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Old 10-03-07, 10:29 AM   #1
Zinn-X
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185mm rotor on XC fork, why not?

I'm looking at adding some Avid disc brakes to my Fox F90 RL fork. Avid's product literature recommends not putting bigger than 160mm rotor on a cross country fork. Why the hell not? I know it will fit on there, so what's the problem? There are some extremely steep hills around here and the extra stopping power would be lovely.

I'd do 160 mm in the back... so, what's the problem? Is this just a weight-weenie / bike fashion faux-pas thing, or is there a practical reason why 185mm rotors = lose on an XC fork?

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Old 10-03-07, 11:11 AM   #2
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On some forks the mounts aren't strong enough to handle the force the 185/203mm put out. On others, it may start to rub the lowers? Not sure.
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Old 10-03-07, 12:32 PM   #3
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You should look to see what Fox says about how big of a rotor you can put on. Avids recommendation is most likely made to cover a wide field of XC forks, some of which cannot handle more than 6" rotors. My guess is that you can put at least 7" up front.
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Old 10-03-07, 02:21 PM   #4
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On the '08 Specialized FSR xc line in a large frame 203mm are standard front and rear.
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Old 10-03-07, 06:54 PM   #5
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well, i looked on Fox's documentation (online) for this fork and it mentioned absolutely nothing about disc brake rotors. I highly doubt installing a 185 rotor would wreck anything, so i'm probably just going to do it. (when i get some $$$)
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Old 10-03-07, 06:58 PM   #6
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As diameter increases, force increases on the rotor and hub. Not the fork.

If what you said were true, then rim brakes would destroy forks.

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Old 10-03-07, 07:00 PM   #7
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well, i looked on Fox's documentation (online) for this fork and it mentioned absolutely nothing about disc brake rotors. I highly doubt installing a 185 rotor would wreck anything, so i'm probably just going to do it. (when i get some $$$)
I know quite a few folks that run 185 rotors on QR forks with no issues. You'll be fine.
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Old 10-03-07, 07:05 PM   #8
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The concept of a lever arm is new to you?
Nope.
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Old 10-03-07, 07:39 PM   #9
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I know quite a few folks that run 185 rotors on QR forks with no issues. You'll be fine.
Quick Release forks? are we confusing threads here? ??
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Old 10-03-07, 07:40 PM   #10
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Quick Release forks? are we confusing threads here? ??
no, we aren't. There are different axles.
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Old 10-03-07, 07:57 PM   #11
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Quick Release forks? are we confusing threads here? ??
No. You wanted to know if it would be OK to put a 185 on your Fox fork whick is a QR fork(not a 20mm through axel) My friend Hambone has one on his Float,Girlscout has one on his Vanilla so yeah you should be fine.
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Old 10-03-07, 08:41 PM   #12
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I'm pimping a 203mm rotor on my 32 talas.
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Old 10-03-07, 08:56 PM   #13
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Quote:
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As diameter increases, force increases on the rotor and hub. Not the fork.

If what you said were true, then rim brakes would destroy forks.

If you knew what in the heck you were talking about, you would realize that rim brakes disperse tension fairly evenly which means the fork won't twist like it will with a disc brake. Yet once in a blue moon you will see a broken fork with rim brakes because of pilot error.

I've never seen a hub destroyed because of a rim or disc brake.
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