265 So I assume I need braided hoses?

Discussion in 'Suspension, Brakes, Wheels & Tyres section' started by Frimley111R, Jan 19, 2016.

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  1. I have DS1.11 pads and uprated braking fluid but on track the pedal went soft at the end of a session (15 mins). I know I need to remove the air deflector flaps in front of the wheel arches to improve cooling but if the pedal was soft this can only be due to heat affecting the brake lines?
     
  2. Nope. Braided lines won't solve that issue. The thermal transfer rate of braided lines compared to rubber compound lines isnt significant.
     
  3. Ok, well that's saved me some £. What can I do about this then?
     
  4. I run 343 discs, DS 1.11 on road and track,and never experienced brake fade. Are you trail braking,as that will over heat,and cause pad deposits?. Any fluid leaks?.Even after very hard brake use,i get caliper discolouration,but not brake fade.
     
  5. Brake fluid does degraded over time and with use so flush it through and try some Motul 660 or equivalent and see how you go.
     
  6. Tbh it sounds like your using the brakes too much and there overheating the fluid. Better air flow would help cool them off a bit quicker but it may be helpful to know what experience you have on track etc, as if not much I'd put it down to not using the brakes properly I.e. braking too early and too long rather than brake hard and brake late!
     
  7. TBH, quite a lot of track experience but in Lotus Elise/Evora which are lighter/have much bigger brakes. I didn't notice fade on the Megane but coming into the pits I noticed how soft the pedal was. A couple of minutes cooling and it came back. I wasn't surprised as its a big lump to slow down.

    Brake fluid is relatively new, just a couple of months.

    So why is the pedal soft? I also considered ducting to help out.
     
  8. Braking hard and late is the wrong technique for controlling and limiting brake temperatures.

    Assuming the same speed, you have the same Kinetic Energy (KE = [SUP]1[/SUP]⁄[SUB]2[/SUB] × mass × speed[SUP]2[/SUP]) to dissipate, but with delaying/hard braking you pump all that energy into the brakes over a short time period. That drives up peak temperatures over the short timespan.

    Early and more gentle braking dissipates the same KE, but over a longer timespan and that allows for greater thermal heat dissipation through the braking system. Not the best technique for racing though.
     
  9. What fluid are you using? You need a 325 Deg C Dry boiling point fluid min.

    It also depends on what you mean by 'soft'. Going half way + to the floor isnt good, but a slight bit of travel post session/cooldown can be normal as the system cools back to ambient.
     
  10. I'm on track driving fast though. I don't want to be thinking 'Brake gently because this car can't handle braking.'
     
  11. I know. That reply was to the dude earlier thinking braking hard and late reduces peak temperatures.
     
  12. Oh ok, sorry. didn't realise.
     
  13. No worries.

    Get yourself that MG ZS and then you will have less speed to kill on track. Job done.
     
  14. This makes no sense.

    You have to look at the braking system as different parts not a whole complete system that you are trying to spread the energy throughout equally.

    The issue appears to me to be that the brake fluid is overheating.
    This is most likely caused by the pad/ calliper being in contact with the brake disc for too long.

    The heat is generated from friction between the pad and the disc, with the conductivity of the metal in the disc it "absorbs" most of the heat generated I.e. it acts like a heat sink.

    With less contact time between the pad/ calliper and the disc there is less time to transfer that thermal energy into the brake fluid so it remains cooler overall and should maintain a more consistent feel - This is why you should never put your handbrake on after you come in as it cooks the brakes.

    With less time generating heat (braking) there is also more time for the discs themselves to cool therefore reducing the amount of thermal energy in the system as a whole.

    E.g. if you have a steep hill a few miles long and you gently but consistently brake down it to maintain a constant speed you will have cook the brakes at some point, but if you coast down the same hill but brake later towards the end your brakes will be much cooler and able to cope to stop you at the end.
     
  15. put some braided lines on mate, makes a difference.
     
  16. Unfortunately your examples are incorrect.

    Its all about Kinetc Energy and the rate at which you transfer it to heat during deceleration. You either do it slowly or quickly. If you do it quickly the peak temperatures achieved are higher.

    Your handbrake scenario is a static heat transfer case. Different scenario.

    Your hill case for your argument about late braking assumes you are coasting, so in that case you don't need to brake anyway down the hill.

    This is basic physics and the laws regarding energy transfer are fixed.
     
  17. No they don't mate. They don't shed heat.
     
  18. The DISK is the heat sink; this is where you want the heat to go. pads have a MUCH lower thermal conductivity, in other words when the pad and disk surfaces touch friction turns the kinetic energy of the car into heat. the vast majority of that heat 'goes into' the disk because it has higher thermal conductivity. the pad will heat up eventually - the longer it is left in contact with the disk the hotter it will get up to the temperature of the disk, eventually you heat up the calipers and brake fluid. energy is conserved. its just preferable to do the conserving in the disk
     
  19. Made a difference on every car Ive put them on
     
  20. yes they do mate.
     
  21. Well you have nearly got it there. You have the Kinetic Energy into heat bit correct, but remember you are decelerating the same car either slowly or quickly and transferring the same energy into heat either slowly or quickly (late braking). If you do it slowly that heat dissipates through the discs and pad to atmosphere over a longer time and peak temperatures are lower. Simple physics.
     
  22. Nope fella. They reduce compressibility but have no significant effect on heat

    Youre welcome to prove me wrong though.
     
  23. -Jamie-

    -Jamie- RSM Moderator

    As above, braided lines make no difference other than feel.


    To the OP, Im surprised your cooking that fluid, I run the same and never have any issues, Even running Carbotech pads which run very, very hot on R tyres. I have binned the defectors mind you so that may help. I need to get some proper auction sorted though as I'm fed up of going through pads and discs so quickly LOL
     
  24. didn't say they help with heat, meant that they help, which they do.
     
  25. The thread is all about heat though, so you need to be more clear with your inputs to avoid confusion mate.
     
  26. Thought it was about a soft pedal
     
  27. It is. Not really sure why the pedal is a bit soft after a session...
     
  28. Soft pedal after a session mate. That's why it's worth reading the thread.
     
  29. So soft pedal then
     
  30. Ha ha I'm actually an experimental physicist, so I think I know what I'm on about.

    Think about it, how is the heat and pad getting rid of heat if it is generating it for a longer amount of time through braking? Its not - its passing that heat into the calliper and fluid for longer therefore overheating the fluid.

    If the braking inputs are shorter and harder, yes there may well be higher peak temperatures but this is "held" in the brake disc not transferred to the calliper and fluid through conduction.

    You can not cool your brakes if your generating heat.

    Your original formula you posted does not take time into account or cooling factors of the brake disc. It also is simplistic in that it is only kinetic energy not rotational kinetic energy.

    I would suggest that this is a better way of working it out

    Say that the heat Q in the braking system obeys dQ/dt=Mav−f(T,v)*, dQ/dt=Mav−f(T,v)*, where M is the car's mass, a is its acceleration, v is its velocity, and f is the cooling function. The temperature of the brakes could then be T=T0+Q/mc*, T=T0+Q/mc*, where T0 is ambient temperature, m is the mass of the braking system, and c is its specific heat. The problem here is f. it's reasonable to take f(T,v)=k1(T−T0)(1+k2vn). f(T,v)=k1(T−T0)(1+k2vn). k1, k2, and n are constants. n should apparently be between 0.5 and 0.8. k1 can be reasonably estimated, but k2 can't. That depends on the details of the airflow around the brake components.

    Your original formula does not tell you how the heat is distributed between the brake pad and disc (and tyre) to approximate that you have to work in the specific heat capacity of the pad and disc materials (and there masses)

    I won't bore everyone with the physics, but if your interested in educating yourself and going a bit more in depth than above i suggest that you read this https://cdn.comsol.com/wordpress/20...-modeling-heat-generation-in-a-disc-brake.pdf
     
  31. All very interesting stuff but you have missed the key point and application to the actual problem. At least you have admitted the peak temperature generated is higher for late braking. That peak temperature is transferred to the piston and fluid. The peak temperature is the critical element for fluid failure. Remember also, and this is a key point, on a circuit that late braking is a constant process in rapid repeated cycles.

    To use a more relevant and real example, in F1 racing, when brake temps become critical, one of the solutions is drivers will pull back their braking point, brake earlier and lighter to reduce the peak value input. It's being monitored constantly.
     
  32. Pop back when you understand what the discussion is about.
     
    StephRS likes this.
  33. you don't seem to grasp the point or your trolling - as every post of yours seems argumentative. Look at what you posted to sunnylunn, I would knock it back to you and suggest you come back when you have a grasp of physics above gcse level.

    Do you not understand that more heat goes into the pad/ calliper/ fluid the longer the pad is in contact with the big metal heat sink I.e. the disc?? The heat transferred is directly correlated to the amount of time the pedal is pressed I.e. how much contact time between the pad and disc, reduce this and you reduce the peak temperatures in the fluid.

    I fail to see how your f1 example is of any more relevance to the hypothetical examples I posted yesterday? The op is not competitively racing in an all out racing car. It is a track day where you have cool down laps and come in etc etc. Your not chasing every tenth of a second.
    I believe my handbrake example is highly relevant as if all components of the braking system where the same temperature (which you appear to think they should be) it would not matter if you put your handbrake on in the pits after a hot lap. As there would be not heat soak from the disc.

    You seem to fail to grasp the idea that the disc acts as a heat sink.

    With upgraded pads and fluid he shouldn't really be cooking his brakes unless his braking technique is wrong, he needs shorter time applying the brakes - simples
     
  34. Your theory though has to be applied to the problem and situation though Statements of pure heat sink theory are just theory unless you apply to the track day/racing scenario. Of course a disc is a heat sink, so is the hub, caliper, pads and all associated components connected to the braking system.

    The F1 and any racing environment where brake temps are monitored is the best example of repeated late braking high peak threshold temperatures. That is exactly the situation we are discussing.

    Keeping it relevant, the other issue with late braking (based on THE scenario here), is the v max at the braking point is normally higher because for a decent lap time you need that max velocity at every point on track. If v max is higher the energy expended at during braking is a squared factor of speed. Hence, also higher repeated peak temps.

    Sorry to have to move away from the theory a bit and apply it to the reality, but that is what actually happens on track/ racing. It's been data logged for years and well understood.

    I'm enjoying the debate though and thanks.

    sunnylun is just fishing and I'd be glad to have a chat if he has something to add to the thread.
     
  35. My theory is applied to the situation though, the specific heat capacity and thermal conductivity of the pad and disc etc are completely different.

    This is why the disc heats up faster and you want less contact time between the pads and the disc.

    You want to try and avoid getting excessive heat into the calliper/ fluid.

    The reason why you get a lot of ceramic / Kevlar, years ago asbestos etc etc fibres in brake pads is due to there low thermal conductivity (among other properties). This is to prevent heat transfer into the calliper and fluid.

    Your moving away from the issue now as your saying vmax will be higher with late breaking producing more heat, I thought we were going on the assumption that it was the same speed (from your original post to me).

    Perhaps my original post of brake hard and late was a bit simplistic, however I would wager its probably user error if the pads fluid etc etc are up to scratch.

    Apologies if some of my posts have been taken the wrong way, however you did appear to be a troll
     
  36. ok
     
    Bowen likes this.
  37. Soft pedal isn't it ?
     
  38. The variation in the vmax was just an additional side issue. Back to the actual case of the same speed, you are still missing the key point and that is the critical issue of fluid failure due to high temp. Once the fluid fails there is no rapid recovery, same for pads fade. It's not about measuring energy exchange for a whole lap, it's about managing peak disc/pad/fluid temp in this case.

    The other issue is you seem to assume is the disc acts as a heat sink but has not real effect on the caliper temp. There is a direct correlation due to pad/disc contact and while the caliper and fluid will be at a lower temp they are related and there is a temp gradient based on disc temp. In simple terms, the disc peak temp produces a corresponding caliper and fluid max temp. That peak value doesn't just escape to atmosphere it's conducted.

    The disc cannot conduct and radiate its temp away in isolation and as as you have already admitted, the value will be higher for later braking. You are transferring KE at a greater rate and most of it goes into more heat over the shorter time period.

    It's well proven.

    Of of course managing the total heat exchange for a full lap is different. But to limit those potential peak failure regimes, you don't brake late and hard.
     
  39. Conduction requires components to be touching, less time the pad and disc are in contact = less conduction, less conduction = less heat in the fluid

    Of course the disc can radiate, conduct (hub etc) and convect it's heat away in isolation it doesn't require the pad/ calliper to be in contact to reduce its temperature - not 100% sure what your on about there??
     

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