Pads are down to 30%, there's a shimmy on the steering wheel when I brake lightly, and I plan to overhaul the front brakes in a few months time. Saw good reports about brakeperformance.com and their prices are great. Everything seemed right until I saw the (edited) review below.

Does anyone have any comments on the technical points made, or the comments about quality and design of rotors from brakeperformance.com. Would I be better off skimming my OEM rotors instead of replacing them with an aftermarket product? And if I did get new rotors, should they be slotted?

"I am a 50 year old engineer and have been doing my own maintenance since I started driving cars. I work in sales and get mileage in excess of 40K per year. I use aftermarket rotors, as the stock ones are too expensive for what you get.

It recently came time to redo my front brakes as I have nearly 90K on my last brake job with Concept R1 rotors. Right now they shimmy the car because of the uneven coefficient of friction around the rotor, probably due to pad material that is unevenly distributed across the rotors. I could possibly get this skimmed out, but this would cost nearly as much as new rotors. And having slotted rotors turned is always a roll of the dice as well.

Brakeperformance.com rotors are steel, not cast iron. That means they are stronger (in torsion, tension and shear) and will tend to rust slower, but those are about the only advantages mild steel has over iron. Rotor design by the auto OEM's is based on cast iron, and the strength of cast iron is more than sufficient for a rotor on a car. Brake designers also rely upon cast iron for its thermal conductivity, allowing it to act as a good heat sink. Cast Iron has thermal conductivity of 55-80 while steel (low or mild carbon) is at a lowly 43. That means steel rotors will not dissipate the heat as fast and you will get more brake fade due to heat build-up.

Cast Iron is more dimensionally stable than steel. That means when pressed hard and they get hot, cast iron rotors will not expand and give a feeling of being warped. So if you drive hard, steel would be quite a bad material to use for a brake rotor.

Brakeperformance.com brake rotors are advertized as zinc coated throughout. However, the inside vanes were NOT coated. I saw a clear line where the coating stopped, and the vanes inside were quite rusted, right from the factory. My R1 Concepts Premiums are coated all the way through the vane structure, and Brembos I have used were coated the same way as the R1's.

Drilled holes are more about bling than cooling, but slots are a feature that keep the surfaces clean. By running slots, my rotors never get grooves in them and stay mirror smooth, even after 100K+ of mostly highway miles. I assume this is from dirt getting removed by the sweeping action between the pad material and the rotor. Both R1 and brake performance have this feature, BUT the slots on the brakeperformance.com rotors did not go all the way to inside diameter of the machined surface, and therefore did not cover the entire area that the pads contact. This means they will not sweep the entire surface of the pad.

But in brakeperformance.com's defense, they do offer an extremely low price and their lifetime guarantee against warping. So the choice is higher price for a superior rotor of proven design or a low price with a steel rotor with some design trade-offs and incomplete zinc coating. The choice is up to you".

 

Interesting ..I'm Waiting For Someone More Experienced To Shed Some Light On This Subject..

 

The author is correct on the most common cause of shimmy- brake pad material that has adhered to the surface of the rotor. Having the rotor skimmed/turned is not the only or the best way of removing it. Any corner garage will have an abrasive pad (looks like Scotchbite) tool that will remove the contamination in no time flat. You can buy your own kit for some DIY

On-line Product Catalog:*3M

He is also correct on the steel vs. cast iron points.

I don't care for either slots or holes- both are bling and serve no real purpose on a street-driven car.

 

The original writer is plausible on the points regarding the use of cast iron and the effect
of the slotting.

Also bear in mind that the pad manufacturer is expecting that the rotor mating to
their pad will be cast iron.

BTW, shimmy in the wheel on light braking is not necessarily caused by the brake rotors. It can also be a suspension problem.

 

He does make one glaring error all the brakeperformance.com rotors that I've been looking at are cast iron.

 

Comments much appreciated.

To be fair, the article was dated 2010, and I don't know whether brakeperformance.com has since commented on the subject.

In any event, the author's actual word were: Brakeperformance.com rotors are steel, not cast iron. I didn't realize that until after I got them. (My mistake there for not reading closely.)

Look here for the full article: Brake Rotors - An Education on all is not Equal - Mercedes-Benz Forum

I am getting the feeling that I should keep the OEM rotors, and skim them to see whether or not I have a suspension problem.

 

You could always buy a new set of your choice and skim the old set as a spare set for the next change. Wash new rotors in very hot water with some dish soap.

The nice thing about old rotors is that they are "seasoned" meaning that they have heat set and more reliably hold their machined geometry after the skim.

If you can find a shop willing to do it, a very light skim using multiple passes at a low feed rate is great.

There are also new style cutters which leave a better micro finish.