Join Date: Mar 2011
Location: Mid Hudson Valley, NY (USA)
Re: front break rotors
While it's one of the alloys that dates back a very long time, making a top quality rotor from grey cast iron is a science. I have just enough materials background to be really dangerous (!), and understand some of the issues related to a binary phase diagram. Basically, making a good rotor has to do with the design and quality of the mold, and whether you can mix iron and carbon and a touch of silicon just right to fill it and maintain the thermal cooling profile to get the right final microstructure. This determines the desired wear, heat transfer, ductility, resistance to cracking, vibration damping, porosity & getting just the right amount of pad materials transfer for grip, resistance to corrosion, etc. You cannot have it all - it's all about balance, and some mfgrs favor some of these characteristics over others. And then there's the whole world of post heat & cryo treatment, machining and finishing. It's pretty easy to screw up and get something that looks great but doesn't work as it should. And all this costs money to do consistently right.
Unfortunately, as consumers, there is very little good info out there to rate one mfgr over another. I'd stay away from anything really inexpensive, as I'd expect quality of the product to be all over the place.
The rotor is a sandwich of two disks and a ventilation gap in between. From a visual standpoint, take a look at the thickness of the disks on both sides. Again it's a balance - You need some gap and fins for good venting and the lowest unsprung weight possible, but you want substantial plate thickness on both sides for wear and the ability to dissipate heat spikes over a large thermal mass. Some cheap rotors have very thin plates. Less material saves money, but at a price...
From there it comes down to reputation, feedback from others on various forums, and some blind faith. Wish I could tell you something more useful on this purchase.
Current: '15 Sienna Limited Premium FWD, '14 Subaru Outback, '13 Honda CRV AWD.
Past: '08 Sienna LE (FWD), '02 Subaru Outback