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#1
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6 or 8 inches front disc?
Hi all,
If you are given a choice to choose between a 6" and an 8" disc rotor for your front disc brake on a single crown fork, on a full-sus XC/epic bike, which would you go for? why? would you also opt for the 8" rear? There are people who would say that a 6" will serve the purpose on an XC, and is "more than enough" braking power, too much braking power will make you endo, lost control on loose soil, etc... There are also people who would say that "more is better", better modulation, better heat transfer, etc..... What's your thought and comment? |
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#2
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6 or 8 inches front disc?
i was faced with a similar dilemma a while back. /terrible/ brake
squeal, pads getting so hot both they and the disk were turning blue... the "recommended" solution was 8" rotors, but i was reluctant for the reasons you state, too much liklihood of endo, etc. effectiveness wasn't the problem - 6" rotors are already /way/ more effective than any rim brake solution i've ever tried. i tried "one last thing" before going down the big rotor road - a different brand of pad. all problems ended! great braking, excellent modulation, no squeal, no overheating... i now use e.b.c. pads rather than shimano and would never bother with a 6" rotor. jb Colin wrote: Hi all, If you are given a choice to choose between a 6" and an 8" disc rotor for your front disc brake on a single crown fork, on a full-sus XC/epic bike, which would you go for? why? would you also opt for the 8" rear? There are people who would say that a 6" will serve the purpose on an XC, and is "more than enough" braking power, too much braking power will make you endo, lost control on loose soil, etc... There are also people who would say that "more is better", better modulation, better heat transfer, etc..... What's your thought and comment? |
#3
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6 or 8 inches front disc?
Colin:
Hi all, If you are given a choice to choose between a 6" and an 8" disc rotor for your front disc brake on a single crown fork, on a full-sus XC/epic bike, which would you go for? why? would you also opt for the 8" rear? There are people who would say that a 6" will serve the purpose on an XC, and is "more than enough" braking power, too much braking power will make you endo, lost control on loose soil, etc... There are also people who would say that "more is better", better modulation, better heat transfer, etc..... What's your thought and comment? Make sure your forks are warrantied for an 8" rotor. Most manufacturers limit rotor size on their particular forks, and void warranties if greater than 6" rotors are used. An 8" rotor is overkill for most off-road applications; only the steepest downhill courses *may* justify these. |
#4
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6 or 8 inches front disc?
Hmm. Interesting thread. Let me make sure I've got this straight.
The choices are 6" rotors and 8" rotors. The 8" rotors, it appears, have more stopping power since they are referred to as being "overkill" amd "more likely to cause endos." Am I with you so far? Now, if these statements are accurate, then it seems to me that the post powerful braking system possible for a mountain bike would be the one that uses 22" rotors: rim brakes! |
#5
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6 or 8 inches front disc?
"Colin" writes:
If you are given a choice to choose between a 6" and an 8" disc rotor for your front disc brake on a single crown fork, on a full-sus XC/epic bike, which would you go for? why? would you also opt for the 8" rear? There are people who would say that a 6" will serve the purpose on an XC, and is "more than enough" braking power, too much braking power will make you endo, lost control on loose soil, etc... There are also people who would say that "more is better", better modulation, better heat transfer, etc..... The advantage of a bigger rotor is primarily larger cooling surface; the disadvantage is greater weight. Unless you are doing very long downhill sections at high speed (as in downhill racing) I find it hard to believe that you need the greater cooling area, and if you're doing an epic you certainly don't want to carry more weight. In this case, less is mo less weight to heave up each hill means more distance covered. -- (Simon Brooke) http://www.jasmine.org.uk/~simon/ ;; in faecibus sapiens rheum propagabit |
#6
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6 or 8 inches front disc?
Tim McNamara writes:
Hmm. Interesting thread. Let me make sure I've got this straight. The choices are 6" rotors and 8" rotors. The 8" rotors, it appears, have more stopping power since they are referred to as being "overkill" amd "more likely to cause endos." Am I with you so far? What gives more stopping power is, ultimately, ability to dissipate heat, since brakes essentially convert kinetic energy to heat energy and then dump the heat energy into the environment. Other things being equal, a larger rotor has a larger radiant surface and is able to dump more heat. Now, if these statements are accurate, then it seems to me that the post powerful braking system possible for a mountain bike would be the one that uses 22" rotors: rim brakes! If you dump too much heat into the system which holds your tyres on, you're going to blow tyres. -- (Simon Brooke) http://www.jasmine.org.uk/~simon/ ;; in faecibus sapiens rheum propagabit |
#7
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6 or 8 inches front disc?
Tim McNamara:
Hmm. Interesting thread. Let me make sure I've got this straight. The choices are 6" rotors and 8" rotors. The 8" rotors, it appears, have more stopping power since they are referred to as being "overkill" amd "more likely to cause endos." Am I with you so far? No, you're not. I don't know where you got the "more likely to cause endos" bit. "Endos" aren't solely reliant on brakes (let alone the type of brake) but involve riding position as well, among other things. The overkill claim comes from the fact that 6" disc rotors provide ample stopping ability for all but the most demanding incline, eg steep muddy downhills with a relatively heavy rider/bike *and* very short distance stopping requirements, such as those in some downhill mountainbiking courses. However, larger disc rotors exert larger bending moments on caliper mounts despite the smaller stopping force exerted by the calipers (compared to smaller disc rotors), and therefore require relatively stronger mounts than those designed for smaller disc rotors. Now, if these statements are accurate, then it seems to me that the post powerful braking system possible for a mountain bike would be the one that uses 22" rotors: rim brakes! You're over-simplifying to an erroneous extent. You would know by now the main mechanical differences between rim brakes and disc brakes; if not, Google will come up with many threads and pages about that in cycling-related newsgroups and websites. By now you must also be aware of the different features of both types of brakes, as well as the pros and cons of both so there is no need to rehash all of that here. If the purpose of your post, however, is to try to dismiss bicycle disc brakes as unnecessary in any case, you need to come up with a lot better argument than what you've posted, addressing all the relevant issues that have been discussed and argued for several years now. |
#8
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6 or 8 inches front disc?
Now, if these statements are accurate, then it seems to me that the
post powerful braking system possible for a mountain bike would be the one that uses 22" rotors: rim brakes! You're over-simplifying to an erroneous extent. I think he was being sarcastic... lol -- Phil, Squid-in-Training |
#9
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6 or 8 inches front disc?
Simon Brooke writes:
Tim McNamara writes: Hmm. Interesting thread. Let me make sure I've got this straight. The choices are 6" rotors and 8" rotors. The 8" rotors, it appears, have more stopping power since they are referred to as being "overkill" amd "more likely to cause endos." Am I with you so far? What gives more stopping power is, ultimately, ability to dissipate heat, since brakes essentially convert kinetic energy to heat energy and then dump the heat energy into the environment. Other things being equal, a larger rotor has a larger radiant surface and is able to dump more heat. Humm. And a rim would have a much larger surface than a 6" or 8" rotor, which again would indicate that the rim brake would have greater stopping power than either size disc brake. Thanks for clarifying that for me. Now, if these statements are accurate, then it seems to me that the post powerful braking system possible for a mountain bike would be the one that uses 22" rotors: rim brakes! If you dump too much heat into the system which holds your tyres on, you're going to blow tyres. I've heard of that happening, although in the 30+ years I've been riding bikes as an "enthusiast," it's never happened to me. Of course, I've also never lived in mountainous terrain with the long steep descents necessary to heat a rim up that much. OTOH in my tour in the Alps in 2002, I never had a problem with rims heating up. My wife and I have never ridden our tandem in the mountains; that's a situation that I could easily see resulting in very warm rims and might warrant a hub brake- but since my wife hates climbing, it's not something I'll ever be likely to test. |
#10
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6 or 8 inches front disc?
Tim McNamara wrote in message ...
Hmm. Interesting thread. Let me make sure I've got this straight. The choices are 6" rotors and 8" rotors. The 8" rotors, it appears, have more stopping power since they are referred to as being "overkill" amd "more likely to cause endos." Am I with you so far? Now, if these statements are accurate, then it seems to me that the post powerful braking system possible for a mountain bike would be the one that uses 22" rotors: rim brakes! You would have a point IF rim brakes generated as much pressure between the pads as disk brakes do. The appeal of disk brakes is not that they provide more stopping power than rim brakes, but rather they the stopping power they provide is almost constant regaurdless of the conditions. Wet, Dry, Muddy, Icey...disk brakes work more or less the same in all those conditions. That is certainly not a claim that can be made by rim brakes. |
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