TDC2001civic

Its been stuck in my mind, so i went over this with my physics professor, I read somewhere on here that larger diameter disk brakes have the same stopping power as normal oem spec sized disks; and that they both use the same contact area when the pad touches the disk. I just want to say that this is not true. Larger diameter disk are better then smaller disks.

My reasoning, think about this a small diameter is rotating faster then a larger diameter if the wheel is moving at a constant speed. So by moving the pad ot to a larger radius of rotation on the disk, it uses less energy to come to a stop, therefore stopping fast. Also in terms of thermodynamics the larger mass as more area to displace heat, therefore staying cooler then a smaller diameter disk. Proof is in the pudding or physics

my thoughts

maxtierney

iTrader: (5)

While I agree with your argument concerning energy expended and heat dissipation...

In the real world of braking, there are more variables to deal with concerning stopping distance. Simply stated, if we are talking identical OEM calipers - any gains one would make would be inversely/directly effected by the increased weight of the larger disc, as well as the outer movement of the rotational mass.

Real world stopping distances would be equal or negligible. IMHO, Increased clamping force and surface contact area (pads to rotor) is what produces shorter stopping distances.

TDC2001civic

Yeah i left weight out of the question, as weight can be equally matched. Contact area would also be greater with larger diameter. if you were to take the circumference of the disk and turn it into a linear form you would have more area on the disk that the pad would touch without overlapping, also there is more torque applied in the opposite direction of rotation further out from the center of rotation.

MindBomber

I'm missing why you felt it appropriate to leave weight out of the question, in order to equalize weight between a larger and smaller set of discs you would need to modify the discs - likely via slotting or drilling them. Slotting or drilling a disc harms braking performance, because although they're supposed to aid in cooling the rotor and allow brake gas to escape they actually do neither. Brake gas hasn't been an issue since the sixties, our pads are more advanced than that now and the decreased mass of the drilled rotor heats up more quickly that solid. Porsche and MB engineers admit that they only continue drilling and slotting the rotors of street cars for cosmetics.

Now, the other issue with decreasing the weight of a rotor is that you have less mass being slowed down by the caliper to enact opposing forced on the axle and stop the car. The question is, do you benefit more from the increased rotational mass when stopping or the decreased when accelerating. That's a question that's been asked many times in the DC2-R and NSX communities, because they can swap caliper brakets with an NA1 or DC2-R and run 5mm thicker or thinner rotors on the same caliper.

Complicated much?
Now factor in that bbks more often than not harm 60-0 stopping distances.

TDC2001civic

as stated, there are different ways for decreasing weight, different metals different forms of casting and forging, so if both were at equal weight, which would stop faster?

and i'm leaving out slotted and drilled rotors cause those are only for looks.

and what you're saying about rotational mass is a small margin because i'm not talking about 0-60 and the fight with static friction of getting the disk to turn. but from 60-0 that larger diameter will stop faster. and i emphasis if both weights were equal.