Why I'm Making My Own Brakes

lambertius

Member
Messages
341
One of the (many) issues with my car is that it needs new brake rotors. Initially this didn't bother me, the OEM rotors are engineered sub-par and selecting a new rotor would be one of many improvements over the initial engineering, fit and finish. Little did I know that Fiat had intentionally gone and selected a rotor with such unusual dimensions that it was nearly impossible to find a direct replacement.

Never mind, I thought, there will be some aftermarket options!

So as I began looking at what was available I realised that I would be either selecting something with the same issues, or even potentially worse than the OEM rotors. The more I looked into it, the more I realised that the only way I could get a safe braking solution would be to engineer my own brakes.

The Problem with the OEM Rotors:

The first problem was fitment. I made a searchable version of the DBA catalogue in excel to see if there were any rotors where I could modify the PCD to fit. Options were very limited and the handbrake shoes on the rear made it nearly impossible.

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In order to understand what is wrong with the brakes you have to understand how brakes work. Most people think that brakes are designed to stop the car, which is the effect that they have, but they are actually designed more like a battery as their job is to store and subsequently dissipate energy. If a car is moving at any velocity it is carrying energy expressed by the equation:

J=1/2mv^2

This means that the energy increase with velocity squared. If we needed to go from 24m/s > 0m/s we need to dissipate 483 840 Joules. https://www.calculatorsoup.com/calculators/physics/kinetic.php

So how much energy is that?

Skipping some of the harder maths, about 70% of that energy goes into the front brake rotors, so 35% per rotor being roughly 169kJ. The specific heat capacity of cast steel is about 510J/kg, and our rotors are about 10.8kg. This is enough energy to raise the temperature of the rotor by 32 degrees every time you change your velocity by that much. So going from 200km/hr > 100km/hr regularly on a track for example.

Ah but our rotors are vented and cross-drilled! - but that is part of the problem...

Things get out of hand very quickly so I'll save the explanation for another day, but vented rotors behave like any heat exchanger (radiator). The amount of energy they can dissipate is directly proportional to surface area and air flow. So you can increase the surface area of the rotor for better cooling (more vents) or make them more efficient and flowing air (directional vents, a type of reverse ducted fan). Our rotors use a pillar cooling design to try and increase the surface area. This is the best technical feature of our brakes. Below is an accurate CAD model of what our brakes look like internally.

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The cross-drilling however is not quite so smart. The first problem is that the cross-drilling isn't chamfered, which significantly increases the rates of cracking and blocking which entirely defeats the intended goal of cross drilling which is ventilation. Cross drilling is a source for corrosion shortening the life of the rotors, and our rotors have all the cross-drilled holes in the same arc which shortens pad life which roughens the pad surface which in turn shortens the rotor life! And believe it or not, cross-drilled rotors exhibit poorer cooling than flat discs because there is less interface surface between the pad and the rotor anyway. So why do cross-drilled rotors even exist? I'll let DBA answer that...

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They look cool, that is why.

If you have a look on their website, and that of any large brand you'll find they all have disclaimers saying cross-drilled rotors are not recommended for high temperature applications. You'll never see it in racing as they're a failure risk. And before anyone says it - yes ceramic rotors are cross-drilled, but those material properties are very different to steel and that is a lesson for another day.

So this is the long way of saying that our rotors are fine for daily use but a liability if you like to do track days. Below is a very loose model of rotor temperatures over time for our car on a track day. The two other curves are a low powered lightweight car, and a high powered lightweight car:

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Our rotors can easily get hot enough to fry wheel bearings, crack and glaze pads in 15 minutes of hard track level driving.

So after all that I decided to look into aftermarket options...

2 Piece Rotors Are Intrinsically Unsafe:

The first problem I encountered with the aftermarket options is that the single piece rotors were a direct copy of the OEM rotors, which means that even for street use they weren't satisfactory as they carried over the same design flaws. The second problem was that the 2-piece rotor sets were also cross-drilled which magnify the problems with 2 piece rotors. And the third was an absolute lack of basic specifications on these sets that would allow me to confirm their safety.

2 piece rotors are often called 'big brake kits', and the reason for this is that they're usually bigger than OEM kits. A lot of people like to talk about how the rotors are lighter for unsprung mass, but that is an intrinsic misunderstanding of what brakes do. Big brake kits are bigger because they need to increase their thermal mass as it has been significantly reduced by removing the hub. My explanation earlier shows that the mass of the rotor is the most significant component of keeping a rotor safe. The purpose of a 2 piece isn't to reduce mass, or increase ventilation, it is to protect wheel bearings and control the rotor temperature to match a specific pad. The pre-disposition to a lighter thermal mass, and the extra fasteners introduced into the system create an intrinsic risk of failure making poorly selected 2 piece rotors quite dangerous. Fortunately brakes tend to be made of literal slabs of steel so the odds of messing up so badly your have a catastrophic failure is nearly zero, still the knowledge that people run these systems without understanding why makes me uncomfortable.

In a situation like racing where its impossible to keep rotors at reasonable temperatures, by separating the hub and the rotor you can protect the wheel bearing. The lower mass means a hotter rotor, but that is okay because you can select a pad that matches your rotors operating profile. The below chart is the mu (friction) characteristic curve of pads provided by Hawk Performance. They're currently updating this chart (I asked) so it is out of date. But you can see that if you know your rotor is going to run at 500c (900f) you can pick a pad that matches that operating temperature and still protect your hub by physical separation.

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This is why it is very important that when you purchase aftermarket brake parts that they provide you with at a minimum, mass data on the rotor. None of the aftermarket options of our cars provide that information, and therefore the risk is unacceptable to me.

So What Next?

I've been tossing up a few idea, but ultimately I've decided to go for a 2 piece design and delete the handbrake.

I've been speaking with Hawk and they're going to provide me with updated pad curves https://www.hawkperformance.com/
I've also been speaking with SpartaEvo and they're going to manufacture my hubs https://www.spartaevo.com/
I've also contacted Wilwood and I'll be replacing my problematic handbrake shoes with an electronic handbrake https://www.wilwood.com/calipers/CaliperList?subname=Electronic Parking Brake

DBA, Wilwood, Alcon and AP all have publicly available information on their rotors and fitment, and a lot of the fitments are common. My current plan is to design a hub that has a common fitment to prevent being tied into one brand. SpartaEvo don't publicly disclose their rotor fitments because of the bespoke nature of their work but if some of their rotors support common fitment they will be used as well. Even better, some of the common fitments support rotor sizes for 330mm, 355mm and 380mm all at the same time, allowing for 2-piece rotors that match or exceed the OEM thermal mass maintaining a safe street use application. By using common fitments it also allows for using a host of materials, including CC! SpartaEvo know that I'm planning to fit another manufacturers rotors to the hubs I've asked them to make, and they've still agreed to do an internal engineering review and manufacture them, which to be honest is pretty amazing.

By going to an electronic handbrake I completely eliminate fitment issues on the rear making it easy to go to a matched set of front and rear rotors.

Our front calipers have a massive 57mm interface, so they're more than suitable for even the most hardcore application - and in my opinion, evidence that Maserati knew they were pushing the rotors they selected to the edge. They were trying to compensate for high temperatures by increasing the interface area to prevent fade.

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This should be fun!
 

Ebenezer

Member
Messages
2,421
So will they fit my QP which has woeful 4 pot brakes? Even though I drive like Miss Daisy I've managed to warp them so that they needed skimming
Eb
 

Ewan

Member
Messages
3,820
In over 20 years and well over 100,000 miles of Maserati driving, including numerous track days, not once have I had a problem with the brakes (or crashed). So the factory ones seem to work just fine with my driving style. Which is a good thing, as the carbon jobs on the Strad are not cheap and I don't fancy having to replace those any time soon!

But of course, a better than factory solution at a lower cost would be fantastic and very welcome.
 

Gazcw

Member
Messages
1,527
Holy **** that blew my small mind.. I admit I may not understand a lot of that but if there are some decent discs at realistic prices at the end of your journey then I wish you good luck.
 

happydaze

Member
Messages
129
The front rotors on my new Porsche 996 GT-3 cracked around the drilled holes, after a very short time. "Not covered under warranty", so it cost me! At the time (2004), Stan Adler was offering a two-piece, undrilled replacement kit using DBA rotors. Due to my concerns over warranty, insurance, etc., I decided to stay with the Porsche ****...
 

alfatwo

Member
Messages
4,689
They need to EU approved for road use insurance purposes, you cant just fit race car stuff!

Dave
 

rockits

Member
Messages
7,713
The one thing about EU approval often though is how much does it actually mean?

The amount of approved electronics especially power supplies adapters I've seen over the years that are dangerous, overheat.and can and do catch fire is plentiful. I'm not saying stuff shouldn't be tested and approved but it doesn't mean necessarily it is flawless or 100% safe.
 

lambertius

Member
Messages
341
So will they fit my QP which has woeful 4 pot brakes? Even though I drive like Miss Daisy I've managed to warp them so that they needed skimming
Eb
I'm not sure, but I know the rotors are common between quite a few cars - it might be worth checking the part numbers.

The front rotors on my new Porsche 996 GT-3 cracked around the drilled holes, after a very short time. "Not covered under warranty", so it cost me! At the time (2004), Stan Adler was offering a two-piece, undrilled replacement kit using DBA rotors. Due to my concerns over warranty, insurance, etc., I decided to stay with the Porsche ****...
DBA rotors have their TUV certification on their website https://dba.com.au/about/certifications/ . If you email them they will respond, and you can find out which countries their rotors have specific certifications for. I can't speak globally, but in Australia a dealership can't deny you warranty on an aftermarket part that is OEM equivalent or otherwise certified for use. Which brings me onto this...

They need to EU approved for road use insurance purposes, you cant just fit race car stuff!

Dave
I don't know what approvals are needed in Europe/UK specifically but the process I'm going down avoids the problem for me locally in Australia, and in Europe. I'm not 'making' anything. The rotors are already an item that exists and is sold, so you can pick a brand that already has the certification you want (say an AP Rotor) and so long as the hat meets that certification then you've bought and installed two certified parts. In my case specifically, DBA are an Australian brand so their rotors are all certified for use in Australia, and if for any reason there is trouble with SpartaEvo they can get the certification, or since I'm doing the design I could get it manufactured by someone with the correct certifications locally, and failing that I can get individual engineering approval as a modified car. More realistically though it will probably just stop as buying an approved rotor and approved hat and that will be the end of it.

The one thing about EU approval often though is how much does it actually mean?

The amount of approved electronics especially power supplies adapters I've seen over the years that are dangerous, overheat.and can and do catch fire is plentiful. I'm not saying stuff shouldn't be tested and approved but it doesn't mean necessarily it is flawless or 100% safe.
It depends on the certification. Some have tests, some just require you to write in and justify your design.

Isn’t cheaper to blow OEM. Discs every 5 years....or longer?
Not for me. AUD is getting obliterated at the moment and brake rotors cost a ton in shipping.
 

lambertius

Member
Messages
341
I have a couple of nice pictures so I thought I would throw out a small update. I'm still going through different rotors to work out what items have a common fit and what don't.

This is the DBA 59382.1

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This is the Wilwood 160-15256

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So what is special about these rotors?

Both of these rotors are suitable as OEM replacements for quite a few reasons. One of the issues with a direct fit aftermarket option I found is that they used a more common fit rotor which reduced the annulus (the swept area that the pad can touch) which requires that the a smaller pad is used instead of the standard pad. This also reduces the mass of the rotor significantly which requires the use of hotter pads to maintain a safe operation. The consequence of this is that during street driving you'll be at the lower end of the operating envelope. This particular aftermarket supplier offers a larger 355mm rotor with dogbones to fit the original calipers, this would presumably be to maintain the OEM pad fitment that they were unable to do with the 330mm kit.

So far these are the only two rotors I've found that:

  • Have a 60mm annulus to maintain the OEM pad (it sweeps 57mm).
  • Has a small enough rotor PCD of <200mm to allow this large annulus.
  • Due to the large annulus and hi vane count, these rotors are relatively massive for floating rotors at over 8.4kg each. This would still allow the use of cheaper and less aggressive pads for daily use without the risk of over heating.
So far these are the only two rotors I've found that fully meet the spec, Alcon has a few rotors that a **** close but not exact fits. They have a slightly different rotor PCD, but it should be possible to get a common fitment on a hat. Otherwise the easier solution would be to go to a 355mm rotor and include dogbones. As my goal is to absolutely minimise the cost and the effectiveness, these rotors would actually be a really good choice with a high level of availability.

I need to get home and confirm the hub dimensions before I get too excited, but at the moment things are looking good up front.
 

Enz0

Junior Member
Messages
31
I think that using Ferrari 456M's rotors (165686 for the front, 144061 for the rear) is reasonable.
http://www.superformance.co.uk/v12m/brakes.html
Though their vents are not optimized for rotational direction, they do not have silly cross-drilled holes and are OEM quality. I think they are good enough for high-temperature tolerant street pads like Brembo HP2000 or Ferodo DS Performance.
 

Zep

Moderator
Messages
4,164
I think that using Ferrari 456M's rotors (165686 for the front, 144061 for the rear) is reasonable.
http://www.superformance.co.uk/v12m/brakes.html
Though their vents are not optimized for rotational direction, they do not have silly cross-drilled holes and are OEM quality. I think they are good enough for high-temperature tolerant street pads like Brembo HP2000 or Ferodo DS Performance.
Have you fitted these? To my eye, the offset on the disc looks different, but I could be wrong.
 

lambertius

Member
Messages
341
I think that using Ferrari 456M's rotors (165686 for the front, 144061 for the rear) is reasonable.
http://www.superformance.co.uk/v12m/brakes.html
Though their vents are not optimized for rotational direction, they do not have silly cross-drilled holes and are OEM quality. I think they are good enough for high-temperature tolerant street pads like Brembo HP2000 or Ferodo DS Performance.
Do you know for sure that is a direct fit? The OEM rotors aren't directional anyway - they use a pillar vented design. Just getting rid of the cross drilling would be a decent improvement on its own. That said with the AUD doing the funky timewarp (the last time it was this awful was 2008) and shipping on 4 rotors, I'm still looking at getting better pricing doing my own rotors and hubs... Pretty stupid. The costs of repairing this car has gone up something like 30% since I bought it!