Cross drilled or Corss Grooved?

As to my knowledge, most perfromance cars like porsches and ferrari's have drilled dics. I thought this was for heat dissipitation(spelling), but was also told that it can't be used on heavy cars, as by drilling the disc you are decreacing the surface area??

The supra is a heavy car, so wouldn't just having the discs cross grooved be better...instead of drilled?

As he grooves can also help the realese of heat...and also provide good frictional values??

Some veiws pls...........thanks!

i was told when considering my brake upgrade NOT to buy drilled discs as they weren't as strong. grooved was supposedly better.

having had drilled/slotted DBAs on a previous (far lighter and less powerful) car, they seemed fine but i bowed to greater experience when it came to the supra. i haev heard this from more than one source too.

It's the same old choice:

Longevity or performance?

The Brembo 356mm kit for the Supra is by far the best front brake solution I have yet come accross. Yes, the discs do crack around the drillings after some time, but by Toutatis do they stop. And then some.

In contrast, I have had experience of various AP kits which use grooves only and have come accross numerous complaints of warpage. Discs getting too hot maybe?

At least the choice is there.

Regards,

Nathan

TDI PLC

ummm...cheers for your views fellas, I also did hear that AP racing have gone bust..or taken over by Brembo??

Various peoepl have said that AP's warp easier than the Brembo's.....personally brembo all the way...

Here’s how I understand it. When the rotors are cross-drilled you increase the surface area of the disc available for cooling (as opposed to the brake pad contact surface area) so cross drilling can help brake rotor cooling but is unlikely to have a huge effect unless some kind of forced air cooling is in place. Cross drilling reduces the mass of the rotor, reducing its overall heat capacity and also mechanically weakens the rotor, cross-drilled rotors are more likely to warp or crack than solid ones. Slotted rotors don’t suffer so much from mechanical weakening but the slots don’t increase the surface area available for cooling by much either. Cooling is not the only reason for fitting cross-drilled or slotted rotors though, when the pads get hot, their organic components tend to boil and produce gasses that build up between the pad and the rotor, this is what causes brake fading. The holes or the slots are there to help dissipate this gas and so reduce brake fade when the brakes do get hot. Personally if I had to choose between the two, I would go with slots.

I always thought it depended on how the disc was made. The cheapo's cast the disc and then drill out the holes, whereas Porcshe, eg Movit, actually cast the disc's with the holes in them thus making them stronger.......

Could be wrong though, but thats what I thought anyway, and they seem ok on porkers

ScoobyJawa has a point here - I remember from my design days back in school (a fair while ago!) that having holes in things (e.g. Brakes) didn't necessarily weaken them.

Metal, like wood (and plastic!) has a 'grain', which is defined by how it is cast and shaped. Machining cuts though the grain of the metal, weakening it. Forging reshapes the grain, and is thus stronger.

I'm sure the engineers on here will tell me that technically I'm talking bollox - but they will know what I mean. Mechanical stresses can flow 'around' a forged hole but will focus on a 'machined' one.

Or - am I talking bollox? Anyone?

Jeremy

I think you’ve got a good point; you’d have to be sure about the manufacturing process.

The overall heat capacity of the rotor is still reduced; don’t know how good the airflow is around the rotors on a stock Supra and if it’d be enough to allow cross-drilled rotors to yield very much better cooling?

I guess my question is, would you have to go about ducting more air to the brakes if you wanted to use cross-drilled discs. If so, are the gains (if any) over a slotted rotor worth the extra effort?

Aiding the brakes with better airflow, should help a bit.

Although "maufacturing process would help decide....but we dont know the exact info, and so cannot make judgement on that aspect.

But, my question is, that by decreacing the number of holes, to say 10 evenly spaced out positions, would that the balance effects between cooling and surface area?

Would it be worth it, as I would image for some proper brake ducting to cost quite a bit, as custom made???

Dude what are the brakes for?, Track? or Road? I fitted the Uk brakes to my Jap car and there isnt a car that has outbraked me yet, and the disc's are solid with the vents in the middle, But if your after track stuff then yeah Brembo Cross drilled are v good, i use AP on my bike and always get the back end in the air?????? and dont have any warping problems!

I'm sure that there are differences in the quality of discs but after seeing the damage that happened on an old collegues car when one of his drilled discs cracked there's no way I'd use them. Fine on a light car like a caterham or elise etc. (or bike), but not for the Supra IMO. grooved/slotted discs should be better than normal solid discs but you will eat pads much faster. Get some race pads and just standard UK spec discs IMO.

Cheers Thorin........cheers for that bit of info......im deffo gonna go towards some grooved discs........

The stock Toyota discs are superb.

Only move to grooved and/or slotted for looks IMO

Different disc and pad combinations will require different methods of heat and pad dust dissapation.

Grooved discs will be grooved if the pads in use require large amounts of dust to be discharged. Drilled discs are usually if the pads create gasses under heavy braking.

BUT any disc that has either grooved or drilled holes will reduce surface area for braking and will not be as effective as a smooth disc.

The Supra has pads designed to work with smooth discs and provide best performance with these discs.

Porches for example have both grooved and drilled dics but this because they have pads that both leave a lot of dust and create gasses that would otherwise be trapped between pad and disc.

Drilled discs (I have been told) are more likely to warp with heavy amounts of braking.

Hope all this is relevant to this thread.

Right,

some points need to be cleared up here:

BUT any disc that has either grooved or drilled holes will reduce surface area for braking and will not be as effective as a smooth disc

No, it doesn't work like that. Yes, holes or grooves will reduce surface area but that does not mean they will be less effective. It all depends how much heat is being generated.

i use AP on my bike and always get the back end in the air?????? and dont have any warping problems!

It's not really a good example. A bike weighs significantly less than a Supra. Plus the discs are stuck directly in a 150mph+ airsteam. Plus bike brakes are massive relative to the weight of the bike. It's about as far removed from a Supra setup as you can get.

after seeing the damage that happened on an old collegues car when one of his drilled discs cracked there's no way I'd use them.

A sweeping statement! Someone better tell Brembo they are doing it all wrong....

I think theres confussion here that has come about from a deviation of the original question ie what is better, holes or grooves.

Now we seem to have examples being given that are miles apart from each other. I agree, cross-drilling a stock Supra disc will do nothing except look nicer (to some) and lead to premature wear and/or cracks.

That doesn't mean a 'proper' cross drilled disc such as a Brembo is an inferior product. Many of the replies being given here seem to be missing the point.

ScoobyJawa: good post.

Regards,

Nathan

TDI PLC

Am I missing something here? Surface area provides the friction and therefore increases the braking potential. Also the hotter the disc becomes the more effective the braking also. But not to let the heat build up so much that the metal becomes warped etc.

The reason a disc requires holes is to aid cooling and to get rid of gas build up between pad and disc. But this also means that the disc needs the holes to not allow the metal to be damaged by heat. It a trade off, but in the end the same disc would provide more friction if there were no holes in it, that was my point.

Originally posted by AJI

Also the hotter the disc becomes the more effective the braking also. But not to let the heat build up so much that the metal becomes warped etc.

If I am understanding the above correctly, you are saying that braking efficiency, up until the point of the metal warping, continually increases.....?!

Most pads will fail well before the disc becomes warped or damaged, let alone become more effective...

It a trade off, but in the end the same disc would provide more friction if there were no holes in it

Potentially more friction, yes, but only if it's not getting too hot...a non-drilled disc will give far less friction co-efficient if it's gassing the pads up...

Regards,

Nathan

TDI PLC

Originally posted by Nathan

If I am understanding the above correctly, you are saying that braking efficiency, up until the point of the metal warping, continually increases.....?!

Not quite, but you're nearly there..... the more heat produced goes hand in hand with the amount of friction being produced by braking. Therefore more friction = more braking. Braking is in effect friction used to decelerate the car.

As the disc increase in heat it must mean that there is more friction to cause the heat, hence more braking. But this can not continue indeffinately as the metal compound used on the disc will have a temperature limit where by it will start to deform permanently.

Pads won't fail due to high temps as these are usually made from carbon compuonds. Most pads also have a gap in the middle of them if they are specifically designed for smooth discs. This does the job of the drilled holes and grooves.

I'm not realy arguing with you because I think we are saying the same thing but from different angles.

AJI, i understand what you mean about the greater the frictional force the greater the heat, therefore more braking. If im right...I think you said that smooth discs work better than grooved ones, as grooved ones loose surface area.(correct me if im wrong)

But, sureley there has to be a balance struck between suface area and cool/gas realese....?

I think that by having grooved discs, although you would be decreacing the surface area, you would cause more friction for when the pad does make contact with the grooves, ie. poking a pen at a fan blade gently over regular intervals....surey this makes up for the small loss in surface area bby the groove.

Nathan, I also understand what you mean about the holes, but if the holes reduce surface area, thus reducing frictional values, meaning that thier is not enough heat being generated for the holes to play thier part in the cooling and for the brakes to work at thier optimum, if this is the case, what is the point of the holes?

Pls correct if im wrong...just a young man trying to make sense of it all........

Regards

Originally posted by AJI Not quite, but you're nearly there.....

Ah, I'm glad of that....was getting worried there...

Pads won't fail due to high temps as these are usually made from carbon compuonds.

Theres many pads that aren't as well, evident by the amount of ones that catch fire at track days...

Your original quote about non-drilled discs giving more friction would, to some people, assume that they would therefore get better braking than those without but that is not the case and depends entirely on whether the brake set in question is reaching damaging temps, which on the car in question (Mk4) is fairly common. Having drilled discs simply means that the goalposts are moved further up the temperature scale which when combined with a bigger disc (more surface area) creates a better brake.

Like you say, I think we both know where we're coming from but I prefer to be more specific with any info I give. Some of the quotes and sweeping statements on this thread must be a bit confusing to some.

Cheers,

Nathan

TDI PLC

Originally posted by AJI

Not quite, but you're nearly there..... the more heat produced goes hand in hand with the amount of friction being produced by braking. Therefore more friction = more braking. Braking is in effect friction used to decelerate the car.

 

As the disc increase in heat it must mean that there is more friction to cause the heat, hence more braking. But this can not continue indeffinately as the metal compound used on the disc will have a temperature limit where by it will start to deform permanently.

 

Pads won't fail due to high temps as these are usually made from carbon compuonds. Most pads also have a gap in the middle of them if they are specifically designed for smooth discs. This does the job of the drilled holes and grooves.

 

I'm not realy arguing with you because I think we are saying the same thing but from different angles.

Smaller discs heat up faster under the same braking force, as there is less surface area to dissipate the heat, but they sure aren't considered 'better' because they get hotter. More friction = more braking, yes, but heat is a *byproduct* of friction, the conversion of inertia energy to heat energy. The less heat generated by braking the better as then your brakes don't 'fade' - a layer of superheated gas from the pad material gets between the pads and the disc, reducing friction a lot, and the brake fluid doesn't boil.

What usually warps your discs is heating them up with hard braking, then parking up. The section under the pad cools down slower than the rest of the disc and the disc warps because of this uneven contraction. I have seen j-spec disks warp at a track day though, which means the discs have been heating beyond their tolerances while under braking.

The pads don't fail per se but they fade due to the buildup of superheated gas from the friction material. Better pads are more resistant to vapourising like this.

Some people think that bigger brakes mean they can stop in a shorter distance. If your brake setup can cause the ABS to cut in all the way to a dead stop, then uprating your calipers/pads/discs will not change the distance this happens in. What it will change though is a) the 'feel' of the brakes, and b) the repeatability. Bigger pads and discs = more heat dissipation (due to the frictional force being spread out over a wider surface area) = more resistant to fade, so repeated stops are possible without overheating the whole system. The slots collect and fling the buildup of gaseous material and brake dust off the disc surface. They are spirally cut so that there is a minimum of slot under the pad at any one time, thus keeping the maximum amount of frictional surface available. "Cross drilled" has the same effect in spades but the actual cross drilling can cause stress fractures at the drill sites. Cast holes are the way to go as they don't introduce stress points, but of course, they are more difficult to produce = more expensive.

You also get better fluid = higher boiling point. Braided brake hoses = less hose flex, therefore better brake pedal feel.

Anything bigger than UK spec brakes is pure willy-waving unless you do trackdays IMOO.

-Ian

PS Nathan, am I nearly there too?

Originally posted by Ian C

More friction = more braking, yes, but heat is a *byproduct* of friction, the conversion of inertia energy to heat energy. The less heat generated by braking the better as then your brakes don't 'fade'

I look at it this way ........ if your brakes are producing a lot of heat then they are providing a lot of braking friction. Heat in this case is a direct result of the braking, therefore more braking produces more heat.

If you are reducing the heat by some method then you are inevitable reducing the braking friction, which is resulting in less effective brakes.

So, from your quote, it's not realy better to have have less heat unless it is causing problems to the materials used in either pads or discs. Would you agree on this?

My original quote of smooth discs providing more friction for braking, I will still stand by that. The limitation of this as we have discussed is that as they inevitably produce more heat they are then prone to warping. But their ultimate potential for providing maximum braking is there because of the maximum surface area available. Grooved and drilled discs are a comprimise as I mentioned earlier (or somebody mentioned earlier). They reduce the ultimate braking potential for an increase in heat release from the disc material.

Finally I'm going to chance these quote tags in order to split up my response

I look at it this way ........ if your brakes are producing a lot of heat then they are providing a lot of braking friction. Heat in this case is a direct result of the braking, therefore more braking produces more heat.

It's more correct to say, if your brakes are providing a lot of friction then they are going to generate a lot of heat as well.

If you are reducing the heat by some method then you are inevitable reducing the braking friction, which is resulting in less effective brakes.

Nope. The friction effect generates heat. Then taking this generated heat away from the braking components by some mechanism, be it cold air ducting, vented/drilled/slotted rotors, whatever, is nothing to do with the actual amount of heat generated *by* the braking components. If the friction generates 100degC per second per square cm (an example, no idea what the real values are), it will generate that much heat no matter what you do with the heat afterwards.

So, from your quote, it's not realy better to have have less heat unless it is causing problems to the materials used in either pads or discs. Would you agree on this?

No, I wouldn't! My quote doesn't say anything like that?! The only time you need heat is with trick racing products that need a minimum temperature to be most effective. My quote says, less heat, the better!

My original quote of smooth discs providing more friction for braking, I will still stand by that. The limitation of this as we have discussed is that as they inevitably produce more heat they are then prone to warping. But their ultimate potential for providing maximum braking is there because of the maximum surface area available. Grooved and drilled discs are a comprimise as I mentioned earlier (or somebody mentioned earlier). They reduce the ultimate braking potential for an increase in heat release from the disc material.

Smooth discs will have a marginally larger frictional surface available, so it will provide more friction for braking at first. But they will then fade due to the brake pad material gassing up and forming a lubricating layer between the pad and the disc. They don't produce more heat (well, only from the marginal extra contact patch), they just can't disperse what is put into the system as well as slotted/drilled/vented discs can. Grooved and drilled discs are only a compromise if you get the cheap stuff that cracks. Done properly they are great, but all this is only for repeated hard stops anyway, i.e. trackday usage.

And as for the marginal increase in frictional surface area that smooth discs give you, you'll find that the tyres give up grip way before the pads on the disc do, so this marginal increase is rendered null and void anyway, you simply aren't going to stop any faster if both setups are capable of locking the wheels.activating the ABS. But, you will *not* stop as many times in rapid succssion because the heat will build up, as will the eroded pad material, and your brakes will fade before a slotted/drilled disc setup will.

-Ian

Total amount of heat generated will be the same (a car travelling at xxxmph has the same amount of kinetic energy, irrelevant of what brakes it has).

What you want to change is the temp change per unit area on the discs, and make that as small as possible. You can do this by removing the heat from the discs faster, by making the area of the discs bigger, or both.

Originally posted by AJI

If you are reducing the heat by some method then you are inevitable reducing the braking friction, which is resulting in less effective brakes.

OK, from another angle:

Are you then saying that cross-drilling a like for like disc will do nothing to improve braking whatsoever, because both will only generate X amount of friction (thus heat) before failing. In fact, in your opinion, cross-drilling a like for like disc will actually reduce the available braking power, due to less surface area? In addition, according to you, throwing in the gassing of pads doesn't bear any weight either because you say that heat is heat, and if a pad starts to gas on either a solid or a cross-drilled disc then the friction is still the same, and if it doesn't gas on the drilled disc then it by definition must be making less friction, thus meaning the drilled disc is LESS effective.

This example is good because it also takes into account all temperatures, right up to and including failing. Using your theory, the heat generation is always relative to the braking effort so doing anything to reduce heat is futile. This is what you are saying, yes?

Regards,

Nathan

TDI PLC