*INFO* Braking/Brakes General Information

*** Disclaimer ***
This information is for interest only and not a suggestion for correct road use.

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# Author: Stuart Lindborg (Cambridge/Slindborg) #
# Date: 22nd December 2008 #
# Contact: lindborg.stuart@googlemail.com #
# Version 0.9.1 #
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Stopping, its kind of important isn't it....

http://www.direct.gov.uk/en/TravelAn...&Rendition=Web

from the RoSPA web site
" The braking distances in the Highway Code also assume a braking deceleration of about 6.5 metres per second squared (6.5m/s2), but again this could be affected by poorly adjusted brakes, worn tyres or the amount of pressure the driver puts on the brake pedal. The road surface is also critical. The stopping distances in the Highway Code are based on a dry road – on wet or icy roads, the braking distance is much greater."
That infers that the highway code braking distances are based on braking at 0.66G ( (1/9.81) * 6.5), quite frankly this is poor if your thinking from a track/enthusiastic road use when most times you will be braking much closer to 1G (9.81m/s/s). Stopping at a rate of more than 9.81m/s/s requires extra down-force and very high grip tyres (slicks for example).
Also think about the effort required to stop your car from rolling while pushing it. Its not much is it? Now think about how much effort you need to stop from 70mph..... you will need much much more.
so this statement from the highway code link might not be the "best" for our use on track.
" 97: In normal circumstances. The safest way to brake is to do so early and lightly. Brake more firmly as you begin to stop. Ease the pressure off just before the vehicle comes to rest to avoid a jerky stop."

In essence we want to stop or rather scrub off speed as much as possible in the least time/road space. This means more of an emergency stop type of braking where you apply lots and lots of pressure to start with and ease off as the speed reduces to prevent locking up. Bear in mind that when on the road you MUST check your mirrors before this type of braking to ensure that your not about to get rear ended.

That's the dull bit over with.
How do brakes work (OK I lied this might be dull too)?
http://auto.howstuffworks.com/master-brake.htm ahh easy
http://www.mech.uwa.edu.au/DANotes/b.../vehicles.html woah hardcore!
Remember at school when you had a thin syringe and a fat syringe liked with tubing and full of water, pushing the small syringe in would move the fat one a small distance but you could lift a heavy weight with little effort...that's basically how the hydraulic system of brakes work.
So that's how you get the force from pedal to pad/shoe.
http://www.howstuffworks.com/disc-brake.htm

Disc size varies the stopping leverage which in turn varies the stopping ability of the vehicle... a light vehicle would need smaller brakes to stop at the same rate as a heavy vehicle (with the same brake pad size and force, and assuming no lock up). As a side line larger discs tend to be vented and have a better heat capacity.

The core issue with braking is HEAT and what to do with it/how to make use of it etc.

Brake Fluid

Firstly, brake fluid!!!
Its almost the most important bit of the system as its the "life blood" of it, without it you are screwed, with poor quality fluid you are screwed, with old fluid you are screwed..... see the theme here? :)

Lets pretend the servo assistance isn't there.
You press the brake pedal and the linkage will translate that to the master cylinder and push brake fluid down the lines to all 4 wheels.
Now this is all well and good for your one big stop, but if you get lots and lots of heat into the caliper and subsequently the fluid it can "boil" (much like a kettle of water but at higher temperatures). And of course when you boil the kettle you get bubbles, the same thing happens in the brake caliper, and this means that you will get air pockets in the caliper. I hope you know that you can compress air easier than you can compress a fluid (yes I know air is a fluid too but not for this purpose), and because air is easier to compress than the fluid the brake pedal travel will increase to try and get the same brake line pressure as the air takes more of the compression force/energy from the system.
Now there are a few options for reducing fluid boiling, but the EASIEST method is to replace the fluid every-time it boils with some fresh DOT4 spec stuff (Note the older the fluid the lower the boiling point).
You can either use cheap sub £10 a gallon DOT4 and change it nearly all the time, or use a higher boiling pointed fluid of a DOT4 spec.
Both ideas work fine and probably wind up costing the same overall, but it depends if you like fit and forget (for 12 months) or a constant tinker.

Personally I like the ATE Superblue brake fluid as its a reasonable price (£20 a litre), easy to get hold of mail order and its blue... helps with bleeding the system, and for a fluid change you can get the same sped fluid in a gold/amber colour so you can tell the difference again.
There are a few other similar spec fluids too:
Motul RBF 600
AP RBF 600
Wilwood fluid
etc
There is also Castrol SRF, but its farking expensive and also its been known to eat brake seals... your call on that one.

PADS

In short, if you can lock the wheels then the brakes are more than capable of stopping the car at least once from sub 100mph speeds. This is where the need for "better" brakes comes from... eg to carry out repeated stops/speed loss from high speeds. If you are running with OEM pads then they will have fairly high initial bite but a low heat capacity as they have to work 100% from cold and get you stopped with the intention of a while before being used again to let them cool down.
When you take OEM pads on track/hard use then you may find that after a few hard brake applications that the pedal still feels firm, but there is simply no stopping effort, this is called BRAKE FADE. Brake fade is essentially where the pad/disc interaction has generated so much heat that the pad material no longer has the same friction coefficient (grip on the disc). One way to counteract this problem is to fit some brake pads with a higher operating temperature range, these usually come in the form of "fast road/light track" "Medium track" and "race/heavy track" titles... personally I don't think those names are of much use (like when they are applied to CAM specs too.. meh). There are pros and cons of fitting uprated pads, obviously the pros are high temperature capacity so you can stand on the brakes and know they will work several times in a row, meaning either later braking into bends or generally being able to stop after a hard session. The cons are things like cost, abrasiveness on the discs, dust is more aggressive, some wear faster than OEM, sometimes they can be noisy etc. Basically the cons aren't really a huge issue for our use, bar cost.
Brake pad size has little to nothing to do with how well you stop, it does have a bearing on the wear rate of the pads though.

The usual suspects for "upgraded" pads are:

Mintex 1144 (More like and OEM pad but with a good temperature range, a little soft so can wear faster than most, VERY good though)
Mintex 1155 (Essentially an 1144 pad but with a longer life and higher heat range, seems to take hard track abuse well)
Ferodo 2500 (Sort of inbetween the 1144 and 1155, very good initial bite, good heat capacity etc)
Ferodo 3000 (Similar to the 1155's)
Performance Friction Braking 97 spec (Carbon Metallic pads, incredible heat capacity, a little noisy, very very abrasive on non heat treated discs)
Pagids ***LEE ADD To this ***
Tarox ** DAN ***

Pad/Fluid interaction.
With a high heat capacity pad you have to bear in mind the heat transfer.
Heat has to go somewhere and the pad material will be the factor of where it goes. An "organic" pad material (Mintex 1144 for example) will act as a fairly good insulator and keep the heat in the pad/disc area, meaning the caliper wont get tooo hot but the discs might take a heat beating (more on that next). A "Ceramic" pad material will act in a similar way to the organic one, in that it keeps the heat at the disc/pad, but can take more of it so fade is reduced. A "metallic" compound will transfer most of its heat back into the brake caliper as its not a very good heat insulator, this means you could potentially cook your brake fluid without much effort (I fitted carbon metallic pads to my car and boiled the fluid during the bedding in process... OK it was old fluid but it never boiled under hard abuse on organics)

Discs

Lets say you have taken the car to its "limits" on the standard discs and uprated pads/fluid, now what?...
The next cheapest option is discs.
If you don't have vented discs, then the obvious step is to get vented ones, this is likely to require a brake caliper change but using calipers/discs from a "bigger" model car is a good value option.

Vented discs mean that rather than a single solid disc, you have two brake discs that are separated by vanes that channel air through them to cool the disc. Also as a sideline they are generally bigger/heavier meaning the specific heat capacity of the disc increases as there is more metal to heat up so the same brake energy is dissipated faster/easier.

Grooves/ X drillings.
Grooves apparently help disperse the thin layer of gas that forms when you are spanking the brakes hard (and can push the pad back to reduce braking efforts), they also help cut the pad surface to be "clean" each time, but might subsequently wear the pads faster.
Drillings are supposed to permit air in/out to aid cooling and also reduce weight, if the holes are cast into the disc then great but if they are added AFTER the disc is cast then there is a chance that cracks can form round the holes after heavy use.

In my humble opinion, You cant fault a good quality set of standard discs for what ever application you are using them in. Eg bigger versions, same size but hard use with scary pads etc. Its my belief that discs should be the consumable in the braking system when you get to a certain point of brake performance, as an example I use the carbon metallic pads that EAT discs so there is no point spending loads on spangly ones, so I simply use Mintex standard discs that are about £25 a corner (288*25 discs).

Its advised that you use a heat treated disc for heavy use, mainly to prevent early wear, but then you start eating heavily into your wonderful pads, swings and round abouts.

There is talk about standard discs not taking heat well and then warping.
I've used GM discs and also Mintex discs as effectively standard items with organic pads and also metallic pads..... neither set of discs warped with either of the two types of pad, and I have had them very very hot. Ive also seen 256*25 discs take a royal beating and they don't warp.
Warping is one of two things,
You get lots and lots of heat into the disc, then stop the car on its nose and keep the pedal pressed (lets pretend you've done a stint of roundabouts and then have to stop at traffic lights). This will keep a spot of localised heat on the disc while the rest of it cools down, its likely that the disc will warp because of that uneven cooling.

The second warped feeling is an uneven pad transfer layer on the disc.
When you bed brakes in what you are doing is putting a layer of brake pad on the disc, if the pad material doesn't transfer evenly for whatever reason then when you brake there is vibration caused through the system. Its only a tiny difference in heights but it is noticeable through the wheels.


A particular "power" level doesn't define how big/what spec your brakes need to be, as you could have a piddly 1.0 8V engine and be such a driver on track that you need some lairy spec brakes to maintain your driving or have 10000Bhp and not be much cop so the brakes seem more than capable as std... OK they are very very extreme examples but the point stands that you don't NEED to fit the biggest discs/calipers etc to make the car stop well and repeatably depending on power output.

Hopefully that's given you a reasonable understanding of how brakes work/what to change to make things better.
Yes there are a few default setups to change to as a start/guide. Like nearly all novas will benefit from changing to 256*25 Astra discs and calipers with something like Mintex 1144 pads as a very very good base (with new shiny fluid of course).

Piston and M/C sizing to come

wow I wrote this in 2009, and yet its still not considered other than folks just slapping 4 pots on lol

4pots is da waay bruv.

Quote:

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Originally Posted by Stuart

You get lots and lots of heat into the disc, then stop the car on its nose and keep the pedal pressed (lets pretend you've done a stint of roundabouts and then have to stop at traffic lights). This will keep a spot of localised heat on the disc while the rest of it cools down, its likely that the disc will warp because of that uneven cooling.

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This annoys the hell out of me when people stamp on the brakes to a complete stop. Not that anyone I know specifically does it though wife

Stu, would you recommend bedding in new pads/discs? The TRD ones I bought for the GT4 a few years back had very specific procedure to follow, but I've never seen any others have much more than 'don't lock up when they're new' lol

The Mintex procedure is nice unless you get instructions with the pads (my pfb97's had a specific procedure which boiled my fluid lol )
the general gist is a few 30-5 slows (note no stops) then 50-5 a couple of times and then a couple of 70-5's
and finally some 30-5 to cool down a bit, making effort to not actually stop persay. That should be enough to get you going

Back in the olden days, bedding in brakes was simply take it steady for the 1st hundred miles, and after that, just drive normally..... I got that info from a technical rep from ferodo. It's always worked for me...also never put new discs or drums in with used pads/shoes, as they will eat the metal quite quickly and wear grooves in the friction material will seriously cut down your contact area until it's all worn down...

If you look ahead enough, you can go for 100miles on a motorway without braking..... so that advise was a load of shit, but then what would we know hey

100 miles cruising your local town Stuart would suffice I'm sure lol

Stu. I've also driven zero mileage cars that has really good brakes. I was once a hire car runner....

I fucking give up.... mintex issue a lovely document to go with their non pads to bed then in. Pfb have bedding in procedures, again for non OEM carbon metallic pads. I'm sure they wouldn't piss about for the sake of it

Quote:

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Originally Posted by Stuart

the general gist is a few 30-5 slows (note no stops) then 50-5 a couple of times and then a couple of 70-5's
and finally some 30-5 to cool down a bit, making effort to not actually stop persay.

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Thats pretty much the TRD procedure. Luckily there was a private straight road coming out of Westlands I could use lol

Hey Stuart, that was a good read.

One thing confuses me though - in the first post you talk about how organic or ceramic compounds will shield your caliper from the worst of the heat, but then you go on to say that you still use carbon metallic pads.

I assume there's a reason for this?

personal preference, but metallic pads can take a truck load more abuse, particularly if you have small pads, but still work for bigger ones. Sure this means you need to pay attention to the caliper/fluid but there will always be somewhere that needs cooling etc.