300ZX Brake Upgrade for FRS/BRZ – Part 2

300zx Brake Upgrade for FRS/BRZ – Part 2 – How will they work?

Assuming you’ve already read Part 1 of the 300ZX Brake Upgrade for FRS/BRZ, let’s cover the rest of this system.

In this article I will talk about how this braking system performs in comparison to stock.  I will try to explain some technical terms and concepts in simple and easy ways so that everyone will find value in reading this article.

In the first installment of this series I shared a new option for upgrading your FRS/BRZ brakes.  I discussed multiple brake upgrade options and how I came upon this idea for 300zx brakes.  The main topic for Part 1 was understanding which parts to buy so that everything bolts on and functions.

Simply “functioning” should not be sufficient for most of us.  There are many “86” owners who simply daily drive and many others who are purely interested in cosmetics and these people probably don’t care about how well a brake upgrade actually works.  For those of us who are performance oriented I want to explore the more technical side of brakes to find out if bolting 300zx brakes onto your BRZ is actually a good idea.  If you’re already well versed in brake technology, feel free to skip down toward the bottom to see the brake bias calculations… which is the most interesting part.

Before I dive into this article I want to make two important statements:
#1 – I am not an expert in brakes.  I have no engineering background and I’m not professionally trained in this area.  What I can do is share what I have learned from others.  I want to credit others who have taken the time to join in conversation, review this upgrade and offer some real professional expertise.  Thank you to the members of the ft86club.com forum – chiefly Jeff Ritter (JRitt) from Essexparts and forum moderator Dave-ROR.  They were instrumental in sharing information and expertise as we explored various technical aspects of braking systems in the context of how my brake upgrade should actually perform vs. stock.  

#2 – It’s important that everyone has a baseline understanding of how brakes work in order to understand the concepts I will discuss, so let’s do that now:   Most people incorrectly consider the caliper to the be source of “performance” in braking, but it should be noted that the tires are truly what stops the car.  Let’s back up and just lay the framework for what actually happens.    When you press the brake pedal, you activate the brake master cylinder to push brake fluid through the lines.  The fluid is pushed into the caliper and fills in behind the piston and forces the piston to move outward.  These pistons push the brake pads against the rotor and cause friction.  That friction slows the revolution speed of the rotor, which is fixed to the speed of the wheels and tires.  As more pressure is applied through the system the traction of the tire against the pavement is what allows reduction in speed.  The more traction you have, the more braking power you have. All those huge calipers and multiple pistons won’t do you a bit of good with crappy tires. Period.

So we’ve determined that with the help of the KNS Brakes bracket, the Z32 calipers do bolt onto the BRZ hub and work with the Legacy GT rotor.  Now let’s analyze these parts and discuss how they work and judge the pros and cons of each part and then we can make a judgment on the value of the whole setup.

Calipers
Caliper Specs: Z32 calipers are 4 piston fixed brakes vs. the stock BRZ/FRS 2 piston sliders.  The piston sizes are 40.45mm for Z32 and 42.8mm for BRZ/FRS.  The Z32 calipers weigh 6.1 lbs while the stock brakes are 14.1 lbs.  So, which ones are better?

   VS. 

Caliper Pros/Cons:  Fixed calipers are generally known to be better for high performance applications.  They typically offer better feel, modulation, and consistency.  From Wilwood, “fixed mount calipers that transfer PSI within the caliper into braking performance with a much higher efficiency are typically used on high-performance cars and for vehicles exclusively employed in racing for that purpose.”  Fixed calipers are also normally lighter than sliding bracket calipers.  In addition, most fixed calipers offer extremely easy replacement of pads by allowing you to pull retainer pins and lift the pads out rather than having to remove the caliper.   There are some downsides to fixed calipers as well.  They are known to be slightly less resilient to imperfections in the rotors.  It should also be mentioned that some fixed calipers (especially aluminum) were rumored to have some “flex” issues, though I think this would be much less risk on a light-weight car like the “86”.  They also require more width which in turn offers less clearance.  In this case, the major downside is that you cannot run the OEM wheels with these brakes without some small spacers.

Caliper Performance:  The caliper’s job is to push the pads against the rotor.  The ability to push the pad against the rotor comes from the size of the pistons and number of pistons per side of the caliper.  The fact that the 300zx caliper has 4 pistons vs. the stock 2 pistons does not result in greater clamping power.   I still don’t fully comprehend the physics behind this, but per Jeff Ritter and a book by James Walker Jr (a brake engineer at Bosch), “Hydraulic pressure x The effective area of the pistons on one side of the caliper = One sided linear mechanical force generated by the caliper.  The caliper reacts to that one-sided mechanical force by turning it into a clamping force. Clamping force is the one-sided linear force x 2, regardless of whether or not it is a slider or fixed caliper.”

The BRZ/FRS caliper has two 42.8mm pistons.  The Z32 has four 40.45mm pistons.  The area of the Z32 pistons is smaller and the result is that the Z32 pistons will offer less clamping power than the OEM calipers.  If analyzed independently of the rest of the system (which we will discuss later), they would reduce braking power by 8%. Is this relevant? Only if we deduce that we’re somehow unable to achieve lock-up at a given pedal pressure, regardless of which calipers we choose. I suspect it will not be a concern.

Caliper comparison conclusion: The Z32 caliper will offer better feel, modulation and efficiency, lighter weight, and easier pad replacement.  However, they have slightly less clamping power and require spacers to run OEM wheels.

Rotors:

Rotor Specs: Legacy GT front rotors are 316mm in diameter by 30mm in width.   Stock BRZ/FRS rotors are 294mm in diameter and 24mm in width.  OEM Legacy GT rotors are 22 lbs while BRZ rotors are 17 lbs.

Rotor Pros/Cons:  My setup uses stock blank rotors for the sake of keeping price down.  Because of this I can’t do a pro vs. con since they are the same technology.  But for the educational value of this write-up, let’s talk about better technology.  A high end BBK (big brake kit) would use much better two-piece rotors which have many advantages such as lighter weight and better cooling.  From Jeff Ritter, ” An OEM-style blank will never have the efficiency of a good aftermarket design. You can make the air gap two inches wide, but if the vanes aren’t shaped properly you’re going to have a lot of turbulence relative to a design built specifically to move air. That’s why a considerably smaller racing disc can run much cooler than a larger OEM-style disc.  With big brake kits, most of the kits on the market go about the same thing via two different routes. First would be the brute force method. This is typically the method employed by street BBK’s. That means BIG disc and big pads. You use mass to combat heat. The second method would be efficient designs. That is the method used in racing. You use advanced technology and materials to address the heat issue at a far lower size/mass. As in every field, advanced technology is more expensive.”  The downside is cost.  Most two piece rotors go for around $800 a pair.  Since my goal was to offer a low-budget alternative I stuck with blank OEM style disks.

Rotor Performance:  A brake rotor’s job is to offer a source of friction.  Friction creates heat and after frequent use that heat quickly becomes too much and then overheats the pads and fluid and that quickly decreases braking performance.  So the goal is to find a rotor that dissipates heat as well as possible.  The Legacy GT rotors used in this kit are significantly larger and wider than the stock rotors.  Per JRitt, “The LGT disc will definitely have superior cooling vs. the OEM BRZ. I have no doubt of that at all. They have a considerably bigger air gap and far greater surface area.”  Another upside to the larger rotors comes from the concept of leverage.  As Dave-ROR points out, “leverage = further from the hub, no different then using a longer lever to apply torque to a bolt vs a shorter lever”.  The downside of these rotors is that they are heavier than stock by about 5 lbs each.  To make things worse, the 5 lbs of added weight goes to “unsprung weight” or “rotational mass”.  The concept behind this is that any weight that is attached to the driveline (directly or indirectly) will have a greater impact on the transmission of power.  Fortunately this is lessened by the fact that it’s a rear wheel drive platform.  But still, from a scientific perspective, the added weight will have some impact on acceleration.  How noticeable this impact will be is hard to judge.

Rotor comparison conclusion:  The larger Legacy GT rotors offer significantly better cooling than the stock FRS/BRZ rotors due to the size and thickness.  The extra cooling capacity will hopefully keep your brakes from over-heating on the track.  I have no way to calculate a number for this of course, but the science behind it says that your chances of overheating your brakes with these rotors is lower.   The downside of the larger rotors is the extra weight.  That weight goes into rotational mass even though the overall weight of the brakes is less thanks to the lighter calipers, the impact of the rotational mass will effectively cause an increase in weight.   Just imagine the weight of those huge Brembos though!

Brake Pads:

Brake Pad Specs:  The Z32 pad is 119.3 x 49.5 x 14.5.  The BRZ pad is 137.5 x 50.1 x 17.6.  The shape of the Z32 pad is slightly more square.

 

Pad pros/cons:  Everyone will make their own choices on which brand of pads you buy, but the shape of the pad is determined by the caliper.  While the BRZ pad is longer, it’s not necessarily more effective due to the leverage issue brought up in the rotor topic.  It does however offer more lifespan since it has more pad material.  The price of these pads could be a factor.  For Ferodo’s top end race pad, the Z32 costs much more than the BRZ.  For others (Project Mu/Winmax, etc) the Z32 pads are less expensive.  This will be hit and miss, but if you are a religious buyer of one brand you should check the pricing on these pads before you consider this upgrade.

Pad Performance:  This will depend on the brand and type you chose.

Brake Pad Comparison Conclusion:  The BRZ pad is better because it has more pad material (both length and width).  More material offers more lifespan.  More lifespan equals less long term cost.  But again, the leverage difference could negate some of the lifespan issues.  Either way, I expect this pad comparison to be a minor issue.

Brake Lines Comparison:  The comparison here is between stainless conversion lines for the Z32 calipers and the stock OEM rubber lines.  I’ll keep this short and simple.   Stainless lines offer an upgrade over rubber lines and you should consider upgrading lines even if you keep the OEM brakes.  Stainless lines are more rigid and have less give under pressure so they will give a firmer pedal feel.  The nod goes to this conversion because it forces the use of stainless lines and those are better than stock lines.

Full System Performance:

From looking at each of the new parts on an individual basis we see some obvious pros and cons. The calipers are lighter and have better feel, but have slightly less clamping power.  The rotors offer much better cooling ability, and better leverage for clamping power, but do so at a detriment for weight.  Clearly there are trade-offs here at a part level basis.  However, to truly understand the value (or performance) of this setup you need to analyze the system as a whole.  Let’s look at the system as compared to stock in three areas:  heat (resistance to overheating), weight (lighter is better), and bias (balance in braking power).

Overall cooling:  The Z32/Legacy GT system will provide significantly better cooling that the stock BRZ/FRS system.  This is due entirely to the larger rotors.  However these are still not professional racing brakes, so you still might encounter brake fade due to heat.  This will depend on how aggressive you are driving.  My opinion is that this kit is a good “happy medium” for the kind of person who does spirited canyon runs, frequent autocross and light track use.  It should prevent brake fade under most of these driving conditions.  If you are a frequent and aggressive track driver, you should save your pennies and go straight to a professional big brake kit.

Overall weight:  For anyone who drives aggressively, weight is the enemy.  The extra pounds require more power to propel.  Since the BRZ/FRS is not exactly well off in the power area, we want to be sure to keep weight down whenever possible.  For overall weight, this Z32 setup is lighter than stock.  We save 16 lbs on the calipers, but we give back 10 in rotors.  So we have a net loss of 6 lbs.   However to be more accurate we need to calculate the effect of rotational mass.  The impact of weight on rotational parts (such as brake rotors) is 3x time actual weight.  So in reality each of these Legacy GT rotors acts like 15 lbs heavier than stock.  This would make a net gain of 30lbs less the 16 lb savings for an overall effective weight gain of 14lbs.  You now have to decide if that gain of 14lbs is worth it compared to the cooling benefit of the larger rotors.

Brake Bias:  Until now we’ve analyzed the clamping power or performance of brakes on an independent basis.  We’ve discussed the fact that the clamping power of the Z32 caliper is slightly lower than the stock slider because it has slightly smaller piston surface area.  We’ve also mentioned that the larger diameter of the rotor moves the clamping point out further from the hub and this adds extra leverage.  What we haven’t discussed is how these issues affect overall braking in terms of “bias” between the power of the front brakes vs. the rear brakes.   So, let’s get an education from Jeff Ritter once more, “A LOT of effort by the car manufacturer goes into finding the proper brake bias for a given vehicle. This is where things get rather messy. Curb weight, drivetrain layout, center of gravity, wheelbase, static weight distribution, aerodynamic downforce, etc. all lead into a model of dynamic weight transfer under braking for a given vehicle. Once that is established, this data is combined with a bunch of data related to the tires, and a rather complex Anti-lock Brake System program is developed.”  “… messing with the amount of rear brake bias can become downright dangerous. In a system with too much rear brake, the car can get extremely squirrely under braking. If the rear wheels lock up before for the fronts, that is an inherently unstable condition. The car can swap ends into a spin as the weight shifts forward under braking and the rear wheels lock”.   It should be said that the BRZ/FRS braking system does include a “nanny” called EBD (Electronic brake-force distribution), which will help compensate for changes, but for best performance we want to prevent the electronic nannies from intervening.

So brake bias is clearly an important topic to consider.  Let’s see how our $600 Z32 brake upgrade fares in calculations of brake bias.

I used this online bias calculator:
Online Brake Bias Calculator

Stock:
front piston size (inches) = 1.685 and 1.685 (42.8mm)
front pad cf I left at .40 (street performance example)
front rotor diameter 11.575
front pad height (I left at 1.875.. not sure how to calc this so I left it at the prefilled value)
rear piston size = 1.49999 (38.1mm)
rear rotor diameter = 11.42
rear pad cf = .40 (same as above)
rear pad height = 1.25 (left at pre-filled value)
Result = Front brake bias 0.697 or 69.7% to front.

Z32 brakes:
front piston size (inches) = 1.5925 and 1.5925 (40.45mm)
front pad cf I left at .40 (street performance example)
front rotor diameter 12.44
front pad height (I left at 1.875.. not sure how to calc this so I left it at the prefilled value)
rear piston size = 1.49999 (38.1mm)
rear rotor diameter = 11.42
rear pad cf = .40 (same as above)
rear pad height = 1.25 (left at pre-filled value)
Result = Front brake bias 0.709 or 70.9% to front.

So the Z32 swap that I have on my car changes the front bias from 69.7% to 70.9% for a variance of 1.2%.

The Z32 calipers judged independently would move brake bias towards the back. I did the calcs with the stock BRZ front rotor and the new calipers with smaller pistons and the bias came to 67.2% which would be moving bias rearward by 2.7%.   *By the way, this means that the WRX 4-pot upgrade is a negative on brake bias.  But, when you add the bigger Legacy GT front rotors the added leverage moves the bias back to the front to a new bias is 70.9%. So you gain 1.2% front bias with this setup.

Brake bias conclusion:   This $600 brake upgrade moves brake bias slightly toward the front.  I think the experts would agree that this is an acceptable change and with the EBD system on the car this would most likely be completely compensated for.   My conclusion is that brake bias is a non-factor with this modification.  It should also be noted that brake pads each have a coefficient of friction.  This is a measurement of how much friction they generate when rubbed against a rotor.  By choosing different front and rear pads the brake bias can be shifted.  In this example, but chosing a slightly high cf brake pad for the rear you can get the bias to almost exactly the stock number.

Summary of technical information about this brake swap:
As with most modifications, there are positives and negatives to this Z32 brake upgrade.   You should get improvements in brake feel, modulation and consistency from the fixed calipers.  You will get increased cooling from the larger rotors that should reduce or prevent brake fade (depending on how aggressive you drive of course).  You will also have the benefit of ease of changing pads without removing the entire caliper.  Brake bias change is minimal so that is not an issue.  The downsides of this modification include, slightly higher effective weight when considering the rotational mass and slightly less pad life.

Do I recommend this project?   Yes!  But that depends on your situation.  If you never or rarely drive aggressively then this upgrade serves only for cosmetic improvement.  Honestly, for some people that is enough.  From a purely functional standpoint I think most FRS/BRZ owners should simply invest in better brake pads and perhaps stainless lines and they will be fine.  For those who run canyons or autocross or run an occasional novice track day, this is a very solid upgrade in cooling capacity to avoid brake fade; for a very low price!  For those who do frequent track days and really push their car, I strongly recommend a professional big brake kit as this setup just cannot compete with the lighter and more advance parts used in those kits.

  

Thanks for reading part two.  I hope you learned something about the more technical aspects of braking systems.   Stay tuned for part three when I talk more about the rear Z32 brake upgrade! Also, if you have questions or comments about this upgrade, please pop in and discuss here: 300ZX Brake Upgrade for FRS/BRZ