Rotor quality and bedding in new rotors

Lets discuss what goes wrong with new rotors and how to avoid problems.

Basically two problems can occur on new rotors in early use after install.

1.	Thermal settling and
2.	DTV (Disc Thickness variation).

It has to be said that rotor quality in general in the aftermarket (in our opinion) has fallen dramatically over the last 3-6 years with the flood of Asian product. We see and hear of main dealers who apologise for their own brake rotor product quality and say that brake discs do not even span service intervals in some cases. EBC has had to adapt brake pad materials to live with “Whats out there” simply because we sell ten times as many pads as we do rotors .We can tell you some discussions with customers can become quite heated. Lets attempt here to explain what we consider YOUR and EBC Brakes best way forward to be without doing a lot of competitor bashing.

First it is clear that all brake rotors coming from Asian suppliers are not “Aged” and are certainly not “Normalised” or heat treated castings which was the old method a few years ago to get a good casting quality. Cast Iron from which all brake rotors are made for cars and light trucks is almost a live or natural material and it needs to settle down or age after it is cast. During the first weeks after casting the brake disc may well settle by a few thousandths.

The amount of this distortion is minimal and will not always show up a brake judder problem. Used with the right pads this minimal brake distortion which people call warped rotors will actually correct by the mild abrasive nature of the pad in early driving. So the small initial rotor distortion is not a problem in itself and using good brake pads that have the correct balance of compressibility, thermal conductivity and ability to gently scrub and correct these minor changes is advisable.

So using good pads and driving the vehicle gently during bed in is a good idea.

It is far more important to bed in a new rotor than it is a new brake pad. When changing brakes you should drive steadily for up to 1000 miles to condition the brake rotor as well as the brake pad. The gentle warming and cooling of the rotor takes it through this ageing or normalising process to some degree that should have been done at the brake rotor factory but unfortunately isn’t. Again the unfortunate fact is that if any brake rotor factory started doing what is needed to produce a thermally stable aged casting, they would go out of business in months from lack of sales because noone would pay the price. So everyone is up to the same tricks in response to market pressures and we all have to learn to live with it. EBC Automotive brake rotors are made from G3000 spec cast iron and full specifications and properties can be seen here.

DTV or disc thickness variation which is the most common cause of rotor vibration problems is not caused by rotor quality but is a VEHICLE problem and we strongly advise you to watch this VIDEO…

Rotor surface finishes such as slots - what do they really do...

Plain rotors cost less and rotors without slots are less money to buy for sure but can exhibit some problems.

Firstly the phenomenon known as rotor galling or brake rotor ribbing or rotor scoring happens everyday with the world being full of fairly soft cast iron rotors. The better the pad the more likely a plain (not slotted) rotor will suffer rotor ribbing. The picture below shows a typical normal rotor that is suffering from rotor ribbing.

You don’t throw this rotor away, it is not ideal but it is not a safety issue either, you just have to live with this condition unless you want to upgrade to a slotted brake rotor. Slotted rotors have a major benefit in smoothing the brake pad gently as it wears through its useful life, the slots do NOT cheese grate the pads away surprisingly enough and lifetimes can actually be BETTER on a brake pads used against slotted rotors than one used on plain brake rotors because the pad runs cooler and more efficiently.

This is what a slotted rotor looks like after 10,000 miles using the same pads as the plain rotor in the illustration above.

The key benefit then of a slotted rotor, is smooth and parallel brake pad and brake rotor wear. EBC make a drilled and slotted rotor with its GD series and these work very well on heavier and faster cars and are a big favourite with light truck users.

EBC does not like the aftermarket idea to cross drill rotors, these can crack, if you want to see this for yourself click here.

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