dandan

Brakes are very subjective. Like suspension setups, people want different things and within the limts of road tyres and road usage temperatures it is very difficult to generate a real life comparison that anyone could understand or buy into as everyone places importance on different things. Some like massive initial bite as it fills them with confidence, some like to save money, some like constant braking throughout a stop, some like that braking force to increase through the stop. Some can live with noise, some hate removing monoblock calipers to change pads Some people just want to fill their wheels and have nice colours in there. Some like a particular brand so it's hard to come up with anything meaningful. I wanted to know where to best spend my money for improved performance. In my mind that "performance" is a combination of balance, weight, caliper stiffness and pedal feel, noise, serviceability and reliability.

I wasn't rating them Jay - I was trying to decide which to buy. To truly rate them you'd really have to go to town with caliper stiffness, noise, dust, weight, inertia, heat transfer (good or bad), wheel size limitations etc etc. I don't have the time or money to buy all those kits and do the testing. If anyone wanted to help then I'd be happy to organize some tests to quantify some of the stuff but to be honest I don't think anyone would be interested. Something to bear in mind that has a massive effect is the pads....but in reality pad selection makes no difference here as you can pretty much use any pad in any kit so it's irrelevant. Edit: To kind of answer your question..... I think it is more than fair to compare these kits based on available braking torque (or piston area and effective radius). With an appreciation of caliper stiffness (and a detailed knowledge of the two piece floating/fixed design of every kit here) I had more than enough info to decide what to do or which to buy. Without the braking torque and bias figures I could not have made any sort of informed choice.

Mine is going ok so far, done about 8000miles or so and looked ok about 1800miles ago. Jamie seemed to have a good one too - maybe their quality control is bad with a percentage of duff ones coming out amongst the rest. It is definitely a clutch with a poor reputation though. Sorry for the grief you are having with it Racman

I read it - what is it about the brake balance that you makes you say "Look at the brake bias bit in particular"? Once again I think I am missing the point of your post, sorry.

To be honest I'm not exactly sure what your answer to your own questions is trying to say or whether you are actually asking something you want an answer to. Anyway, I'll try to answer your question as best I can. The comparison is a mathematical one...yes 100%. For a given coefficient of friction, pedal force, pedal ratio, and boost ratio it tells you how the braking torque and more importantly the braking bias changes for various aftermarket options available. That's it. If for example you decided to upgrade to KAD's six pot front caliper on your OEM 323mm disc then it's not obvious or published anywhere that the available braking torque on your front axle drops by almost 8%. That drop also ties in with a shift in the brake bias of almost 3% to the rear. A lot of people have absolutely no comprehension or appreciation of this and believe whatever they read thinking that they have "upgraded" their brakes. This is not necessarily the case and this is what I was looking into when I did the comparison. There is no error in the maths and the comparison is valid as long as you know what the assumptons and limitations are. On a slightly different track, Paul Mac adapted an AMG kit to fit.....excellent, made a smashing job of it. However, if someone for example adapted the 997 turbo kit to fit they would be throwing the brake bias to the rear by almost 10% without means to address this. This is exactly the sort of thing I wanted to find out for my own benefit...and I did. I'm not arguing against anything Toyota have done, quite the contrary. I am looking to see how the big brake kits we could lay our hands on have actually deviated from the original bias. Does that answer your question?

Jagman - I think it's fair to say that your "perspective" is something that has already been talked about a lot here on the board and nobody disagrees with it or is trying to say anything to the contrary. This is about direct comparisons between different setups.... Ultimately tyres, weight transfer heat etc are key limitations - nobody is disputing that and I'm not trying to show anything different by looking at the numbers. I'm not sure if you're getting the wrong end of the stick and trying to put forward an argument of some sort but nobody is actually arguing

If you need it put up on a CMM give me a shout Tony.

It is brake torque but that is only related to clamping force by the coefficient of friction. For comparison's sake it can be thought of as the same thing if the coefficient of friction is constant. For my numbers I was using a shade under 0.4 but it doesn't really matter as I am not looking for absolute values - only relative values between different setups. What I was really doing was investigating brake bias on big brake kits to see how far they deviate from OEM and comparing that to my options for my own custom made kit. To get the brake bias you need the front and rear braking torque but once again - only in relative terms.

Pad size is 100% not in there Paul. It plays no part although a lot of people think it does. The area cannot affect the coeff of friction, the coefficient of friction is a physical property of materials in contact and is not related to size. This comparison is done with an arbitrary pressure applied to the piston areas to generate the clamping force. This clamping force is applied at the effective radius and the coefficient of friction is used to give the retarding force (acting at the effective radius) which is obviously 90degrees to the clamping direction. There is a calculator here that looks like it follows the same approach...I'd need to run some comparison numbers at work to see if they tie exactly. http://www.tceperformanceproducts.com/brake_bias_calculator.html And a couple of halfway interesting links where they mention pad area... http://www.automotivearticles.com/Braking_Basics_and_Break_in_Practice.shtml http://www.driverstechnology.co.uk/brake-pad-area.htm

Or Fowey Hall in Fowey: http://www.foweyhallhotel.co.uk/family_hotels_uk.asp Tregenna Castle in St Ives: http://www.tregenna-castle.co.uk/thehotel/ I've not stayed in either but have been to both and they were nice and I'd imagine the rooms would be nicer than the two in Pentire...could be up at a similar price to Bedruthan and The Scarlet though.

Oh dear - not good. I've also stayed at the Bay and Esplanade hotels in Pentire (opposite end of Fistral beach to Newquay) and they were ok....nothing like as nice as the other two and the rooms were a bit dated but the reception areas/bar/food etc are good. You can stay there and be 100% not involved with Newquay as well which is nice At this time of year you might need to pay the additional £10 or so for a guaranteed parking space on site.

I recently stayed at Bedruthan Steps in Mawgan Porth and it was very nice. I would only stay there if you can get a sea view room though as there's no aircon and the other (non sea view rooms) were very hot. Prices are the same for sea view rooms. Now that we are into the summer holidays this could be pretty expensive though as they are a family friendly hotel and they have a price change right about now. More upmarket, and with no kids, would be The Scarlet (a stone's throw from Bedruthan Steps) but that is a lot more expensive.

Which compound are you running? I am trying to choose between the AX6 and XP8 right now. My only real concerns are increased noise plus faster disc and pad wear from the XP8's as they won't always be at optimum temp on the road (and apparently wear rates are higher when this is the case). For the calipers I have the price difference from AX6 to XP8 is only about an extra £40 so price is not a concern.

If you have the time to get under there yourself and cut it all to length then here a few sources for bits. Could save yourself a whole lot of money and just take it to a competent welder to weld it up after you've trimmed it to size and marked it up. 1) Flange http://cgi.ebay.co.uk/3-Exhaust-flange-Stainless-Steel-Universal-/260511933311?cmd=ViewItem&pt=UK_CarsParts_Vehicles_CarParts_SM&hash=item3ca7b8a37f 2) Expand to 4" http://cgi.ebay.co.uk/4-3-stainless-steel-tube-reducer-exhaust-pipe-/220438668241?cmd=ViewItem&pt=UK_CarsParts_Vehicles_CarParts_SM&hash=item33532b23d1 3) 4" stainless tube http://cgi.ebay.co.uk/4-101-6mm-T304-Stainless-Steel-Exhaust-tube-PIPE-1m-/370337617320?cmd=ViewItem&pt=UK_CarsParts_Vehicles_CarParts_SM&hash=item5639d795a8 4) Hanger rod https://www.jetex.co.uk/jetex/store/index.php?_a=viewProd&productId=3077 5) A rubber mount https://www.jetex.co.uk/jetex/store/index.php?_a=viewProd&productId=3051 If you have to have a smooth bend anywhere then you could trim this to suit: 6) Bend https://www.jetex.co.uk/jetex/store/index.php?_a=viewProd&productId=3017 And depending on the back box connection (welded or slip fit) you may want one of these: 7) Clamp https://www.jetex.co.uk/jetex/store/index.php?_a=viewProd&productId=3026

No sweat chaps - don't worry about the questions or "picking" - doesn't bother me Like I said, I put this little lot together a while back for myself when trying to make some decisions about a kit. There's a few bits of info I need to complete what I have so far (Brembo, K-SPort and AP rear piston sizes and confirmation of KAD rear caliper pad depth) and then it'll be reasonably complete and useful. I have nothing useful on the Stoptech and Rotora so the people running those kits need to come forward Jagman's question about ducting....a lot of people duct to the outer face(s) of the discs rather than feeding the "eye" on the back to pump out through the vanes. This doesn't give ideal temp variations in the discs and can (apparently) lead to problems. Not something I've looked into first hand though. Jamie - the pad sizes would be useful to check which one of the two in Brembo's catalogue is correct. The length of the blue arrow on the pad picture on the previous page is the key one (the depth or height of the friction material - not the backing plate).

I like your thinking - stamp harder, save the cash! I'd like to make it clear that I am not a "big brake kit seller" or anything like that - I only posted the numbers up as people have been talking about comparing calipers and kits and how good the UK parts are so I thought I'd share the numbers. Good point.... The pad thickness doesn't play any role at all, it is the depth as shown by the blue arrow here. I should have posted that earlier to make it clear. Hydraulic pressure is directly linked to the braking torque and is completely linear..... double the pressure = double the torque. However it is almost impossible to throw that into the mix to show up anything useful. This comparison was only to compare one brake setup to another for a given set of inputs (same pad compound, same pedal effort, same master cylinder etc). As Jagman said - stamping on the pedal will increase the hydraulic pressure and increase the braking torque, that is a fact. However, it has to be kept constant in order to make any meaningful comparison between setups or else you could quite rightly say that the brake system off a Fiesta is as good as that on a Supra as long as it's balanced, you can stamp hard enough on the pedal, the seals can handle the pressure and the whole lot can cope with the heat.

The area doesn't play a direct role. The clamping force is generated in the hydraulic system and acts over the piston area(s). This force is applied direct to the back of the pad and then that exact same force is applied to the disc face (no force is "lost" going through the pad). Pads of different areas can still only transmit the force they get applied to them from the piston(s). None of that force is lost and the pad can't generate any more force on its own - it all comes from the pistons. The contact pressure between the pad and disc will change as pad size changes...more area = less contact pressure but the applied force doing the braking is still the same. There are other effects of contact pressure changes (and pad size and material - not least pad and disc wear) but I wasn't going to get into any of those here as they don't affect the maths for the brake torque (similar to heat and caliper stiffness). Now if the pad depth (or height depending on how you want to think of it) changes then that does have to be taken into account. The force acting on the disc has to be applied at a certain radius in order to get the brake torque. This radius is usually referred to as the effective radius and that is the disc radius minus half the pad depth. So a 360mm disc with a 60mm deep pad will have an effective radius of 150mm. The same disc with a 46mm deep pad will have an effective radius of 157mm meaning that the clamping force is applied closer to the edge of the disc. This will increase the braking torque. A good example to make you think about this is the AP CP5555 vs Brembo Monoblock. The AP's pad depth is pretty big at 54mm compared to the Brembo's 49mm and yet the AP still generates more torque on the same size disc....reason being the AP has more piston area. If you put a 49mm deep pad in the AP caliper it would generate a tiny bit more brake torque than the UK spec whereas the Brembo is approx 4% shy of the UK spec. So basically ... pad depth plays a direct role. If the disc face design and pad retention mechanism will allow it, the brake torque and bias can be adjusted by altering the pad depths. This isn't ideal as the discs are designed to work with a particular depth pad in order to stabilize the disc temperature variations but it can be done...and people do it.

Done.

Done - jigged a few things around so post 9 has it in.

Cheers chaps - just making a few changes to make it more understandable. Originally I had the improvements/reductions based on the front calipers and used the bias to tell the rest of the story. The more I thought abut it the more unfair this seemed as, for example, the 997 turbo makes use of immensely powerful rear brakes...somehow. The percentages for improvements/reductions are now based on both front and rear totals compared to the UK's front and rear totals. That is why some of the data has disappeared where I have no rear caliper info. A couple of questions to anyone looking... 1. Does anyone have a Rotora or Stoptech kit they could take some measurements off? 2. Could any of the Brembo users tell me the rear caliper piston size please? 3. Could any of the AP users tell me the rear caliper piston size please and ideally the part number of the caliper too?

Others Alcon 6 Piston Monoblock - 323mm (54mm pad depth) with a UK rear setup Braking torque: 0.3% improvement Front/rear bias: 0.1% extra to front Alcon 6 Piston Monoblock - 325mm (54mm pad depth) with a UK rear setup Braking torque: 0.8% improvement Front/rear bias: 0.3% extra to front Alcon 6 Piston Monoblock - 330mm (54mm pad depth) with a UK rear setup Braking torque: 2.1% improvement Front/rear bias: 0.6% extra to front Alcon 6 Piston Monoblock - 343mm (54mm pad depth) with a UK rear setup Braking torque: 5.4% improvement Front/rear bias: 1.6% extra to front Alcon 6 Piston Monoblock - 355mm (54mm pad depth) with a UK rear setup Braking torque: 8.4% improvement Front/rear bias: 2.4% extra to front

Have a look here Paul... http://www.mkivsupra.net/vbb/showthread.php?t=225007 8th post If you get chance it would be great if you could get some measurements of the pad depths to be 100% bang on...the numbers won't change but but it would be nice to be 100%.

Alcon Alcon 6 Piston Monoblock - 365mm (54mm pad depth) with a UK rear setup Braking torque: 10.9% improvement Front/rear bias: 3.1% extra to front Only seen this kit in one place - Autralia!! http://www.tweakit.net/shop/product_info.php?cPath=57_228_229_243&products_id=1506

997 Turbo Brembo 6 Piston caliper - 350mm (66mm pad depth) with 350mm rear 4 Piston monoblock caliper (60mm pad depth) Braking torque: 14.6% improvement Front/rear bias: 9.6% extra to rear 996 Turbo Brembo 4 Piston caliper - 330mm (60mm pad depth) with 330mm rear 4 Piston caliper (61mm pad depth) Braking torque: 6.6% reduction Front/rear bias: 2.6% extra to rear SL55 AMG AMG 8 Piston - 360mm (65mm average pad pad depth) with a 330mm rear 4 Piston caliper (45mm pad depth) Braking torque: 7.7% improvement Front/rear bias: 0.2% extra to front Paul Mac - I know the front pads are extremely deep at something like 80mm with the extra material around the mounting lugs. Would you say the 65mm "average" pad depth seems accurate? Edit: (I just changed the rear pad depth to 45mm - thanks)

K-Sport K-Sport 8 Piston caliper - 356mm (54mm pad depth) with a UK rear setup Braking torque: 0.5% reduction Front/rear bias: 0.1% extra to rear K-Sport 8 Piston caliper - 356mm disc (54mm pad depth) with K-Sport 4 Piston rear caliper on 356mm disc Braking torque: ??% reduction Front/rear bias: ...(need rear caliper info) K-Sport 8 Piston caliper - 380mm disc (54mm pad depth) with a UK rear setup Braking torque: 5.0% improvement Front/rear bias: 1.5% extra to front K-Sport 8 Piston caliper - 380mm disc (54mm pad depth) with K-Sport 4 Piston rear caliper on 380mm disc Braking torque: ??% improvement Front/rear bias: ...(need rear caliper info)