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Rotors

Old 03-09-09, 04:30 PM
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Rotors

I'm new to disc brakes, like my first set of BB7s are in the mail new, but I've been researching them for a while and have been lusting after them for a month or more, and I'd like to see what people think about the different rotors available.

Do they actually make a difference? Will a rotor with more vent slots cut in it brake less but cool better and warp less? Setting aside size, are there rotors/rotor materials which perform significantly better?

I'll be using stock 185mm roundagon rotors with my setup, should be more than enough for the mostly XC riding I do, but if I were to ride more aggressively (my new parts are already doing this to me ) would there be any benefit to going with clean sweep or other rotors?

Also what makes centerlock any better than the 6 bolt IS? I understand it's different and proprietary, but why even bother?
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Old 03-09-09, 05:02 PM
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a rotor is a rotor basically, most are made of hardened steel, and brake pads are too soft to scratch them, they will all last forever xc riding unless you bash one on a rock.

larger rotors create more stopping force because of the added leverage i suppose. however rotors larger than 185 mm can have issues with standard quick releases, in other words they could rip them selves out of the drop outs.

i have noticed a difference between my standard avid rotors (roundagons?) and the clean sweaps, my standard avid rotors almost always have debris on them. the clean sweeps are alot cleaner, hence the name. the standard rotors are almost solid on the contact patch.

clean sweaps make more noise though: a subtle humming warblely sound. its hard to hear if they are adjusted right and not wet.

holes in rotors on the contact patch are mainly for shedding debris. heat isn't a huge issue unless you plan on riding the brakes for 20 minutes straight down the face of a mountain.

holes away from where the calipers contact the rotor are for saving weight, and looking cool. they do aid in cooling but i suppose its a marginal variable in the scheme of XC riding

the oldest set of rotors i have are cheapo-entry-level-shimano 160 mm. they have not warped. they are about 4 years old and. i have commuted for 4 summers to school and work. commuted one winter to work. i have close to a thousand dirt miles on that bike to and they are good as new, the contact patch of the rotors is the same thickness as the rest. basically i went through 3 sets of pads on the rear rotor and they look new.


i cant tell you whats better, centerlock or 6 hole. i prefer sixhole. however centerlocks are easy to swap between rims. i am probably going to buy a centerlock-to-six hole rotor adapter to expand my choices of brake rotors. the centerlock selection is rather limited. pretty much every company besides shimano uses sixhole
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Old 03-09-09, 05:06 PM
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Anybody know if there is any merit to the idea that Centerlock rotors are truer than 6-bolt?

As for the original question, my experience is that too many holes and slots and holes actually degrade performance because there is less metal to absorb and dissipate the heat.
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Old 03-09-09, 05:33 PM
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Ah, that's something I hadn't considered. There's definitely a lot more mass to heat up without the holes and metal transfers heat well.

They even seem to have rotors with inner sections designed to be a fan to cool the rest of the rotor..... seems kindof gimmicky to me.
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Old 03-09-09, 06:21 PM
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The metallurgy that goes into making rotors has to be amazing. I liken them to samurai blades because the red hot steel is cross-folded and flattened repeatedly... like in swords or cymbals where the molecular direction of the material becomes cross-hatched. Sometimes my rotor develops a slight side wobble from a knock, and this slight bend disappears after a really hard brake run. It gets really hot and when it cools down it kinda self-straightens because of it's metallurgy... I can't remember the correct term for it.

The cut-out patterns are not only there for cooling, and dispersing trapped dirt, but also for controlled expansion. Remember that unlike motorbike and automotive counterparts, bicycle rotors are only 2mm thick!

On extended downhill braking sections, these rotors get so hot you'd get heat-branded if you touched them. The outer "ring" expands more than we realize and the funny shapes are there also to control expansion and contraction to minimize metal stress and fatigue.

That's one of the reasons why the "spokes" on the rotors are usually curved and not straight - and why rotor designers prefer narrow pad contact areas rather than wide ones like in cars and motorbikes. You also have to take note of the "arrow" for the direction of rotation when installing them. The shape is deliberately stress oriented and it would be detrimental for the rotor if installed the wrong way.

.
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Old 03-09-09, 06:45 PM
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Originally Posted by Lebowski View Post
a rotor is a rotor basically, most are made of hardened steel, and brake pads are too soft to scratch them, they will all last forever xc riding unless you bash one on a rock.

larger rotors create more stopping force because of the added leverage i suppose. however rotors larger than 185 mm can have issues with standard quick releases, in other words they could rip them selves out of the drop outs.
I have heard the same thing.....but I have never seen it happen.
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Old 03-09-09, 06:53 PM
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Originally Posted by MIN View Post
Anybody know if there is any merit to the idea that Centerlock rotors are truer than 6-bolt?
In theory the big badass aluminum spiders looks like they would stay truer and brake quieter.

In practice, I have noticed precious little difference.
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Old 03-09-09, 06:55 PM
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^well I'f I haven't done it yet I suppose it cant happen... I broke everything else, LOL
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Old 03-10-09, 12:41 PM
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There is some difference in rotors,
I like the big wavy rotors as they do shed heat better or faster than the standard round ones.
Being a DH / free-rider and weighing in at 225lbs, I like good brakes. lol

That all being said, it's your first set of disks.
The BB7s are nice and will work well.
Ride with them and see if you really want / need the upgrade.
If you are not racing or do not need to have the absolute best, the standard 185s you have should be just fine.
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Old 03-11-09, 03:38 AM
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BB7s are all you will ever need. WANT ... now thats another issue.
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Old 03-11-09, 06:44 AM
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True,
Need and want are 2 very different things
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Old 03-11-09, 07:54 AM
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I'm interested in new rotors.. I got alligator serrated to save weight but i notice heat fade very quickly on steep descents less than a quarter-mile long. They brake noisily but saves 40 grams over roundactagons and stays cleaner. this is a 160mm rotor on a 700c cyclocross wheelset so i'm sure it introduces more torque into the equation than on a 26" mtb due to the larger radius.

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Old 03-11-09, 03:57 PM
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^ Very cool.

Seeing as there's very little metal left on that rotor + plus your heat fade issue, why don't you try different pads to see if it will improve... (harder or sintered pads, if it doesn't have those already)?

EBC makes an after-market sintered bronze pad that may work better for that rotor design.


.

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Old 03-11-09, 04:13 PM
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No rotor will give you more stopping power. Just the size of it will give you more power.
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Old 03-11-09, 06:47 PM
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Dang, there's nothin' to that there rotor
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Old 03-11-09, 06:53 PM
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Originally Posted by MIN View Post
Anybody know if there is any merit to the idea that Centerlock rotors are truer than 6-bolt?
I dont know, but I've got 6 bolt out back and centerlock. I personally think centerlock is one of those things to make you buy something new. I will say, while working on my bike at home, centerlock is a heck of a lot easier to deal with because you just drop a cassette tool in and pop it off VS having to take an hex key to each and every bolt.
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Old 03-11-09, 06:54 PM
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^^ If they took out any more metal, it'll be dental floss!
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Old 03-11-09, 06:58 PM
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Originally Posted by pocko View Post
^^ if they took out any more metal, it'll be dental floss!
lol!
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Old 03-11-09, 07:00 PM
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Originally Posted by WannaGetGood View Post
No rotor will give you more stopping power. Just the size of it will give you more power.
I can't agree... the diameter effects power and modulation, but so does friction (pad compound) and surface area (determined by the amount of holes/vents the rotor has.)
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Old 03-12-09, 03:21 AM
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Here's some more exotic ones... the second and the third are floating.





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Old 03-12-09, 01:54 PM
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that last one, looks like a saw.
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Old 03-12-09, 02:15 PM
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^ You'll notice the floating rotors don't have curved or diagonal spokes because the fasteners actually allow the outer disc to expand and contract, and also arrests heat transfer. This prevents or minimizes the risk of rotor warpage.

I think the Shimano center-lock rotor design kinda in-between a one-piece and 2-piece floating design. Some of the Shimano rotors are riveted to the alloy center so it would allow rotor spoke movement when the outer disc heats up and expands and so therefore reduces stress on the metal.

I don't know if it really matters in the end, because I haven't seen any one-piece rotors explode or crack even. I prefer the simplicity and the interchangeability of the universal 6 bolt standard rotors.

.
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Old 03-12-09, 10:56 PM
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Originally Posted by MIN View Post
I'm interested in new rotors.. I got alligator serrated to save weight but i notice heat fade very quickly on steep descents less than a quarter-mile long. They brake noisily but saves 40 grams over roundactagons and stays cleaner. this is a 160mm rotor on a 700c cyclocross wheelset so i'm sure it introduces more torque into the equation than on a 26" mtb due to the larger radius.
the g2 is lighter than the roundagon and the g3 is even lighter than that, prolly give you similar weight savings to those things you have with less noise and heat issues due to increased surface area

however how the heck do you get heat fade on a mech disc brake, their are 3 types of fade from heat (as far as I know): pad fade, you glaze your pads by overheating some of the bonding agents in the pad compound or somthin, you have to sand or replace your pads (so your ride is prolly over didn't sound like what you have) #2 fluid fade which is when you boil your brake fluid, lever goes to the bar and no stopping happens do to gas in the line, but you have mech brakes so... and lastly gas fade, this is somthin that happens on cars i don't think it can happen on a bike but what happens is some of the stuff in the pad vaporizes and you get a gas barrier between the pad and the rotor and the pads "hydroplane" exept on gas. Bike pads are prolly too small and too far from the rotor (cause the rotor isn't floating) for gas to build up, and the slots whould suck any gas out, that is one of the reasons fancy car rotors have slots or are drilled/dimpled.
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Old 05-30-10, 07:19 AM
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you want some of these:


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Old 05-30-10, 11:09 AM
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rotors don't determine stopping power; the tires to. you can have 48 pistons and 1200mm rotors, but you can't stop any faster than your tires let you.
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