How 'perfect' should brake rotors be?- Mtbr.com
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  1. #1
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    How 'perfect' should brake rotors be?

    Hey folks,

    so I got my Kona Unit in December - love the bike itself, but the back brake/rotor is slowly but successfully driving me insane. Scrapes, whistles, howling - not when braking but when just riding. Can't say how many times I've tried to calibrate the stock Avid G2 Clean Sweep (160mm) rotor and the pad distance (first using this guide, but later on I've just been winging it since it doesn't seem to matter).

    So how perfect should a brake rotor be? As far as I could tell, the rotor weren't perfectly 'straight' to begin with, so I've very carefully bent it more straight. However, it also seems like the rotor is a smidge out-of-round so it rotates unevenly height-wise. Living in a smaller city, I've talked to this bike mechanic who's got the best reputation but even he couldn't help much. Might have to talk some sports store since they may have more knowledge when it comes to MTB's, but rather not do that since they'll take forever to (eventually) fix anything. Like weeks.

    So, what's my options? Will buying a new rotor sort me out? Should I replace the brake pads as well? It's bugging the hell out of me and it's gotten to a degree where I'm actually not enjoy riding the bike that much anymore. Any pointers?

  2. #2
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    If you can't adjust the brake caliper so that the brake doesn't drag anywhere in a revolution then the rotor is still buckled slightly. The inside pad needs to be as close as possible to the rotor without dragging (otherwise the brake will feel spongy) and the disc needs to be flat to set it up like that.
    If you can't true the rotor any better than how it is now then get a new one and fit that, plus some new pads in case they're contaminated. (or try degreasing them).
    It's important to bed brakes in properly too - 10-20 hard stops from speed, until the rotor is hot enough to boil water, is the usual way.

  3. #3
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    I actually have to adjust the brake in such a way that the pads are as far out as they can be. The result is a spongy and "late" brake feel. As far as I can tell, I did bed the brakes properly when I first got my bike - I don't know if they were hot enough to boil water but I sure did brake hard (at least 15 times). Going on what you're suggesting, it looks like I have to get a new rotor (and pads) and see what happens.

    Should I go for the same rotor or is there another/better one that I should go for instead?
    Last edited by jocke; 05-08-2015 at 02:21 AM.

  4. #4
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    Tosses match onto gasoline soaked thread...

    IMHO, rotors are rotors. Inexpensive Alligator rotors work just fine. Or you can spend a lot and buy arotor with an aluminum center. Either way, there's no way to know how the rotor will arrive at your door -- straight or wobbly. I've purchased from both ends of the spectrum and price has not really proven to be a guarantee of precision once you factor in the contribution of <insert shipping organization here>.

    It takes a little time and patience, but it is possible to true a wobbly rotor. I don't claim to be able to make one perfectly straight, but I can make them straight enough to quiet them down.

    I'd suggest replacing the offending rotor so you can ride, but I'd also get a set of truing tools and practice on the old rotor...
    -- let's ride

  5. #5
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    Just find out where it is rubbing and bend it back with a rotor truing tool or adjustable crescent wrench. dont worry about making it straight, just correct the rub. because as soon as dump the bike on the trail or ride the brakes too much you'll probably get another bend

  6. #6
    Clyde on a mission!
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    Quote Originally Posted by jocke View Post
    Should I go for the same rotor or is there another/better one that I should go for instead?
    Get better brakes.

    I've been in exactly the same spot, riding a kona unit that used to have bb7's and avid rotors. I rode them for a year or so, once in a blue moon they would run great, but most of the time I had the choice between brake rub or spongy brakes.

    A year in I bought some cheep shimano hydros and a set of ice tech rotors and they have been working like a champ ever since.

    I honestly find the bb7 design lacking. Having only one moving pad, bending the rotor towards the stationary pad every time you brake, that's just silly. IF, by pure luck, you manage to get the rotor nice and razor straight so you're able to adjust both the stationary and moving pad nice and close, you'll probably end up ruining it the next time you have a flat and struggle to put the wheel back in place without the rotor hitting the pads. Tighten the quick release slightly more or slightly less than before and you'll probably end up with the brake rubbing again.

    Shimano hydros starts at roughly $30 for a pre-bled kit with lever, hose, caliper and pads, all you need to add is a rotor. The advantage of two moving brake pads and self-adjusting pistons is huge, I've had zero maintenance on mine apart from replacing worn out pads once in a while. You can probably get away with keeping your current rotors, I splashed out another 20 bucks for some nice, straight ice tech rotors with a two-piece design.

  7. #7
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    Avid's are known for making noises ,I had some Juicy's that made noises at times.I had some exlicer's that were bad enough to get replace with some Shimano's.

  8. #8
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    Sounds like you just need to replace your rotors or take the time to true them. I have no issues with my BB7's as long as my rotors are relatively straight. Truing them isn't hard, but can be annoying.

  9. #9
    since 4/10/2009
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    A perfectly true rotor is really what you want for optimal use and performance and minimal irritation/frustration.

    Want a precisely trued rotor? Do this:

    Disk Brake Rotor Precision Truing

    Park makes rotor truing tools:
    http://www.parktool.com/product/rotor-truing-gauge-dt-3
    http://www.parktool.com/product/dial...ator-kit-dt-3i
    http://www.parktool.com/product/rotor-truing-fork-dt-2

    Feedback:
    IB13: Feedback Sports? Sweet Truing Stand w/ Disc Brake Rotor Guide, Fat Bike Stands & More

  10. #10
    Clyde on a mission!
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    I get why a truing fork can be useful but why would you need a rotor truing stand and optional gauge when you can just leave the wheel on the bike and use the brake pads for indication? Just dial you bb7 pad a bit closer to the rotor until it starts rubbing, use the fork to bend the spot that rubs, dial the pads one click closer, repeat bending whatever spots rub and so on. I don't see the difference between detecting and correcting a warped disc with an adjustable metal rod on a truing stand vs. an adjustable brake pad on something like the bb7.

  11. #11
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    Quote Originally Posted by Sandrenseren View Post
    I've been in exactly the same spot, riding a kona unit that used to have bb7's and avid rotors. I rode them for a year or so, once in a blue moon they would run great, but most of the time I had the choice between brake rub or spongy brakes.

    IF, by pure luck, you manage to get the rotor nice and razor straight so you're able to adjust both the stationary and moving pad nice and close, you'll probably end up ruining it the next time you have a flat and struggle to put the wheel back in place without the rotor hitting the pads. Tighten the quick release slightly more or slightly less than before and you'll probably end up with the brake rubbing again.
    This sums up my experience pretty much perfect so far. The front rotor is actually decent, so it doesn't rub when just riding (straight) but every other hard turn or so it rubs/howls. The back rotor/brake is way worse - currently I choose from A) riding with a howling jungle cat for a bike or B) super spongy back brake and almost completely rely on my front brake.

    Looks like those Drumstix truing forks are a nice addition to the toolbox, but honestly - I don't ride that hard at all. And if I can get away without this noise/headache by switching out brakes, I just might do that.

    Thanks for the help, folks.

  12. #12
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    Get new rotors.

  13. #13
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    I'm surprised at the love hate relationship people seem to have with BB7's. I personally haven't had any issues with mine in the 4 years I've used them and have no thoughts on replacing them. Lining up the caliper and having a fairly straight rotor is key though, but isn't that with most systems? Either way, I wouldn'tbe so quick to ditch the BB7 system. Sounds like the rotor needs servicing or replaced with a straight one. Once dialed in the BB7s are a solid system. Just my opinion though.

  14. #14
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    Not that I'm the most experienced guy on here - in fact, quite the opposite - I sense there's this 'either it's good or it's just not' type of scenario with the BB7 system.

    MikeAK, it's not that I don't believe you - it's just that I haven't been able to dial my brakes in even after countless tries. And if I somehow manage to somewhat dial the brake and pads in (in my case, it's the rear brake that's messing with me), I can't even get to work (just under 20 mins of commute) before the break is scraping, rubbing or screaming at me. Haven't made my mind up just yet on weather to get new rotors or just trying out a different system, just as Sandrenseren suggested. I'm leaning towards the latter though if I can get away somewhat decent prise-wise.

  15. #15
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    Quote Originally Posted by MikeAK View Post
    Once dialed in the BB7s are a solid system.
    Problem is, you can't just dial BB7s in once, they need regular dialing in to keep working.

    That might explain the love/hate relationship. I'll admit that when BB7s are dialed in and the rotors are properly straight they work just fine. Trouble is, that very rarely happens and it takes no more than a puncture to mess it up. BB7s, in my experience, is a constant fiddle.

    Not so long ago hydros used to be expensive, making mechanical brakes the preferred choice - and as mechanical brakes go I can understand the affection for BB7s and their adjustability. I shudder to think of non adjustable mechanical brakes. I get why people like BB7s for being the best mechanical brakes around.

    But hydraulic brakes are no longer expensive, you can get a decent set of shimano hydros for the same price as a BB7 setup and they work a whole lot better. Hydro brakes, in my experience, is set and forget. Yes it's a bit fiddly to cut the hose to length when you initially install the brakes, but once done and bled there is literally zero maintenance left to do. Years of strong, reliant braking with no fiddling what so ever.

  16. #16
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    I think you're making the BB7's come across as more of a headache than they really are and making hydros come off as being hassle free in the process. Plenty of people around here have just as many issues with hydros as you have with BB7's. There are a strong amount of riders who can also claim "set it and forget it" when it comes to the BB7's. I just know that I haven't had the same level of issues you seem to have had with the BB7's and I'm far from an experienced bike mech. Most of my knowledge has come from either doing it or watching videos on youtube. I am of the mind set of "If I can get them dialed in than anyone can". The BB7's have been a great system for me and it doesn't take the stars aligning for them to work, and/or work on a regular basis either. Many other riders share this view. There is a reason they are in the argument for best mech brake system ever.

    At the end of the day though, too each their own. I certainly don't think you can go wrong with either system in today's game. I just know that I wouldn't go out of my way to buy hydros and replace the BB7's because I know the BB7's are a solid system and not sure it's a forward movement, or a worthy expense. I can think of other upgrades that would have a larger impact.

  17. #17
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    I'm sure it's a great system once properly functioning and dialed in. But just like Sandrenseren, I'm having huge problems getting my brakes hassle-free and while I'm not a bike mech, following every goddamned guide is not working. Sure, I just might've gotten a crappy brake/rotor since my front one works so much better than the rear.

    In any case I was just interested and it sure seems to be several different experiences - and it does come with some comfort, hearing others that have struggled as well.

  18. #18
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    Quote Originally Posted by jocke View Post
    I'm sure it's a great system once properly functioning and dialed in. But just like Sandrenseren, I'm having huge problems getting my brakes hassle-free and while I'm not a bike mech, following every goddamned guide is not working. Sure, I just might've gotten a crappy brake/rotor since my front one works so much better than the rear.

    In any case I was just interested and it sure seems to be several different experiences - and it does come with some comfort, hearing others that have struggled as well.
    No doubt it helps to have others experiences align with your own. I will just add that each users situation is going to be different no matter how similar it sounds. Cables, pads, alignment, etc... so many variables come into play. The BB7's are far from a bad system and I wish you could get what I and many others are getting out of ours. The way BB7's have been working for me has me nowhere close to thinking of switching anytime soon. Saying that though, if I wasn't happy I certainly would be looking elsewhere. No doubt about it. When it comes to my bike it has to work, feel and look good in the process. Anything less and it's off. Good luck.

  19. #19
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    BB7's blow goats compared to TRP mechanical discs. My comparison is based on experience with BB7 mtb brakes & Spyre road discs so it's not quite an apples to apples comparison but I'm willing to bet Spykes will be taking a fair share of sales away from BB7 unless Avid redesigns them to engage pads from both sides. My BB7's were a literal & figurative headache & I am glad to never be dealing with them again.

  20. #20
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    Quote Originally Posted by MikeAK View Post
    No doubt it helps to have others experiences align with your own. I will just add that each users situation is going to be different no matter how similar it sounds. Cables, pads, alignment, etc... so many variables come into play. The BB7's are far from a bad system and I wish you could get what I and many others are getting out of ours. The way BB7's have been working for me has me nowhere close to thinking of switching anytime soon. Saying that though, if I wasn't happy I certainly would be looking elsewhere. No doubt about it. When it comes to my bike it has to work, feel and look good in the process. Anything less and it's off. Good luck.
    Sincerely appreciate the input - I'm glad some folks around forums are still helpful and civilised (one of the many reasons I like MTBR.com). I really had my hopes up that this bike of mine would be super fun, and don't get me wrong here - it really is, it's just a bummer when a single component brings that smile upside down. As said earlier, I'm still not entirely sure on what to do yet but thanks for the helpful pointers (goes to all of you who answered.)

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