Peter Carmichael Posted June 25, 2003 Share Posted June 25, 2003 I have been wondering a bit about my brakes. I have the latest R400 Race spec with four pot fronts and twin pot rears. Vented discs all round, race master cylinder, broake proportioning and pagid RS14 pads. The stopping is phenomenal, but modulation is... beyond my finesse with the pedal. At MIRA, I shed speed from 110 to 67 mph into the control tower with a carefully contrived dab. The datalogs show almost perfect retardation at more than 1G, so why should I be worried....hmmm. well I felt like a passenger at the time. I have been coping with a growing feeling that the brakes are a tad too sharp, biomechanics being what they are. Is it time to resort to a lower friction pad? Nice problem to have? The stop switch of dreams? Some people don't know when they've got it good? Link to comment Share on other sites More sharing options...
Luke Beaumont Posted June 25, 2003 Share Posted June 25, 2003 My simple brane would say that you need to increase the mechanical advantage in the braking system - i.e. a master cylinder with more travel and smaller bore. I've just woken up mind, so I could be speaking 🙆🏻 Link to comment Share on other sites More sharing options...
Peter Carmichael Posted June 25, 2003 Author Share Posted June 25, 2003 I think it is something to do with that, but I think the other way. Bigger bore. The pedal is not wooden. It is rather too effective. Link to comment Share on other sites More sharing options...
caterhamnut Posted June 25, 2003 Share Posted June 25, 2003 When I was lucky enough to drive your car one of the things that stood out was the pedal travel, or lack of, compared to our car. The brakes were like a switch in comparison to our soft, spongy long travel lever! They did feel great, and I am seeking to reduce the travel of ours. But its all down to that indefinable 'feel'. The equivalent to me stamping hard on our brake pedal, gradually increasing or moderating the pressure over the longer stroke of the pedal, is that 'carefully contrived dab' of yours! Reading what you have said helps me to understand what you said when I asked you about if it was worth upgrading our brakes, with say a race master cylinder. You replied that doing that could 'ruin' our car. That longer travel (and all the other contributing factors such as not so 'intense' pads etc) do make it more user friendly in everyday use, and I expect Iam used to it now. I would probably embarress myself at every set of lights with your set up. Not really saying anything here, except understanding what you are saying about brake feel. Just going back to pedal travel though - I very much liked the shorter travel of your set up, particularly the tiny movement on the clutch, when I drove the car at Brooklands last year. However, I was shocked to discover after what felt like a very rapid 0-60 (first time in a 250bhp+ car) that I had only been using 2 thirds of the accelerator pedal movement - and that there was MORE! Awesome car. I would like to try 1G retardation I must say. New site! mycaterham.com here 42,000 in 23 months! Link to comment Share on other sites More sharing options...
Peter Carmichael Posted June 25, 2003 Author Share Posted June 25, 2003 I guess where I am coming from is that when you hit the brake pedal to decelerate at 1G, you yourself decelerate along with your car at 1G. This means that the inevitable forces of momentum want to drag your weight onto the brake pedal; you get pushed against the harnesses; you get pushed against the brake pedal. It might just be your leg getting pushed against the brake pedal, but its decelerating mass adds to the braking force applied to the pedal. If the braking effect of this grows disproportionately compared to the initially applied force and desired overall braking effect, then it feels like you have no modulation in the brakes and it feels like the quantity of braking was determined by the initial guesswork of how hard to push the pedal. I think I am in this position. The brake pedal effort is too light. There is no problem with superfluous travel on the pedal, but the pedal effort to achieve any given level of braking is too light. Link to comment Share on other sites More sharing options...
caterhamnut Posted June 25, 2003 Share Posted June 25, 2003 The first paragraph above is why there has always been an issue with joystick controlled cars (ie: getting rid of the steering wheel and pedals) Do you push the joystick to brake, or pull to brake - both has an effect as far as momentum of hand/arm goes - if you pull back to brake, the harder you brake, your arm/hand/is being thrown forward therefore potentialy decreasing the desired braking force. Perhaps the leg, with more mass and power, is better at doing this, and is easier to modulate. Umm - difficult to explain (this late) but is leg/foot pedal system better at damping unwanted movement than a hand/joystick system. sorry - talking b*llocks and hi-jacking your point Peter, specific to your car/set up No idea what I am on about - I will get back to drawing childish cartoons 😬 New site! mycaterham.com here 42,000 in 23 months! Link to comment Share on other sites More sharing options...
Lawrence_Z Posted June 26, 2003 Share Posted June 26, 2003 The brakes are indeed phenomenal My brakes, in comparison are poor, yet they are as they always were really good..... At the right hander, I wanted to scrub off speed gently into the turn and carry speed thru'... but with your brakes the car halved its speed in half my expected distance resulting in too slow a corner. You are welcome to try my new twin master cylinder setup ( similar to chelspeeds) if you fancy it. Lawrence Link to comment Share on other sites More sharing options...
Lawrence_Z Posted June 26, 2003 Share Posted June 26, 2003 The other thing that's worth mentioning, regarding the applied brake pedal pressure.... Is that if you can arrange your seating to allow yourself to sit fully balanced with your feet just in the air, or at least using very little effort, then any G effects can be minimised. So little added pedal pressure. Lawrence Link to comment Share on other sites More sharing options...
Luke Beaumont Posted June 26, 2003 Share Posted June 26, 2003 Peter, what I mean is that a smaller m/c would allow you to press the pedal with less force for a given braking effect, enabling you to modulate it better. The way I see it a bigger m/c would be even worse, turning the brakes even more into an on/off switch. A parallel (since I'm no physicist): I used to do the angle tightening on K head bolts with a regular 3/8 ratchet. I had to really heave on it to turn the bolts through the last 180degrees, and it was a bit hit & miss as to how much you turned them. Then I started using a 3' breaker bar, and now I can turn them with almost fingertip pressure on the end of the bar, and get the bolts turned to the nearest degree. Link to comment Share on other sites More sharing options...
I reply to every thread Posted June 26, 2003 Share Posted June 26, 2003 Spray some silicone on the disks 😬 Link to comment Share on other sites More sharing options...
charlie_pank Posted June 26, 2003 Share Posted June 26, 2003 Peter, I know exactly what you mean, I have the same problem when I drive my dad's cavalier with very servo assisted brakes. Because the resistance to my foot is so light (in this case due to the power assist, rather than the setup you have) it is very difficult to modulate correctly and get the smooth on-smooth off effect I'm looking for. As there is very little resistance to my foot, and it has an inertia-reel seatbelt I slide forwards onto the brake more, so I end up braking much harder than I want to. I have always been of the opinion that if your brakes are capable of locking your wheels at 100mph then they are good enough to stop the car. Any upgrades after that should be to reduce fade and increase feedback. Ironically as you are suggesting, increasing feedback doesn't necessarily mean making them easier to push! I think ideally you want the brake to engage immediately you put any pressure on it, but there should be some travel between gently applied and fully applied. The travel should be progressive too, so that the closer you get to maximum travel, the harder the brakes are to press. All of this is just how I like brakes to be of course, other people may prefer a different feel. C Charlie'n'Kermit The plan is: Leave for Le Mans on the 7th S5EVN Link to comment Share on other sites More sharing options...
KevSull Too Posted June 26, 2003 Share Posted June 26, 2003 You probably need to bleed the entire brake system, and refill with new fluid. Before refilling give the bottle a bloody good shake! This will give you much more modulation. Press the pedal to the floor once to bleed a little speed. Press it twice to slow down. Keep pumping it up and down for hard braking. Hope this helps 😬You laugh at me because I'm different, I laugh at you because you're all the same. 😬 Link to comment Share on other sites More sharing options...
V7 SLR Posted June 26, 2003 Share Posted June 26, 2003 My setup: 4 pot fronts, single pot rears, bigger m/c and standard Caterham-sourced pads. My observations: Virtually no pedal travel (about a 1/2 inch from nowt to lock-up). Initial "bite" missing altogether requiring you to give a hefty push when pressing-on. Feel is a tad wooden at "road" speeds but when you apply the effort needed to really get the brakes working they liven up. I reckon I can always tell what's going on but would happily trade some of that for better initial bite. I suspect the pads are crap. Haven't tried anything better, but based upon everyone's recommendations I'll buy a set of Pagids when I can afford it and when I've changed the rear single pot clampers for something better. I'm waiting for those twin potters we saw at the Autosport show with the integral handbrake. Worcs L7 club joint AO.//Membership No. 4379//Azure Blue SLR No. 0077//Se7ens List Tours Link to comment Share on other sites More sharing options...
V7 SLR Posted June 26, 2003 Share Posted June 26, 2003 BTW, you're welcome to try it out on the Redditch dual carriageways when you're next this way. Don't think you'll like it though. Lent it to Tom7 and another local chap for a spin after MIRA and they both thought V7 was incredibly heavy to drive. The effort required at the steering wheel, clutch and brakes surprised them both. Worcs L7 club joint AO.//Membership No. 4379//Azure Blue SLR No. 0077//Se7ens List Tours Link to comment Share on other sites More sharing options...
Paul Ranson Posted June 26, 2003 Share Posted June 26, 2003 Conventionally the big master cylinder setup causes a high pedal effort. Which is an acquired taste. In this case Peter seems to have too low a pedal effort. Which implies the pads may have too high a friction value for the usage. Options would be to ballast the car with a couple of passengers, or try alternative pad materials. A twin m/c setup with a balance bar is worth investigating, I don't like the idea of proportioning valves, and you could change the sizes of the front/rear cylinders to taste. My recent race pad experience is with Performance Friction C93. Which works well in hilclimb applications. Perhaps a set of C93 or C90 would be an idea? Paul Link to comment Share on other sites More sharing options...
Tight fart Posted June 26, 2003 Share Posted June 26, 2003 I changed the pick up point on the brake lever to master cylinder. This gives more travel, more leverage, and more feel. SLR for sale (but not till after Le Sept) T.F@O.F. www.griptv.com Link to comment Share on other sites More sharing options...
Miraz Posted June 26, 2003 Share Posted June 26, 2003 Have you tried adding a brace for the heel of your foot? My car has become much easier to control under hard braking with the floor mounted pedal setup - I suspect that a fair amount of this is down the additional support available for the leg and foot. Link to comment Share on other sites More sharing options...
R2D2 Posted June 26, 2003 Share Posted June 26, 2003 I have always thought that sorting out feel, braking effort and stopping performance is quite a delicate balancing act and maybe we all have different preferences. We have recently been setting up our rally car with a bias bar and finding settings to suit either gravel or tarmac with completely different tyres, Knobblies for gravel, moulded slicks for dry tar and intermediates for wet. We have always tried to set up the pedal travel/feel so that we can use cadence braking effectively even on dry tar and avoid "snatchy" sudden lock up. This means the pedal needs at least a few millimetres of travel. This allows feel but isn't too time consuming when all you need is a sudden stab between bends as sometimes you may only need to transfer some weight to get more steering. I would tend to start by chosing a pad with the most consistent performance under a range of speed/temperature conditions as this will help with the optimum set up. I tend to think that the lower friction pads such as Mintex also give the highest level of variation. I have been using black Pagids on Tarmac stages up to about 25 miles long and they have been very good but the coefficient of friction is high. I would then adjust the hydraulic effort (master cylinder sizes, caliper types, pivot points etc) to give the best balance between effort and movement. A bias bar is useful for this type of adjustment. If is still difficult to find the right combination you could consider fitting a pad with a smaller area of friction material. I think it is generally better to make the biggest adjustment with hydraulics and then fine tune for consistency with pads. Link to comment Share on other sites More sharing options...
Rob Walker Posted June 26, 2003 Share Posted June 26, 2003 Peter What you also have to consider when using RS14 compound is that the initial cold coefficient of friction is 0.45 and as the pads heat above 300C this rises up to .055 at 500C and is stable up to 700C. If you were to compare this with say Mintex 1144 they start of at 0.45 but only reduce in friction as they heat up. Therefore at full working temp the effect you are experiencing is inline with how the pads are designed to work. Rob Link to comment Share on other sites More sharing options...
Peter Carmichael Posted June 26, 2003 Author Share Posted June 26, 2003 I've been doing a few web searches and that seems to make sense, Rob. The key phrase used is "pedal finesse". Some pads need it some pads don't. I guess I am just experiencing the effect of pads that need pedal finesse. It makes the spec of Performance Friction C93 and related compounds seem quite interesting. Link to comment Share on other sites More sharing options...
V7 SLR Posted June 26, 2003 Share Posted June 26, 2003 That's tremendously interesting. Has brake fade anything to do with co-eff friction reducing with temp rises as per Mintex? Also, has cold co-eff friction anything to do with initial "bite"? Would you happen to know what the standard Caterham-sourced pads are (both make and co-eff friction)? Worcs L7 club joint AO.//Membership No. 4379//Azure Blue SLR No. 0077//Se7ens List Tours Link to comment Share on other sites More sharing options...
tony pashley Posted June 26, 2003 Share Posted June 26, 2003 As an aside - a couple of you mentioned a desire for a heavier pedal (irrespective of length of travel)... Caterham do (or, at least, used to do) pedals of a revised ratio, with the pivot at a different point relative to the overall length. Link to comment Share on other sites More sharing options...
Rob Walker Posted June 26, 2003 Share Posted June 26, 2003 Nig, IIRC the standard Caterham pads in the AP big fronts are Mintex 1122 which are a road pad, the stock rears are a Lucas road pad with similar performance to the 1122. I would expect these to have a cold coeffecient of 0.4 and fading away after 300C. The Pagid RS 14 pads are quite unique in having a high coeffiecent of friction when cold which rises when hot, they also do not eat your discs or wear out quickly. A very good Pad and not expensive when you factor how long they last. My only regret is that I did not find out about them before fitting uprated front brakes as I now think the standard fronts would have been more than up to the job with RS14 pads fitted. Link to comment Share on other sites More sharing options...
Joe 90 Posted June 26, 2003 Share Posted June 26, 2003 A lot of people have suggested the trade between pedal force and pedal travel, but Peter's setup seems to have low force and low travel! This is normally considered desirable, and tin-tops are fitted with servos to achieve this goal. If you have brakes that are efficient but hard to modulate, pads are the biggest factor, but brake bias bars can cause problems, as they suffer signficantly from friction and sticktion. I've thought about the biomechanics of the brake pedal in the past when I noticed how difficult it is to modulate braking on bumpy roads. I came up with the idea that the ideal pedal would have a pivot axis coincident with your ankle joint. I don't know if anyone has ever tried this though. Crash team to the Upgradeitis ward, the withdrawal symptons are getting worse ❗ Link to comment Share on other sites More sharing options...
Bilbo Posted June 26, 2003 Share Posted June 26, 2003 Hi Peter Seems we have 2 posts on the same subject starting at opposite ends of the spectrum and converging. *smile* As I posted here I have the opposite problem. However, whatever I have had on the front peddle travel is a minimum and soon hard. If the travel starts to get long I use the 'never used' hand brake a few times with a VERY pull and its back near the very top of the peddle. Need to do that before MIRA the peddle is rock hard and the fluids not been changed for 2-3 years or bleed. Its just not needed it. However, fast stopping requires a little effort and you can easily vary the degree of force its not all or nothing. I have bent the throttle peddle and slightly widened it by adding a bit of 2 mm ali so I can brake and blip the throttle at the same time. I will avoid using the term double declutching because its incorrect. I just blip the throttle whilst pausing in neutral on a down change to make a clean change. The change to big fronts is a result of fad from cold Green Stuff not when their hot. The Tower corner at Mira is a good example so I hope that the bigger front will cure this i.e. more area and nothing more than that. Could be argued more area = less warm up but I doupt it. Similar problems occur on motorway driving with cold pads miles on need fast stop pads cold the harder the pads the worse it gets. So I have shied away from harder Pads no trailer here for runs to track days 😬 V7 SLR as you infer talks about initial Bite, has blood sucking tendency's 🤔 😬, Well me thinks this is just the same problem I have with the brakes cold good old standard pads do bite quickly but fad worse when hot. So Tower bend at Mira too cold then you need to make a mental correction for the 90 bend into the straight that their now HOT to avoid initial over braking, not that difficult only made as a point. Also unlike others have posted the rear pads but not the disks seem to last for ever this makes me consider others may have the rears binding on just a tad. Then again I well known as not the fastest on the track. Then again the cars heavier than most ad modestly I say so am I its near 2 up compared to some still I enjoy the days a few seconds off my own times keeps me more than happy. fail at Mira but what the hell ☹️ 😬 So I have ordered Green all round last post makes me consider Pagid RS 14 is better Well the EBC web site is naff on detail but here gives more info upgrades brake performance by 30-50%, friction co-efficient of 0.48µ excellent initial bite resulting in instant response - no warm-up required class-leading fade resistance on the road - heat stable to a blistering 500ºC extremely low disc abrasion - due to high Kevlar content low dust formula, great for alloys - due to zero carbon content low vibration - smooth operation So Rob not much to choose when cold RS14 0.45µ verses greenstuff's 0.48µ but it is better at 0.45µ or have I got this wrong way round I think I am correct so IF all claims are true RS14 is not as good as greenstuff's when cold. Rears see less braking so should be fine on the back I have only gone for Green rears as it does keep the rims cleaner. might also avoid rear wheel lock up when hot, not that I currently suffer that but others seem to do so. So hopefully the initial 'bite' will be better but the higher temperatures seen sooner and a little more brake peddle travel with the standard master cylinder set up. If you look at the Red stuff here seems more constant than better on the graph What's the advantage of a race master cylinder 🤔 'Can you hear me running' ......... OH YES and its music to my ears 😬 😬 😬 1988 200 bhp, 146 ft lbs, 1700cc Cosworth BD? on Weber's with Brooklands and Clamshell wings, Freestyle Motorsport suspension. Edited by - bilbo on 26 Jun 2003 20:46:23 Link to comment Share on other sites More sharing options...
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