Mike Stevens | Oct 18, 2008

I get asked questions daily about cars and their components, and one question that seems to follow me around is the question of brakes: "What do I do to improve braking performance?" The only way to deal with it is by putting pen to paper, so here goes.

An acquaintance of mine loves cars, much like the readers here at TMR, and he is just now taking his first few baby steps into the unfamiliar world of track days. You see for him, driving a performance car on the roads is becoming both increasingly dangerous and just downright unacceptable. With more traffic and stronger punishments, coupled with more speed detection devices than ever before, my friend has decided to follow an ever-increasing trend in getting his 'need for speed' out of his sytem through track days.

Simply put, track days offer you both safety and satisfaction you just can’t get these days from an early Sunday morning blatt on your favourite piece of blacktop.

The question he posed to me arose because of things he had read on the internet. He had posted a few questions relating to track days from more ‘experienced drivers’ and had been told he will need to upgrade his brakes before he does his first track day.

Of course everyone has opinions. But asking for advice via the internet can be a scary proposition because you just never know if the person you’re asking is in fact an authority on the subject.

While I’m no authority, I have learned a thing or two from the race teams I’ve had the pleasure of mixing with. So, he then asked me if a brake upgrade was needed because of the type of driving that he was about to undertake. On top of that, he wanted to know what exactly would be necessary to upgrade and why?

I guess before I answer the questions posed I need to explain a few things, and some of the basic physics principals involved. So if your first reaction now is to roll your eyes and moan (because you reckon you know all this stuff anyway), just click on the next TMR story - because I intend on 'braking' this down (pardon the pun) into layman's terms.

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Firstly, brakes don’t stop cars, tyres do! During braking, brakes convert the kinetic energy, or ‘motion of the vehicle’, into thermal energy . They produce heat and plenty of it! The trick is removing the heat from the area pronto - more so with cars intended for track use.

Ever seen a racing car on TV with its rotors glowing red-hot? It’s not uncommon for brake temps on race cars to soar well past 600 degrees centigrade!

Passenger cars' braking systems do not have to cope with those extremes, but they do have to work reliably time after time. Pretty much most new cars can wash off their top speed in one single stop more than once; its only after repeated heavy use of the brakes that your standard anchors won’t stand up to the job. It’s not because they aren’t big enough, it’s simply because they can’t remove enough heat.

Heat is the enemy here people, that’s the reason racing cars use big brakes. Although you might get some nut job telling you that a larger rotor is the only important thing, it’s not the be-all and end-all. Sure, increasing the surface area (swept area) is a good thing, as is the increased torque you get from a larger outside radius of a larger rotor. But what’s far more important is the removal of heat, and bigger brakes generally do this better because of increased surface area and bigger air flow. So, yes, bigger is better, but bigger doesn’t necessarily mean shorter stopping distances: thermal capacity is the key!

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What’s thermal capacity I hear you ask? With risk of sounding uncomfortably like your year 10 science teacher, thermal capacity is the brakes' ability to absorb and remove heat by its conductivity, via a transfer in both convectional and radiational heat. Sounds complex doesn’t it, but it’s not.

(Every time you press the brakes on your car, there is enough mathematics and physics principals at work to keep MENSA happy for the next decade, so don’t worry about that too much.)

So, fitting bigger brakes to your car is the right thing to do then, right? It must be, because removing more heat is better, so obviously I’m going to stop better and stronger... right? Well, no. Sorry! While bigger brakes are generally better, there are other things to factor in.

You see, for most of us driving modern cars fitted with ABS brakes there are two ingredients that need to be considered: pressure volume and pressure torque (and both these two little critters are measured by your ABS system every time ABS is activated). So while fitting larger diameter brakes is better, due to better heat removal, increasing clamping torque and increasing swept areas will mean ‘more brakes’ doing ‘more work’.

But here is the catch: chances are, unless you’ve had your entire brake system recalibrated to your newly upgraded brakes, you’re not taking full advantage of what your bigger brakes have to offer. Recalibrating allows your ABS module to make the necessary calculations with pressure volume and pressure torque.

Here is where things get heavy. Your ABS unit has been calibrated and matched for the standard brakes fitted to your car, so when you upgrade your brakes with larger calipers, rotors, pads and brake lines (as the case may be), you’ve changed the values of both pressure volume and pressure torque (and, as the values have changed, your ABS unit is wondering what it should do). Not good.

Sure, your upgraded brakes may no doubt ‘feel’ stronger as the pedal feel firms up, and perhaps initial bite is stronger under small to medium dabs at the pedal. You might find even occasional hard stomps (before the ABS kicks in) also work better. But under hard constant braking - like what you’d experience at a track day when your ABS is working overtime - you may encounter ‘ABS confusion’ and that’s not going to be at all pretty. Your car may even become unstable under braking as a result, affecting your times and your cornering.

But let’s say you’ve had your brakes properly calibrated allowing the ABS unit to work with the new values of pressure volume and pressure torque. You’ll then no doubt have some serious stopping power for those track days? Yes, you will! Not only will you have strong brakes that aren’t under any confusion, but you will also have more control as brake pressure will be better balanced due to correct calibration. And, as you know, control is everything on the track.

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There are some other measures that you can take to make sure you are really getting the best stopping power available to you and your budget. Fitting 'stickier tyres' will also improve braking ability as will a suspension setup designed for track use. This will have your brakes working less, thus working longer before they become overheated and need to be cooled down with a little ‘time out’ or having a moment off the brakes (giving them a little breather before stomping on them again).

You see, no matter how strong you make your brakes or even how big they are, heat is still the enemy and even with massive brakes you can still have excessive heat build-up. Removing as much heat as possible will mean stronger braking, and for longer periods of time.

Fitting two piece 'hat mounted' brakes is an excellent way to remove heat, as it reduces conductive heat and replaces it with connective and radiational heat which is the lesser evils.

It also helps reduce 'brake fade' if you use a brake fluid designed for sustained higher temperature operation.

'Brake fade', now that’s another equation we haven’t touched.

I’m sure everyone who has plugged away reading this article has no doubt at one time experienced brake fade. It’s that nasty feeling you get when the brake pedal sinks lower and lower to the floor but with what seems like bugger all response to your stomping on the anchors. If it’s going to happen anywhere, the race track is as likely a place as any.

Firstly you need to understand that brake fade can happen in two very different ways.

The first way is because your brake fluid is getting so hot, it causes your fluid to bubble, and the reason your brake pedal feels ‘squishy’ is because, when you jump on the brakes, you are compressing those tiny air bubbles. So how do you stop your brake fluid from bubbling? Simple, just use a high temp brake fluid that can withstand the higher temps that a hard-working big brake system will require.

Phew, that was easy. Well, not quite! You see there are various types of brake fluids, and just because you’ve used a high temp fluid doesn’t mean it’s going to solve the world’s problems as you need your entire brake system to cope with the upgraded fluid. For the time being though, I’ll leave brake fluid alone and come back to it with a later article.

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The second cause of fading brakes is when the temperature between the pad and the rotor exceeds the thermal capacity of the pad (thermal capacity once again is ability to absorb and remove heat by its conductivity, via a transfer in both convectional and radiational heat). Then the pad loses friction capability due to ‘gassing’ of the binding agents in the pad compound. Having slotted or cross-drilled rotors is one way to combat the gassing effect by removing it with a cutting action. More recently, pads are becoming available for passenger cars with compounds that greatly reduce gassing.

You’ll know what I mean when you do get the gassing effect (and no... not the type of gassing effect your father gets when he asks you to pull his finger in the classical 'Dad joke') as the brake pedal firms up compared to that soft, mushy, sinking feeling you get with bubbling fluid.

With gassing, the car just won’t stop and usually you’ll also get a nice grinding noise the harder you stomp your blundstones to the floor (the first sign of things going horrible wrong). Then, after a small panic attack because you aren’t slowing down, you will detect a terrible but familiar smell of what can only be described as 'heat' - and if heat did have a smell, it would smell like this.

So, having gone through all that, let's return to where we started with our track day friend.

Have I answered any of his questions? Well, no! If anything I’ve added to his confusion and that was the true purpose of this article. You see, while I’ve been able to identify what our young track hound wants from his car and I’ve been able to advise him of what he needs to think about, it will be later when he wants to wind it up a notch that he will need to get really serious about getting a purpose-designed brake system fitted (by an expert).

A few track days a year doesn’t warrant going to a massive rotor and caliper setup with pads that are almost unusable for everyday use. (They can be rubbish when cold and make more noise than a Screaming Jets concert when slowing down to a stop outside school on the early morning school run.)

So, that’s it really. Your brakes should instill confidence, but they don’t need to detach your retina every time you use them, not unless you’re going to spend most of your time at the track.

If you take away anything from this article, I hope it’s the understanding that a car is just a big bunch of metal and plastic governed by a whole lot of maths and physics. It’s in understanding those sciences that will help you get a better driving experience and performance from your car. While you can quite easily fit bigger brakes to a car, you can’t defy the laws of physics. So you've got to get all the elements properly sorted out.

Till next time, happy and safe motoring.

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