8" rotor on rear of EVO?? Anyone..

[RED5]

tried this or know if it's possible? After riding Bootleg Canyon (http://www.bootlegcanyon.com) this past weekend and destroying my Deore Hydros, it's time to upgrade to Hayes. I'm considering 8" rotors front and rear, but am unsure if it will work on the rear. Anyone tried it or even looked into it, have any info would be helpful. Thanks in advance to all.  

[jimbo]

How did you destroy your hydros

[IFO]

first off teh Deores are a XC brake and also they use mineral oil which has a much lower boiling point...

my guess is u baked em.... and found their power dropped off correct?

to bad u cant upgrade the Deores to larger rotors... but they use a properiatory adaptor, and of course shimano aint gunna be making any larger rotros for those brakes...

i bet you'd be fine with a hayes 6"s on the rear....

[RED5]

was from lots of high speed braking. Basically, boiled them as IFO said. Wore out a set of pads in two runs, which fried my spring and cooked the caliper causing it to seize up, because without the spring to retract the pad (that was gone, left with only the metal plate it's applied to) it just dragged the whole way causing it to overheat and bake.

I'll give the 6" rear a go, since I don't want to waste the money and time trying the 8" rear. Thanks.

[IFO]

no prob...

anytime...

[GET]

Sounds like you may already have your answer, but I do have an 8" Hayes rotor on the rear of my 5500C.  I think the carbon swingarm has similar geometry as the EVO.  I'm sure someone knows more about that.  The 8" rotor will give you significantly more cooling surface.  Its not that you need more braking power, you need more cooling.  The 8" rotor does give more braking torque as a bonus.  It is heavier, however.

[jimbo]

Can running 6 inch Avids get screwed up too by running them too hot on downhills?

[Matno]

Man! You'd have to be running REALLY hot to boil your cables!

I suppose any brake could overheat if you pushed it hard enough. Haven't ever heard about any Avids "burning up" though.

[jimbo]

Yeah, this is the first time I heard of any disk brakes getting screwed up.  All this seizing calipers talk got me thinking it might be better to run bigger rotors up front.  I always thought the worst you could experience was brake fade, worn pads, but destroying calipers is not good.

[Matno]

Consider the source... I think Red5 is a much more serious rider of scary terrain than most on this board. Certainly crazier than I am! That crowd he hangs out with are nuts. Not that there's anything wrong with that... But I'd wager that he could burn out a brake a lot sooner than I ever would.

(Of course, I don't actually know Red or his buddies, but the pics I've seen and stories I've heard look pretty tough).

[jimbo]

I found an interesting reply to another question at mtb-oz.com that has some relevance to this question.  It sort of make sense, but it could be BS.



"There are some exceptionally good pads out there and some real good impersonations.

Hayes original pads are great, but, like any original pads, very hard on the coin. The Brits seem to be the leaders in this market as EBC and FIBRAX are two of the best pads on the market. KOOLSTOP are renowned for the best V-brake pads and are also now making Disc pads, however I have not yet used them so if any one has, let us know if they're kosher. Pads come in different grades and can vary between manufacturers. Kevlar compounds are super grippy and excellent for DH but last about as long as a few DH runs. Sintered metal pads are an excellent pad for XC and trail riding, they last for quite a while and work well in wet and muddy conditions, but if you ride lots of fast downhills they can heat and warp your rotor( not good at all). EBC also do a pad that is halfway between the two. Hope this helps you.

       

***you can only go as fast as you can stop!!***



-----------------

Tweak-freak extroadinaire.

Freewheel Tech. editor."

[GET]

Some of what is quoted is good and some of it is off-base.  As Dennis mentioned in an earlier thread, brakes serve one function;  they convert mechanical energy of the bike and rider into heat.  For a given amount of braking, a fixed amount of heat will be generated, no matter what style or brand of brake is used.  That heat must then be dissipated or the temperature of something is going to increase significantly.  Most disc brakes are designed to dissipate the heat through the rotor.  The heat is generated at the contact point of the pad and rotor.  Most pads are designed to essentially insulate the rest of the caliper from this heat.  The pad contact surface gets very hot while the pad backing stays (relatively) cool.  The rotor, on the other hand, is designed to transfer as much heat as possible to the air as it rotates away from the pads.  They are, therefore, cooler than the pad surface at the point it re-enters the pad contact area.  Since heat “flows” to lower temperature, more heat is transferred to the rotor than to the pad.

So, downhill brake design is more about greater heat dissipation than about increased braking torque.  Regardless of pad material, running cross-country disc brakes on sustained downhills will cause overheating of the brake.  Contrary to the quote, metal sintered pads actually tranfer more heat away from the rotor.  Metal sintered pads are not the cause of warped rotors; exceeding the capacity of the brake design is.  From a safety point of view, it is better to warp a rotor than to trash a caliper (a warped rotor can still function as a brake.)  Kevlar downhill pads are actually better insulators and result in more heat going to the rotor (and, therefore, less to the caliper.)

So, sintered metal pads are designed for long wear while maintaining high coefficient of friction.  They are, however, better conductors (worse insulators) of heat.  Composite pads (for example, kevlar) are better insulators and protect the caliper better.  But, they wear poorly.