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  1. #1
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    My rotor hit my fork

    well it used to, i would hit the brakes, rotor would flex and hit the fork. this would force it into an out of dish condition (not out of true, there was no wobble, but it was bowed outwards towards the fork)

    rotor was replaced and the problem imediatly went away

    fork was a Dart3, hub was stock specialized rockhopper disc hubs. so whatever they call it, brake setup was Avid BB5s with a 160mm clean sweep, all were bolts torqued to spec, and the quick realease was very tight

    and yes the rotor was installed in the proper direction

    ummmm other than that... explaination would be nice, it doesn't bother me anymore but hey, it's an odd problem so have at it.

    Pictures: sorry about the iffy quality, taken on my mobile

    Quote Originally Posted by Lelandjt
    Do you mean an out-of-true condition? Like the rotor would develop a wobble? This is puzzling but I assure you there are no lateral forces applied to the rotor. Look at it. When you apply brake to a spinning wheel the caliper applies equal pressure to both sides of the rotor. This does create very strong torque force between the rotor, which is attached to the hub and the caliper, which is attached to the fork. Look at the various connections between the caliper and rotor. Caliper mounts are pretty stiff (looks like you have post mounts on your fork which are very stiff), rotor mounts on hub are pretty stiff (I've never noticed flex from a 6 bolt hub).
    This leaves the fork/hub interface and the hub axle and bearings. Is your hub of high quality with properly adjusted bearings? If so it probably isn't flexing much but its axle will flex some. The thinner the axle the more flex. What axle/fork interface do you have? If it's a standard hollow axle with a QR skewer that is a known flexy system. A solid 9mm QR like Specialized's Skraxle (sp?) is stiffer and of course QR15 and 20mm thru axles are much stiffer.
    This is all meaningless speculation because you've managed to solve the problem with a different rotor but I can't see how this made any difference besides possibly a slightly smaller outer diameter that doesn't reach the fork, despite the other components flexing just like before.
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    Last edited by AlexJK; 08-22-2009 at 01:36 AM.

  2. #2
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    why is the lower 3-4 inches of your fork broken off?!?!?! That is what i'd be worried about. Have you replaced this fork yet?

  3. #3
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    You should copy and paste my long hypothesis from the other thread. Now that I know what fork, hub, and brake caliper you were using it makes more sense. That is a very flexy fork and hub. That brake, being cable actuated, pushes the rotor from only one side. It's up to the mechanic to set the static pad as close to the rotor as possible to minimize lateral flex of the rotor.
    If you get a chance try a friend's bike with stiffer everything and you'll immediately feel the difference.
    Keep the Country country.

  4. #4
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    well, this is the umpteenth dart3 that i've broken, i finally got smart and bought a Reba

    thing is is that the rotor was replaced with this same setup, problem went away.

    and will do

  5. #5
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    Quote Originally Posted by Vortechcoupe
    why is the lower 3-4 inches of your fork broken off?!?!?! That is what i'd be worried about. Have you replaced this fork yet?
    it broke because it would flex (ALOT) under braking, over time it would just crack

    then again i do weigh 220

  6. #6
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    I just bought a pair of BB7's. I have a Dart 3 on my bike. On the rockshox website it says the max size of rotor you should put on is 160. I orderd a 185 in the front and im not sure if it will rub or anything or wreck my fork. Does anybody have this setup or will I have any problems with it?
    Thanks.

  7. #7
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    depends on your weight, my problem was that i would hut the brake and the rotor bould twist and hit the fork.

    whats your weight?

  8. #8
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    A larger rotor creates more torque. Rockshox knows this is a flexy fork and that a 7" rotor will twist it. The kind of riding that would necessitate a 7" rotor (long, brake heavy descents on large, grippy tires) would be outside the intended use of this entry level XC fork anyway.
    Either you bought the wrong rotor for your riding or the wrong fork.
    Keep the Country country.

  9. #9
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    he is right, the BB7s should be plenty, HOWEVER! the lighter you are, the more you can get away with, back when i had a Dart3 i searously considered dropping to a 140mm rotor because i weigh 220 lbs. that would trade off with braking power though.

    i suggest you go and get a RS Tora or somthing similar, it's such a MASSIVE upgrade it's not even funny (well from Dart 3 to Reba Race, i can't really comment on the Tora, but i'm 100% sure that it's 100% better)
    i know that the Reba has gobs more adjustibility, the dart's rebound goes from fully slow to wide open in like 1/3 turn.

    The Reba does the same in like 7 turns, as well as having dual air chambers, external floodgate adjustment and optional remote lockout.

  10. #10
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    I weigh like 120. Im just a 13 year old kid who discoverd the great sport of mountain biking. I know if my Dart 3 sucks but I will have to live with it until I upgrade. I don't know what the LBS said but I will tell them about it.
    Thanks.

  11. #11
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    At 120lbs you don't need a 7" rotor. Get a 6" and everything will be fine.
    Keep the Country country.

  12. #12
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    Quote Originally Posted by AlexJK
    well, this is the umpteenth dart3 that i've broken, i finally got smart and bought a Reba

    thing is is that the rotor was replaced with this same setup, problem went away.

    and will do

    2 words:

    Through-axle.
    Oh noes. I'm going to drink the Kool-Aid.

  13. #13
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    yeah, i'm 15 weigh 220 and i still run my 160mm with BB5s, it stops me just fine, one finger stoppies are pretty easy (i don't really ever do that but i can if i want to) as is locking the front wheel (don't try that, it's a bad idea if your not REALLY good with your bike, and even then it's a bad idea)

  14. #14
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    Quote Originally Posted by jcaino
    2 words:

    Through-axle.
    you mean the DT swiss things or like a Maxle?

    i REALLY wanted the maxle fork but i didn't have the money to spend on a hub to work with it

  15. #15
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    thanks. I will consider those ideas. It's nice to talk to people who know what they are talking about and have some experience.

  16. #16
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    Quote Originally Posted by AlexJK
    you mean the DT swiss things or like a Maxle?

    i REALLY wanted the maxle fork but i didn't have the money to spend on a hub to work with it

    Yes, Maxle is a type of though axle.

    Way more sturdy for you bigger guys. Somewhat safer if you're already breaking things...
    Oh noes. I'm going to drink the Kool-Aid.

  17. #17
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    Quote Originally Posted by jcaino
    Yes, Maxle is a type of though axle.

    Way more sturdy for you bigger guys. Somewhat safer if you're already breaking things...

    that was exactly my logic. i was thinking that maybe in the future i'd swap the lowers with a maxle style lower.

    and at the same time maybe upgrade the frame


    until then i've been running the shock pressure slightly lower and setting the negative at 7 psi above the positive. that along with running the tires at around 40psi, all to reduce the forces in everything to keep things together

    i need to get some stans sealant to do ghetto tubeless, all the shops have is the stans kits.



    on another note, i just got my hub replaced and couldn't ride for about a week and i hopped back on and the front end seems alot harder to pull up on... normally if i can't ride for a while i start doing things like a pro when i get back on. this time it's like riding a completely different bike...

  18. #18
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    Wow, just wow. But yeah at 120lbs you can safely run a 9" rotor lol.

  19. #19
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    the only thing I can imagine that would cause the rotor to flex and hit the fork is if the caliper is tragically mis-aligned. if it was straight, there would be no reason for the rotor to flex enough sideways to hit the fork. there is no side-to-side force on the rotor with a reasonably aligned caliper. The caliper would have to be really, REALLY, jacked sideways.
    09AS-Rsl/09Six

  20. #20
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    the LBS was pretty stumped too, the caliper was aligned properly.

    it would only do it if i was moving, and it was damn hard to explain to him cause hes a stubborn as f*ck asswhipe...

  21. #21
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    it would flex like a wheel would if the dropouts arent tight

  22. #22
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    I suppose if there was some flex somewhere between the hub and post mounts then the caliper would temporarily mis-align.. but I don't see how a new rotor could fix that.
    09AS-Rsl/09Six

  23. #23
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    well it did...

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