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203mm on my XC bike?

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flag odin333
Posted: Dec 2, 2007 at 18:00 Quote
alright so right now i have my XC bike (trek 6000) and just before the end of the season i somehow managed to grind a log with my front disc, and my back disc was already bent up. so now i need to get a new set of discs, right now i'm running 146mm not exactly sure though (its the average disc brake size).

so then i was thinking why not just put on some 203mm, i have Shimano Deore XT BR-m765 mechanical brakes by the way and i'll just buy the adjusters if i do get 203mm rotors.

but would it affect how i ride? most of the time i go really fast, actually beat a time record on a trail last year for my age group and i'm finding that its feels like the rotors are bending or under alot of preasure?

so should i go with 203mm or 146mm or another size?
flag foxmtbing
Posted: Dec 2, 2007 at 18:03 Quote
put some 160mm rotors on it. perfect for xc
flag crs-one
Posted: Dec 2, 2007 at 18:05 Quote
odin333 wrote:
alright so right now i have my XC bike (trek 6000) and just before the end of the season i somehow managed to grind a log with my front disc, and my back disc was already bent up. so now i need to get a new set of discs, right now i'm running 146mm not exactly sure though (its the average disc brake size).

so then i was thinking why not just put on some 203mm, i have Shimano Deore XT BR-m765 mechanical brakes by the way and i'll just buy the adjusters if i do get 203mm rotors.

but would it affect how i ride? most of the time i go really fast, actually beat a time record on a trail last year for my age group and i'm finding that its feels like the rotors are bending or under alot of preasure?

so should i go with 203mm or 146mm or another size?

phew! for a second i thought you meant a 203 mm fork!

anyways, no, don't run 203 mm.

if anything, what your feeling is brake fade, which can be alleviated with either new pads or huge rotors. i run deore hydros too, and i lvoe them, but pick up some new pads. there's some fade i find, but only when i heat them up so much that my spit sizzles on them.

but why not 203 mm? just overkill. you mentioned you hit your rotor on a log. running either a 140 mm rotor or 160 mm you hit a log, then chances are running a 203 you'll hit even more stuff. and frankly, for xc its just not necessary.

if you really want to upsize instead of getting new pads or something, then either get 160 mm if you're running 140 right now, or try out 185, but i would recommend that only if you're REALLY fast for an xc rider, and only on the front
flag bicyclerockers
Posted: Dec 2, 2007 at 18:09 Quote
i agree with him i thought you meant fork Eek
flag superfly26
Posted: Dec 3, 2007 at 6:36 Quote
I woldn't go more then a 185 unless you have a 20mm thruaxle. I have a friend who is very experienced with bikes and he told me that going with a 203 with a QR front axle is risky as the tourqe put on the rotor may in some extreme circumstance twist the wheel right out of the drop outs. I'm running a 185 rotor on the front of my bike with the BB7's and there is more then enough breaking power there. Even on really long decents. I did a 13 MILE downhill in Moab and they were awesome.
flag lilwalters
O+
Posted: Dec 3, 2007 at 6:51 Quote
i cant really see an XC bike needing more than a 6 inch rotor... DH bikes use 8 inch because they're 45 pounds and come screaming down the mountain... there isn't nearly as much momentum behind an XC bike... smaller discs also runner a smaller chance of warping and getting bashed off things...
flag louiffe
Posted: Dec 3, 2007 at 7:13 Quote
160mm disc is just on target. If you really want to try new things, you could put 185mm front and 160mm rear.
flag Ox-Bikes
Posted: Dec 3, 2007 at 7:29 Quote
What fork are running? Still have the stock Suntour XCR that comes on those? That fork is only rated for 185mm max if you check their website.
flag Quik5ilver
Posted: Dec 3, 2007 at 18:00 Quote
Correct me if i'm wrong, but the fork on his bike is a Rock Shox Dart.
This is taken right from the Sram/Rock Shox website
bigquotesMax. Recommended Rotor Size: 203mm
I agree with the other posts, 160mm rotor is pretty much perfect unless you really want more power. I would only upgrade/switch my front rotor to a larger size, as the front is where you get most of your braking power from.
flag nateb
FL
Posted: Dec 3, 2007 at 20:24 Quote
What you would ever need that much braking power for I have no idea. Don't do it, it's not needed and will look stupid.

nate
flag creamsoda
Posted: Dec 3, 2007 at 20:34 Quote
i'd go for the 7 incher if i weighed more than 180... otherwise stick to 160. i was looking at fsrxcs for a friend and noticed that the larger-sized bikes come with 7" in front and 6" in the rear, rather than 160mm (6") at both ends.

i've never seen or heard of a bike that runs less than 160mm in the front though... care to post your bike, disc side?
flag creamsoda
Posted: Dec 3, 2007 at 20:38 Quote
okay, i just went through your pics, bb5s don't even come in less than 160mm, you're running 6 inches front and rear right now, dude. it looks like a large or even xl frame so you'd probably benefit from running a 7 inch brake in the front. keep the rear at 6" and you'd be fine.
flag jack-gerry
Posted: Dec 5, 2007 at 7:43 Quote
203mm rotors would be a bit large for xc/all mountain riding and then force could bend your fork and/or frame.
flag fantaman
Posted: Dec 5, 2007 at 8:04 Quote
I did a year ago XC with 203mm rotors,They are not that overkill especialy for the long and fast decends.But i used them on any XC course and they never give's me goosebumbs that everthing gonna break.It's just maked the bike a litle heavy'r but it's ok to me.

I'd say give it a trySmile
flag rick76
Posted: Dec 7, 2007 at 14:38 Quote
i thought my 183mm was a slight overkill for xc but 203 is going a bit mad even dh'ers are mostly running only 180-183mm . go for 160 or 180 at the most even more so check with the fork makers that they are warrantied for large brakes as some fork companys dont warranty anything over 180mm !!
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