Skipjacks

Does the hole pattern in a brake rotor make any performance difference?

I've heard claims that a pattern like this...

...where the holes are traveling in line with the rotation of the rotor are quieter and smoother than a rotor where the holes run across the path of the rotation like this...


Does the pattern of the holes matter at all?

Does it impact performance?

Can it change how noisy they are?

Or is it all just a marketing gimmick to make different rotors stand out?

jimc101

Different brands, different designs, still a steel rotor; in use, they will both perform the same

fietsbob

Who are you going to send a collection of discs to, to do a scientific test ..

of the minute differences there may be between the many options,
to actually get data results.??

one thing I Read,
when the Cyclocross Worlds , 1st had a few bikes using discs, was,
they had to scramble a set made,

Made , and shipped overnight, because .. the race lap has a sand pit,
and the holes in the disc ,
retained enough sand grit, that the disc pads did not even last an hour ,
the length of the Sr Men's race.

so needed a set with no holes at all..


carry on..



...

hokiefyd 

The rotors on my bike resemble the ones in your second picture. If I lightly drag the brake with the bike on the stand, or brake with moderate force at speed out on the road, I can hear the "singing" of the openings in the rotor. It sounds like the old playing-card-in-the-spokes trick, only much less intense obviously. With the rotor in the top picture, it probably makes sense that you'd hear less of that. From my understanding, the only "hard and fast rule" is you want the entire surface of the pad to be scraped by an opening in the rotor, to help keep them cleaned off. The rotor in the first picture looks like it could potentially leave the upper and lower edges of the brake pad without an opening to keep them scraped clean. If you switched to a rotor like that, you may want to observe how the pad material is laid down on the rotor, to see if you have any pad material above or below the holes that doesn't get scraped (if that "rule" is really valid in the first place). The pad material laid down on my rotor shows that no part of the pad is not scraped.

Other than that, I think rotor styling is mostly cosmetic. "Road" rotors tend to be pretty circular without a lot of shape to the circumference. Maybe to address fears of personal injury during a crash? I don't know. A lot of "mountain" rotors seem to have much wilder styling, perhaps to appear to different personalities riding the bikes. I'm personally drawn to rotors like in your first picture, only because I think those look more conventional (like automotive and motorcycle brake rotors). I don't think the styling likely makes much of a difference. Different metallurgy and structure probably matters more to performance.

The rotors do seem to quiet down as they wear in. My rotors were pretty loud initially, but they've quieted down after a few hundred miles, to the point where I really don't hear the brakes anymore unless I'm specifically listening for them.

TimothyH

What matters is mass.

A rotor with more mass is able to absorb and dissipate more heat - able to withstand repeated stops and prolonged use better than a lighter rotor.


Not all rotors are plain steel. Shimano Ice Tech rotors are steel braking surfaces over an aluminum core. The design is supposed to help conduct and dissipate heat better.

jimc101

If that, or performance was an issue, you would choose a better rotor, not either of the 2 pictured, for the average rider, the difference is not going to be noticeable in normal use.

fietsbob

Another opinion collection You really cannot expect more for the price of the entry ..

Skipjacks

What's your story?

I asked an honest question to help myself better understand a biking component. You immediately gave me a bunch of junk about how I couldn't have rotors scientifically tested or something.....

Now you're upset that people are offering opinions....that I specifically asked people to offer?

Just skipping the thread and ignoring it was an option.

To the rest of you in this thread....I appreciate your opinions and insight. I've wondered about this for a while and there is surprisingly little information about the hole patterns in brake rotors online. As I've only used 1 set of disks I don't have comparative experience to see the differences first hand.

It seems like you all feel the quality of the metal the disk is made of is more important that the hole pattern. That makes sense.

fietsbob

I'm saying a large sampling sizeneeds be collected to assess difference .. and collect the data..

test controls ... the whole consumer reports lab set up.

you just wanted opinions. i got an 'X' and I like it abounds..

Cyclist0108

He has that huge post count because he pollutes pretty much every thread with his random word generator and arbitrary sentence constructor.

Occasionally there is a small signal buried within all the noise.

Rarely.

Skipjacks

Oh. So it wasn't just me then.

Cool.

I feel better.

hokiefyd 

I asked a similar question here a few months ago: link. Though, in that question, I was asking more about the cooling vanes/fins and/or extra material in the center of rotors often marketed towards road bikes. I took responses in that thread to say, generally, that road bikes have the potential of higher braking duty cycles (though some disagreed), and that was the reason for the difference in rotor styles (extra cooling on road rotors). Some MTB rotors indeed appear to be pretty skeletonized, with seemingly more open areas than braking surface sometimes! If you search eBay for "mountain bike rotor", you see all sorts of oddly styled shapes and colors...again, mostly cosmetic I presume.

The specific rotor in your first picture appears to be a SRAM Centerline. You can Google that and find various SRAM marketing pages and user opinion on those (which seems to be all positive). For single piece rotors, they're not cheap (over $30 each), but I presume they're of good quality. (There look to be a number of fakes sold on eBay as well!)

I can only guess that a heavier rotor and/or one with fewer holes might be better-suited to a bike with more braking demands, and I imagine this type could contribute to rotor or pad glaze if not worked hard enough (to raise the temperature). Highly skeletonized rotors may be better suited for bikes with a lower braking demand, as they may help keep the pads scraped better. That's only a guess.

Like you, I'm often drawn to ponder things like this. Why is something the way it is? This forum is usually good at enabling that for me.

cyccommute 

It's not quite that simple and counter to what we know about heat dissipation. A heavier disc without more surface area...i.e. a solid disc... would retain more heat, not dissipate it.
With holes, a slightly heavier disc might dissipate heat faster because it would have a slightly larger surface area due to being slightly thicker but it would only be slight and mostly overshadowed by the larger retention of heat due to the mass of the metal.

cyccommute 

I can see how the rotor with the longer holes could be quieter because the pads aren't sliding over as many holes. It would be difficult, however, to say if they would be more effective at stopping. The second rotor looks like it has more surface area due to the greater number of holes. It might dissipate heat better. I would say that heat dissipation is far more important than noise mitigation in terms of performance.

Cyclist0108

Nope.

It is his MO. He just scans the title and posts whatever pops into his head, oblivious to any context.

Here is a quite striking example:

https://www.bikeforums.net/bicycle-m...-11-speed.html

(Anticipating a more rational objection on the same lines, I opened the question with a formatted boldface heading explaining why I might want to do this. But it is all wasted keystrokes for Mr. Feits. He already knows the answer, so no point in actually reading the question, lest he be delayed from dispensing even more of his valued wisdom elsewhere.)

Skipjacks

So many things just work and I don't NEED to know why....but I desperately WANT to.

fietsbob

Have an engineering course of study planned?

asking the question is the easy part..

Asi

Engineer coming trough.
For breaking there are several design factors to consider:
Mass, cooling surface, brake area, lateral stiffness, pad material.

1. Mass - more mass -> better at storing energy in the initial breaking. Given the same cooling area (and same other characteristics), more mass is always better for braking. (not better for dynamic response of wheel suspension and others but better for absorbing energy in heat form.. it will heat slower, dissipate heat slower, but overall is lower temperature than a very thin disc that will heat in an instant to very high temperatures)

2. Cooling surface => more is always better. There are several types of cooling possible:
Double disc ventilation with a webbing between two braking surfaces (like a car rotor)
https://speed.academy/wp-content/uplo...-Brembo-03.jpg
This is one of the best cooling designs,

Cooling fins outside of the breaking area (the biggest problem is the speed that heat migrates from the braking surface to the cooling fins - for this there are oddities with heatpipes inside the solid disc near braking area to connect with a massive finned radiator on the hub - the biggest problem is brake rotor thickness since it will be big it will be more easy to make it double disc type ventilation, and the fact that heatpipes are not that great for any range of temperature but a quite narrow interval between 150-230degrees celsius for example. Also heatpipes are affected by centrifugal forces and might interfere with the movement of the water vapor inside heatpipes from the hot site near the outside to the cold side near the hub).

Next in line is increasing surfaces on the brake surface with holes and slots - it's a very weak increase of cooling since the thickness is not that great and not much surface is added and have big disatvantages (weaking the rotor, thermal shock in hole area, less surface of contact will limit maximum brake force since the pressure can't be increased. Their primary function is/was completely different (explained a bit further)

The lowest form of added cooling is adding fins on the hub area. It might have great cooling potential, but the heat travels slowly trough thermal conduction of the steel/iron disc. - usable for a solid rotor with lots of mass (like a car disc with 3kg mass and 12mm of solid disc thickness).

3. Brake area. More is better (given the same outside-inside diameter). So any holes that decrease the area will give less braking force. The reason is the limiting factor: the pad material that withstands only a set limit of pressure lets say 0.4MPa. So for that kind of pressure on the pad, if the area is less, then the axial force from the piston must be less. This is easily corrected by putting larger pads trough design to mitigate the pressure problem.

4. Lateral stiffness is important to prevent warping of rotors. Rotors warp because of thermal difference (on the outside of braking area vs the hub area) and because of minor differences in pad pressure left-right (slight differences in drag of pistons, or resistances in the sliders or a floating caliper, or others). Ways to improve the stiffness - make it thicker, separate the brake surface from the center spider support with a loose fit to prevent transfer of heat from brake surface to the hub spider (done often on motorcycle brakes), add more "give" and play in the system to limit the need of stiffness for any imbalance of the pad forces (floating caliper, floating disc and a mix of these. especially important on very thin disks)

5. Pad material is important since not all recipes give the same performance. For this there are the friction coefficient variation with temperature and the decomposition of the pad material into gases or liquids resulting in brake fading. So a normal recipe for standard pad material is one that gives higher coefficient of friction when cold and a lower coefficient when hot with no gas or liquid decomposition at high temperature. - this is standard for most cars and i believe is quite similar to bike brake pads.
Sport/competition pad materials were engineered to have high coefficient of friction when hot. Older sport pad had several disadvantages in releasing gases when heated, and those gases were trapped between the brake surface and the pad. This is the reason for crossdrilling and slotting of rotors - to evacuate any gases that might be trapped. Newer sport pads have diminished the gas generation through other pad recipes and materials thus needing less (or no) drilling or slotting. Look at heavily engineered vehicles to confirm this: look at F1 rotors.. older 90' and 2000' had drilled and slotted rotors, newer F1 have plain braking surface with no drilling or slotting present.

Now from all of these i can see the following being applied for bike brakes:
Low energy to disipate = > in theory a very thin disk with tiny breaking surface to maintain the maximum pressure on the pad surface. But since thickness of rotor can't be less than what already is (structural integrity) and the pads can't be very small to operate at their limit pressure.. so a "normal" looking sized pad will operate at a MUCH lower pressure than it's maximum for that pad material. So since there is a lot of room to spare in the pressure department might as well throw a fancy design on the rotor that will increase the pressure on the pad (and even so will be likely still way lower than it's maximum pressure rating). Any cooling bonus from the massive cutouts are welcome but not needed in any way (because of the low energy). - if cooling was a major issue a double disc ventilation would have been adopted but as you can see even in motorcycles.. the hassle of heavy double disc is avoided by several tricks with solid rotors. Mainly because the energy is low even in a motorcycle.. braking 300-400kg at the max deceleration supported by the motorcycle before front flipping (same for bikes) is a lot lower than a car that has quadruple mass and can develop the max deceleration limited by the tyre-road interaction rather than tipping point on taller short vehicles.

In summary bike forces are quite low and is room to spare on that standard size brake rotor to throw cool designs and skeletons and holes and waviness and whatever and the marketing department will tell a cool story about how it has improved performance or whatever.

A correctly sized rotor for a bike brake can have a very small area of braking to reach the max limit pressure on the pads but this will increase the pressure in the hydraulic system as well needing a lot more travel and force to reach several hundreds of bars inside the lines opening another can of worms. So i feel bike brake rotors are way bigger than needed to have low pressure in system and have less issues with leakages and piston/pump tolerances.

As always, any finite product is a compromise in engineering. And for bikes the part that is compromised at it's to lower price by needing less perfect levers and rotors and calipers and use normal materials for pads/fluids/rotors.. so any approach at designing a better braking system for a bike will probably look different, and a LOT more expensive (by using special materials, higher pressure, high tolerances, etc), probably lighter just a bit for about the same performance.

cyccommute 

I r a engenier

(Brakes, no "breaks". Through not "trough"...that's what horses drink out of)

If you have power to spare, mass isn't a problem. But bicycles are limited in the amount of mass that they can carry so the brake rotors have to be a light as possible. And, as you have pointed out, the thin rotors for bicycles heat to very high temperatures very quickly so they need to shed heat as quickly as possible. The smaller mass will dissipate heat more quickly in the lightweight system of a bicycle.

In many respects, this is a failing of the hub mounted disc brake for bicycles. Rim brakes are already spinning disc brakes but they have larger surface areas and deeper heat sinks (tire, tube and rim) so they can absorb more heat and dissipate it better.

That works for cars but not for mass limited vehicles like bicycles. Adding internally finned rotors like what cars and motorcycles use would cause unacceptable increases in wheel mass that no cyclist outside of some downhill mountain bike riders would accept.

Again, any increase in pads increases weight which is unacceptable.

Still a mass problem. And another failing of the hub mounted disc rotor for bicycles. The rotor is easily bent and not so easily straightened.


I don't think that the holes in the rotors help much with gas management but I do think they are needed for heat management. People are reporting that their rotors glow red at night which tells me that the rotor is heating too much and needs something to help shed heat. The larger surface area from the cutouts help and self-propelled bicycles really can't afford a mass increase that would come with double walled rotors or solid rotors.

I would most certainly agree with your conclusions. The difference in performance between the rotors above would probably be minimal. It might be important in competitions but not in day to day use.

fietsbob

way back was these :

disc , the friction material, pads were metal

Asi

Sorry for my bad English.. not my first language and auto-correct corrected to the wrong thing. About the rotors.. i was talking in general. In particular for a bike, the mass and cheapness of parts is more important than actually redesigning a brake system for the actual bike loads. So there is plenty of room to shave weight so the massive cutouts are primarily for that (rather than gas management). So what I was trying to point out is that a bike rotor is not actually engineered for those loads.. but something that works and that it can be made thinner and weaker because it's plenty of room to spare - hence the wild designs.

Same thing happens even in automotive world.. i see plenty of sport brake kits with drilled rotors and slotted rotors but they are not using the gassy type pads, but the new gas-less pads.. so it's done only for show and design and actually is bad because of high thermal stress around holes that crack rotors near every hole. Fortunately this in not happening when real engineers redesign the whole braking system to match the actual vehicle forces like in F1 or airplanes.

There is a reason why you will never see such wild designs (with so many cutouts, nearly 50% of the surface) of brake rotors for cars.

cyccommute 

Just yankin' your engineer chain. We chemist like to make fun of engineers. No insult meant by it just having some nerdy fun

I'm not a car person but I get what you are saying and I agree with your points. I don't think there would be any real difference between Skipjacks rotors in terms of performance. His first example is a bit more ascetically pleasing, however.

gsa103

The top design is a typically Avid/SRAM, which have a reputation for being noisy (google Avid turkey warble).
The bottom design a standard Shimano, which are generally considered to be good.

In theory, rotor design might play a role. But user experience indicates that the top design is definitely not a noise cure-all.

TiHabanero

I worked in the motorcycle parts biz and hung out with the motorcycle racing crowd for a few years. We all sold parts and used to joke about the idiots spending huge dollars on rotors thinking they were getting super awesome stopping power because the holes were arranged just so or it had waves like this or that.
Just get a decently thick rotor to resist warp and let the marketing and project managers worry about how it looks.

Skipjacks

So that search sent me down a rabbit hole of research

A lot of people say that if the turkey warble isn't there initially and only starts after the bike has been ridden a mile, it's because the temperature of the rotor is adding to the problem.

I have this issue. The rotors make god awful noise after I've ridden for a bit. And its' worse in the summer than the winter. So this heat thing has merit to me.

Seems like a rotor design that dissipates heat better is worth trying. The whole pattern shouldn't impact that. But other design features can.