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Todd!! Long time no chat! Great to see you on these boards, Sir.

I'm a little late to this thread, but I'd like to add a couple of points. There are about 5 things that make up and define a brake. Swept Area per Ton, Torque Arm, Rotor Mass, Coefficient of Friction and Hydro-mechanical Functions. The later was covered in depth with your calculations...nicely done, Jack. But some might not know the correlation of the first items in my list.

Swept Area per Ton - This is the surface area of the rotor that actually touches the pad, times both sides, times all 4 rotors. This surface area is then divided into the weight of the vehicle. If you take an F-250 4x2 Regular Cab Long Bed and do a 60-0 stop, it might take 180' (estimating. ABS, road conditions and adhesion are assumed). If you put a pallet of concrete blocks in the bed, it'll take 260' or more to do the same thing. Conversely, you take the same brakes and put them on you Ranger and it will suck the eyeballs out of your head and stop in about 100'.

The next part is Torque Arm - This is the distance from the center of the pad to the center of the axle. The longer the torque arm, the more negative torque the brake can develop. So, you take a 13" rotor with a fat pad that reaches all the way from the OD of the rotor to the inside radius of the hat...and a 15" rotor that has these little skinny pads. Same swept area, but the bigger rotor will make a lot more negative torque than the smaller rotor. The same principle occurs in reverse with regard to tire height. The bigger the tire, the less torque the brakes can apply to the road surface because of reduced leverage. Rule of Thumb - Every inch of tire you go up, you loose almost 10% of the braking power. This principle is lost on our urban youth that feels the need to put 24" solid aluminum wheels on their 99 Ford Crown Vic Police cars. Sometimes I just have to shake my head.

The next part is Rotor Mass - The brakes turn kinetic energy into heat energy. The only job the rotor has is to get hot and dissipate that heat. The bigger the rotor, the heavier the rotor, the more mass, the better it can absorb that heat and dissipate it back to the atmosphere. There are aberrations to this with respect to sprung and unsprung weight, but for most stock style vehicles, the principle still applies.

Pad material and coefficient of friction has been outlined above. But the best way to understand the bell curve for high temp pads is this. Say you've been driving down the interstate for 20 min at speed, and you need to slow down for an exit. You reach over and put your foot on the pedal and start a slow deceleration. If you've got an organic type of compound for light duty, the truck will slow down in a linear fashion given the same force on the pedal. If you've got the higher temp pads on, the truck will start to slow, then about 4-seconds in, it will be like you throw the anchor out. As the temps come up, coefficient of friction comes up and the truck will slow more dramatically without moving your foot on the pedal. Personally, I like the ceramic pad compounds that have come out lately. Ceramic compounds are what comes OE on most of the newer vehicles. It gives you a linear CF through the transitional brake temps. If you get them too hot, they will fade, but they stay good for quite a while.

Which brings me to my last point. Todd and I have had many conversations about this over the years, and I respect him greatly, but my point has to do with cross-drilling. Todd's Kits aside, CROSS DRILLING ROTORS IS THE BEST WAY TO SCREW UP A BRAKE SYSTEM. Given the points I outline above, when you cross drill a rotor, you're reducing the swept area of the rotor. If it's not touching the pad, it's not part of the swept area. So if you punch 100 holes in the rotor surface, you've just reduced the swept area by the diameter (Pi*R^2) of the holes and the hole count. This adds up quick. You also reduce the mass of the rotor. The cuttings that end up on the floor used to be part of the rotor and the mass. You have just reduced the mass of the rotor by the cuttings, so now the rotor has to get that much hotter to do EXACTLY the same job. Yeah, it cools quicker, but now you're heat cycles become more dramatic leading to thermal stress and cracks. The holes also concentrate the heat load and give the rotor a place to crack.

Todd's kits are all designed and engineered with this in mind. So too are the Porsche GT3's that have 15" rotors that look like Swiss cheese. If you engineer it that way, it works great. But when the kids order cross-drilled rotors for the Honda Civic and think it's gonna stop quicker, you just have to laugh.
 

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Hi Doug, hope you're doing well.

I pretty much gave upon the drilled vs non-drilled rotor thing some time ago. With so many ideas, opinions, references etc I've come to learn its best to just let the custom select what he/she wants. Unless it's a dedicated track application...in which case the buyer should know better anyhow.

And in the case above I'd say the overall mass increase is large enough to support the option without too much of a gamble. When used within reason I don't have a problem with the drilling, like you; I just think folks should make a smart decision.
 
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