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Do I realy need 8 inch rotors?

Murf

Chimp
Mar 28, 2008
8
0
I just do trail riding so do I need 8 in rotors. I have hfx 9's and need to get some new rotors. I have 8 in on the front now and it works great but would 6in work ? Also I weigh around 200lbs and my bike is 32lbs
 

Timekiller

Monkey
Oct 9, 2006
697
0
NJ
I like my 8"-er's... I had 6 on my trailbike, didn't like them, but they were also bottom of the barrel Shimano Deores.

You should be fine with 6
 

ultraNoob

Yoshinoya Destroyer
Jan 20, 2007
4,504
1
Hills of Paradise
If you're not doing gnarly decents where you're on your brakes for an hour or you're not going at insane speeds and expect to stop quickly, then you won't need 203's. Used to run 203's on my trail bike, but I had Hayes Sole's (ultima suck, never buy that model) and that was the only way I could come to a stop. With 9's, all you'd do with 203's on your trail bike is look aggro.
 

jeremy_2640

Monkey
Oct 4, 2007
114
42
Melbourne
Why would you want to change though, it would be negligble weight difference and price for an 8 inch would be cheaper because you'd need an adapter to run 6"....
 

MikeStanfill

Chimp
Mar 24, 2008
27
0
Alaska
On my xc bike I run 8" in the front and 7" in the rear. I'm not a big guy (140 lbs), but I do appreciate the extra stopping ability of them. Also, sometimes I do a little downhillish stuff up in the mountains near me, so they help out there too.
 

FR4life.

Monkey
Nov 2, 2004
606
0
The Bay
I run a 7" front 6" rear on my ht. I have both 8" on my dh rig, but I kind of want to swap out the rear for a 7 or maybe even a 6. having an 8" back there just makes my back wheel lock up too easily imo.
 

ultraNoob

Yoshinoya Destroyer
Jan 20, 2007
4,504
1
Hills of Paradise
... having an 8" back there just makes my back wheel lock up too easily imo.
That's a great point! When I rode at snow summit last, I ran a 6" rear brake setup and I felt more in control on the super loose stuff. Granted I was running a clapped out Hayes HFX with worn pads that wouldn't lock the rear tire unless I'm riding up hill, but my rear tire rarely locked up on the steep and loose.
 

moose99ps

Chimp
Jun 11, 2008
69
0
bend, oregon
so im noob to the disc brake stuff on mtb. how is it that the larger rotor stops more? does the caliper change with it? giving it a larger pad? im a auto technician by trade so im not completely bike retarded but sometimes these things make me feel that way
 

Lelandjt

Turbo Monkey
Apr 4, 2008
2,508
822
Breckenridge, CO/Lahaina,HI
so im noob to the disc brake stuff on mtb. how is it that the larger rotor stops more? does the caliper change with it? giving it a larger pad? im a auto technician by trade so im not completely bike retarded but sometimes these things make me feel that way
Come on, you can't figure out leverage by looking at it. Yikes, this is why I work on my own car. The calipers and pads are the same, it's purely differences in leverage. You've never seen a car with a "big brake kit"? They're popular with sport compacts.
 

ansdy

Chimp
Jul 27, 2008
5
0
The way I see it, it depends on a whole bunch of stuff- How heavy you are, what tyres you use and what surface you're on etc etc...
What you're aiming for is the ability to lock the wheels, once you've exceeded the tyres ability to grip the trail under braking- you really don't need any more power. To acheive the maximum braking force the tyres need to be just on the limit before slidding. It is the ability to hang around a sweetspot that people often call modulation- or alternatively we've all heard of the Hayes on-off-lack-of-modulation feel.
On my DH bike I "could" lock the back wheel with a 6" disc but I would have to pull the lever soooo hard that it would have no feel (or modulation) at all, I'm running an 8" at the moment but considering dropping down to a 7" cos it just locks up too easily-
So do you need 8" rotors- erm maybe?!

sorry for rambling- don't even know if it makes sense!!
 

miatagal96

Chimp
Feb 7, 2007
54
0
I run Avid Juicy 3's with 7" rotors on my FR/DH bike and I cannot lock the tires on very steep downhill stuff. (never have this issue with the less-steep x-c trails and my BB7/6" rotor set-up). Decontaminating helped a bit, but I still can't lock up the brakes on steep stuff. I've been told that Avid's aren't real downhill brakes compared to Hayes, but I like the idea of being able to modulate.

I'm considering 8" rotors. So far, I'm fine with what I've got, since it seems like I reach a comfortable terminal velocity, but if I want to hit these steeps a little faster, I'm afraid that my comfortable terminal velocity will turn into an uncomfortable acceleration!!
 

nelsonjm

Monkey
Feb 16, 2007
708
1
Columbia, MD
Avid Juicy 3's are intended for XC, not DH, it even says this on their website so getting larger rotors probably wont help too much. Try the avid code 5s or codes.
 

aphex2k

Chimp
Sep 7, 2008
19
0
Depending on your weight, 160 front and rear would be fine for XC. I'm 190lbs and use a 180mm up front and 160mm at the back and manage to stop fine.

You need to check what is the max size rotor your forks are warrantied up to before installing new ones!
 
Feb 23, 2005
436
2
Spokanada
On my up-downhill bike I was running 160s but always got sketched out on the fast steep stuff. Kicked the front up to a 180 and feel much more confident in controlling my speed.

I'm running Juicy 7's at 185#
 

Harry BarnOwl

Monkey
Jul 24, 2008
174
38
Avid Juicy 3's are intended for XC, not DH, it even says this on their website so getting larger rotors probably wont help too much. Try the avid code 5s or codes.
Whaaa? You do NOT need codes! Juicy 3's, 5's and 7's all have more than adequate power for downhill. I and a number of my friends (we all race) run juicy's and they're faultless. I can't see why you'd ever need more power.