Original Cooper S disc brakes VS new grooved discs

[Benny]

You may loose surface area, but you gain friction with the multiple edges.

No, it's all about swept contact area. Extrapolate this out to where instead of having just a couple of grooves, you had dozens and dozens criss-crossing the surface of the rotors. I think we can all agree that this would result in diminished braking, correct?

If your theory were true, the trend would be toward packing as many groves on there as possible, rather than just a few to clear the gasses.

[pad4]

An edge on a groove doesnt give any friction - there not there for that

pad

[Smiffy]

Why do you think they wear the pads out quicker.

[pad4]

because the groove edge takes of a millionth of a midgys dick every time it passes the pad - as the pads overheat the surface glazes up (becomes shiny and slippy) giving reduced friction - the groove helps to wipe off this glaze hence reducing the life of the pad - you see much more brake dust coming off grooved discs than std discs.

imagine this

std disc rotating

as the pad heats up it starts to glaze, every rotation
glazes the pad more and more - now your getting brake fade

Grooved disc rotating - a 2 groove disc

starting from first groove the pad starts to glaze when it gets to the second groove the pad surface is cleaned - frsh grip on the second half of the disc , process repeats its self over and over so youre kind of getting a fresh pad surface every 180 degrees of rotation

its not the groove that increases friction its the fact that the grove cleans the pad and gives fresh grip again

2 grooves per side of disc work fine on a fast road car , totally fine on a mini

pad

[Smiffy]

LOL and how does it clean the pad

[pad4]

Seriously ... I guess then everyone is wrong, a disc with 500 grooves in will offer better braking especially when used with halfords brand super fast sports pads

So would you care then to explain what the grooves are for so we can all learn.

ive just emailed the tech department at AP racing and complained about the false info on their website




Keith Calvers talking s**t as well



Obviously they also havent a clue either, next thing we will all be using metro vented discs on road cars

So - care to enlighten me and race technicians all over the world to this new and fascinating information

pad

[In the shed]

Right. There are some physics and mechanics misconceptions above!!!

You put your foot on the brakes. The fluid exerts a force on the backs of the pads via the pistons. The effective pressure is force/area. The name of the game is getting as much force on the biggest area. If you can't do that, you can try and move the force outwards so that it has a greater effective force (bigger discs)....like using a longer breaker bar.

So, you are stuck with a set of pistons, pads and discs. How can you alter them to improve things?

1. What is green fade? You get newish pads and rape them, the resin turns to gas at high temperatures and creates it's own pressure between the disc and the pad which reduces friction. How can you reduce this? Drilled/Grooved discs.

2. What happens when brakes glaze. You try and do too much with your brake pads and you heat the hell out of them and they glaze up. This is like polishing them. You reduce the imperfections which facilitate friction. You lower the potential friction of the system. How do you reduce this? Fit pads which don't readily glaze up (Carbon Metallic) or you get something which de-glazes the pads (takes 1/2 a gnats fanny off every 500 revolutions). Glaze is probably harder than the underlying pad and when you get a groove go over it, it flexes casing the glaze to break up on a micro level.....this is then shed by the disc grooves, rather than being forced into the surface of the pad.

3. The name of the game isn't keeping the disc cool....these don't matter much, it is providing a heat sink....a colder area for the heat to flow away from the pads and fluid. So, you cool the disc, fit alloy wheels, vent things, etc.

The problem is that pads which don't glaze up have a lower coefficient of friction at a lower temperature, so you have to get them hot to work. This is no good on a road car.

Personally, I found green stuff with standard discs fine. I used to drive like a total retard in the mini as well. I think you have to get them really really really hot and then they're fine. When I say hot, I mean smoking hot and paint coming off wheels hot.

[Smiffy]

Seriously ... I guess then everyone is wrong, a disc with 500 grooves in will offer better braking especially when used with halfords brand super fast sports pads

So would you care then to explain what the grooves are for so we can all learn.

ive just emailed the tech department at AP racing and complained about the false info on their website
Keith Calvers talking s**t as well

Obviously they also havent a clue either, next thing we will all be using metro vented discs on road cars

So - care to enlighten me and race technicians all over the world to this new and fascinating information

pad

It's a fooking fashion accessory, I've used them and if you want to cool the brakes you need vented disc's.

[Frogeye61]

Right. There are some physics and mechanics misconceptions above!!!

You put your foot on the brakes. The fluid exerts a force on the backs of the pads via the pistons. The effective pressure is force/area. The name of the game is getting as much force on the biggest area.

I don't usually get involved in these types of discussions because someone always gets a hard on and tries to tell me how wrong I am, but I really must say that from my first semester of college the general rule of friction is:

"The force of friction is independent of the apparent area of contact between the two surfaces."
See; Laws of dry friction; http://en.wikipedia.org/wiki/Friction

True enough that the force is the pressure times the area, but that is true for the normal force of the pad onto the disk due to the pressure of the fluid. When it comes to the pad onto the disk, the normal force is already defined. It's proportional to the foot force on the pedal. The specific force (force per square area) has only the coefficient of friction to provide braking force. Not the area.

This is though a generalization and non-linear systems will not follow this precisely. Without actually testing the systems myself, I would strongly suspect that brake pads on steel are a non-linear system. However, the minimal reduction of surface area that groves will do, say around 5 to maximum 10 percent, I would also suspect no noticeable change in braking force/normal force ratio. I would also suspect that any cutting, scraping, abrading of the pad surface requires energy. That energy comes directly from the rotating motion of the disk and therefore helps increase the braking ability (again marginally).

What would be much more desirable though is actually keeping the brake pad within the designed operating temperature range. Again, without actually measuring it myself, I would suspect; Racing pads for the track, performance pads for performance street driving will probably do just fine.

[In the shed]

I didn't elaborate my first point enough. I meant to digress into how that pressure interacts with the physical attributes of the materials to give a resistance to movement. Whether it's actually an interaction between physical irregularities in the surface, or whether there are chemical bonding forces involved....(which I doubt).

What the physics lot have done is looked at the relationship between pressure and friction and attempted to use really serious maths to explain the non-linearity of it. Like good mathematicians, they have got beyond the layman after about the 4th line.

It comes down to how properties (particularly surface finish) vary with temp. Unlike the physics super maths explanations, the science of brakes is largely determined empirically. They then attempt to rationalise their discoveries.

[Frogeye61]

Ahh, yes area. is one of the big points.

Bigger brake pads DO brake better. This is due to the fact that they are - bigger. They contain more mass. They take more energy to heat them up. They take longer time before they go out of the usable temperature range. Same is true for disks. Bigger is better. Air cooled (vented) is better.

But it doesn't have much to do with the actual surface contact area - UNTIL we start looking at the wear characteristics. Bigger area -> less unit pressure(1) -> less heat generated.

(1)(pounds force per square inch [psi], or newtons per square meter [Pa], your choice)

But the original question, vented or non vented, go for vented every time, go for larger every time, go for brake pads that MATCH the driving style. If it's a street car used on the track on weekends, change to racing pads for the weekend.

Sorry, I don't want to step on anyone's toes. I myself have been a "layman" for many years and I enjoy combining that with the theoretical approach. (Yes, the theory was developed from empirical results)

[Vegard]

I'm not sure if I agree. Why would you use vented discs on a street Mini?
It's just more unsprung weight for no benefit...

[AustinSuperSeven]

Wow its getting deep
Personally i would keep the setup you have and upgrade your brake fluid first.... then try them...
If then no good... change the pads.... if still no good..... check what the works minis used 'back in the day' and try that setup... worked for them

[graham in aus]

Works Mini's had pads that still used asbestos, do you really want to find some!

[AustinSuperSeven]

Works Mini's had pads that still used asbestos, do you really want to find some!

Good point!!!!

[Frogeye61]

I'm sorry, I really must stick my nose in where it doesn't belong... again.

I'm referring to brake fade due to exessive heat!!!! As I was braking like mad going down that hill.
Fluid is fine. Was replaced 6 months ago when I replaced the soft lines.

I must take him at his word and say it's getting too hot.
I would think the problem is not fluid related - reasonably new, no pedal drop.
Fade means too hot. Too hot means keep it cooler, or use pads within the temperature range.

I'm not sure if I agree. Why would you use vented discs on a street Mini?
It's just more unsprung weight for no benefit...

I shall imply that keeping the brakes cool is actually a benefit, more unsprung weight or not. Alternatively using pads that are effective in the Very High temperature range. These Mini Spares carbon-metallic pads sound very good. Just be sure they are good enough for lower speeds / less agressive driving.

[Smiffy]

Bet theres not much difference, between alloy 4 pots and vented disc's turned down to 7.5" and the standard set up.

[Lord Croker]

Works Mini's had pads that still used asbestos, do you really want to find some!

I think the works used pads that were known as DS11's, we used them on our rally 'S' & they worked perfectly well when the discs were glowing a nice bright red! Most standard modern pads do not give that kind of performance, the carbon metallic are the way to go, (unless you can find some NOS DS11's). Grooved discs have the advantage of dissipating gas build up, but I would try different pads first.

[minimans]

discs.jpg

There's always the Rolls-Royce solution?

[Vegard]

Ahh, yes area. is one of the big points.

Bigger brake pads DO brake better. This is due to the fact that they are - bigger. They contain more mass. They take more energy to heat them up. They take longer time before they go out of the usable temperature range. Same is true for disks. Bigger is better. Air cooled (vented) is better.

But it doesn't have much to do with the actual surface contact area - UNTIL we start looking at the wear characteristics. Bigger area -> less unit pressure(1) -> less heat generated.

(1)(pounds force per square inch [psi], or newtons per square meter [Pa], your choice)

Also, you say that bigger is better. But, even if you fit the same caliper and the same brake pad to a larger disc, you get better brakes. I'd think that leverage is the key factor here. Newton anyone