE split.

Hopefully this entry and the spreadsheet have helped you determine the brake bias you have and then how the modification you intend to do will impact that.

Up next, I will address what else to look for and think about in a brake system.

Previous installments:
Part I – Getting Started
Part II – Picking Calipers and Rotors
Part III – Staying Flexible
Part IV – Handling the Hydraulics
Attached – V8Mongrel Brake Calculation Worksheet
Part V – Making the Match

Better Brake Balance
In the first five parts, I have made reference to brake balance, aka bias. Now it is time to start addressing it.

Starting at the beginning, what is brake balance?
Brake balance is how the front and rear brakes work together. Getting proper brake balance is making sure that the front and rear brakes provide the maximum effort possible. Ignoring ABS for the time being, perfect brake balance would be when the front and rear wheels lock up simultaneously. Naturally, this is easier said than done since there are many variables when the brakes are applied. Is the car going downhill? What speed is it traveling? Is it turning?

So what is brake bias?
Brake bias is the mathematical expression of how the brake force is split front to rear. It is often written as a ratio, 60:40 or a percentage 60%/40%. Front is always before rear, in my experience, which is part of why brake balance is important.

Why is brake balance important?
Brake balance is important for two main reasons. First, it minimizes stopping distance. Second, it helps the driver control the car. Excessive front bias is can cause long stopping distance, but excessive rear bias can be downright dangerous. Without ABS, if the rear tires lockup first, chances are the car will spin. This is why it always best to err on the side of caution when it comes to rear brake percentage.

Much like the when doing the pedal to caliper ratio, computing brake balance starts with the OE setup as the baseline. On tab two of the V8Mongrel Brake Calculation Worksheet, “Force”, is how I compute brake balance.

Columns D through N represent different setups for friends’ Nissan 240SXs. They were all based on the data calculations made in the “Hydraulic Only” tab. Although the master cylinder diameters vary, they are options found on different year 240s, or from other Nissans that are known to interchange.

The balance is expressed in lines 50 and 51. There are two types of bias shown – clamping bias and torque bias. The number for each is the front value. So .72 is a 72/28 bias. Columns D, F and G represent the brakes of the different cars in their current configuration. As you can see, the figures are all in the high sixties to low seventies. We can assume that this is a safe range to target when making modifications.

In Part VII I will cover all the different variables that make up the final bias numbers. For now, I will just cover why there are two different bias values. When balancing brake bias, it is possible to undo the work done when calculating the hydraulic portion. The clamping bias shows what (if any) change has occurred solely from the hydraulic portion. This number should not stray too far from the stock setup. If it does, the hydraulic ratio that was computed before has been altered.

The torque bias includes the effects of the pads and rotors. If these components introduce more force, as is often the case, they can make the final bias seem like nothing has been changed. However, the lower clamping force could have an undesirable effect on the feel of the pedal. As long as the numbers input for the master cylinder and calipers are based on the work in the “Hydraulic Only” tab, then there should be no problem.

Up next, a detailed look at all the variables that go into brake force and brake bias.

Previous installments:
Part I – Getting Started
Part II – Picking Calipers and Rotors
Part III – Staying Flexible
Part IV – Handling the Hydraulics
Attached – V8Mongrel Brake Calculation Worksheet

Making the Match
Last time, I gave a simple example of how to calculate what caliper piston sizes could be used to substitute for the OE calipers. Keeping the ratio of master cylinder to caliper bore areas the same, it is possible to avoid a mismatch of parts that can result in a pedal that is less than ideal.

Astute readers may have already realized that the mismatch could also be used to their advantage. Since we can predict the outcome of the mismatch, we can attempt to tune out an undesirable feature in the car. If, as is common in many vehicles, your car has a brake pedal that is softer than you would like, you can fit a caliper with slightly smaller pistons to reduce compliance volume. The area ratio will decrease when doing this.

The difficulty with this approach is that it is based on a guess. We are guessing that the soft pedal is due to the compliance at the caliper piston. This may not be true, even if it often is. Furthermore, because the smaller pistons will require greater pedal force to reach the same clamping force on the rotor, there will be more hydraulic force generated. This will increase the pedal travel if the compliance is not in the caliper.

Beyond compliance volume and pedal feel, working with an imperfect match can compromise brake bias. While the subject of bias is far more complex than just the simple area ratio covered so far, it can be difficult to overcome a poor master to caliper match. Brake bias will be covered in the next installment in more detail, but at this time, it is just another reason to keep the area ratios between master and caliper as close to stock as possible.

So what happens when the proper master cylinder to caliper match is just not attainable with available calipers? The best bet is to change the master. Very often, manufacturers will use the same mounting pattern for master cylinders on different cars. With some research, it is often possible to find a bolt-on solution that is the proper diameter for what you need. Beyond that, there are aftermarket units, such as those offered by Wilwood, with slotted ears designed to accommodate different mounting dimensions.

Figuring out which master to use is simple when you employ the V8Mongrel Brake Calculation Worksheet. You can plug in different master cylinder sizes in row 2 and match them with available caliper specifications entered in rows 4 and 6. The result in row 9 will give you how far you have moved from stock.

When swapping masters, my experiences have taught me a few lessons.

• Keep changes to ±1/16″. Generally speaking, the booster is capable of handling a 1/16″ change with minimal complication. Beyond that, you may not like what you get.
• Be very careful with the pushrod length. Make sure that it is long enough to engage the booster properly. Too long is better that too short as shortening is easier than lengthening.
• Make sure that you do the calculations twice – once for the front and once for the rear. Most swaps concentrate on the front, but the rears cannot be totally forgotten.
• German cars up to about year 2000 all used ATE masters (or clones) with a similar mounting pattern. If you have one brand of German car, look at others if you don’t find what you need “in house”.
• Similarly, Japanese cars shared a mounting pattern that appears to be very close to the old Lucas type. Some cross-brand shopping amongst Japanese makes might yield what you are looking for.

When the calipers available aren’t what you need from a hydraulic standpoint, the best way to do is to try and swap masters. Remember, the goal is to keep the area ratio as close to one as possible.

The next entry will cover brake bias – how to calculate it, modify it and make sure you keep it where you need it to be.

Previous installments:
Part I – Getting Started
Part II – Picking Calipers and Rotors
Part III – Staying Flexible

Handling the Hydraulics
Picking the wheel end components is the easy part of a DIY big brake kit. It is immediately obvious when such components are unsuitable because the fit is physical. Hydraulic components have an element of physical fit, but at the same time, the biggest issue is the internal size (volume) and whether or not it will work with what you have planned. The reason to go through all the hydraulic computations is to avoid creating a long, soft pedal or one that is too high effort.

Backing up a step, the calipers are part of the hydraulic system. However, it is important to first deal with the physical fit before the hydraulic side. The hydraulic system can be modified more readily than a caliper made to fit. While not always easy, it is often the case that a larger or small master cylinder can be found to deal with a change in the caliper bore if one that is not a suitable match for the original master proves elusive.

Step one in the hydraulic portion of a big brake kit is figuring out what you have. This information is critical because from it will derive a baseline that will serve as the foundation of all later calculations. Many times, the master cylinder bore (the most critical dimension) is on the body of the unit itself. If not, you will likely have to get creative. Anywhere that sells master cylinder rebuild kits should have a catalog that lists master cylinder bores. If that fails, the factory service manual and many of the better independent repair books also have the bore diameter. If all else fails, a junkyard, a hacksaw and a measuring caliper can bring you answer you need.

V8Mongrel Brake Calculation Worksheet

Click the above link to download an Excel workbook. Note, all measurements are in the imperial system. The metric system was designed by the French, therefore it is liable to abandon you when you at the first sign of trouble. Use anything other than inches at your own peril.

For now, we will work only in the tab marked hydraulic only. Note, you enter only in the cells that don’t have red text. I know that there are far more elegant ways to indicate access to a certain area, but this is the simplest and easiest understood, in my opinion. That data that is in cells D2, D4 and D6 are examples; in this case a Nissan 240SX. You can change those values, as you see fit, but I will use them as guide for this post.

You need three data points.

1. Master Cylinder Bore – Line 2
2. Caliper Piston Bore – Line 4
3. Number of Pistons in Each Caliper – Line 6

These are all self explanatory, except number 3. You must double the number of caliper pistons if the pistons are all on one side of the rotor. This is a sliding caliper design, and each piston does the work of two, so you need to double it.

Once you have entered the data in column B, all of column C will compute. This will take any fixed two piston caliper or single piston slider and convert it to a two piston slider or four piston fixed. I include this because it takes the two most common OE setups and converts it to the two most likely big brake options. The result that you are interested in is line 4. This is the theoretical piston diameter needed to duplicate the OE hydraulic setup with aftermarket components.

The key word in the previous sentence is theoretical. That is what would be a perfect swap were it available. There is a very good chance that it isn’t. So the next step is to pick from your list of calipers that will fit the car the ones that are closest to that theoretical target. Pick the one that is closest but larger, and the one that is closest but smaller. From there, input the caliper piston diameter and quantity into the spreadsheet in columns D and E, keeping the master cylinder the same, and get an idea of how large a change this will make.

The goal here is to keep the last line (9) as close to 1.000 as possible. If you can find a caliper that is absolutely the same volume (area) as stock, regardless of the number of pistons, it will have negligible impact on pedal feel. This is the easiest way to perform an upgrade.

Up next – what to do when the numbers don’t line up like you want.

Previous installments:
Part I – Getting Started
Part II – Picking Calipers and Rotors

Staying Flexible by Allowing for Upgrades
In the first two installments in this series, I presented some of the basics of adding bigger brakes to your car. These centered on what calipers and rotors can be fit as part of the wheel end assembly. Now it is time to decide on which parts to get and why.

It is fair to assume that most people fit larger brakes to their car because they have exceeded the capacity of the stock system. Yes, there are people who do it for looks or because service parts have become NLA (no longer available), but those likely represent a small minority. So, if the reason for going to a big brake kit is because of obsolescence of equipment, it seems to make sense to me that one should design in the ability to make sure that this same obsolescence doesn’t happen again. Or that if it does happen, it can be accommodated with minimal investment.

For the first and likely last time, I will address one of the most common forms of big brake upgrades – the like model upsize. There are plenty of examples where a car can use the factory uprated brakes for that same model to great effect. So, if you have a base Mustang, you fit the 13″ Cobra brakes. A BMW 325i; you grab the M3 setup. Integra brakes onto your Civic and so on. Easy. Too easy. You must make sure that the OE setup isn’t trading one set of problems for another.

Your first clue in determining whether the easy upsize is a viable option is component availability. Are there a ton of used M3 setups around? Find out why. It could be that they fall short. Second clue is the pad availability. If there are no race pads available for that Integra setup, this could mean that the setup is being removed because it doesn’t work well. Chances are, even if it will work for you, you are going to be doing a lot of development. Finally, look at the availability of alternate setups for the donor car. A healthy aftermarket of big brake kits might mean that they are needed. Find out first before doing this type of swap why they are half a dozen options to upgrade those Cobra brakes to something even larger.

I generally dislike the easy upsize because it is often a dead end. Once you go to the factory performance setup, if more capacity is needed, you likely have to start all over. There are some exceptions, but more often than not, the parts you buy won’t transfer to a later upgrade. Sure, these parts can be sold, but I want to minimize all the buying and selling I need to do as, in my experience, things lose value the longer you have them.

So here is a component-by-component look at how you can keep your kit from being a dead end.

Pads
It has been said before, but it is worth repeating: make sure that you can get a wide variety of friction formulations. It doesn’t matter if you think you will never need them when you first put the brake kit on. You cannot predict the future. What if a track opens near you that is real brake killer? What if you suddenly discover a couple of extra seconds a lap at your favorite circuit and that goes way beyond the capacity of your favorite pads? What happens if you suddenly decide to fit a blower? A big-block? A blown big-block? Worst of all, and one I have experienced, what happens if your favorite pad is discontinued or the formulation changed for the worse?

Rotors
The ability to be upgraded is where the two piece racing rotor comes into its own. While there is some appeal to the factory units from a different car, if you are looking long term, the switch to racing rotors makes a lot of sense. With the same hat, you can add larger diameter rotors with a bracket change. You can add thicker rotors with a caliper change. But, much better than those, the racing rotors have the ability to be upgraded without any other components being changed. Look on Wilwood’s website and you will see that they have many different options for rotors in the same size and hat mounting pattern. Using these different rotor configurations will allow for increasing the performance potential of a braking system without changing anything other than the rotor.

Calipers
Calipers influence both pads and rotors, but they area also an area where upgrades can be made independently. On most race calipers and a few production calipers, the pistons can be upgraded to higher performance units that improve shielding of the fluid from heat. Buying a caliper that has multiple piston sizes available can mean that a caliper change will be all that is needed to accommodate a major change in the braking system on the other axle. Also, if the mounts are of common dimensions, an entirely different and perhaps superior caliper can be fit without changing anything else.

The ability to make more changes is often not the first thing someone has in mind when they are upgrading. But the fact remains that an upgrade to bigger brakes is made because the capabilities of the original system were exceeded. That can happen again. With a little planning, the impact can be minimized.

Next up, the dreaded hydraulic system and its role in making all the parts place nicely together.

Previous installments:
Part I – Getting Started

Picking Calipers and Rotors
Once the measurements for the axial and radial dimensions have been made, the next step is to select rotors and calipers that will fit within those dimensions. In my experience, the process is for two parts but must be done as one operation. The caliper and the rotor can be thought of as one assembly since the dimensions of one affects the other without fail.

Much like how the selection of wheels is based on tires, the selection of a caliper can be very much dictated by the consumable – the pad. Custom pads are far easier to find than custom tires, but the cost can be prohibitive. Finding a caliper that has an excellent supply of readily available pads is just common sense. In my experience, when it comes to pad selection, there is the inevitable trade off found in any decision. If you choose a caliper from a production car, you will likely have an excellent selection of street compounds, and, depending on model, a selection of race pads that ranges from terrible to decent. Race calipers are generally the reverse.

I have found ways to circumvent each of these problem. If you choose a production car caliper, choose one that is used on a high performance car that you commonly see on track. One of the best is the PBR Pad Guided Caliper used on the Mustang Cobra and the C4 Corvette. Not only is it made with lightweight aluminum, it is also common enough that the race pad selection is quite good. While not as cheap as those for race calipers, the pads are reasonably priced compared to many other production car sets. For race calipers, the solution to a lack of street pad selection is easy – run dirt circle track pads. They need a pad that works well when cold and offers lots of initial bite. Just like a street pad. No, they won’t be dust free, quiet and smooth like your Akebono Pro-Acts or Raybestos PGDMs, but they will be perfectly serviceable. Also, there are new compounds coming out all the time, so check regularly what is available.

With rotors, much like calipers, there is the choice between production and race units. A production rotor can be easier since it is often found readily and requires no special measurements. It is what it is and that is really all there is to it. Two dimensions can be changed – center bore and lug pattern. Center bore can be adapted via a step up spacer or by turning the rotor larger. The lug pattern can be re-drilled at home using a template aligned with the center bore. Be warned, however, that going from five lug to four lug or vice versa can often result in two holes sharing the same real estate. Either way, check the axial and radial clearance on every rotor you consider.

Racing rotors are two pieces: the hat and the disc. Hats are selected in basically the same manner as production rotors, although the ability to buy them completely undrilled removes and issues with hole location. The offsets are, like the full catalog of production rotors, available in steps. For those designing their own brake system, the hat is the place where the axial clearance is most critical. The total stack height (hat and rotor thickness combined) must not contact anything on the inboard side. The most common point of contact is the lower balljoint, which is as far from the centerline as possible on a production car to reduce scrub radius. Then, the outboard size and shape of the caliper must not contact the wheel spokes.

For the rotor in a two piece setup, the thickness is often determined by the caliper to be used. The aforementioned PBR caliper from the Mustang Cobra is designed for a 1.10″ thick rotor. The other choice to be made is the rotor to hat bolt pattern. If given the choice, I suggest running the 8 on 7″ pattern. It is as close to the standardized bolt pattern as there is. Consequently, the cost and availability of rotors are at their best when it is selected.

Having gone through this process a few times, here are some lessons I have learned.

• Axial clearance (hub face to wheel spokes) is usually a huge problem on front wheel drive cars. Plan on using a production sliding caliper since outboard pistons often won’t fit. The fixed caliper can be done, but be prepared to make sacrifices elsewhere.
• When checking radial clearance (inside diameter of the rim), make sure that you remember to take into account the caliper. If the inside diameter of your wheel is 13″, you cannot run a 13″ Mustang Cobra rotor because there would be no room for a caliper.
• Check your balljoint clearance. Twice. In an effort to squeeze the biggest caliper and rotor under a given wheel, it is tempting to push the assembly as far inboard as possible. If you go too far, you will roast the grease in your balljoints. Don’t despair, a 0.125″ spacer between the hat and the hub is usually all that is needed to get things back to normal.
• Always check everything with a new set of pads, a new rotor and the caliper you intend to use. While it is tempting because of cost to get some junkyard parts for mock up, what clears with worn pads and rotors could be a nasty surprise with new parts.
• If you plan on using production parts, get on the internet and find the forums for the OE application. This can teach you a lot and save you money in the long run.

The selection of calipers and rotors is ultimately based on what fits, but when given a choice, my advice for all choices is to go common. Specifically:

• The Mustang Cobra / C4 caliper is the sliding caliper of choice, while for fixed calipers, the Wilwood Superlite is what I think works best for more cars under 3000 lbs.
• For production rotors, use something common and is the right thickness for your selected caliper. This will take work to find and often is most easily accomplished by keeping the OE caliper with its OE rotor. Alternately, you can get race rotors to run under you production calipers or perhaps get lucjy and find a perfect fit.
• For race rotors remember to stay with the 8 on 7″ rotor to hat bolt pattern. For use with race calipers, the two common thicknesses are 0.81″ and 1.25″. Go thick up front, no doubt. In the rear the 0.81″ will probably work just fine, but the appeal of having a single rotor fit all four corners might make you forget about the couple of extra pounds.
• The most common diameter race rotor is the 11¾”. Think long and hard before you decide to go just slightly larger, like a 12.2″ unit. You are trading a huge amount of cost and availability for less than ½”.

Don’t limit yourself to what I have suggested here. Find something new. You can never be faster if you only do the same thing as the other guys.

Next up, how to design in the ability to upgrade economically.

In recent days, I have been helping my three friends Jason, Andy and Ryan design a brake upgrade for their 240SX Nissans. I have previously upgraded the brakes on my Focus to use the calipers from a Mustang Cobra and 12.2″ diameter, 1.1″ thick rotors with custom hats. I then helped my friend Vincent Keene perform the same upgrade to his Chevy Cavalier; and he subsequently adapted re-drilled 13″ Corvette rotors.

This isn’t to say I am an expert when it come to big brake kits and or brakes in general. If you want a true expert, talk to Todd Cook at TCE Performance Products. Todd is the man when it comes to special, one-off braking solutions that you don’t want to tackle yourself. And you never have to worry with Todd if it will be good enough. Every year, he races up Pikes Peak where if his brakes fail, he could have a thousand foot free fall to consider what went wrong.

The next few posts will be pretty text intensive. There really isn’t a lot of pictures that can describe how to do this. Also, you will need to have Excel or a spreadsheet program that will read Excel. There are freeware Excel viewers available for download too. Since I completely forgot to document the process when I did this for the Mongrel, I will be using the 240SX project I am working on as an example. At the end, hopefully I will remember enough about the Mongrel brake project to make a post on what I did there.

Starting Point
Where do you start when you are making your own big brake kit?

You start at what actually stops the car – the tires. While this might seem odd at first, it should make sense. Unless you are a pro team with a major tire manufacturer sponsoring you, you must chose a tire from the catalog. The overall height and width are going to be the best you can find, but inevitably they will embody many compromises. One of these compromises is the rim diameter, which is really where we begin to see a major impact on brakes. Except for a few isolated examples, you must fit the brakes inside the wheels.

Wheel diameter, generally determined by tire availability, sets the first dimension – radial clearance. This is the maximum inside diameter of the rotor and caliper that can fit inside the wheel.

Beyond that, the wheel also sets the axial clearance – the distance from the hub face to the wheel spokes. This distance can be tuned by using different offset wheels, spacers and even different wheel brands to a much greater degree than radial clearance which is usually very close between different wheels of the same diameter.

Once you have these two dimensions, how do you know what will fit? There are two ways; either look for OE fitments that you can adapt and, based on what is on the original car, you know will fit under the chosen diameter wheels or go full custom and use the incredible data found on Wilwood’s website. If you go to the caliper area of their website, you will find detailed clearance dimensions for each of their calipers on a variety of rotor diameters. This user friendly information has made me a huge proponent of Wilwood components. Technical information like this is, unfortunately, the exception rather than the norm, and I support those vendors that provide whenever I can.

Next up: is picking the right rotor and caliper for you.

Good brakes always top my list of things I demand in a car. For reference, I made a brake upgrade for my Focus that uses 12.2” diameter 1.1” thick rotors mounted to aluminum hats, and then added calipers from a Mustang Cobra. When it comes to brakes, there is no point in messing around. It is no exaggeration to say that your life depends on your brakes, and running a car with as much power as this Mongrel will have, good brakes are mandatory.

It is common knowledge that brakes do not stop a car – tires do. A car can only stop as fast as the tires will allow. Once lockup (or if equipped, ABS activation) is present, more braking torque is irrelevant. Thus, using torque output as the main goal in designing a brake system is foolish. Inability to generate enough torque is rarely the biggest shortcoming of a brake system.

Where brakes generally fail is in their ability to perform repeated high torque stops. Heat buildup in the system leads to lack of torque, a soft pedal and increased stopping distances. This is usually referred to as fade. There are many ways to beat this, but I hold the opinion that the cornerstone of any high performance braking system is rotor mass. Mass is king. Large rotors capable of absorbing, dissipating and dispersing the heat of repeated high torque braking are required.

Which leads us to this:

The stock setup

Moving beyond the blatantly obvious problems of insufficient mass to stop a 200hp car, never mind one that will have 300 or more, the factory has presented some challenges. First, and most seriously, the rotor and front wheel bearing race seats are part of the same casting. Thus one cannot substitute another rotor without having to deal with the issues of perhaps also needing to change the bearings. This can be very difficult to do, as matching it to the spindle snout is required.

Currently, there are a few ideas designed to circumvent this problem that are under evaluation.
1. Machine the rotor down and then drill what is left to accommodate a bolt pattern that is used commonly on two piece hat and rotor combinations. 8 on 7” circle is common and may work. Problem is that the rotor is vented, and thus not just a plate that is easy to put holes in.
2. Update to 1984 or 1985 spindles that allow for easy adaptation of second generation RX-7 (FC3S) hubs. These hubs are not integral to the rotor and would allow for a more typical hat and rotor combination. Problem is the expense of the hubs and the fact that my bolt pattern will be changed. While I have no loyalty whatsoever to the esoteric 4×110 now on the Mongrel, I would have to consider buying new wheels and drilling the rear axle flanges in the cost scheme.
3. It was noted by my friend Scott Johnson that the spindles of his 1973 Celica are very similar to those on the RX-7. You can see what Scott did to his front suspension and the Celica uprights here. The Celica uses a hub that is not part of the rotor casting, but is complicated by the fact that it uses a plate to mount the rotor to the back of the hub rather than a hat. According to Scott, there are many years of Toyotas that could be adapted, so that could change. Making sure that balljoints will work and everything lines up is a big unknown. The known problem is again the bolt pattern. Toyotas, along with everyone manufacturer other than Mazda, never offered a 4×110.

The other serious problem with the rotor is the lack of clearance between it and the balljoints. This means that the mandatory extra width will have to be accommodated by the space on the outboard side. This pushes the outboard side of the caliper further into the wheel, causing clearance issues or a compromise in wheel offset. Nothing major, just another thing to that has to be accounted for.

Stock caliper, soon to be paperweight.

Fortunately, the caliper situation is somewhat easier as no part of the stock setup needs to be retained. Mazda uses a nice bracket that connects the caliper to the spindle. Since this bracket uses bolts on both ends, it is very easy to make a new one that will allow for the use of a different caliper. This makes fitment of a four-piston fixed caliper on any diameter rotor simple. The fixed caliper returns better pedal feel, superior wear due to less flex and, if the right caliper is selected, a huge array of racing pads at prices well below what a similar pad would cost for most any production caliper.

The difficulty is that the stock caliper piston is tiny. At about 39mm diameter, it simply does not have the area that most four piston calipers have. Normally, on a single piston caliper, the piston is large enough that finding a four piston caliper that is hydraulically equivalent is not that hard. Since the four piston caliper is fixed mount, the area of the single piston in the sliding caliper has to be equal to that of only two pistons. In terms of the Mongrel, the small factory piston means that the hydraulic system on the car will need serious evaluation before a caliper can be selected. That will be handled in Assessment – Brakes – Pedal & Hydraulics.