Guest Usmann A Posted May 21, 2003 Share Posted May 21, 2003 Interesting....... Quote Link to comment Share on other sites More sharing options...
400BHP Posted May 21, 2003 Share Posted May 21, 2003 In my humble opinion and 3 years of college doing my city and guilds, cross drilled discs are the best IF they are good quality, the surface area will be the same as a normal disc near enough but what your looking towards is the loss of heat overall, the cooler your brakes the better they perform. Good quality steel with a good carbon content will not crack around the holes prematurely, all discs will eventually wear out and thats whats likely to happen before any cracking. Just look at established racing car mfrs, they use cross drilled discs, and if the weight is an issue, take a look at an SL500 mercedes discs.... Quote Link to comment Share on other sites More sharing options...
400BHP Posted May 21, 2003 Share Posted May 21, 2003 Originally posted by AJI . Also the hotter the disc becomes the more effective the braking also. Hmmmm... Perhaps if your brakes are made from Carbon and you have Kevlar pads and your name is Rubens, heat is definately not a good thing on a road car. Quote Link to comment Share on other sites More sharing options...
Gordon F Posted May 21, 2003 Share Posted May 21, 2003 Surely the friction area of a brake is the surface of the pad, not the disc. As the disc is rotating under braking, the drillings are moving across the pad surface all the time, so the loss of friction area is not really an issue. Discs are drilled or slotted to help dissipate heat. Drilled dissipate heat better, and are (normally) lighter, but can be prone to cracking. Slotted ones are not so good at dissipating heat, are (normally) heavier, but are usually more hard wearing Quote Link to comment Share on other sites More sharing options...
GavinL Posted May 21, 2003 Share Posted May 21, 2003 How about this gents http://mkiv.com/tmp/pulp_friction/ Quote Link to comment Share on other sites More sharing options...
Guest Usmann A Posted May 21, 2003 Share Posted May 21, 2003 great read Gavin...... ... Quote Link to comment Share on other sites More sharing options...
AJI Posted May 21, 2003 Share Posted May 21, 2003 I think everyone is trying to shoot me down on this one. Best just to read that article and find out in black and white! I'm not wrong!!!!!!!!!!!!!!!!!!!!!!!! :flame Dev Quote Link to comment Share on other sites More sharing options...
Need4Speed Posted May 21, 2003 Share Posted May 21, 2003 There's some fascinating ideas going on here. The main reason for slotting discs is to prevent the pads depositing material on the disc and therfore reducing the effectiveness of the brakes. The only way a car slows is by converting kinetic energy into heat (and a little to sound). A brake will operate most effctively at the designed operating temperature. This will be low in a family saloon and very high in a carbon/carbon systen such as found in F1. The Supra discs are ventilated internally (note a LH disc is different form a RH disc because it rotates in the opposite direction) and the best way to cool this type of disc is to duct cold air into the ventilated area from the centre. This enables both surfaces of the disc to cool evenly and avoids warping. The rotation of the standard discs draws air through anyway, but a big duct picking up air from the front of the car will help. If you are only doing ordinary track days, good pads and standard discs will be OK. If you are trying to get an extra tenth off your lap times at Goodwood, you may need a little more. If all you want is to look the mutt's nutts, then big, drilled, slotted discs with soft pads are the way to go. If all you do is road driving, the standard UK brakes will never let you down (Toyota spend £millions designing this stuff). What ever you do, don't fit carbon/carbon on a road car. I heard somebody turned up for a track day at Brands with F3 brakes on a Mitsubishi EVO and cooked them, leaving the car with nothing more than a handbrake at the end of the straight - good thing there's a big gravel trap. Quote Link to comment Share on other sites More sharing options...
Syed Shah Posted May 22, 2003 Share Posted May 22, 2003 For two identical discs, providing adequate traction (no ABS needed), a smooth disc will stop you faster (marginally), but only once or twice, due to a larger surface area. The only need to drill disks is if doing repeated high-speed stops (trackdays only really), to dissapate heat and gases. For racing, where longevity does not matter, they are a better option. The trade off: Smooth discs: better braking (without heavy repeats) and long-life. Best for road cars, that do little serious braking and are not serviced regularly. Drilled: better braking when doing many high speed stops. (technically not as good for a one-off stop though). But, shorter livespan, so not for the average car, only something doing few miles, on tracks etc. If you do track days and don't mind replacing disks often, drilled are better for you. If not (99% of road cars), keep with smooth discs. Toyota chose them for a good reason, they are perfect for the average driver, with enough capacity for some fast driving as well. Quote Link to comment Share on other sites More sharing options...
Steve Cargill Posted May 22, 2003 Share Posted May 22, 2003 Optimin braking is obtained within a temperature range, if the disks and pads are too cold they won't bite and when they get too hot - see pages and pages above Coincidently I was reading some car reviews the other day and a Vauxhall Zafiea 1.6 does 70-0 in 45 metres, a new Impreza does it in 48m - my wifes bus stops from 70MPH 10 feet shorter than an Impreza Turbo..... Quote Link to comment Share on other sites More sharing options...
Nathan Posted May 22, 2003 Share Posted May 22, 2003 Again, the recent posts are waaaayy off track. We all know that brakes have a limited operating temperature. We all know that slotted are best for longevity. We all know that the best cross-drilled discs have the holes cast in them (like Brembo). The crunch was when AJI posted this: 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, why do we cross-drill discs? In fact, why do we even bother using ventilated ones? If friction is finite, and is entirely reliant on heat, why do we want to take the heat away.....? The answer is dissipation. Yes, we all want friction, but we also want to get rid of the by-product: heat. Holes and vents do that, allowing the friction to remain the same rather than mounting up and cooking the brakes. So, by reducing the generated heat you are certainly NOT reducing the friction, as was stated. Wow. Summed up in one paragraph. Regards, Nathan TDI PLC Quote Link to comment Share on other sites More sharing options...
Ian C Posted May 22, 2003 Share Posted May 22, 2003 Well, the article says it's the interface between tyre and road that stops the car, no suprises there. And the brake disc acts as a frictional interface and has to absorb & dissipate the heat generated by braking. Same as what we've been saying all along. Assuming the OEM engineers have done their job properly, every brake setup can produce enough clamping force to lock the wheels up. That means you can put on discs as big as you like, but they aren't going to stop you any faster, because the wheels will still lock up first. You can have smooth discs the same size as drilled ones, but they aren't going to stop you any faster, because the wheels will still lock up first. They just mean you can stop hard more times in a row because the generated heat is dissipated faster. -Ian Quote Link to comment Share on other sites More sharing options...
Need4Speed Posted May 22, 2003 Share Posted May 22, 2003 every brake setup can produce enough clamping force to lock the wheels up Ian - you're obviously not old enough to remeber drum brakes at the front:D Quote Link to comment Share on other sites More sharing options...
Need4Speed Posted May 22, 2003 Share Posted May 22, 2003 On the question of road/tryres/brakes/heat - yes the tyres stop the car but the brakes stop the tyres. Now will sombody post a full resolution of the component forces in operation here:) Quote Link to comment Share on other sites More sharing options...
AJI Posted May 22, 2003 Share Posted May 22, 2003 Originally posted by Nathan So, why do we cross-drill discs? In fact, why do we even bother using ventilated ones? If friction is finite, and is entirely reliant on heat, why do we want to take the heat away.....? TDI PLC I think you're getting confused between heat produced by braking and redundant heat caused by braking. I am talking about the actual heat produced by braking, the more heat that is produced inevitably means you are converting more kinetic energy which means you are stopping the car faster. Once this heat has been produced then yes it is a good idea to get rid of it by either air venting or disc vents etc. BUT the hotter the brakes become means that you are stopping faster deosn't it, or else where is the kinteic energy going? Syed Shah worte a good post and I think he is on the same wave length as me. I'm looking at it from a physics point of view, same method as in that article. Cross drilled and grooved discs are purely for show and won't stop your car and faster! Quote Link to comment Share on other sites More sharing options...
Gareth Davies Posted May 22, 2003 Share Posted May 22, 2003 Great thread guys, thanks. But it really does look like you actually all agree with one another and are just arguing the symantics! It's all redundant anyway you all want some nice ceramic brake systems so you don't have to worry about heat / warping etc at all. Not so cheap the last time I looked though. Arghh, I just noticed I wondered into technical... sorry i'll show myself out Quote Link to comment Share on other sites More sharing options...
Adam W Posted May 22, 2003 Share Posted May 22, 2003 Aji - I think you have cause and effect the wrong way round. The harder you brake, the more heat energy is generated. But this heat energy can easily build up to the point where pads melt and discs warp. Excess heat is no good for brakes. This is whay poepl upgrade pads and fluid - because performance items will continue to function at higher temperatures than the stock ones. So the quicker you dissipate that heat the better, either by having a larger disc surface area for it to radiate from, by ducting cold air to it, or the internal vaning of the discs that comes as standard on the supra. The faster you cool the brakes, the more often you will be able to use them hard. The heat is an unavoidable side effect of the braking effect, it is in no way desirable. Quote Link to comment Share on other sites More sharing options...
Nathan Posted May 22, 2003 Share Posted May 22, 2003 Originally posted by AJI I think you're getting confused between heat produced by braking and redundant heat caused by braking. With all due respect I am most certainly not getting confused and in light of that being the second comment you have made about me not understanding I will again post what you wrote: If you are reducing the heat by some method then you are inevitable reducing the braking friction, which is resulting in less effective brakes. The quote above, without the controls you only now mention in your most recent posts such as 'redundant' heat, etc, can be interpretated in many ways and I would wager the most common being that people would assume that removing heat from the brake is pointless, which we all know is wrong. Like Gareth says I think that we all know how it works AJI but, and I mean this in the nicest way, I personally think your explanations can be confusing. Cross drilled and grooved discs are purely for show and won't stop your car and faster! Again, without you adding 'unless the brakes are overheating' to your quote above it is indeed, wrong. Regards, Nathan TDI PLC Quote Link to comment Share on other sites More sharing options...
Terminator Posted May 22, 2003 Share Posted May 22, 2003 It all comes down to "energy can not be created or destroyed, it is merely converted from one form or another" The energy put into the car causes motion to retard that motion you need to dissipate that energy to get the car to slow down, to do that quickly you need brakes. Friction at the interface of pads and brakes generates heat and the dissipated heat is energy. If some form of assistance is provided to enable the brakes to dissipate that heat more quickly the brakes will be able to dissipate more energy and will be more efficient. So cooling and size matter Quote Link to comment Share on other sites More sharing options...
Ian C Posted May 22, 2003 Share Posted May 22, 2003 M'lud, in the case of AJI vs Basic Laws Of Physics, I honorably step down from Physics' defense as my head hurts from I shall watch from the bench as the plaintiff attempts to I think you're getting confused between heat produced by braking and redundant heat caused by braking. Backtrack confusingly. -Ian Quote Link to comment Share on other sites More sharing options...
Nathan Posted May 22, 2003 Share Posted May 22, 2003 In light of Ians post giving me something to laugh about (gotta be some good to come out of this thread I think I will also join him on the bench. Thankyou, and goodnight. Anyone fancy a pint? Cheers, Nathan TDI PLC Quote Link to comment Share on other sites More sharing options...
Ian C Posted May 22, 2003 Share Posted May 22, 2003 Did you know that pints taste better the warmer they get...? Mine's a bottle of Bud -Ian Quote Link to comment Share on other sites More sharing options...
Jez sutherland Posted May 22, 2003 Share Posted May 22, 2003 This is one of the most entertaining threads I've seen in a little while. I'm no technical genius by any standards - but this issue actually seems really obvious to me! I'm not going to kick this off again with any controversial comments - but I think there are some excellent explanations of the physics (and practicalities) of braking here. Even if some are a little 'comfused' Thanks guys - you've livened up a boring day - I'm just off to warm my brakes up with a blow torch now - this is a good thing to do isn't it:D Jeremy Quote Link to comment Share on other sites More sharing options...
AJI Posted May 22, 2003 Share Posted May 22, 2003 Why is everyone trying to complicate everything!! I give up. Best just read that article it explains everything. Quote Link to comment Share on other sites More sharing options...
Guest Usmann A Posted May 22, 2003 Share Posted May 22, 2003 great input guys........now all bow to the THREAD MASTER.... :flame Dev Nice one...... Quote Link to comment Share on other sites More sharing options...
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