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Old 11-28-04, 09:56 AM   #1
mosk
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Mechanical disc question -- best size for XC?

I'm going to be adding an Avid BB7 front disc to the new XC bike I'm building. I'm a 185 lb rider, and don't ride super aggressively. However, I do like to do some technical stuff, and also enjoy bike camping (where I might be carrying 20 lbs in panniers).

There's little price difference in the Avid BB7 series, as about $30 is all that separates their 160mm brakes from their 203mm brakes.

Any reason NOT to go with the 203's, or would that be overkill for someone not riding DH or FR?

Thanks,

Jeff
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Old 11-28-04, 10:32 AM   #2
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Its overkill. Unless you are 400 pounds, 203mm for xc is overkill.
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Old 11-28-04, 10:33 AM   #3
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203mm would probably be overkill for your weight and riding. I'm pretty light (150 lbs) but I've done some pretty long, steep downhill sections with my 160mm Hayes hydros and have never had any problems (Except when I broke the front brake lever in a crash and had to use only the rear brake on a 7-mile downhill...that overheated it.) That being said, the weight penalty should be unnoticeable and stronger brakes are never a bad thing.

One thing to watch out for: I've heard that some forks are not waranteed for use with 203mm rotors, many of them XC forks. It puts too much strain on the fork. Be sure to check for your specific fork.
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Old 11-28-04, 10:47 AM   #4
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Thanks for the info. Do you think the 185mm size is overkill as well? To me, it's a case of "for $10 more and little weight penalty, a bigger/better brake makes sense..."

This will be my first disc setup, so I have nothing to base this on. Oh, and FWIW, the fork is a Fox F100X.

Thanks,

Jeff
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Old 11-28-04, 10:49 AM   #5
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I am 270 and still use 6" rotors for xc. That should answer your question as to what I think
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Old 11-28-04, 11:09 AM   #6
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6' are really all you need. for $10 I would go with the 185s tho.

go out on any given ride and really keep track of your braking... how often and hard. Then just go off that. Most XC riding I do not really even brake all that much. When i do, it is for short distance quick stops. in all truth, 160s will be fine but at the same time it will give you a piece of mind when you have the 185's. I like knowing that I can stop really fast if I need to do so but I really only needed the 6"
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Old 11-28-04, 12:56 PM   #7
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i weight 150lbs and i used take my bike when i go camping. Although i dont' use panniers but instead i put my stuff in my 50L backpack which weight around 33lbs.

185mm rotors does make a big difference when you are decending like 30mph for quite a long distance.. but definitely you don't need a 203mm.

i used to own a pair of avid BB7 but i sold them and take the old 02' XT disc. But i am still using the avid rotors which i find them has the best braking performance. I am running 185mm on front and 160 on rear with my XT disc. I choose the 185 on front for the balance of weight and brake performance.

see my bike while camping

http://community.webshots.com/photo/...27540208suumIi
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Old 11-28-04, 01:37 PM   #8
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Your camping setup looks great -- similar to what I take with me.

I think I'll go for the 185's -- for an extra $10, it seems like a good deal.

Thanks, everyone.

-Jeff
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Old 11-28-04, 01:48 PM   #9
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I'm 180 and the standard disc can lock up the front wheel with light pressure on my Avid cable activiated discs. That's good enough.

Al
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Old 11-28-04, 02:57 PM   #10
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youll be very happy with the avid mechs. they're so adjustable, its great.
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Old 11-29-04, 12:19 AM   #11
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Originally Posted by Maelstrom
I am 270 and still use 6" rotors for xc. That should answer your question as to what I think
I'm a bit lighter and I use the 6" rotors for XC as well. I've never needed more.
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Old 11-29-04, 06:33 AM   #12
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I run front brake only, but went from a 203 to a 160 for safety reasons. I was told the 203s put a lot of strain on your hub, axle, and fork. For DH/FR this is ok because they have beefier forks, hubs, 20 mm axles, etc. Not so good for lighter XC parts.
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Old 11-29-04, 02:55 PM   #13
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Quote:
Originally Posted by enduro
203mm would probably be overkill for your weight and riding. I'm pretty light (150 lbs) but I've done some pretty long, steep downhill sections with my 160mm Hayes hydros and have never had any problems (Except when I broke the front brake lever in a crash and had to use only the rear brake on a 7-mile downhill...that overheated it.) That being said, the weight penalty should be unnoticeable and stronger brakes are never a bad thing.

One thing to watch out for: I've heard that some forks are not waranteed for use with 203mm rotors, many of them XC forks. It puts too much strain on the fork. Be sure to check for your specific fork.
What happened when it overheated? Whenever I screw up something on a steep descent, I try to turn as opposed to the trails' way by skidding rear and move to the side.
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Old 11-29-04, 04:51 PM   #14
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It started squealing really loudly and the power faded out. There was a significant reduction in braking power, so I stopped every once in a while to let it cool, then it was back to normal. I ended up skidding around a lot of turns to try to reduce the heating (the trail was mostly gravel so it didn't do any damage).
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Old 12-02-04, 12:52 AM   #15
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not to mention the extra stress applied to the disc attachment on the hubs because of the longer moment arm. BB5 are enough. I'm 200 lbs
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Old 12-02-04, 01:01 AM   #16
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not to mention the extra stress applied to the disc attachment on the hubs because of the longer moment arm. BB5 are enough. I'm 200 lbs
BB7's are so much better.
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Old 12-02-04, 01:02 AM   #17
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get the 160mm verrsion. if you feel you need more later, it's pretty easy to go up to a 185mm in front. all you need is the new rotor and adapter.

i've got a 185 front/160 rear setup on one bike, a 160/140 on one, and 160/160 on another. out of all those, i prefer the 185/160 combo. i only weigh 140, plus another 10-25 depending on clothes & pack weight.
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Old 12-02-04, 01:18 AM   #18
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Thanks. I ended up ordering a 160mm setup, so I'll see how that works out. I was all set to go with the Avid, but decided at the last minute to give the IRD mechanical Dual Banger setup a try. I'll post a review after I finish building the bike and ride some trails.

-Jeff
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