Rotors, blank, slotted, drilled?

[knucklesplitter]

If my rotors are in really good shape with no pulsing and no significant wear, how necessary is it to turn them when replacing street pads? I always have thought it was necessary to at least "break the glaze" but my rotors are in such good shape.

[Kevin M]

I've gone through a zillion different pad sets, and less than half a zillion rotors. Never turned even one. No issues even going from street to track/autocross pads.

[Dean]

I only turn rotors when they are heavily grained/grooved have uneven pad build up, glazed or surface cracked.

I have gone from full thickness to well below minimum without turning on some vehicles and I'm older than Kevin...

Only turn as needed. Having them ground is even better, but I don't think we have a shop with a rotor grinder in Reno, much less most of CA. At one point, my grandfather's shop had the only disc grinder in N. CA and I have no idea where it ended up when he shut down his shop many years ago.

Grinding leaves them with that buttery smooth surface with swirls like they come from the factory.

[knucklesplitter]

I love advice that corresponds with what I wanted to hear.

Thanks.

[cody]

Um, buttery smooth?

[fuente]

Back to the topic...I had to replace my rotors and pads at 40K and I got Stoptech Slotted Rotors and Hawk pads from JSC Speed and I have abused them like craxy and they have been awesome, no wear at all. Even though you do not cahnge your calipers, the braking power, I would say, is increased by about 50-60% over stock. I would go with that.

[AtomicLabMonkey]

Originally Posted by Dean

Min thickness should be stamped or cast into the rotor.

Pick up a cheap digital caliper at Harbor Freight.

Dude, I wouldn't exactly trust calipers from a cheap chinese factory. Granted accuracy isn't that critical with a rotor, but still..

[bigrobwoot]

Originally Posted by cody

Pair. Okay, thanks. I'm not a big fan of turning rotors though. I can never find a place that does it on the weekends, you end up with less heat sync material, pulsing always comes back, etc, and it's just too much of a hassle when new ones are so inexpensive.

i know napa in carson does it on the weekends, i dunno about the napa up here tho. i would assume that they would.

[knucklesplitter]

Originally Posted by AtomicLabMonkey

Dude, I wouldn't exactly trust calipers from a cheap chinese factory.

Yeah, always go for a quality name brand like Mitutoyo...

[cody]

That'd be rad if NAPA off Panther Valley did it. I need a new tire gauge and possibly some cheap calipers anyway.

[khail19]

None of the Napas in town will turn rotors, they don't have a brake lathe at any of the locations.

[AtomicLabMonkey]

Originally Posted by knucklesplitter

Yeah, always go for a quality name brand like Mitutoyo...

Holy crap. +/- .005? That's awful.

[sperry]

Originally Posted by AtomicLabMonkey

Holy crap. +/- .005? That's awful.

Seriously... why bother with .1mm resolution if the instrument is only .2mm accurate.

[knucklesplitter]

Originally Posted by sperry

Seriously... why bother with .1mm resolution if the instrument is only .2mm accurate.

An instrument can be repeatable within 0.1mm but only accurate to 0.2mm (or worse). When comparing 2 parts that have the same nominal dimension an instrument is more accurate/useful then if it has to measure something to an absolute accuracy of the same magnitude. In other words that caliper prolly can tell the difference between a part that is 25.0mm and one that is 25.1mm, but you cannot rely on it measuring something 150.0mm accurately within less than 0.2mm. Does that make sense?

[sperry]

Originally Posted by knucklesplitter

An instrument can be repeatable within 0.1mm but only accurate to 0.2mm (or worse). When comparing 2 parts that have the same nominal dimension an instrument is more accurate/useful then if it has to measure something to an absolute accuracy of the same magnitude. In other words that caliper prolly can tell the difference between a part that is 25.0mm and one that is 25.1mm, but you cannot rely on it measuring something 150.0mm accurately within less than 0.2mm. Does that make sense?

No, I get the difference between accuracy and repeatability.

But for a set of calipers, where accuracy is usually the desired trait, why does the display have a .1mm resolution if the instrument is only accurate to .2mm? Shouldn't the last digit always be a multiple of .2mm to give the most accurate measurements?

[knucklesplitter]

Originally Posted by sperry

No, I get the difference between accuracy and repeatability.

But for a set of calipers, where accuracy is usually the desired trait, why does the display have a .1mm resolution if the instrument is only accurate to .2mm? Shouldn't the last digit always be a multiple of .2mm to give the most accurate measurements?

It's even more pronounced on the inch side - resolution to .001" with accuracy only to .005".

Kinda like I tried to explain, the electro-mechanical system in the instrument can accurately distinguish a movement as small as .001" so that is what they set the resolution to. But the overall accuracy of the instrument, probably due to it's length and maybe it's user-zeroing method and user-thumb-pressure-dependent measurement method, is only good for +/-.005". For some instruments the accuracy is spec'd as a per-length spec - like .001"/inch.

[Dewey]

Originally Posted by JonnydaJibba

Did you ever read that thread about the guy that used socks in place of an oil cap in his M3?

WTF???

[Dewey]

There are some EBC dimpled and slotted on eBay right now, also for sale by a Nasioc member. Ill see if i can find you the link, I may be wrong, but I dont think the dimpled ones have an issue with cracking.

[sybir]

They might not crack, but they're the most godawful annoying "WHIRRRRRRRRRRRRRRRR" you've ever heard in your life. Stay away from dimples on a dd.

[cody]

Originally Posted by khail19

None of the Napas in town will turn rotors, they don't have a brake lathe at any of the locations.

Apparently a couple of the Kragen's in town will, but meh.

What do you guys think about these? http://www.tirerack.com/brakes/brake...r=&perfCode=A# (Hope the link works, LMK if not)

They're only $5 more than the Brembo blanks but they're supposedly "cryo treated". I also like that they've got a nice black coating.

Would spending twice as much on rotors that have a Left and a Right side be worthwhile? I imagine the veins in the middle can then be made to be directional or something?

[Dean]

Directional rotors cool better, but unless you are going to the track regularly, you won't notice. Spend the extra on the RCE brake ducts instead.

Those look OK. Most any coating will come off once really heat cycled, but nothing wrong with Cryo and probably worth $5.

[cody]

I just wish I knew if that brand was good or not. I hate to steer away from OEM when I've been so impressed with the stockers. But I'm going to be ordering some rotors and pads for my GF's Civic so I thought I'd just get it all from Tire Rack.

[Dean]

Cast steel is mostly cast steel... All rotors come out of one of about 5 factories in China, Italy, Japan or I can't remember where. Company X buys those blanks, does the finishing and sells them.

There really is no magic in the OEM replacement rotors market. Subaru OEM rotors are as likely to come out of the same batch as these or any other OEM size.

Ground rotors are about as good and flat as you can get because if properly done, they are equally loaded while being "turned", so the material is not stressed or bent while being machined.

Cryo has shown a minor improvement in wear, but only if done slowly. Flash Cryo has not been shown to have significant benefit that I am aware of.

As I said, there is basically no low cost coating that can handle brake temperatures, so they will only look nice until you use them hard and then they will rust like every other steel rotor in the universe.

Since for the most part, "warping" doesn't actually exist, it is pad build up, so just be sure to bed your rotors properly.

So.... BUY THE CHEAPEST DAMN ROTORS YOU CAN FIND and don't pay more than $5-10/rotor for cryo if you really feel like it.

[cody]

Thanks Dean. That makes me feel better about trying them.

[cody]

They're on the way: