JDurk
Well-Known Member
Are you sure it's not play of the pads in the caliper making the noise?
WTF is up with those SRAM brakes?
- Thread starter carvegybe
- Start date
carvegybe
Well-Known Member
Yes, but I am happy with Hope brakes. Just not the rotors.
carvegybe
Well-Known Member
There is no noise when I put SRAM floating rotor on...so don't think it is the pads. In fact, I can feel a bit of play in the rotors simply by handling them.
Do you have a link to these floating rotors from sram? Never heard of them and am curious
Karate Monkey
Well-Known Member
Two-piece=/=floating. Common misconception about bike rotors for those coming from motor-sports.
Floating rotors have the literal ability for the brake track to move on/around the pins (bearings)...bicycle rotors--with the exception of Hope/fly-by-night AliExpress crap--are firmly fixed to the spider.
thats what i was suspecting as well, which is why i asked for a link instead of calling it out as a misunderstanding.
carvegybe
Well-Known Member
My bad...I thought 2 piece is floating. This is the type of rotor that does not make noise with the Hopes and all is well...except color matching:
www.sram.com
Looks like Hope rotors are floating. But floating should not mean cracking sound during braking is normal...right?
CenterLine X Rotor - RT-CLN-X-A2 - SRAM
CenterLine X Rotor, RT-CLN-X-A2, SRAM. CenterLine X rotors are the lighter weight version of SRAMs quiet, smooth, and robust CenterLine rotors. The CenterLine X rotor features a two-piece ...
www.sram.com
Looks like Hope rotors are floating. But floating should not mean cracking sound during braking is normal...right?
Clicking noise under braking would qualify as a likely unavoidable thing for rotors designed to float or slide along the axis of wheel rotation (some clearance between the pins and holes is necessary to allow movement) but not cracking or creaking.
carvegybe
Well-Known Member
Hmm clicking vs cracking...it's annoying. Is the unavoidable clicking worth any incremental benefits of a floating rotor over a 2-piece rotor? I am guessing not, based on my own riding style. My bike needs to be noise free...except in the wet I can tolerate braking noises.
I hope you find a solution
Karate Monkey
Well-Known Member
My bad...I thought 2 piece is floating. This is the type of rotor that does not make noise with the Hopes and all is well...except color matching:
CenterLine X Rotor - RT-CLN-X-A2 - SRAM
CenterLine X Rotor, RT-CLN-X-A2, SRAM. CenterLine X rotors are the lighter weight version of SRAMs quiet, smooth, and robust CenterLine rotors. The CenterLine X rotor features a two-piece ...
Looks like Hope rotors are floating. But floating should not mean cracking sound during braking is normal...right?
Nah, they can make noise while actuating the brake.
The trade-off is that the brake track resists warping better than a solid rotor...but two-piece rotors work almost as well. So: if you're chasing final percentage points of performance, go for it. If you're not, you'll probably be happier without them.
I don't understand this argument. There is less thermal mass on the two piece rotors. At least the ones I have seen are plastic or resin center hubs hense concentrating the heat on the brake track.
If the center spider is al or some other more cundictive material with a heat dissipating shape then sure.....
Not that it matters to most people in NJ since the downhills just aren't long enough to generate the heat needed to warp them. Most warped rotors are actually caused by external intervention such as a stick or rock hit (or dropping the bike rotor side down)
Karate Monkey
Well-Known Member
@shrpshtr325 they're definitely made of aluminum. The only place I could imagine plastic being used would be as an aero-extending shape (which would probably be served better as an actual part of the rotor that could conduct heat, anyway).
There's no clear "that's better" regarding thicker rotors vs. exotic construction (ie: finned aluminum/steel sandwich rotors). One has an overall higher heat capacity (but takes longer to cool down, consequently), one cools more rapidly. Short answer: physics is a bitch.
The heat warping that a floating rotor would combat isn't really out-of-true warping. If you honk hard on the brakes, and ask a lot of them, you'll probably notice a light scraping sound that eventually stops. That's heat warping. There are a few places in NJ where you can get cooking on a road bike, only to have to come to a screeching stop at the bottom of the hill--those usually result in scraping rotors for 10-20 seconds, while they cool back down.
For MTB, rotors live a pretty easy life in NJ outside of Creek. The only ones that I've seen that were overheated were 1) grossly under-sized for the rider, or 2) contaminated pads.
There's no clear "that's better" regarding thicker rotors vs. exotic construction (ie: finned aluminum/steel sandwich rotors). One has an overall higher heat capacity (but takes longer to cool down, consequently), one cools more rapidly. Short answer: physics is a bitch.
The heat warping that a floating rotor would combat isn't really out-of-true warping. If you honk hard on the brakes, and ask a lot of them, you'll probably notice a light scraping sound that eventually stops. That's heat warping. There are a few places in NJ where you can get cooking on a road bike, only to have to come to a screeching stop at the bottom of the hill--those usually result in scraping rotors for 10-20 seconds, while they cool back down.
For MTB, rotors live a pretty easy life in NJ outside of Creek. The only ones that I've seen that were overheated were 1) grossly under-sized for the rider, or 2) contaminated pads.
Idk why I'm bothering here but apparently I am. Especially since there is some stuff in here that's just scientifically inaccurate as anyone who has taken material science and thermodynamics/heat transfer should notice.
I agree that the differences will be minimal hence my initial statement that two piece rotors don't resist warping(even if the center is a more conductive material whatever interface is between them will likely negate any additional conductivity of the material). Even the floating ones are mostly targeting the caliper/rotor misalignment typically caused by pistons not being truly even in a caliper as it advances the pads(these are even worse for heat transfer since there is an air gap between the spider and the brake track to allow it to float) There is alot of math going on to try and determine that these different designs are better at ______(fill in the blank) but the overall improvement is going to be minimal and likely unnoticed by the rider (definitely in NJ where long downhills are kind of uncommon)
this is the inaccurate parts, heat warping won't go away on its own, once a rotor is warped it stays that way. If a rotor truly gets hot enough to warp it also alters the metallurgical properties of the metal(this is why you dont turn rotors for you car if they warp). An occasional scraping after a stop that shortly goes away is almost certainly the result of a lazy piston retraction, caused by lack of piston lubrication, dirty fluid, or obstructed hydraulic lines.
There is alot of math that we could do if needed, but its unlikely that you will be warping rotors by overheating them in this area.
Maybe the ones im thinking of were encased in plastic i honestly dont remember (although they do make plastics that would be lighter and plenty strong enough) and it's been a long time. That also wouldn't provide any benefit to anything really....(plastic is an insulator after all)
I agree that the differences will be minimal hence my initial statement that two piece rotors don't resist warping(even if the center is a more conductive material whatever interface is between them will likely negate any additional conductivity of the material). Even the floating ones are mostly targeting the caliper/rotor misalignment typically caused by pistons not being truly even in a caliper as it advances the pads(these are even worse for heat transfer since there is an air gap between the spider and the brake track to allow it to float) There is alot of math going on to try and determine that these different designs are better at ______(fill in the blank) but the overall improvement is going to be minimal and likely unnoticed by the rider (definitely in NJ where long downhills are kind of uncommon)
this is the inaccurate parts, heat warping won't go away on its own, once a rotor is warped it stays that way. If a rotor truly gets hot enough to warp it also alters the metallurgical properties of the metal(this is why you dont turn rotors for you car if they warp). An occasional scraping after a stop that shortly goes away is almost certainly the result of a lazy piston retraction, caused by lack of piston lubrication, dirty fluid, or obstructed hydraulic lines.
There is alot of math that we could do if needed, but its unlikely that you will be warping rotors by overheating them in this area.
Uneven heating of the brake track compared to the spider will cause elastic deformation until it is plastic.
isn't this worsened by the fact that it is a "circle" - expansion of the outside, while the spider holds it has to cause
temporary warp of the track ?? unless the term warp is wrong (ie warp implies the deformation was plastic.)
uneven heating in this case would imply that you are only heating say 90degrees of the brake track as opposed to the entire 360deg circle. Not likely you will touch the brakes for less than one wheel revolution and generate enough heat to do anything. Yes the outer ring will heat up faster than the spider, but that shouldn't cause warping out of plane unless the rotor is already out of flatness(technical term for being in plane)
Please show your work.
Consider the angular expansion (wants to create a larger diameter) but the spider holding it back -
Here is my thinking.
fix the ends of a metal bar so they don't move, heat it - has to deform off its axis, rather than expand linearly along it. ??
you gotta have a fancy simulator at work..
Technically yes but in actuality the absolute expansion is still very small. (Coeeficient of exnapsion for steel btw 5 and 9*10^-6 in/indegf and al ~13* 10^-6in/indegf) The amount of heat required would be massive. I don't think that a <250lb bicycle&rider moving at human speeds generates that much heat energy without some seriously long hills
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Thank you