bigpat wrote:Agree that the reduced unstrung weight, and smaller gyroscopic effect of the lighter carbon discs will help lap time, but not ultimate braking power. As i said, cast rotors and their pads produce higher friction values.At high speed with their downforce F1 cars are not traction limited. it is physically impossible to lock the wheels, that's why the drivers stamp on the pedal as hard as they can. Once the grip and speed wash off, and the cars are grip limited, it doesn't matter what brakes you use, as you can't harness all their stopping power. In this case or when there is low grip, iron brakes are more drivable as they exhibit better modularity.....
As for heat rejection, that's not right. Carbon has better insulating properties than iron brakes. As they need higher bulk temperatures, the brakes themselves need less cooling, but the hubs and bearings need to be considered as well.
As mentioned elsewhere, carbon brakes will start to oxidise at 1000 deg C, so while they can take that temp as a peak, you can't keep them elevated. The carbon pad and disc wear together, and as they do, there is physically less mass to absorb the heat, and wear accelerates. This is what happened to Kimi Raikonnen at Spa this wear, when a helmet tear off blocked a brake duct. Cast iron brakes on the other hand can sustain high temperatures peak temperatures, but the pads taper easier, and can fade. When Champcars raced at street circuits, they regular saw 900 deg C brake temps, and drivers still had good pedals, due to advancements in caliber and pad technology.
Heat rejection involves several mechanisms, conduction, convection and radiation. Iron brakes rely primarily on convection (mostly through internal fins after the heat is sunk in the rotor). Conduction is largely undesirable beyond the rotor. And radiation is marginal in that heat checking and warping occur at temps at which radiation becomes effective. The Champcars may have seen 900° C at some limited location, but iron is not at all happy at that temp, i.e. shows warping and heat checking at maybe 700°C on a good day when heat soaked. I don’t claim to know but suspect the Champcar improvements involve a more effective heat rejection and maybe a bit of nickel in the rotors.
Long term, carbon brakes actually require somewhat greater heat rejection for a given heat load than iron since, having a low heat capacity, they reach higher temps with a given heat input. However, since carbon functions fairly comfortably at 900° to 1000° C, the radiant heat rejection mechanism becomes exponentially (to the fourth order) more effective with increased temps. Carbon brakes reject heat primarily through a differing mechanism relative to iron brakes,
Heat rejection has been discussed in a bit more detail at;
http://www.f1technical.net/forum/viewto ... brake+heat