Hello, I write here because I've got such a big problem. I am currently modding a LMP3 car and when I want to setup the brakes, I get strange values in terms of brake torque. I don't see where I make a mistake but I get about twice more torque as I read for the other mods. Here are the datas from the car (I give for the front only, rear is the same) : Pedal ratio : 5.44:1 Max force on brake pedal : 80 kg = 784.8 N That gives 5.44x784.8=4269.312 N to the master cylinder. The master cylinder has a 19.1 mm bore so a 286.52 mm² area. So there's already a problem here as it gives me a pressure of (4269.312)/(0,00028652)=149 bar when I measure a maximum of 77.6 with data acquisition (meaning the driver probably put a bit more force and maybe blocked a bit). There are six pistions per calliper (three different on each side), sized 26.94, 31.69 and 38.09 mm. This gives a calliper pistons area of 4995.5 mm². So the force on the front pads is [(0.0049955)x(4269.312)]/(286.52)=74450 N The pads have a friction coefficient of 0.548 so it gives a 74450x(0.548)=40799 N force on the discs. The firction radius is 0.1443 m so the brake torque is finally 40799x(0.1443)=5887.3 Nm. When I look to other prototypes data, I see that P1 cars have numbers like 3500 and P2 have some like 3200. I can't be so much higher ! That makes me think that I have to divide it by two or something, but I don't know why. Maybe because one master-cylinder gives pressure to two callipers ? This probably wouldn't explain such high pressure, except if the car measures it on the callipers but it's not the case... Might it be because of the brake bias also ? The brake pressure sensor is located after it on the car but I don't see why it would divide my trque by two. I hope you will be able to give me a good explanation as I have to enter this calculation into my thesis and it has to be precise. Thanks in advance and have a nice day !
rF2 brake torque assumes 100% bias to that end (so for example 4200Nm on the front brakes would only be achieved with a full pedal press with 0% rear brake bias), and a single master cylinder does both front wheels. I think that would match what you've calculated? If you halve for each wheel you end up around 2900, which is a nice step down from the 3500 and 3200. I could be wrong, too
So you think I just need to halve the torque ? It was what I did for testing and it seemed nice, but I still can't clearly explain why... My default brake bias is 53 % on the front and 47 % on the rear for information.
I *think* it's just that you're calculating 1 master brake cylinder and calculating the torque on 1 wheel - when it will be acting on 2 wheels. So yeah, just need to halve it. In practice you'll end up with 2 cylinders (front and rear) with 53% and 47% distributed to them, so your 5900Nm goes 26.5% to each front wheel and 23.5% to each rear wheel overall. I hope I'm not leading you up the garden path here
Ok, I think I see what you are explaining me. I will try this, I hope it will work well. Now let's write it so that everyone can understand it. And if somebody else can confirm that would be nice Thank you for your answer mate !
The high torque is a direct result of using 80 kgf for pedal force and applying all of that to the front master cylinder. If you work it back only 41.677 kgf is required to generate 77.6 bar in the front master cylinder. If 41.677kgf is all that is required to lock the tire, are you gaining anything by applying 80?
I tested again and again with half the values I found, and it seems very good so I kept it Thank yoiu all for helping me (but you wil; have to help me soon again in another thread)
