Guys, The reason they "recommend" replacing the rotors is to.................MAKE MORE MONEY off you. There are specs stamped on the outer rim of the rotors. So long as the rotors are within those specs you are good to go. Before they do ANYTHING.....MAKE them mic the rotors and tell you the specs ahead of time. THEN let them turn the rotors. The rotors shouldn't need to get turned more than 2-4mm, IF they even need it at all. If they are taking more material off than that I would call BS! Todays brakes are so easy to change it's silly, especially since the overwhelming majority of them are disc breaks. I taught my wife how to changed the brakes on our Expedition. It's not that hard. Do NOT let them scare you into buy new rotors. Especially not "$1500" rotors. That is such a burn! They will try to sell you a load of crap that, "if the brakes aren't even the car can pull under braking" BUSH*TS!!!! The piston SELF ADJUST, and the pads wear unevenly anyway. Especially if you only have a single piston caliper, where the piston is on the inside of the caliper, that is the pad that tends to wear faster. AAAAHHHH!!!! If it ain't broke DON'T FIX IT!
See my post above about 30 track days on a set of rotors. After my 29th track day, the brakes were giving a judder under braking. So we had the rotors turned. The next track day, after the 3rd heat, the juddger was back. When we got the rotors off at the shop and laid a straght edge over them there were all these little parabolic depressions that exactly corresponded with the pins separating the inner and outer rotors. The heat in the rotors and the pressure from the pads were enough to put the steel in a plastic state where it "slumped". Thus, you need not only enough mass in the rotors, you need enough thickness too. And these rotors were "in spec" if only by the merest couple of thou.
Actually, the claw type single pistons you describe are the most typical on roadcars and most likely to need replacement as pad/rotor sets or pad/turned rotor sets due to the wear you describe. You can get all kinds of poor braking and car darting under braking due to interactions with ABS and weird wear paterns. Pad taper and caliper drag are a mother of multiple problems. I hear what you are saying and it is mostly true but you have to check before you go your direction. Brakes will work doing it your way but that's now what I want my wife to be driving. A DIY'er should check for rotor runout to decide if just dumping pads on is acceptable. Optimum performance requires flat rotors and flat pads if you are going to change either. Squeals and groans and pulling are signs of mismatch on street systems. Racer's don't worry about noise which is inherrant in their systems of floating rotors and temperature specific pads. As pads wear on all calipers ,claw type especially, mismatch of the componants increase while braking performance decrease.
I'm sure not all cars are the same, but I know the last few brake jobs I have done myself it was fairly cheap to buy new rotors. In fact on my Dad's Ford Taurus I ended up also buying new "loaded" calipers because one of the old ones wouldn't collapse. It honestly wasn't much more than just buying pads!! Had I known that I would have just done it from the beginning!
I'm no expert, but just read a book about brakes that states that yes, drilled rotors will crack, so slotted is better in the author's opinion. There was an entire chapter that went into detail about the heat issue, and basically as stated above, the stopping of a car really happens (or is limited by) how much MASS your rotors have, because they have to asborb the HEAT of the pads on them to convert the forward movement (energy) into another form of energy (HEAT). The author's other point was that what stops a car is the tires! Again, I'm not a physics expert or mechanic, but that all made sense to me.
Correct "TIRES" are what determines how short your stopping distance is. Big brake kits (BBK) that only address the front brakes are not "balanced" & the stopping distance is often LONGER than with the stock brakes. This is due to the increased leverage or "arm" of the caliper mount relative to the hub. The increased torque from the caliper makes the ABS kick in sooner & actually increase the stopping distance since its cycling the brakes to keep from skidding the front wheels. Checkout some of the tuner articles Car mags publish. Often the braking distance is greater than the stock car in comparison. Then they do multiple stops & average out the results. The only benefit of BBK is during multiple hard stops in a row where the increased heat is dissipated over a larger heat sink (rotor) Well, I guess the real benefit of a BBK for most people with street driven cars is when you put dubs on. Without it you have huge gap between your rotors & rims.
You are right tires or sticky tires is what you need to decrease stopping distances at threshold braking (in moderntimes meaning ABS active). Front BBK = longer stopping distances are only sometimes if the front BBK is not matched to the master cylinder and dynamic brake bias is not engineered and tested. So if you guy a Stoptech kit or brembo BBK you are going to see an improvement. If you have Bob's raceshop put big brembos on the front to fill the inside of the wheel and there is no testing, no engineering, no regard for mastercylinder volumes you are going to be in a world of hurt. That big heat sink for repeat brake abuse is critical when pushing it. In SCCA T1 racing corvettes we cracked new OEM rotors in 2 days and carbotech xp16 pads lasted 2 days. If you ran the pads down too far you still stopped but increased your pad taper and then the pad knockback and then spread your calipers so then you had to buy new ones after about 6 race weekends. When we went to either NASCAR type AP front BBK or in my case Stoptech developed a front and rear caliper BBK kit on my racecar using the stock master cylinder, all of our problems went away and stopping distances dropped because both kits were engineered for our cars. We still had to balance the benefits of good braking over increased unsprung weight. There is no free lunch.
This thread gave me a flashback to about 1979 after I had purchased my first car, a 1973 MGB. I was at the parts counter of the local foreign car dealership in northern NJ that sold MG, Triumph, Jaguar and Porsche. They had a used Porsche 917 rotor on the counter. I remember being impressed by it because it seemed to be twice the diameter of my MG rotors. I remember that the rotor was drilled and that there were dozens of very cool looking small cracks that interconnected all the holes.
