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Old 07-06-2013, 06:12 AM   #1
Sp4Mike OP
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Wavy, drilled, and slotted rotors

I found this article that was about rotors on cars. Does it apply to bikes as well?
http://automotivethinker.com/brakes-...d-and-warping/
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Old 07-06-2013, 07:38 AM   #2
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Proof that actual knowledge is not required to write an article....
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Old 07-06-2013, 08:06 AM   #3
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Originally Posted by Motomedic View Post
Proof that actual knowledge is not required to write an article....
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Old 07-06-2013, 10:46 AM   #4
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Also listening.
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Old 07-06-2013, 11:18 AM   #5
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Originally Posted by Sp4Mike View Post
I found this article that was about rotors on cars. Does it apply to bikes as well?
http://automotivethinker.com/brakes-...d-and-warping/
Which part of the article are you questioning?
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Old 07-06-2013, 11:23 AM   #6
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Originally Posted by Motomedic View Post
Proof that actual knowledge is not required to write an article....

Even though the writing and grammar in the article suck, the guy is spot on.

Drilled rotors don't really matter for most motorcycles since the discs are made from steel or stainless steel, not cast iron like the rotors in most cars. The metal is a lot less likely to crack from a stess point at a hole. Also, the advantages of a drilled rotor on a motorcycle outweigh the disadvantages, where the quest for less unsprung weight is king, and the rotor gets WAY more airflow than one packed inside a wheel. Thus, removing some of the heat-absorbing capacity of the system is not as big of a concern, since the heat that gets into the rotor is more quickly dissipated to the ambient air.
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Old 07-06-2013, 11:28 AM   #7
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Question. Does anything automotive use floating rotors?
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Old 07-06-2013, 11:44 AM   #8
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Question. Does anything automotive use floating rotors?
Yes, but its very uncommon I think. I've heard of a few high performance applications using floating rotors (I seem to recall maybe the Z06/ZR1 Vettes having them, but don't quote me on that) but that's about it.
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Old 07-06-2013, 12:15 PM   #9
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article is mostly true......for automotive applications

porsche and others cast extra material where holes are to be drilled, but in extreme use they will still crack

motorcycle weights 1/10 of a large car. they also have small contact patches so brakes dont get the same amount of energy. rotors are also directly in the airstream

after market rotors with big brake kit usually have aluminum hats and floating rotors. BMW made floating rotors for M cars with comp package and others probably offer it
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Old 07-06-2013, 08:42 PM   #10
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Question. Does anything automotive use floating rotors?
Yes. Many brake upgrade kits do.
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Old 07-07-2013, 07:35 AM   #11
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Question. Does anything automotive use floating rotors?
Yes, as davidji said, there are quite a few big brake kits that do. But the only applications you will find them stock would be the top end of sports cars. Usually they are mostly found on track cars though.
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Old 07-07-2013, 11:10 AM   #12
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So it begs the question, do motorcycles need drilled flower petal rotors or not? I thought the drilling was for cooling, and it actually reduced the surface area for the pads to bite into.

As has been pointed out, motorcycle brakes are out in the wind and have much less weight to haul down from speed, making the cooling argument kind of moot. So basically it's just for looks.

Ultimately it doesn't matter, my bike stops great. It's not like I'm looking to shave a couple tenths off my commute to work! Just thought it would make for an interesting discussion.
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Old 07-07-2013, 11:25 AM   #13
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I have cast iron on my Guzzis.

I have always understood that drilled rotors offer the motorcycle better cooling through increased surface area, better wet weather performance by offering the water a place to go, and lighter weight.

Wavy rotors are supposed to offer additional cooling through added surface area at the outer edge, but who knows?

Iron or stainless, every modern motorcycle has drilled rotors. It works for motorcycles.

Auto rotors are constructed differently from those on motorcycles and have venting in the middle on the fronts of many cars. Basically, a double thickness rotor with cast-in ducting for cooling.

I used some aftermarket drilled and slotted rotors on my Miata and they performed better than stock, with no warping (like the stockers did) or cracking.

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Old 07-07-2013, 11:55 AM   #14
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Likely the stock pads on the Miata weren't up to the heat you generated in aggressive braking. That left uneven deposits of pad material on the rotors, caused the brake judder, and warping got the blame although the rotors probably measured very little run out and not actually warped. If you used a higher grade pad with the new rotors, the new pads held up better under your service. Here's more: http://www.stoptech.com/technical-su...l-white-papers I've several years and 100,000+ miles on slotted rotors and Performance Friction pads on my truck, excellent dry and wet braking, very slow pad and rotor wear. Good combination.

The floating or semi-floating rotors on bikes is a way to allow heat expansion without a very heavy rotor. An equally light solid rotor would crack.

Are the wavy rotors for bikes more about marketing.....???
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Old 07-07-2013, 03:39 PM   #15
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Some empirical evidence for ya...

I own a Buell S3T. Came with a drilled 340mm single rotor front brake. At one point, I crashed it (car coming down the hill was passing over the double yellow line, I rode into the ditch to avoid becoming a hood ornament). A friend was working for the US distributor for Braking, and gave me a Wave rotor to replace the trashed stocker.

I lived on a twisty two lane road with around a 2000' elevation gain/loss from my house to the freeway. I commuted on the Buell almost every day. I worked at SJHD for around 9 mo before I drove my truck there for the first time.

With the stock rotor, I could easily fade the brakes by the time I got to the freeway. With the Wave rotor, no matter how spirited my ride, I still had brakes at the bottom of the hill.

I'm sure someone will be along to tell me it wasn't the rotors, the blah blah blah was the reason my brakes were no longer affected by the heat. I for one firmly believe that the cooler the pads stay, the longer I can abuse the crap out of them before they fade. I also believe Wave rotors help keep things cool.
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