Brake Bias

General General Lotus Talk
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quote:Originally posted by SimonS:I take your point.Phew! [image]http://www.exiges.com/ubb/NonCGI/images/icons/grin.gif[/image]However, I must be driving like a wimp, cos my brakes have been fine on track [image]http://www.exiges.com/ubb/NonCGI/images/icons/grin.gif[/image] Can I blag a ride in your car next time we’re at the same circuit, please?

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I too have had problems with the brakes on my Exige. I only use mine on the road and it’s totally standard with origional discs/pads. I find that I get a shudder through the brake pedal when I really give it some stick down the country lanes (whilst obeying all appropriate limits etc.). It feels like the discs are warped but what is strange is that, when I let the brakes cool off, the shudder goes away again. There are no cracks on the discs and no signs of discolouration through overheating. Is this a common problem and can it be rectified through fitting better pads?All advice gratefully received.

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Pesky,yes if I’m about.Randy,take the disks off and have a GOOD look at them in daylight, bet the inner surface is bolloxed.What happens with some pads is they put so much heat into the surface of the disks, they distort the outer surfaces, if you keep going, the disk will then warp, but I am guessing you have backed off way before this point, and when they cool down, they go back OK.I know I get abuse for saying it, but this is the sort of issue with cheap pads (including the Lotus std fit ones), they are fine for ~80 of drivers on road, but if you start to explore the braking limits, they soon show up their limits.I also wish there was another pad as good as Padgid (I don’t like paying for them any more than you do), but the simple fact is that I have yet to find anything close.Other point worth mentioning is that Padigs are not hard on disks, I have not had to replace mine yet after some 20+ sets if pads.Simon (S)

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Thanks for that info Simon. Have you or anyone else tried opening up the ducts at the front and piping the air onto the back of the disc. If so, what sort of results does this acheive? It would seem like a sensible place to start. I will definately put some decent pads on as soon as this set wears out.I find it incredible that Lotus sells such a performance orientated car with brakes that are clearly not up to the job!? If I am having trouble on the road, the track must destroy the discs in no time.It’s all forgotten after a good blast in the countryside though… May go out for another one in a minute.

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quote:Have you or anyone else tried opening up the ducts at the front and piping the air onto the back of the disc. If so, what sort of results does this achieve? It would seem like a sensible place to start. I will definitely put some decent pads on as soon as this set wears out.I find it incredible that Lotus sells such a performance orientated car with brakes that are clearly not up to the job!? If I am having trouble on the road, the track must destroy the discs in no time.Your falling into the trap of believing that Lotus designed the brakes for the Exige (or the Elise for that matter).The original design was for a 600Kg’s car with MMC brakes and 118Bhp, everything after this was a bodge to get by.The biggest single problem is the design of the disks, they were a compromised design from the start (for the MMC’s) and the steel ones were just copied from that.They have two big problems, the first is that they are vented backwards (in an attempt to give the disk some offset for expansion) and they are made from something really cheap.Thus if you try to duct air to them, you can’t because the vent is on the outboard face of the disk, all you can do is try and cool the inner running face (which is like ****ing into a force 8 gale).Ultimately, the solution is to change the disks for 2 piece items, with a separate center bell and outer rotor. This has several advantages;1) the vent can be made the correct way round2) The center can be made of ali (thus much lighter)3) The rotors can be properly spec�ed with curved vein etc.Going this route has no downsides (apart from your wallet), I run plain disks with ali bells and do not have air ducts to them (although I don’t have the splash gards fitted to the uprights either) and have yet to manage to over-heat them (even in 2 hour races on slicks).Only thing to note is that just because a disk has a separate rotor, does not mean that the material used for the rotor is any better, like everything in like, you get what you pay for!Simon (S)PS. I am currently working on a new brake kit (for EliseParts) to change out all the brake parts, using 295mm disks, 4 pot front and 2 pot rear calipers etc.Appart from braking performance, it will also reduce the mass of the brakes by some 16+kg’s.I am currently testing the prototypes, and expect then to be ready for sale in ~4-6weeks.

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Thanks again for the advice. I don’t think I have ever heard of reverse veins on brake discs before, seems rather bizarre to me but I guess it helps explain the problems. Can’t do much for the high speed handling of the car.Your new brake setup sounds interesting. If you are using disc bells does this mean that you will be using floating discs? I don’t know if I could justify the expense of putting new calipers on the car as it is unlikely to spend much time on the track (I have a race car for that) but I would certainly be interested in some decent discs and pads to run with the normal calipers.I will keep an eye on elise parts.

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Simon, as I mentioned before, I’ve been having some problems with my brakes.And I like the idea of bigger disks as well, but I have a question: in you new bigger disks setup, why go for dual pairs of opposed pistons? I mean, if you have been running with the standard size disks on slicks so far and ok, increasing the disk size will already increase braking torque for the same pistons and foot force, do you really need the extra pistons?Intuitively, and if not many people have had brake problems before, I would prefer to have a bigger disk setup that was easy to swap, and balanced (IE, to not upset the front-rear braking bias). That is, without changing the pistons.Randy,on the side of the vents, Simon put it well, and yes, I have been thinking of making my front vents real, I have warped my disks on 3 occasions. I am heavy on the brakes as well.Skimming your original disks could bring a temporary solution, as the disks surface is the one that has by now been chemically altered and at this point will not benefit even from other pads. Disks surface have been permanently altered. Changing for the same type of (original) disks and using the same pads will see the problem reappear. You need to change to alloy belled disks and different (Pagid?) pads. [image]http://www.exiges.com/ubb/NonCGI/images/icons/smile.gif[/image]Uldis[This message has been edited by Uldis (edited 22 April 2003).]

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Uldis,why 4 pots?Several reasons…1) They are smaller/lighter (for the same piston area)2) they spread the load over a larger physical area.3) They look way better!Although we are going to use a larger diamiter disk, the sweep raduis will be about the same (ie, we are just moving it out). There are NO big 2 pot calipers that will fit with a larger disk (without changine the wheels).The 4 pot we are going to use has about the same piston area as the 2 pot AP it will replace, but is half the wieght and has a way smaller ‘overhang’.The rear 2 pot is to replace the single pot sliding cast iron bit of crap that’s std, this will vastly increase the effecivness of the rears, and the kit comes with a bias valve to enable a proper balance to be found/set. The new caliper is something like a quarter of the weight of the std cast iron one.Reason we are using larger diameter disks is for cooling, this also enables us to use a much thinner (thus lighter) disk.Another up-side to all this (appart from better/lighter brakes) is from a service perspective, both calipers will use the same pad type, thus bringing the cost down.Simon (S)PS. I currently am NOT using the std size disks (or rear calipers)[This message has been edited by SimonS (edited 22 April 2003).]

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So the Eliseparts belled disks should in theory work with ducted cooling as the air can escape on the inside ? They are not curved vanes though …Will the new caliper setup work with these disks ?

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Simon,interesting, but you may find out that there is still 1" of space in the 16" Exige wheels (outside of the caliper to the inside of the wheel). Enough for a 1" increase in diam.Still, since I have always been heavy on the brakes I like the idea, especially the same pads, bias adjuster and lighter overall system.Do you think I can put it to the test?Keep me posted, I am willing to see if they are the solution I’m looking for.Do you have some pics? prices? Please email me separately.Andy, no, Geary’s, (which I have) are not the ideal ones for ducting, since they are full of holes and gaps. The ideal ones would be the Bremsport or AP race type, where the alloy bell completely closes the gap with the disk so that the air coming inside can be routed ONLY through the vanes. The way it is, air will go through the holes directly outside. [image]http://www.exiges.com/ubb/NonCGI/images/icons/smile.gif[/image]Uldis

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Uldis,no pics yet, we only have prototype stuff so it would be miss-leading to use them as examples.Yes, I appreciate that Exiges have 16" front wheels, but as we are trying to cater for 340R/Elise as well, we stuck to the largest we could safely fit in the worst case. Also, it’s not 1" more, it’s about 14mm to be exact, so next std disk size would be 305.Your sort of right about Geary’s current disk&bell offerings, he went a bit mad with the holes in the bells, having said that, they don’t require seperate venting, as long as you have removed the spash gards (not all cars had them) they will stand up to 99% of the abuse, (Blink’s Honda engined car has these fitted, and Jonny has not managed to kill them yet!)Mail wise, address?Simon (S)

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quote:Originally posted by SimonS: They have two big problems, the first is that they are vented backwards (in an attempt to give the disk some offset for expansion) Thus if you try to duct air to them, you can’t because the vent is on the outboard face of the disk, all you can do is try and cool the inner running face (which is like ****ing into a force 8 gale).Ultimately, the solution is to change the disks for 2 piece items, with a separate center bell and outer rotor. This has several advantages;1) the vent can be made the correct way round2) The center can be made of ali (thus much lighter)3) The rotors can be properly spec�ed with curved vein etc.PS. I am currently working on a new brake kit (for EliseParts) to change out all the brake parts, using 295mm disks, 4 pot front and 2 pot rear calipers etc.I am currently testing the prototypes, and expect then to be ready for sale in ~4-6weeks.SimonNow you leave me with a dilema… go for Geary’s current ally belled discs (when i need to replace my existing ones) and RS14 pagids with my existing calipers or… wait till your proposed set-up hits the streets. I am especially interested in the weight saving bit. ANy idea as yet of a ballpark cost?2. COuld you attempt to explain to me what you mean by the current discs being vented backwards? and how does this figure with attempts to allow room for expansion? I know it might be tough to explain by eMail if I don’t already understand but could you educate me?As further evidence of my ignorance could you (or Uldis) explian how the vent is on the ‘outboard’ face of the disc ?? I thought it was up the middle between outboard and inboard faces ??3. Do Geary’s current ally belled discs fit the criteria you mention at the end of the quote above??CheersRox

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Simon,I re-measured, and it is 24mm, closer to an inch. of space. But of course you also need to leave a gap, so maybe usable space is half of that. I’m sure you have taken that into consideration.I just updated my email in my profile, here it is: [email protected]! too many questions!But the main thisng is that te terms can be misleading. The airflow on (or in) a wheel is outwards, because there is a low pressure zone on the ouside of the wheel.It means that air is going to be moving from the hub/disk area to the outside. In the case of a solid disk, the cooling takes place in the inner face of the disk (because there is no other one, it’s solid). Air moves over the disk and then out.In the case of a vented disk, air would cool the iner face, but some of it would go beween both faces and cool from the inside the outer face. In order for that to happen the vents should be visible from the inside, but in the case of our beloved car they aren’t, they are visible from the outside.They did that because of the non-offset nature of the design, perfect fro an allow belled one (in fact, a racing design) but if done as a one piece cast, the iron needs some distance from the hub mounts to the disk itself for thermal expansion (otherwise it would crack immediately), so they did this convoluted design and connected the hub face to the inside disk face. I guess to avoid the cost of fitting it with the allow belled disks it was designed for.So, air doesn’t move through the vanes, the cooling is “by chance”.Now, it still works in the back, but at the front, if braking hard, you overcome the cooling capabilities. Better alloy belled. But since you just started having these problems (welcome to the club) I would recomend the sensate way first, get the alloy belled disks and Pagids only for the front for the time being.It gives us time to evaluate Simon’t system later (but I’m sire the problems would go away anyway, it’d be just for the sake of weight) [image]http://www.exiges.com/ubb/NonCGI/images/icons/smile.gif[/image]Cheers,Uldis

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Rox,Uldis has covered most of this (except for the reason why they were flat in the first place was just a ****-up! watch the video)The kit will first be avaliable for the Elise, for the 340R and Exige it will also include new ali rear uprights to replace the crappy steel ones.Reason for this is that it was too hard work to engineer new mounts for it (Lotus make a replacement one for their kit), and the new Ali one is significantly lighter and stronger (made from solid billet, not extuded).Upside to this is that you looking at about another 2-3Kg’s saving in wieght and a vastly superiour upright incorporating a proper toe link mount (no more bent bolts/sheared links!)Price wise, it’s not set in stone yet, but for the Elise (ie. without the uprights) it’s looking at ~�1,500 and the Exige/340R (and Elise with steel uprights) ~�2,200 (the uprights will come complete with bearings and toe links etc., it will be cheaper if you do not require these)Uldis,yes it’s more than 14mm from std, but I was talking about the largest disk that will fit std wheels, to the largest that will fit Exige wheels (if that makes any sence!).Simon (S)

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Uldis, SimonThanks, but I think I need to see a ‘for-real’ version of how this should be done properly before I will correctly understand - or you can draw me a picture the next time we meet [image]http://www.exiges.com/ubb/NonCGI/images/icons/wink.gif[/image]In any case this bbs is just great…rox

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SimonSorry about this but… quote:Originally posted by SimonS: Ultimately, the solution is to change the disks for 2 piece items, with a separate center bell and outer rotor. This has several advantages;1) the vent can be made the correct way round2) The center can be made of ali (thus much lighter)3) The rotors can be properly spec�ed with curved vein etc.Only thing to note is that just because a disk has a separate rotor, does not mean that the material used for the rotor is any better, like everything in like, you get what you pay for!Do geary’s current ally belled discs meet any of this ‘outline’ spec??

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Yes and no.1) Yes they are vented the right way round2) Yes they have an Ali bell section3) They are a better material than stdthey are certianly a world better than std Lotus item, however, they are not top spec race items.They are designed as a direct replacement for the std disks and will eaisy out-perform them. (Blink’s Honda engined car killed the std brake disks off in 1 day at Donnington, and has yet to have a problem with Geary’s ones yet.)The only real downside to them is that they are still quite heavy (mainly becuse of sticking to the Lotus physical sizes).Hence the reson for the new kit, however, it will not be as cheap.Simon (S)