You are correct

 

Ignoring air resistance and rolling resistance, it's pretty easy to calculate, work done is just energy initial - energy final. It is especially easy because the numbers chosen are super duper convenient. K=MV^2, so double the speed, obviously quadruple the energy.

So From 120-0 is 4x energy, and 60-0 is 1x energy, so obviously 120-60 is 3x energy.

Agree for street driven g35.

but at the track(autox doesn't count), bigger rotors do dissipate more heat, and have less fade, which is sorely appreciated for our heavy cars.

 

People please read prior to commenting. Deceleration is not a constant linear rate. Mass is not a constant rate either as it shifts during breaking. The time to brake or distance from 120-60 is not known either. Also kinetic energy is not a measure of work done. So no, 120-60 is not simply 3x the energy. Not a single thing you said was even remotely correct.

Almost no one on this forum tracks their G35 in any competitive form, the handful that due are exempt from this topic. Rotor size has almost nothing to do with brake fade. Brake fade is a function of pad material.

 

I did read the previous posts, and all the half-assed pseudo physics convinced me to post.

hahaha "mass is not a constant" really tickles my fancy.

I guess technically it is accurate, as you may shed like 2 grams of brake dust while braking. So I guess if you are aiming for like 8 sig figs you would have to factor that in your model. I think what you mean to say is that the normal force on each wheel is not constant, which is true, but is really of not that much interest in this instance, since once you hit the tire limits, the weight shift stays fairly constant.

haha, "LISA, IN THIS HOUSE, WE OBEY THE LAWS OF THERMODYNAMICS"
A change in kinetic energy is a measure of work done (which is path independent!). So unless you are storing the energy in the form of chemical (hybrid car), or other form of kinetic energy (F1 KERS), the kinetic energy from the movement of the car and the rotation of the wheels has to be dealt with somehow, mostly in the form of heat (conservation of energy). Of course, not all of it goes to the rotors. The tires gain some heat, there is some lost to heat along the body with air resistance, heat to the engine from engine braking, heat shed through the transmission and all the various differentials and gears and bearings, but the VAST majority gets turned into heat at the brake pad/rotor interface, and of that, like 80% goes to the rotor. How else do you think brake systems work?

----> http://www.engineeringinspiration.co.uk/brakecalcs.html

You don't have to track "competitively" to get angry at brake fade. In fact, I would say people who track competitively have less of an issue than HPDE folk. If you track competitively, you run race pads that work at like a billion degrees, and heat dissipation is a function of difference in temperature from the 2 media, so you can dissipate the energy faster if you run your rotors hotter. But you can't run race pads on the street, and because of the bedding issue, swapping brake pads and swapping rotors is a pain in the ***. So I run hybrid street/track pads (have tried hawk hp+ and stoptech street performance), which still always keep un-bedding on the street and still fading at the track.

But yes, you would have to be doing something seriously illegal and trying really hard to fade good street pads on the street (like bedding them in).

edit: Bonus reading
Bigger rotors dissipate more heat.
http://en.wikipedia.org/wiki/Convective_heat_transferdQ/dt ∝ Area

edit 2: I've spent way too much time on this.
can't find a great article on modeling and measuring heat dissipation from rotors and diameter. probable because it's kind of a semi-retarded question to be asking in a journal. Also, most of the papers are behind a pay-wall.
here is a kind of crappy article that doesn't take into account like anything (flow through vanes, conductive heat transfer) http://www.fem.unicamp.br/~phoenics/...referencia.pdf

Here are some semi interesting papers if you have access:
http://www.sciencedirect.com/science...90072907000853
http://pid.sagepub.com/content/217/8/657.short

anyone have SAE access want to pull these articles?
http://papers.sae.org/780352/
http://papers.sae.org/2005-01-3943/
http://papers.sae.org/751014/

edit 3: why am i still here?
http://www.scribd.com/doc/30859455/Vented-Brake-Rotor

formulas 1 and 2 rate of convection ∝ area

 

there's also this magical thing called pedal feel, its a crazy thing that can effect a driver's confidence while doing spirited driving

 

You clearly have no understanding of the topic and not worth my time to try to correct you. Please start at the beginning and reread what has been posted until you understand.

 

Agreed and it was not discussed. But you are correct that a BBK will change the pedal feel and provide the pseudo effect that the car has more stopping power. The increased confidence often causes drivers to push the car harder believing their braking has improved.

 

Actually brake feel is the ability to better determine the braking force and to be able to modulate the brake force. It doesn't give the driver any false sense of the braking system's capacity

 

nope, not about the feel of more stopping power at all. it's the feedback, the OEM floating piston calipers have "on/off" braking, the OEM Brembo adds a "medium" to the mix and a full 6/4 will add even more "steps" to the spectrum. additionally initial "bite" is much better due to larger friction surface, try spinning a bike wheel and stopping it with just your index and thumb, then try your whole hand, then both hands. yes, there are MANY variables that come into play when dealing w/braking but that doesn't negate EVERY aspect of a BBK

 

errr... do you really understand what brake fade is? maybe that's the problem here in that we aren't using the same definitions...

sorry in advance, on phone now, but i can add pretty charts and references later if you care to give an actual reply.

so i didn't mention it because i thought it was too obvious, but you do realize the coefficient of friction between brake pad and rotor is dependent on and changes with temperature right? so usually brake pad fade is due to the coefficient of friction dropping off at high temperatures. race brakes and sport pads work at higher temps than cheap pads, but they still do drop off at high temperatures. so when you brake, the rotors heat up, then when you are not braking, the system dissipate heat through convection to air through rotors and calipers, and through conduction to the axle and radiation in ir. so through repetitive braking, you build up heat and the system eventually ends up at an equilibrium on the track where the heat dissipated during corners and straights equal the heat buildup during braking. so the ways to reduce fade, are to get friction materials that run at higher t, and at improving the rate of cooling to get the equilibrium temp down. bigger rotors dissipate more heat, so your track temps are lower. bigger calipers also dissipate more heat, not as big of a deal as the rotors, but they do help.

in the case of one time braking, cooling becomes less of an issue because the input of heat far outstrips the dissipation that the effects are kind of minimal. but heat capacitance on the other hand has a huge impact on the system temp, and bigger rotors have a bigger heat capacitance

 

Please go back and reread. Brake fade is very clearly defined and discussed.

 

Picture of a NASCAR brake system. Not street driving of course. But a relatively heavy car running very high speeds requires a brake system of a certain power, feel and thermal capacity



Now with THAT, I'll tell you this. I upgraded from the small 2003 brakes to the larger 2005 brakes. Both are still floating and not considered a BBK. But the 2005 brakes feature twin piston front calipers and larger rotors. Rears use the same calipers but with larger rotors. The increased brake force from the larger rotors allows the 2005 brakes to match the 2003 brake 60-0 performance WITHOUT having to use such aggressive pad compounds.

 

are you trolling? am i being retarded by actually spending time on this?

 

Correct, you are a waste of time. Please reread your posts to understand why.

 

op is an idiot. seems like he is butthurt because he cannot buy a BBK so he is bashing all the "stock" G35 for having them.

put 2" rotors on your G35 and go down the nearest mountain rd and tell me fade only happens in the pads.

Heat builds up in the pads because the heat into the brake system is greater than the heat being dissipated by the brake system. Larger rotors with internal vanes dissipate heat better.

Keep spewing your garbage and making up the rules as you go along to validate your original post.

Totopo...were wasting our time here.