Alcon Answers Your Braking Questions
Bedding In

Back in October the team at Alcon invited a handful of Speedhunters to take a tour around its UK HQ and R&D facility. We had a raft of technical braking questions presented to us in the comments section, so we put them to the team at Alcon, and here are the answers…

Nerd mode engaged…

Alcon Brakes Tour by Jordan Butters Speedhunters-72

Why don’t we get ‘raw’ aluminium brakes with the brand logo/name machined to the surface instead of painted calipers? Does the paint have any benefits?

Alcon: All of our calipers are ‘Hard Anodised’; this provides a hard-wearing surface (inside the bores). However the colour is very limited and very difficult to maintain consistency, and therefore paint is applied to provide an aesthetically-appealing and environmentally-robust finish.

Alcon Brakes Tour by Jordan Butters Speedhunters-88

While upgrading to aftermarket brake systems, is it important to keep the brake bias of the new system to be as close as possible to the OEM front/rear bias or it doesn’t matter and just let the electronics (eg EBD) to sort it out?

Alcon: We would always recommend that brake bias split between front and rear is matched as closely as possible to the OEM setup.

Coventry MotoFest 2018 by Jordan Butters Speedhunters-4137

When upgrading to an Alcon braking package, i.e. calipers, rotors and bells, does the unsprung weight change make much difference to braking motion? Is this something which is often overlooked?

Alcon: One big advantage of lighter brakes is reduced unsprung mass – this is a key performance target for any race car and one which has a direct benefit for all road vehicles as well.

Alcon Brakes Tour by Jordan Butters Speedhunters-56

I’m curious as to whether there is any meaningful discussion regarding staggered rotor sizes, or having the rear discs a few milimetres larger than the front, with the front running four-piston and rear two-piston. This is an off the shelf option for my car available from StopTech, and they state that it is fine to run on track. What are the benefits or drawbacks to this?

Alcon: We calculate a safe balance for brake torque from front to rear via a combination of disc size (from the effective radii), piston sizes and pad friction. We also take into account the thermal capacity of the discs and work rate for the pads for both axles. If the space for a disc means that we have a larger rear disc than front, we compensate with friction and caliper piston sizes. Therefore, the relation between front and rear rotor diameter is not an issue as long as the rest of the system is specified accordingly.

Alcon Brakes Tour by Jordan Butters Speedhunters-57

Two-piece rotors (or floating rotors) are considered better. However, this would let the disc piece super heat and not being dissipated. How can we optimize this? Just use single piece rotor?

Alcon: Two-piece rotors are designed to enable the rotor to be the heat store and the bell to be the carrier, we perform predictive thermal brake calculations to ensure we size the rotor appropriately for the application, this enables us to design the bell in lighter materials reducing rotating mass. Our two-piece assemblies are bolted together using ‘bobbins’ which allows for different thermal expansion rates between bell and rotor due to the use of dissimilar materials.

Braking Bad
Alcon Brakes Tour by Jordan Butters Speedhunters-83

Some people use titanium shims between calipers, pistons and pads to keep the heat from boiling brake fluid. How would this be optimized to prevent the pad from going into super heat cycle? There are ideas of letting other components act as heatsink, but how far do we isolate the heat?

Alcon: This is something used more extensively in Motorsport applications where caliper, brake fluid, disc and pad temperatures can be monitored and tuned and balanced accordingly – on occasions keeping heat in pads so that they remain within their optimum temperature range can be a benefit.

Alcon Brakes Tour by Jordan Butters Speedhunters-32

How do you calculate master cylinder size once you have changed to calipers with a bigger piston size or more pistons?

Alcon: We have our own in-house calculation software for which allows us (based upon vehicle data) to make accurate recommendations for master cylinder sizing. For aftermarket, we design our kits very carefully to make use of existing actuation hardware already fitted to the vehicle.

Alcon Brakes Tour by Jordan Butters Speedhunters-28

How do you calculate master cylinder size to account for removing the brake booster? (This one is for all the LS swap guys!)

Alcon: We have target pedal efforts and specify the master cylinder sizes to target what is safe and, if used on the road, legal. We have to take into account the pedal ratio and wheel brakes. A full system calculation is required and needs to be carried out by a qualified brake system engineer.

Alcon Brakes Tour by Jordan Butters Speedhunters-60

Drilled, slotted, and grooved rotors seem to really only wear pads faster with marginal if not negligible gains in performance. How can we differentiate between the real performers from the gimmicks?

Alcon: Grooved rotors have become the norm in aftermarket and motorsport applications as they present a cleaning edge to the pads, the ability to disperse gassing given off by pads, improved initial bite and more consistent wet weather performance. Drilled rotors offer similar benefits but suffer more with cracks emanating from holes – as a result drilled rotors are now more limited to carbon ceramic options where disc cracking is not an issue.

Alcon Brakes Tour by Jordan Butters Speedhunters-19

I recently upgraded my brakes in my 2006 Honda Accord from stock to slotted rotors. After a hard stop the pedal starts to get soft. Am I overheating my brake fluid? Whats the best way to choose an upgrade for my needs that matches my rotor upgrade?

Alcon: The issue could indeed be the result of boiled brake fluid causing gas bubbles to form within the fluid itself, which is far more compressible and in turns gives a soft, spongy pedal feel. If the only change made is to slotted rotors this would not give any additional thermal capacity and any brake performance gain will be minimal. Depending on how much brake performance increase you require we would recommend larger discs with improved thermal capacity, performance pads and a caliper upgrade.

Coventry MotoFest 2018 by Jordan Butters Speedhunters-3827

Does disc size play a major role in stopping power?

Alcon: Disc size can be split into two aspects; disc diameter, which increases stopping power by increasing the turning moment (leverage effect), and disc mass, which allows more heat to be stored, which in turn allows pads and calipers to operate more effectively.

No Fade
Alcon Brakes Tour by Jordan Butters Speedhunters-46

There are lots of companies out there offering ‘big’ brake kits, but how do you filter out the ones that properly work and those which perform as good (if not better) than OEM?

Alcon: The market has indeed been flooded with a number of companies selling ‘big’ brake kits, our advice would always be to choose a company with heritage and a reputation in designing high performance brakes. We’re sure that it comes as no surprise that our recommendation would be Alcon!


Why do some companies think bigger is better in terms of caliper pistons, is there any truth in that?

Alcon: Caliper piston sizes are derived from a full system calculation. What we want is for the driver to have a good pedal feel when stopping the vehicle safely. We specify the most appropriate piston sizes, large or small to achieve this. For disc and rotor only brake kits, increasing the piston sizes can be very dangerous as it can affect the vehicle balance (making it unstable), make the master cylinder bottom out of fluid and cause issues with stability control systems.

Drift Masters GP Round 2 Hungary by Jordan Butters Speedhunters-8315

Does the weather (specifically rain) have any effect on certain discs? Is there a design which is better in the wet or does it make no difference?

Alcon: Early carbon ceramic systems had issues in the wet. We’ve moved on considerably over the last ten years and there is now very little difference in disc materials for wet running.

Alcon Brakes Tour by Jordan Butters Speedhunters-21

Why do some people go for brake booster delete – what’s the pros and cons?

Alcon: The booster reduces the pedal effort. Modern cars have boosters that can have ratios between 5:1 and 11:1, depending upon the unit. Therefore, removing the booster will increase the pedal effort. There is a good chance that, on some vehicles, removing the booster will increase the efforts above the legal limit for road use.

The advantage of removing the booster is that there can be a high kick-up, giving a much lighter feel at the low end and the booster can add efficiency losses into the system. Any removal of a booster should not be done on a road application without the advice of a responsible and qualified brake engineer.

Alcon Brakes Tour by Jordan Butters Speedhunters-89

What’s the maximum temperature your carbon ceramic brakes can withstand?

Alcon: This depends upon how the temperature has been generated and the design of the disc geometry itself. Often, it’s not the discs that are the issue, but the pads (with fade) and brake fluid (with boiling).

Coventry MotoFest 2018 by Jordan Butters Speedhunters-4419

Does brake caliper position help with brake performance?

Alcon: The position will not help with performance, but will help with servicing and safety. Calipers are generally positioned as close to three o’clock or nine o’clock as possible to make them easy to bleed. In a motorsport application, for example Formula One, they position the caliper best they can to lower the centre of gravity, however this is more susceptible to knock-off if the hub design isn’t robust. The more common practice for motorsport is to run trailing calipers front and leading rear to bring the weight more towards the centre of the car.

Responses by Alcon

Photography by Jordan Butters
Instagram: jordanbutters



Comments are closed.


by Oldest
by Best by Newest by Oldest

Very informative!


thanks for the answers alcon and the effort by speedhunters! great article


I am sorry, but being a big fanboy of SH, and a die-hard DIYer, this article is pointless. Answers are marketing bullshit, and there's absolutely no usefull information for the DIYer, or anybody else for that matter.
I understand some stuff can't be explained without a full page of formulas. But i don't think that is the case here. They could have explained the general principle behind each answer. Here, they just don't answer to the questions !


In a way your right and I have some similar feelings as to the techness of this article. however if your actually looking for good information and the real "meat and potatoes" of the brake system look into the tech articles on Stoptech's website.


plus dont buy a BBK kit if your going to hardpark the asthetics are a waste of money.


You cant ask for information from a company as a DIYer and expect you to hand over there secrets and classified information just so you can make it yourself and stuff. if you have the cash to blow on a custom brake kit its usually like 2300+ for a custom one fit one. so just save your pennies and buy one, its not like anyones gonna run out at a show and go MAN I REALLY WANNA BLOW 2300 on my 500$ drift missle 240SX now those BRakes will make me faster.


You want a reputable company that has to take safety VERY seriously to give specific advice over the internet so a DIYer can mess around with their brakes? Right…


What I'm trying to say is SH has provided great nerd articles so far like engines at WTAC. So when I saw the title I expected more specific answers than this.
Pics are nice though.


I love how people are down voting Max because he's actually asking for substance. If you can't answer anything because of legal ramifications and lawyers you shouldn't be writing articles like this.

Teach / inform properly or sit on the bench so someone else can do the job correctly.


As engineers, they have to be VERY careful with the information they supply to DIY'ers. You cannot supply any recommendations without having a calculation specific to the application to back it up. There are legal ramifications if they say too much, and someone can claim that "an engineer said it was ok to do this". This is especially true where any element of safety is involved, such as a braking system on a car.


Alcon: Disc size can be split into two aspects; disc diameter, which increases stopping power by increasing the turning moment (leverage effect), and disc mass, which allows more heat to be stored, which in turn allows pads and calipers to operate more effectively.

Tsk tsk Alcon, it's not a brake size that has the largest effect on stopping distance: it's tire compound. Some of these answers were a little vague imo.

As for the question about big brake kits they can make certain cars slower. Needing a big brake kit and upgrading to one are two very different things. Cooling has large implications on the performance of a braking system as well. The word cooling wasn't mentioned one time in this entire piece.

Welp that's all I got.


Where does it say that brake size has the largest effect on stopping distance?


I don't think you read that correctly. They didn't say that disc diameter had the largest effect on stopping distance, they stated that larger diameter discs aid in stopping power due to leverage...

That's not to say you're wrong regarding tires and stopping distance


"not to say you're wrong"

I'm not wrong at all. 0% in fact. "Not to say" implies there is some wiggle room about the validity of my point. There is not.

What I stated is a cold hard fact. Tire compound > everything when it comes to stopping distances. The size of your rotors is honestly the last thing when it comes to braking effectiveness.

They didn't say that disc diameter has the largest effect, but they didn't say what actually matters either. This whole article read like a BS marketing ploy that SH is taking dollars on. There have been a few of these articles and they are killing the fanbase with those of us who are informed and aren't looking to get converted into revenue on a spread sheet.


What are you even arguing with? Someone questioning why you brought something up that wasn't asked in this article and making out like your putting everyone in their place? The fake-news sponsored-content website, the sh*t-loads-of-championships-winning company, the other car guys replying, you showed them!

It was a question about disc size, not 'Disc size' vs 'Sticky tyres' vs 'A brick wall' vs 'Pushing the pedal with your strong hand instead of your foot'. You talking about stuff that's beyond the scope of the question and its reply isn't relevant. "0% in fact" haha xD

Good to know that disc size / width is irrelevant too though, I'll sell my AP's (I couldn't afford to be converted to revenue on Alcon's spread sheet) and be happy in the knowledge my 239mm solid front discs will be fine as long as I throw some slicks on...


239mm rotors would be fine depending on the weight of the car, tire compound and the rest of the balance. It all depends on the application but tires > all. Sorry, that's a fact.

You would absolutely be fine doing that if your car was light enough. It all depends on application, ace.


I still don’t understnd why you’re talking about tyres when you’re literally the only person at mentioned them. The question was SPECIFICALLY about brakes, and they answered it.

Maybe ring Michelin and see if they can give you advice on what discs to use?


You're scrambling kid. This thing is collapsing and you're trying to hold it together. Let this one go. Tires are the single most important factor when it comes to stopping distance.

You're ignorance and your age are both showing now. This is the part where you close your mouth and do some research. Have fun.


The question was about brakes, SPECIFICALLY. Here it is again, because you're clearly struggling:

"Does disc size play a major role in stopping power?"

Please tell me again about how the answer should have been: "No, tyres." and how that would've made any sense.

What part of this don't you understand – no one said they weren't the most important. You're literally arguing with yourself here. I mean, by your logic, technically the most important part in stopping distance is the solid object you're about to hit, because nothing will bring you to a halt like a brick wall. Incidentally, that feels like what I'm banging my head against trying to get you to actually read what was written.


Flame me all you want, but from a question-and-answer standpoint, this was complete garbage.
Most of the questions weren't even answer directly, much-less fully; and if there was more than one question they would pick one portion to answer.
I understand they cant give away industry secrets, or provide too much personal advice for a variety of reasons, but you could at the very least write more than 2 sentences in response.
I love this site and 99% of the content, but this was a major flop; more-so on Alcon's part than S.H.


I'm suddenly very thankful about how informative KW always is. Was Alcon's PR guy in some sort of a rush?
Oh, I see. He stopped each question, as quickly and efficiently as possible.
I wasn't hoping for recommendations or diy tips, as much as I was hoping to learn more about the physical processes that go on during braking. Understanding the physics going on in and around your car is a tremendous help in all aspects of driving and operating it, not simply modifying it.
Oh well. I'm sure this is a better Q/A than Brembo would have done...
Audience member: Is there any way to mitigate the squealing that cold carbon cermaic disks make?


Did you ask a question about the physical processes that go on during braking?

If not then you missed a chance there, because had someone have asked it they would have answered.


Excellent article. It's always awesome to learn more about braking systems. The topic about larger rotors with same sized calipers was something I didn't know about!


Interesting article!