Harry Flatters Posted January 23, 2003 Share Posted January 23, 2003 Don't quote me but with the Racing 4 caliper and 280mm discs these should run behind KN Minators (a la Caterham) but not Superlights. *arrowright*Harry Flatters *arrowright* AKA Steve Mell of Su77on Se7ens Link to comment Share on other sites More sharing options...
fordy Posted January 23, 2003 Author Share Posted January 23, 2003 interesting I have 14" minators and 13" unknown minilite type. Anyone know how you tell your minilite from your minator from you superlite? Any others? Link to comment Share on other sites More sharing options...
Peter Carmichael Posted January 23, 2003 Share Posted January 23, 2003 ISTR (but I could be mistaken) that somebody watching my runs at the Llandow club sprint last year commented on the glow coming from my brakes. (apologies to the environmentalists for the smoke from the tyres). This was on braking from 116mph to ~20mph, equating to the dissipation of 1.5 million joules of kinetic energy. Cast iron has a specific heat capacity of 0.449J/g/K. I run vented disks all round (12.6 kilos of cast iron), which means my brake disks would have seen an average temp rise of 265 degrees C. Now there is a whole bunch else going on to do with air cooling and distribution of temperature but what it means is that the highest temperatures in my front brakes would be a whole lot higher than 265 degs C (plus ambient of 20 degs = 285). I don't think it is unreasonable to suppose that the surface hotspots could have been 100 degrees higher than this. 385 degC. If I had been attempting this with standard sierra disks (2.45kg) the average temp rise would have been 340 deg C and the guesstimate rise ~440 deg C. Even more for skimmed lighter disks. SG cast iron is generally good for 500 deg C in braking applications. Draw your own conclusions. It is probably not the best idea in the world to advise Arnie on braking until you have a comparative experience of brake failure. My AP calipers do not have dust seals. Link to comment Share on other sites More sharing options...
Harry Flatters Posted January 23, 2003 Share Posted January 23, 2003 Cheers Peter, I knew we could rely on you for some solid maths here. And I knew I was correct about the AP dust seals *arrowright*Harry Flatters *arrowright* AKA Steve Mell of Su77on Se7ens Link to comment Share on other sites More sharing options...
scooby dooby doo Posted January 23, 2003 Share Posted January 23, 2003 Eventually I'll goto Hi-spec with my car to check everything fits ok. But a volunteer with mnilites and other wheel types will be needed... HOOPY 500 kg R706KGU Link to comment Share on other sites More sharing options...
Harry Flatters Posted January 23, 2003 Share Posted January 23, 2003 Once I've got my front suspension on, anyone is welcome to bring their wheels round to try over my Hi-Spec brakes. *arrowright*Harry Flatters *arrowright* AKA Steve Mell of Su77on Se7ens Link to comment Share on other sites More sharing options...
I reply to every thread Posted January 23, 2003 Share Posted January 23, 2003 As I think Peter alludes to those who know Arnie will be aware that he has first hand experience of brake failure (& it's consequences). Something that I would not care to immitate. "AP = Brand snobbery & bar room punditry"? An interesting view. Yeah what do Caterham & AP know? Link to comment Share on other sites More sharing options...
kjp Posted January 23, 2003 Share Posted January 23, 2003 I am not so sure about the break temperature guesstimates. The entire energy disappation takes a few seconds maximum and is dominated by the surface convection/radiation from the disk, the heat transer into the body of the disk will be small during the stop and the bulk temperature rise of the disk will occur after the stop. I doubt that the temperature difference at the surface of the disk is more than a couple of degrees different between solids and vented disks during the first stop. I don't think anybody has suffered fade in a Caterham breaking from Vmax to zero during there first stop whatever breaks they have. Is the requirement for vented disks goverened by vehicle performance (power and losses). With a Caterham we generally have low power (by many standards) and high aero losses. At the end of any given straight we will not be going any faster that a GTI which is twice the mass. I have never seen a Caterham with 'cooked' brakes or even heard people complain about fade with proper pads. Don't the AP's seem a bit excessive?? Didn't all of the 'Paul Harvey' built Nurburgring 24hour cars have solid disks? Ken P KenP Link to comment Share on other sites More sharing options...
scooby dooby doo Posted January 23, 2003 Share Posted January 23, 2003 with vented disks and AP 4 pots running 1144 pads i've cooked them totally on a track. but i think RS14 pads and solid disks will cope much better and be lighter. I now have EBC red stuff - they work fine but don't have much feel. HOOPY 500 kg R706KGU Link to comment Share on other sites More sharing options...
Tony C Posted January 23, 2003 Share Posted January 23, 2003 Pardon the oar insertion Brakes slow your car by changing kinetic energy into heat energy from the friction between the spinning disks and the stationary pads. One has to ask. Where does the heat energy then go? It would be best to dissipate it into the atmosphere ASAP, ready for the next brake application. Vented disks have a greater surface area in contact with the atmosphere; QED My guess is that if the heat cannot be dissipated quick enough, the disks will get hotter and hotter with each brake application, to the point when the friction coefficient between the disk and the pad reduces significantly Oar out! Link to comment Share on other sites More sharing options...
scooby dooby doo Posted January 23, 2003 Share Posted January 23, 2003 so you use pads that are happy at a higher temperature. at the higher temperature heat can be lost to the atmosphere more readily. hence solid disks and RS14 pads. HOOPY 500 kg R706KGU Link to comment Share on other sites More sharing options...
Peter Carmichael Posted January 24, 2003 Share Posted January 24, 2003 Cast iron gives up at 500 deg C. Heat cracks. Blueing. No good any more. The crystalline structure breaks down. If only I had my phase diagram to hand. The pad material isn't the only issue here. The hotter the disk gets the hotter the caliper gets which means the fluid gets hotter as well. You are talking about ditching 2 kg of mass out of the brake disks. 2 kg less heat sink. I personally think that you are daft as a brush to contemplate compromising a primary safety related function for marginal benefits to mass, which quite frankly you will never notice. Ken, I think you are broadly right in your critique but perhaps misunderstood my emphasis. Yes, Caterhams are light on their brakes because they are lightweight (the losses aspect means that top speed is never that great). I took all of this into account in totting up a total of 1.5 million joules. The question now becomes: how do I absorb or dissipate 1.5 million joules of heat energy in 5 seconds? The bulk temperature isn't really my concern, but it was the easiest thing to calculate from readily available figures. But the balance is between (as you say) convection/radiation from the disk and conduction into the disk. If as you suggest, the bulk temperature takes some time to settle, then the surface temperature will be higher. Radiation and convection are functions largely dependent on surface area. The radiant area of a vented disk is hardly any bigger than a solid. The convection potential is much greater with a vented disk. The radiation is easy to calculate a best case scenario: 280mm disk with a 50mm deep friction surface. Lets presume that on application of the brakes the surface temperature is immediately raised to 500 degrees C. The surface area of the disk (both sides, presuming that 30 degrees are covered by the caliper is 0.037 m^2. The temp is 500+273 = 773 K. Ambient is 293K. The temperatures need to be raised to the fourth power and subtracted. This gives: 349670855040 K^4. Presuming the disk is a black body, the radiant power is given by: 349670855040*0.037 * 5.672*10^-8 = 728 Watts. Therefore in a five second braking zone, 3640 joules can be dissipated by radiation, leaving 1,496,000 joules to be stored or dissipated by convection. I will have a think about convection, but I reckon there is a reason brake disks are big and heavy. Look at heavier cars. They run big wheels so they can fit big brake disks. I would suggest that the appropriate person to right-size a brake disk for a Caterham is not hoopy on a mission to ditch 8 kilos from whereever he can find it. Wibble alert. (and yes I didn't get much sleep last night. ) Link to comment Share on other sites More sharing options...
EFA Posted January 24, 2003 Share Posted January 24, 2003 Ken, If your V-max over sa given distance cannot exceed a GTI's then you are perfectly correct in that you will likley never get brake fade. However, for those of us who use full throttle..... 😬 *tongue* My original jibe at Hoopy was to say that I cannot see the appreciable benefit in changing the front brakes when the differences are pretty slight at the end of the day. Undoubtably it is harder to get fade on cars reaching lesser velocities on given circuits, but fact remains, even the AP's will loose their edge after 20 minutes pounding on a circuit. Fluid choice has a big impact here, AP600 extending the envelope further. I recently did a "track day" at Brooklands on the new tarmac which had been converted to a pait of straight approx 300m long linked by two U turns. I noted then that the heat generated in repeadly accelerating from around 20mph to 100mph and then braking as late and hard as possible caused no problem whilst actually moving, but the lack of provision of any slow down lap meant my front brakes actually caught fire when the car stopped. They never faded though. Also it would be interesting to understand the difference in energy dissipation between slowing from 130mph to 100mph and 100mph and 70mph. This, I think you will find will show that the rest of your car (i.e. engine) has a fundimental effect on the requirments placed upon your brakes either considered or factual. Perhaps Mr Carmichael could assist here?? After my accident, which involved spinning backwades off Goodwood at the end of Lavant straight at approx 130mph, hitting the tyre wall and barrel rolloing 3 or 4 times , I think you might understand why I, and in particular my backside, consider more than adequate brakes to be fairly high on the agenda. Caterhams big brake kit is good value (I think it is still around £550 +VAT as it was in 1994 when I bought mine). The component prices alone for similar parts (CP3344) plus the discs equates to a very much higher price. The Caterham big brake kit has to represent excellent value anyway. *VES has jsut bought one! It would appear, reading AP's literature that the solid discs weigh only 1.5kgs less than the vented variety. This is for a 253mm sold vs a 262mm vented. How much that extra 9mm's weighs?? Finally regarding dust seals, are you boys not aware the AP has an integarted piston/dust seal? Arnie Webb The Fat Bloke back @ 512k Link to comment Share on other sites More sharing options...
DanB Posted January 24, 2003 Share Posted January 24, 2003 AVES, Somewhat surprisingly, you have totally misread my post. If you read it carefully, you'll note that I did not at any stage comment upon AP or Caterham's technical abilities or the quality of their products. It was a direct response to Harry Flatters post asking a much-loved member of the Caterham community what his assessment of the relative merits of different braking systems was based upon. Now, if an independent and technically impeccable source said 'APs are better than Wilwoods' and explained why, then I'd accept that pretty much at face value. Dino's 'if Caterham use them they must be great' argument and Arnie's wholly unreasoned response don't quite match that. Dan Link to comment Share on other sites More sharing options...
scooby dooby doo Posted January 24, 2003 Share Posted January 24, 2003 As Peter's calcs demonstrate - radiation is not the way the heat is dissipated. The majority of heat loss is going to be by mass flow aided conduction to the atmosphere IMO - conection current won't get established. There are several quick cars running solid disks (chelspeed for one) without problems, so it becomes a cost / benefit question. I'm not on a "Ditch the AP" mission, but I would like to save weight where possible. If this is combined by saving money as well then all the better. so a simple swap to solid disks (a tenth of the price of the vented items) and pads that can take a bit more heat would seem to be a good option. I am in the middle of conversations with both Fluke and Hi-Spec at the moment and will see what they have to say on the matter. HOOPY 500 kg R706KGU Link to comment Share on other sites More sharing options...
I reply to every thread Posted January 24, 2003 Share Posted January 24, 2003 Dan B Your suggestion was that FA based his selection criteria & recomendations on "brand snobbery, bar-room punditry and the undisputable fact that anything Arnie has on his car is better than anything else.... " That is not the case as I know from my discussions with him on this very topic. End of matter. Link to comment Share on other sites More sharing options...
fordy Posted January 24, 2003 Author Share Posted January 24, 2003 So, as I started the thread.........I am none the wiser on which setup has the best price performance ratio. All i'll be after is a brake upgrade that will improve my track day safety with a 1.4SS. I figure so far any of the 4 pot upgrades will be fine for my uses. I am not that interested in saving weight (actually I am guilty of buying the ali freestyle dampers because they weigh less, but I promise not to do that again guv unless I am on a full-on weight saving mission!) so VFM is a pretty large criteria. Given the significant experience of several people on the various types of 4 pot systems available, is there a general consensus on which system is the one to go for? One of the Willwood setups can be had for around £400 which seems to be pretty good VFM and I believe the Hispec ones are similarly priced. Looking at the number of applications Willwood have on their US website, I don't doubt that they know how to stop cars and I would assume a kit sold as a Caterham upgrade kit should do the job. The AP's obviously have the backing from Caterham and many happy customers as a reference plus the valued endorsements from the ever watchful PC and FA. The one side of me says be a sheep and stick to the tried and tested and pay more for the AP's. The VFM side of me err's on the less well known entities of Willwood and Hispec. Then of course the Alcons lie between these options. Or am I wasting my money because the standard brakes will be fine repeatedly hauling me down from 100mph at Cadwell for 2 full days in May? 😬 Link to comment Share on other sites More sharing options...
Peter Carmichael Posted January 24, 2003 Share Posted January 24, 2003 Hoopy, I think you are missing the point.The majority of heat loss is going to be by mass flow aided conduction to the atmosphere IMO No. The majority of heat is not going to be lost. It is going to be stored. (by the way, add the term "forced convection" to your dictionary - I think it is appropriate). The storage requires disc mass. We have heard about solid discs being used on formula ford and on some notable sevens, including the roadsports (certainly of a few years ago). I am happy with this proof of concept that solid discs in good condition are good enough. The bit I have a problem with is the intention to skim a kilo off a perfectly good disc. This will increase temperatures. The temperatures are already hot enough to crumble Mintex 1144 pads and Green Stuff at the back where the ventilation is poor. I think this is asking for disaster. Cast iron does not conduct heat that well, even though it has a high specific heat capacity. It suffers from a tendency to hotspots. Hotspots cause localised phase changes in the iron, leading to the formation of iron in the cementite crystalline structure (as opposed to ??? austenite? dunno - still no phase diagram) and they also cause the initiation of cracks and rapid failure of the disc. Sevens are lower powered than many other cars, but they tend to be higher powered than any other cars that run around on 13 inch wheels. 1.5 million joules. Where are you going to put them? Come on... you have five seconds to decide... Link to comment Share on other sites More sharing options...
Harry Flatters Posted January 24, 2003 Share Posted January 24, 2003 1.5 million in jewels - in the safe of course 😬 😬 *arrowright*Harry Flatters *arrowright* AKA Steve Mell of Su77on Se7ens Link to comment Share on other sites More sharing options...
AMMO Posted January 24, 2003 Share Posted January 24, 2003 I approach things in a completely different manner. I'm not an qualified engineer or mathematician but I've been innvolved with motorsport a long time. I believe in good old trial and error. You bolt something on. If it works you keep it. If it doesn't you take it off, put it in the bin and fit something else. Engines ,brakes, chassis, whatever. Engineers have calculated how to build bridges that have flapped around in the wind. They make guns that jam and aeroplanes that fall out of the sky. NASA even made a space shuttle that failed. Some of the really talented guys I have met in motorsport left school at sixteen but can build a mean racer. They have experience which they know how to apply. Some of it is instictive. I made a brake set up on my bike that was reputed by all the professional riders that piloted to be the best they ever sampled. There were about six different brands of components in the kit. To arrive at the end product we put a lot of stuff in the bin along the way. A serious amateur can produce something better or that is better suited to his needs than what is commercially available. Amateur is not a derogatory term in my dictionary. It is someone who does something out of love. I've done work for big budget teams and chicken **** teams as well. The chicken **** teams all whinge that if they had the factory suff they could win (usually not true due to lack of talent). Occasionally a clever chicken **** team would come along and make clever use of their resources and beat the big knobs. Everybody loves the underdog in racing. That's why I like Sevens. An old design that beats modern exotica around a race track. Fantastic. It's even better if you haven't chucked squillions of quid at your Seven. I look at my car as a hobby. I like to experiment and I like to do my own thing if possible. If I had the money to spend on an AP kit (which is very good) the only fun would be waiting for the courier to arrive with the box of bits. I'm not for one minute saying that all engineers are daft and all illiterate mechanics are geniuses. There are good and bad engineers and mechanics (as there are lawyers, doctors, plumbers etc.). There is no one solution to a problem. The best way is sometimes to try something different to see what happens. Sometimes you will be disappointed sometimes you will be pleasantly surprised. Let the guys that are happy with their AP's to be happy, but also let the guys who want to try something different get on with it. A Seven is an individualist's car after all. Not usually owned by sheep. AMMO Link to comment Share on other sites More sharing options...
kjp Posted January 24, 2003 Share Posted January 24, 2003 I thought we really all agreed and had just got lost in semantics but perhaps this is not the case. We agree that cast Iron is not very good at conducting heat. So after the first stop the surface temperature of all disks, vented or not is about the same? (and presumably not critical). So the only remaining question is can we disspate the heat before the next big 'event' . If we ignore the fact that the vented disks dissapate heat more efficiently than solid disks (by convection, I think Hoopy called this something else but was describing convection) then the mass of the disk is irrelevant. Mass delays thermal runaway if you are not getting rid of heat fast enough and plays no part if you are able to get rid of heat fast enough. So the only question remaining is can a solid disk get rid of heat fast enough from the surface (competing with a vented disk going which looses heat in both directions) and ehhhh...... I havn't got a clue if it can but could probably simulate it. The best data we have is peoples experience. Do people suffer from brake fade or damaged disks with proper pads and solid disks?? I haven't (remeber no power or talent) but we must have the answer between us. KenP Link to comment Share on other sites More sharing options...
EFA Posted January 24, 2003 Share Posted January 24, 2003 Ken, A vented disc has lower mass relative to its surface area. It is not one or the other of these compnenets whihc makes them offer improved braking, but a combination of both. But they are heavier........ Regards Arnie Webb Trip Organiser To book for this years Le Mans Trip see The Le Mans Trip Website Link to comment Share on other sites More sharing options...
kjp Posted January 24, 2003 Share Posted January 24, 2003 Ammo We are not fighting, we are not stopping anybody doing what they want we are sharing our knwoledge, experience and ideas and ....it's interesting and it's what the forum's all about isn't it??? I will stop at once if it detracts from anybodies fun Ken P Link to comment Share on other sites More sharing options...
kjp Posted January 24, 2003 Share Posted January 24, 2003 Ammo We are not fighting, we are not stopping anybody doing what they want we are sharing our knwoledge, experience and ideas and ....it's interesting and it's what the forum's all about isn't it??? I will stop at once if it detracts from anybodies fun Ken P Link to comment Share on other sites More sharing options...
kjp Posted January 24, 2003 Share Posted January 24, 2003 Arnie All mass does is buy you time and not very much time if you can't get rid of the heat, surface area is important and mass is a consequence. Peter has already established that two big stops will cook even the vented disk if you can't get rid of the heat. Mass is a second order effect surely?? Ken P Link to comment Share on other sites More sharing options...
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