brakes... whats good and whats better?
Turbo Mini Forums

well, I have been delving into the world of braking the last couple of hours, and have an interesting observation....

Fisrt off this is ignoring things like pad mu, the effective radius of braking due to the distance from the centre to the inside and outside of the pad (from the clutch discussions) and just looking at the pressure given by the calliper for a given pedal pressure, ie total piston area...ie pressure exerted on the pad/disc interface.

and in order of total piston area...


ok first off the 997/998 cooper caliper used on 7" Discs, the piston diameter is 41.1mm for the 2 pistons this give a piston area of 2350mm.

next is the S caliper with pistons of 44mm, this gives a total piston area of 4250mm

next which suprised me is the KAD 6 pot calliper, with its pistons of 25,28 and 30mm diameter it gives a piston area of 3630mm

what next?

the metro 4 pot, 4 pistons of 35.9 giving an area of 4050mm

and finally top of the heap!!

the humble 8.4" 2 pot caliper with its 2" pistons giving an area of 4250mm.

Awsome. Good old two pots! I think ill stick with what ive got and get some better discs.

aye, thats why my 7.5s are so fecking rock soild!

i need a smaller m/c

This is something I've been meaning to sort out for ages.

The attached scribbles show that for a given pedal pressure, the bigger the slave cylinder total area, the larger the pressure exerted by a given pad on the disc.

But the larger the pad, the lower the pressure exerted on the disc.

Also the larger the slave cylinder total area, the longer the pedal travel.

What you want is bigger/more slave cylinders and smaller pads. But you need to keep the pads big to discipate the heat

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Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

is that right with the pads? its not somthiing i had considered, i have just focused on the idea of all the mechanical and hyraulic ratios. I guess so though, after all F=P*A

hmmm, food for thought.

what i was thinking of working towards was the "braking pressure" (which will now ave to take into account pad area) coupled to the efective ratio of the pad from the wheel centre, to give a bracking efectiveness number related to pedal pressure, kind of like engine size and bmep.

I allways thought as far as friction goes (which is ultimatly what we are after yes?) area is irrelivent.

Yes more area = less pressure but also more area = more area to 'make friction' so the 2 cancel out as such. I know when we did it at college area wasnt a factor, it was force, and a coefficient of friction relating the the meterials being used.

Edited by slater on 6th Mar, 2009.

We had a similar discussion about clutches a short while ago.



It all falls down if you accept that friction is dimensionless and that pressure and the coefficient are all that matters.

Edited by Paul S on 6th Mar, 2009.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

My head is hurting enough as it is trying to do some uni calculations, reading that other thread has made it 10 times worse!

I use the KAD 6-pots with modern Ferodos and vented discs when racing with HSR. I have 5.5" mag Minilites for rains and 6" Revolutions for drys. Other vintage organizations here require the stock Cooper S calipers and discs, which I run with the old Ferodo DS 11 pads. I run 3" vents from the turn signal locations in the bodywork to the calipers. In normal (?) racing I don't notice any difference in performance, but if you get in too deep, at the limit the Cooper S brakes will fade and the car will become agricultural. I can overcome the spec tire (Hoosier) grip with the KADs on a hot dry track. I did run a few SCCA races with slicks, I never had more brake than tire with slicks. So far the KADs give me more brake than I have bravery; damn nice brakes.

obviously big two pot calipers are the best ........
thats why all modern high performance and racing vehicles use them !?
who needs the brain ache with the maths ?

Thats good to no. Ive got kad 6pots and im hoping there great.

Rick

Hi there guys,

Im not too well up on brakes, but my 7.5 calipers and groved disks dont seem to be stoping me too well.
my m/c has a green band around it. do i need a smaller one?

Something I forgot. The KAD 6-pots are race brakes, they have no dust seals. Road filth will get to the pistons. So they probably are fine for a track-day car, probably not suitable for high-mileage street use.

I'm a 1 pot man well one on each side of the car.. stops well

I run a supercharger and I don't care the TB is on the wrong side.
VEMS + 12 PSI + Liquid Intercooler = Small Bore FUN!

Ive got S brakes with a 0.70" clyinder and it doesnt work too well. I think the Coopers had a 0.625" cylinder insted which would improve matters.

Im thinking of just swapping to alloy calipers tho! i assume they are the same as the metro 4 pots in piston area?

The only Mini to have a smaller MC diameter was the 997 Cooper.

Edited by Paul S on 10th Mar, 2009.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

I have a set of Cooper S on one car and a set of KAD 4 pots on the other both with the same compound pad the 4 pots where far superior but when I changed the Coopers setup to carbon metallic pads the braking effor on the cooper s is astounding dam near lifted the back of the car off the ground.

The math on piston area and pad swept area is interesting, but in road racing the performance becomes limited when you generate more heat than you can dissipate before the next corner. This is one of advantages of the the six pot, air gets in and heat gets out easier than a two pot. The next advantage is that the designers employed 3 different piston sizes in the caliper, the leading edge pistons are smallest, for even pad wear and it helps the pad temperatures to stay uniform across the pad. I suspect the alloy caliper dissipates heat better than the iron caliper, and I also suspect it holds more volume of fluid. Its a monoblock caliper, so it doesnt flex, and its lighter. It's blingish too. OK, that's all the good stuff I can think of, on the bad side its expensive. Meanwhile, the stock 2 pot Cooper S caliper is good even for racing, and very good if you castellate the pistons and duct air to the caliper.

With brakes , I think heat is the key , drum brakes will work just as well as discs until the heat build up causes fade , likewise with single and multi pot calipers .
Horses for courses as the saying goes
The more you need your brakes , the more heat you're going to generate , the more sophisticated / expensive the braking system will need to be
Maths gave me a head ache at school and it hasn't got better with age !

You also forget about the radius of the pads. Of you're using three small pistons, these can be spaced further from the centre than one big. Hence you can use a longer and shallower pad at a bigger radius. Same area, better leverage.

Edited by Vegard on 12th Mar, 2009.

the bean tin type is .70 there is an bean tin on the Mk1's that was .75 but not available anyone. the yellow tag is .70 to the rear and .75 to the front. The yellow tag uses different size unions as it was a dealer upgrade when the old units failed that were .70 front and back..

I run a supercharger and I don't care the TB is on the wrong side.
VEMS + 12 PSI + Liquid Intercooler = Small Bore FUN!

very true,

the pads in the kad 6 pots are connsiderably longer than other mini stuff and the same(ish) width, but the pistons appear to be pretty much on the centre line of the pad.

I have no doubt that 6 pots fuction more efficiently than 4 or 2 pots, but i cant see (yet) how they can make up for the apparent lack of power in the hydraulic section.

still much to look into here.

dont they run smaller pots to deal with it.. I have been in a Zcars mini that was running Tarox 6 pots on the front and the ford rear disc conversion he was using a bean can clutch cylinder modd's with a return spring and it stopped as well as it went. he did change from .625 split AP cylinders, he wanted to push more fluid, the clutch cylinder is a .75 single

Edited by gr4h4m on 10th Mar, 2009.

I run a supercharger and I don't care the TB is on the wrong side.
VEMS + 12 PSI + Liquid Intercooler = Small Bore FUN!