butterfly disc vs. normal?

[NeolWhyt]

Hey guys, I wanted to know the difference between butterfly discs and a normal circular one. Can someone link me to an article or explain? I can't find anything about butterfly discs on google.

[totalllama82]

Try 'wavy discs' instead? I presume you mean them?

Believe they're meant to give better bite. Haven't looked into them a great deal but they do look cooler
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Gone: Haotian HT125-8 / Yamaha YZF 600R Thundercat / Kawasaki ZX9R C2
Current: Kawasaki ZZR 1400 A7F

[Rogerborg]

My understanding is that they are variously claimed to:

Clear crud off when used offroad.
Dissipate more heat from the extra edges.
De-glaze pads.
Shave a few grammes off of unsprung weight.

My opinion is that they are fitted because they look sick weapon, blud, and are good for at least an extra 10mph down the pub.
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[SQL]

[Matt B]

Kawasaki like them and fit them as standard - ZZR1400 as an example.

Wouldn't choose a cheap but sick looking set of wavy discs over a quality set of normal ones though.
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[MarJay]

They provide more leading edge for the pads to bite, and they look cool. That's pretty much it.
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Remember kids, bikes aren't like lego. You can't easily take a part from one bike and then fit it to another.

[Northern Monkey]

[Musketeer]

They look cool. That's about it.

Standard ones are better, because more pad surface touches the discs. That's why you don't see wavy discs in racing

They are more for off-road.
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Current Bike: Yamaha XSR900 Previous bikes: Honda CBR1000RR Fireblade, Kawasaki ZX-6R Ninja, Aprilia RS125 2-stroke

[Rogerborg]

[Albigularis]

[Northern Monkey]

[Nemo]

[Kickstart]

[Rogerborg]

[Nexus Icon]

Actually, carbon-ceramic.
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[weasley]

[NeolWhyt]

Thanks guys

[talkToTheHat]

Carbon disks are prone to crack/shatter/explode if there is a flaw in them that concentrates stress. They are very fragile. You will note that motogp carbon disks are not vented, slotted or drilled as carbon is a worse conductor off heat than steel, so unless the disk is thick enough to vent radially as per a formula 1 disk, drillings mostly create local hotspots that hinder rather than help performance. As the disks are comparatively large, the heat mostly on the surface and are in the airflow, such provisions are not required in motorcycle racing when using carbon/carbon brakes. Yet.

Racing in controlled conditions on a closed course on a closed course of clean tarmac and are inspecting after each run ensures that brake performance me managed. Friction surfaces can be machined to deglaze as required, and will be cleaned after each run if required.

Contrast this to road riding where winter roads are filthy with grit and salt, and brakes do many thousands of miles between planned maintenance. Or off road bikes ridden through all kinds of adhesive gritty muddy slime. Or sand. Here the relatively light duty means ultimate braking performance can be compromised for more reliable braking.

A wavy disk can help remove debris from pads, much in the same way as a slotted or drilled disk can, only more so. They can also apply a light cyclic radial load to the pads which may keep the pads from sticking, and clear debris between the pad and caliper. There is also a big advantage in unsprung weight which will improve handling.

However, less weight of disk means less thermal mass, so the brakes will come up to operating temperature faster, and potentially overheat faster, depending on how well the excess heat can be exchanged with the airflow. A wavy disk has a high surface area to volume ratio and better structural integrity than a drilled disk with the same surface area and volume, so if chosen well, a wavy disk can offer moree efficient braking by reaching operating temperature faster and dissipate heat to the air more efficiently, or offer better streenght than a drilled disk.
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Bandit. does. everything.

[Pete.]

[davebike]

I seen well made ones that are fine but beware the cheap poorly made ones Saw one bike that was eating pads in 2/3 k miles EBC hh at that had same rider same use same pads but knackered UEM disks been doing 10K+

Good one look great if that is you thing
Cheap ones can prove expensive
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NC750Xdct + others at work !
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[totalllama82]

[lihp]

[Wafer_Thin_Ham]

[MarJay]

[talkToTheHat]

I have not paid careful attention to the use of them in WSB and BSB. I need a bigger TV. Have been reading around but I am a cheapskate and being out of academia no longer have decent access to engineering journals.

3 factors appear prominent: preventing glazing; allowing binder gasses to escape; and cooling. Wet performance is mostly unaffected.

Ideally, there should be uniform drilling or slotting of the rotors across the working portion of the disk. Drilled disks are easiest to machine, and with a good drilling pattern, an almost uniform pattern can be achieved across all but the edges of the disk. Slotted disks are an advance on this, with less thermal hotspotting and better stress distribution as curvature radii are grater. They sill do not sweep the entirety of the disk. A wavy pattern is perhaps best thought of as a slotted disk with slots at the inner and outer edges of the disk and can thus sweep the pad uniformly.

However slot size is limited by the size and compressibility of the pad. Some high performance brakes use one pad per piston as opposed to having several pistons acting on a single pad, which reduces the size of the hole that can be cut into a disk without the pad moving and wearing unevenly.

As the size of each slot in a wavy disk is large compared to the holes in a drilled disk, the amount of pad that domes slightly when passing over a slot is greater (try this with a clean sponge to visualise) the wear is accelerated.

Thus wavy disks perform favourably compared to slotted or drilled disks of the same ferrous metal. However proving they work in high stress environments is a complex FEA task, and in motorcycle sprint racing, uneven pad and disk wear is not a huge issue. Furthermore, development costs and higher pad wear rates are likely to offset any financial advantage in reduced glazing unless a specific glazing problem exists.

It may be the case that wavy disks favour a less compressible pad material than drilled disks, so may work better for riders preferring pads that give a harder lever feel.

I suspect the lack of slots or cross drilling in carbon disks is because they would de-laminate and flake around the slots. The radially drilled vents in carbon disks in formula 1 are a most impressive feat of manufacturing.

I suspect the right formulation of steel is more important than slotting design, which is where cheap disks may lose out over those from established brands.
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