Banned Sock Puppet
The larger diameter will have greater surface areas on both the rotor and cooling fins to dissipate heat, thus less fade. The slight caliper mechanical advantage can translate to less effort/better modulation.I don't know why you guys are worried about the surface area of the disk that the pad hits. If the rotor is connected to a plate that is the full internal diameter, that calc isn't right either. My disks have a metal heat dissipater that goes from the disk all the way into the hub, and it's vented!
The only braking is done by the pad! Which is virtually the same size on most brakes. The only thing that changes is the distance from the axle.
Of course you will only notice the "less fade" part if you are in a situation where fluid may boil.The larger diameter will have greater surface areas on both the rotor and cooling fins to dissipate heat, thus less fade. The slight caliper mechanical advantage can translate to less effort/better modulation.
If your fluid boils, it's not fade, but rather brake failure. Fade occurs when the rotor and/or pad overheats and lose friction during heavy application. Fluid boil is often caused by prolong dragging of pads on the rotor with light application, or a big no-no when it comes to proper braking techniques.Of course you will only notice the "less fade" part if you are in a situation where fluid may boil.
I promise you the area of the entire circle isn't 15 or 20 square meters... and we're only talking about the swept area.I'm no smartypants, but it's surface area that is significant here. Doing the calculation Pi * R * R:
For a 140mm disc, 3.142 * 70 * 70 = 15,396 sq mm
For a 160mm disc, 3.142 * 80 * 80 = 20,109 sq mm
Difference = 4,714 sq mm
So, the 160mm disc has 30.6% more surface area than the 140mm.
Of course I am reminded of a quote from one of my favorite posters on this forum, DCGriz, who wisely said, "With bicycles in particular, it is important to separate what is merely true and what is important". A bike with 140mm disc brakes still has more stopping power than a similar rim brake bike. Unless you plan on riding your brakes down 1-mile long steep hills or longer, the 140mm disc brakes will slow and stop you just fine without melting.
Umm, your conversion from sq mm to sq m is off by a few decimal points. 15,000 or 20,000 sq millimeters = 0.015 or 0.02 sq meters. That IS the area of the entire circle.I promise you the area of the entire circle isn't 15 or 20 square meters... and we're only talking about the swept area.
Lol, I agree, I used diameter instead of circumference, but I obviously knew my maths as I used radius (being half diameter) and calculated circumference increase (which is what affects area: add 1mm to circumference and you get over 6mm squared volume extra... the non linear nature is what you missed, actual impact on area depends on depth of area heated by brake, and then actual heating depends on materials used etc). But well done, you keep on focussing on diameter and ignore the exponential difference in surface area. 140 to 160.... no big deal you say (ie what is an extra 20 on 140?). Bad maths if you are talking about either surface area (cooling) or braking impact, where again distance from hub is not linear in effect.You've forgotten your maths.
Every mm increase in radius = 2mm increase in diameter. Circumference is the word you were looking for. A 140 or 160mm disc is just that...140mm or 160mm diameter. Trying to sound smart only works when you get everything right.