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#21
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Why do some forks and frames have brake rotor size limits?
On 2017-10-22 09:06, Jeff Liebermann wrote:
On Sun, 22 Oct 2017 08:07:48 -0700, Joerg wrote: (...) The rear is native 160mm and currently has a 160mm rotor. I'd like to upgrade both front and back to 203mm or 8". Mostly to reduce rotor heating during long descents. Have you considered adding a water mist brake cooling system instead? You already have a battery pack for your lighting and a water bottle. A small automotive windshield pump and IR over-temperature switch should be easy additions (famous last assumptions) to your existing machine. If the brake disks are fairly flexible, they should not shatter when suddenly cooled. If the brake pads are made to operate in the rain, a water spray mist should not affect their stopping power. The water mist might also be useful for keeping the disks clean. I am carrying enough on the bikes as it is. A bigger rotor should fix that much better. I did some quick searching for applicable patents, but found nothing specific to bicycle brake mist cooling. It MIGHT be patentable. I did find bicycle misting systems designed to cool the rider, but not the brakes: https://patents.google.com/patent/US8714464B2/en https://patents.google.com/patent/US9296001B2/en https://patents.google.com/patent/US9186691B2/en You can buy cooling misters for bike handlebars. I do it the low-tech way: An cleaned empty yoghurt beker rides in the right pannier. That gets dunked into rivers et cetera and then dumped over my head. Until the T-shirt is all soaked. This beker doubles as an emergency bowl for when I find a dehydrated run-away dog. I was also thinking that it might be possible to add some vanes to the spokes near the disk brakes. These would direct additional cooling air towards the brake disk. However, when I realized that they would also direct mud and crud onto the disks, I decided that was a rather bad idea. Drivel: Here's a patent application for yet another bicycle light. https://patents.google.com/patent/US20040090040A1/en The light is simple enough, but the "predicted applications" include almost every possible bicycle accessory and application. It then wanders into the realm of barbeques, lava lamps, fireworks, bicycle calendars, etc. A light with a pop-out mirror ... great ... -- Regards, Joerg http://www.analogconsultants.com/ |
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#23
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Why do some forks and frames have brake rotor size limits?
On Tuesday, October 24, 2017 at 11:39:40 AM UTC-7, Joerg wrote:
On 2017-10-22 18:05, Frank Krygowski wrote: On 10/22/2017 11:07 AM, Joerg wrote: On 2017-10-21 17:19, Frank Krygowski wrote: On 10/21/2017 4:07 PM, wrote: On Saturday, October 21, 2017 at 7:12:03 AM UTC-7, Joerg wrote: When researching upgrades to larger rotors I read that there may be limits for frames and forks. Why? Explanations were usually scant and contradictory, with some saying it doesn't matter and some saying it does. After all, when increasing the rotor diameter by a couple of inches the brake force on the caliper goes down by about 30% and then due to it being positioned farther out this should cantilever back into the same +30% into the frame or fork bosses as before. The maximum deceleration achievable on each wheel remains the same, until it is very close to locking up. So it should be a wash, shouldn't it? Now THAT is something that Frank should be able to answer. I don't believe that leverage forces are linear are they? Give me a photo and I'll see what I can do. This is what I am planning to do: https://ep1.pinkbike.org/p4pb12868017/p4pb12868017.jpg The fork has this kind on there right now because the rotor is 180mm (or in my case 7") and the fork is native 160mm: https://ep1.pinkbike.org/p4pb12873429/p4pb12873429.jpg First, to really do a proper job on this I'd need to see a clear side view of the entire disc brake and rotor (or rotors), plus lower end of the fork, plus (ideally) the lower portion of the wheel. I haven't given tremendous attention to disc brakes, because I'm not going to be needing one. I'm having to make some guesses based on what I can glean from your photos, plus a few others I found on the web. This is the front brake: http://www.analogconsultants.com/ng/...rontBrake1.JPG The rear brake: http://www.analogconsultants.com/ng/bike/RearBrake1.JPG Next is the whole MTB. I'll do a separate post with that because it can help people with increasing the payload capacity on full-suspension bikes: http://www.analogconsultants.com/ng/bike/Muddy4.JPG This is the kind of adapter I am planning to use: https://erpimgs.idealhere.com/ImageF...963c864243.jpg It'll move the caliper outwards and also sideways for (hopefully) a total of 21.5mm increase in distance from the axles. I am not an ME but my guess is that the load on the swooped upper rear post would increase by 15-20%. That post has a lot of meat, about 0.400" by 0.400" and the welds look beefy as well. But: Since the pads contact the disc at perhaps a 45 degree angle above the horizontal line through the axle, they put a downward and backward force on the disc. IOW their force is tangent to the circle that's at their radius of contact. That means the reaction force on the caliper is opposite, up and forward. There's a matching force downward and back on the dropout. Those two forces form a couple which applies bending moment to the bottom of the fork blade. Certainly, a steel road fork blade designed for a caliper brake is likely to be fairly thin and a bit flexible down there. It's not designed to resist that moment. Brazing mounts onto such a fork to take a disc brake would be unwise. But that's addressing disc brake vs. no disc brake (IOW, vs. caliper brake). What about a larger disc on a fork designed for a disc brake? ISTM the braking force on the bike is the horizontal component of the force the caliper applies to the disc. The total force it applies is upward on an angle. This means a disc is already sort of inefficient (in some theoretical sense) because of the typical location of the pad and that aforementioned angle. The total force applied must be much larger than the required braking force, since a big component is "wasted" upward. If you move the contact point further outward, ISTM that the angle gets worse. The force on the disc is even more vertical. For a given braking force (measured at the tire-to-road point, or at the axle) the pad force will have to be even higher, since more of it's vector total is wasted upward. On a stout mountain bike fork like you showed, I really doubt any of that will make a difference. The ejecting force (trying to kick the axle down out of the dropouts) will be higher, but if you're running a through axle, I doubt you'll have problems. However, getting back to the caliper itself: It's mounted on two studs. The discs reaction force on the caliper must be resisted (or transmitted to the fork) through those two studs. Increasing the standoff distance will change the nature of those forces, increasing bending stress on the studs, and perhaps changing the force on the lower stud from compression+bending to tensile+bending. Whether any of this will make a difference in your case, I can't tell. But I doubt it; I think you'll be OK. That's my guess (tm) working without any good dimensions or other numbers. I'll note, though, that I still don't understand why front disc calipers are positioned behind the fork. That's because that part of engineering is wrong on bicycles but not much can be done about it by the rider. ... If they were on the front, the force on the disc would be nearly horizontal, so there would be little or no wasted vertical component. Application force for a given deceleration would be lower. Lower application force would cause longer pad life. There would be no ejection force on the axle, so through axles would be unnecessary. But we've talked about this before. Yup, we have. One of my next mods after the brake upgrade will be to replace the QR axle with a solid CroMo axle and the old-fashioned big outer nuts. The QR is too wimpy. It could also fail. Now before anyone ridicules this as paranoya this is exactly what happened to a friend a few weeks ago, the QR skewer snapped. Luckily it was the one in the rear axle but since he is usually pulling a trailer that can also make for an "interesting" situation. I don't think that you're going to increase the loading on the fork or swing arm mount enough to worry about. But I do think that your brakes are going to get considerably more sensitive. This is something you really have to be careful of. While it would reduce the wear on the disk with all of that weight you carry I don't think that it will be a noticable change in disk and pad wear. |
#24
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Why do some forks and frames have brake rotor size limits?
On 2017-10-24 14:17, wrote:
On Tuesday, October 24, 2017 at 11:39:40 AM UTC-7, Joerg wrote: On 2017-10-22 18:05, Frank Krygowski wrote: On 10/22/2017 11:07 AM, Joerg wrote: On 2017-10-21 17:19, Frank Krygowski wrote: On 10/21/2017 4:07 PM, wrote: On Saturday, October 21, 2017 at 7:12:03 AM UTC-7, Joerg wrote: When researching upgrades to larger rotors I read that there may be limits for frames and forks. Why? Explanations were usually scant and contradictory, with some saying it doesn't matter and some saying it does. After all, when increasing the rotor diameter by a couple of inches the brake force on the caliper goes down by about 30% and then due to it being positioned farther out this should cantilever back into the same +30% into the frame or fork bosses as before. The maximum deceleration achievable on each wheel remains the same, until it is very close to locking up. So it should be a wash, shouldn't it? Now THAT is something that Frank should be able to answer. I don't believe that leverage forces are linear are they? Give me a photo and I'll see what I can do. This is what I am planning to do: https://ep1.pinkbike.org/p4pb12868017/p4pb12868017.jpg The fork has this kind on there right now because the rotor is 180mm (or in my case 7") and the fork is native 160mm: https://ep1.pinkbike.org/p4pb12873429/p4pb12873429.jpg First, to really do a proper job on this I'd need to see a clear side view of the entire disc brake and rotor (or rotors), plus lower end of the fork, plus (ideally) the lower portion of the wheel. I haven't given tremendous attention to disc brakes, because I'm not going to be needing one. I'm having to make some guesses based on what I can glean from your photos, plus a few others I found on the web. This is the front brake: http://www.analogconsultants.com/ng/...rontBrake1.JPG The rear brake: http://www.analogconsultants.com/ng/bike/RearBrake1.JPG Next is the whole MTB. I'll do a separate post with that because it can help people with increasing the payload capacity on full-suspension bikes: http://www.analogconsultants.com/ng/bike/Muddy4.JPG This is the kind of adapter I am planning to use: https://erpimgs.idealhere.com/ImageF...963c864243.jpg It'll move the caliper outwards and also sideways for (hopefully) a total of 21.5mm increase in distance from the axles. I am not an ME but my guess is that the load on the swooped upper rear post would increase by 15-20%. That post has a lot of meat, about 0.400" by 0.400" and the welds look beefy as well. But: Since the pads contact the disc at perhaps a 45 degree angle above the horizontal line through the axle, they put a downward and backward force on the disc. IOW their force is tangent to the circle that's at their radius of contact. That means the reaction force on the caliper is opposite, up and forward. There's a matching force downward and back on the dropout. Those two forces form a couple which applies bending moment to the bottom of the fork blade. Certainly, a steel road fork blade designed for a caliper brake is likely to be fairly thin and a bit flexible down there. It's not designed to resist that moment. Brazing mounts onto such a fork to take a disc brake would be unwise. But that's addressing disc brake vs. no disc brake (IOW, vs. caliper brake). What about a larger disc on a fork designed for a disc brake? ISTM the braking force on the bike is the horizontal component of the force the caliper applies to the disc. The total force it applies is upward on an angle. This means a disc is already sort of inefficient (in some theoretical sense) because of the typical location of the pad and that aforementioned angle. The total force applied must be much larger than the required braking force, since a big component is "wasted" upward. If you move the contact point further outward, ISTM that the angle gets worse. The force on the disc is even more vertical. For a given braking force (measured at the tire-to-road point, or at the axle) the pad force will have to be even higher, since more of it's vector total is wasted upward. On a stout mountain bike fork like you showed, I really doubt any of that will make a difference. The ejecting force (trying to kick the axle down out of the dropouts) will be higher, but if you're running a through axle, I doubt you'll have problems. However, getting back to the caliper itself: It's mounted on two studs. The discs reaction force on the caliper must be resisted (or transmitted to the fork) through those two studs. Increasing the standoff distance will change the nature of those forces, increasing bending stress on the studs, and perhaps changing the force on the lower stud from compression+bending to tensile+bending. Whether any of this will make a difference in your case, I can't tell. But I doubt it; I think you'll be OK. That's my guess (tm) working without any good dimensions or other numbers. I'll note, though, that I still don't understand why front disc calipers are positioned behind the fork. That's because that part of engineering is wrong on bicycles but not much can be done about it by the rider. ... If they were on the front, the force on the disc would be nearly horizontal, so there would be little or no wasted vertical component. Application force for a given deceleration would be lower. Lower application force would cause longer pad life. There would be no ejection force on the axle, so through axles would be unnecessary. But we've talked about this before. Yup, we have. One of my next mods after the brake upgrade will be to replace the QR axle with a solid CroMo axle and the old-fashioned big outer nuts. The QR is too wimpy. It could also fail. Now before anyone ridicules this as paranoya this is exactly what happened to a friend a few weeks ago, the QR skewer snapped. Luckily it was the one in the rear axle but since he is usually pulling a trailer that can also make for an "interesting" situation. I don't think that you're going to increase the loading on the fork or swing arm mount enough to worry about. It is already a serious problem. The only way to prevent the left side of the front axle from sloshing partly out of the fork upon heavy braking is to oil the heck out of all QR moving parts and then close it as tightly as possible. The left dropout has already wallered out noticeably. That's just got to stop. ... But I do think that your brakes are going to get considerably more sensitive. No problem. The Promax Decipher modulate nicely and right now I have to reach in hard to slow down on a steep downhill. This is something you really have to be careful of. While it would reduce the wear on the disk with all of that weight you carry I don't think that it will be a noticable change in disk and pad wear. It will not reduce pad wear but will reduce rotor wear. However, that's not my objective. The objective is to reduce heating of the rotor on long downhill stretches. Not having to pull the lever so hard anymore is an added benefit. Ok, I could also lose 30lbs instead but we all know that's not going to happen ... -- Regards, Joerg http://www.analogconsultants.com/ |
#25
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Why do some forks and frames have brake rotor size limits?
On Tue, 24 Oct 2017 10:15:53 -0700, Jeff Liebermann
wrote: On Tue, 24 Oct 2017 16:19:42 +0700, John B. wrote: On Mon, 23 Oct 2017 10:09:20 -0700, Jeff Liebermann wrote: Impressive. I'll assume it's a carbon-carbon rotor, since all F1 cars seem to using them. Undoubtedly so. But if the advantage of "carbon" bikes can be extolled that a carbon-carbon frame must have twice the bragging rights :-) I don't think it would be a good idea to brag about having a bicycle made from the same stuff that caused the Challenger space shuttle disaster. The leading edges of the wings were made of carbon-carbon. When the wings were hit by ice during takeoff, it punched some rather large holes in the carbon-carbon. ????????????? "Disintegration of the vehicle began after an O-ring seal in its right solid rocket booster (SRB) failed at liftoff. The O-ring was not designed to fly under unusually cold conditions as in this launch. Its failure caused a breach in the SRB joint it sealed, allowing pressurized burning gas from within the solid rocket motor to reach the outside and impinge upon the adjacent SRB aft field joint attachment hardware and external fuel tank. This led to the separation of the right-hand SRB's aft field joint attachment and the structural failure of the external tank. Aerodynamic forces broke up the orbiter." Given the coefficient of friction between a 1.25" wide rubber tire (32mm) and a wet road probably dragging the feet will work. :-) Good point. Perhaps an anchor and rope thrown overboard might be more suitable for stopping the bicycle on a wet road? -- Cheers, John B. |
#26
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Why do some forks and frames have brake rotor size limits?
On Sun, 22 Oct 2017 09:06:07 -0700, Jeff Liebermann
wrote: Have you considered adding a water mist brake cooling system instead? Curses, it's not going to work. The problem is that a very fine water mist sprayed at a red hot brake disk will vaporize (evaporate) the tiny water droplets before they hit the red hot brake disk. That's nice for evaporative cooling the air around the brakes, but does nothing to cool the actual brake disk. To do that would require larger droplets, a higher velocity droplet spray, or both. Dumping liquid water on the brakes would also work, but that's like having your own private rain storm, which was the original problem. Grumble... -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
#27
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Why do some forks and frames have brake rotor size limits?
On Tue, 24 Oct 2017 11:47:12 -0700, Joerg
wrote: On 2017-10-24 07:27, wrote: On Tuesday, October 24, 2017 at 2:19:48 AM UTC-7, John B. wrote: On Mon, 23 Oct 2017 10:09:20 -0700, Jeff Liebermann wrote: On Mon, 23 Oct 2017 12:48:29 +0700, John B. wrote: On Sun, 22 Oct 2017 20:51:15 -0700, Jeff Liebermann wrote: On Mon, 23 Oct 2017 07:02:08 +0700, John B. wrote: But re disc brake cooling F1 car brakes appear to work with the discs red hot. In the 1,000 degree (F) range. And they use Carbon Fiber discs too :-) And everyone knows that CF is better. "Thermal Conductivity of Carbon Fiber, and other Carbon Based Materials" http://www.christinedemerchant.com/carbon_characteristics_heat_conductivity.html "So...Is Carbon Fiber a good heat conductor? As usual the answer is "it depends." The short answer is NO not when regular carbon fiber is made up in regular epoxy and expected to conduct heat across the thickness. IF a highly carbonized pan fiber with graphite or diamond added, is measured for heat transmission in the length of the fiber it is very good and can rival and exceed copper." On the other hand, they seem to work pretty well :-) See https://www.youtube.com/watch?v=h5JcHAEmIYM for a visual indication of heat dissipation. :-) Impressive. I'll assume it's a carbon-carbon rotor, since all F1 cars seem to using them. Undoubtedly so. But if the advantage of "carbon" bikes can be extolled that a carbon-carbon frame must have twice the bragging rights :-) http://www.racecar-engineering.com/technology-explained/f1-2014-explained-brake-systems/ (4 pages) "A typical road car uses a cast iron brake disc with an organic brake pad. In an F1 car, though, the same material is used for both disc and pad, and this material is known as carbon-carbon - a significantly different material to the carbon-fibre composites used in the rest of the car" In other words, the F1 brakes are NOT made from CF. Some detail on Formula 1 brakes: https://www.youtube.com/watch?v=ev6XTdlKElw Fun destroying brakes: https://www.youtube.com/watch?v=KslGsXMgmqg The brake starting at 4:45 sure looks like CF but I'm not sure. Maybe twin disk brakes would be easier? http://nuovafaor.it//public/prodotto/75/nccrop/DOPPIO_FRENO_CROSS_ENDURO.jpg https://i.ytimg.com/vi/Pvwj-WWlKkg/maxresdefault.jpg https://gzmyu4ma9b-flywheel.netdna-ssl.com/wp-content/uploads/2011/09/Gatorbrake-dual-hydraulic-front-disc-brakes-carbon-rotors01.jpg https://lh4.googleusercontent.com/-cDfAFWrGR6Q/VHKPsm-f6YI/AAAAAAAAX10/2FCyj87xs0g/s640/14%2520-%25201.jpg https://www.minibikecraze.co.uk/wp-content/uploads/bs0978.jpg https://endless-sphere.com/forums/viewtopic.php?f=28&t=56268 Given the coefficient of friction between a 1.25" wide rubber tire (32mm) and a wet road probably dragging the feet will work. :-) Joerg's experience is with full suspension MTB's. These things are incredibly heavy and long wheelbased. He has his judgement of disks and it is no doubt quite accurate for his experience and riding. I have disks on a much lighter and shorter wheelbased bike. I know the failings up close and personal. I simply cannot imagine WHY a person would want a more complicated system than that offered by the Campy Skeleton brakes. The reason can be summed up in one word: Rain :-) But last Sunday I started out my "weekend" ride in the rain. It had been raining nearly all night and the roads had a lot of water on them - note we have been having floods here in Bangkok lately - but it appeared that the rain was ending so off I went. Unfortunately my weather forecasting facility wasn't working very well and I rode 20 Km of a 30 Km ride in light rain and flooded roads in many places. I was splashing through water in some places and cars were splashing through (and splashing me) in others. Of course, Sunday is much lighter traffic then on work days but still, Bangkok is rated as one of the cities with the most chaotic traffic in the world, and I did have to stop suddenly several time, on flooded roads with wet wheels and brakes. My brakes worked just as they do in the dry. Back brake stops me somewhat slowly and front brake stops rather suddenly, both brakes together provides best stopping. No long wait after grabbing a brake lever although I did think of you with your stopping problems and I have the feeling that the brake lever pressure might be a tiny bit more to stop in the rain but if it was it was so little that it couldn't be quantified. But of course I am using quality brake pads. Why it costs me US$12.12 a wheel just for pads alone.... but they do last a year or more. -- Cheers, John B. |
#28
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Why do some forks and frames have brake rotor size limits?
On Tue, 24 Oct 2017 11:39:39 -0700, Joerg
wrote: On 2017-10-22 18:05, Frank Krygowski wrote: On 10/22/2017 11:07 AM, Joerg wrote: On 2017-10-21 17:19, Frank Krygowski wrote: On 10/21/2017 4:07 PM, wrote: On Saturday, October 21, 2017 at 7:12:03 AM UTC-7, Joerg wrote: When researching upgrades to larger rotors I read that there may be limits for frames and forks. Why? Explanations were usually scant and contradictory, with some saying it doesn't matter and some saying it does. After all, when increasing the rotor diameter by a couple of inches the brake force on the caliper goes down by about 30% and then due to it being positioned farther out this should cantilever back into the same +30% into the frame or fork bosses as before. The maximum deceleration achievable on each wheel remains the same, until it is very close to locking up. So it should be a wash, shouldn't it? Now THAT is something that Frank should be able to answer. I don't believe that leverage forces are linear are they? Give me a photo and I'll see what I can do. This is what I am planning to do: https://ep1.pinkbike.org/p4pb12868017/p4pb12868017.jpg The fork has this kind on there right now because the rotor is 180mm (or in my case 7") and the fork is native 160mm: https://ep1.pinkbike.org/p4pb12873429/p4pb12873429.jpg First, to really do a proper job on this I'd need to see a clear side view of the entire disc brake and rotor (or rotors), plus lower end of the fork, plus (ideally) the lower portion of the wheel. I haven't given tremendous attention to disc brakes, because I'm not going to be needing one. I'm having to make some guesses based on what I can glean from your photos, plus a few others I found on the web. This is the front brake: http://www.analogconsultants.com/ng/...rontBrake1.JPG The rear brake: http://www.analogconsultants.com/ng/bike/RearBrake1.JPG Next is the whole MTB. I'll do a separate post with that because it can help people with increasing the payload capacity on full-suspension bikes: http://www.analogconsultants.com/ng/bike/Muddy4.JPG This is the kind of adapter I am planning to use: https://erpimgs.idealhere.com/ImageF...963c864243.jpg It'll move the caliper outwards and also sideways for (hopefully) a total of 21.5mm increase in distance from the axles. I am not an ME but my guess is that the load on the swooped upper rear post would increase by 15-20%. That post has a lot of meat, about 0.400" by 0.400" and the welds look beefy as well. I think that you are talking about the difference between a 160mm disc and a 203mm disc. The radius of the 203mm disk is 101.3mm and the radius of the 150mm disk is 80mm. Thus the moment arm of the larger discs is ~26.6% longer then the smaller. But this is a two way street as any force applied to the wheel will be multiplied 1.26 times with the larger disc and of course the effect of any force applied to the rim of the larger disc will be multiplied 1.26 times at the center of the wheel with the larger discs :-) A 6061 - T4 aluminum, a common aluminum alloy, has a yield strength of 21,000 psi. 0.4" x 0.4" is 0.16 square inches so the theoretical load that will cause it to bend the mount bracket might be as high as about 3,360 lbs, or 1.68 tons :-) -- Cheers, John B. |
#29
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Why do some forks and frames have brake rotor size limits?
On 10/24/2017 8:13 PM, Jeff Liebermann wrote:
On Sun, 22 Oct 2017 09:06:07 -0700, Jeff Liebermann wrote: Have you considered adding a water mist brake cooling system instead? Curses, it's not going to work. The problem is that a very fine water mist sprayed at a red hot brake disk will vaporize (evaporate) the tiny water droplets before they hit the red hot brake disk. That's nice for evaporative cooling the air around the brakes, but does nothing to cool the actual brake disk. To do that would require larger droplets, a higher velocity droplet spray, or both. Dumping liquid water on the brakes would also work, but that's like having your own private rain storm, which was the original problem. Grumble... No problem. You pump it into the right end of a hollow axle, and provide channels connecting that with the inner hollows in a double-sided disc similar to an automotive disc, like this: http://www.autopartsapi.com/eEuropar...169e817e2b.jpg The water flows out radially, carrying heat with it but leaving the braking surface dry. You keep forgetting that for Joerg, weight doesn't matter! ;-) -- - Frank Krygowski |
#30
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Why do some forks and frames have brake rotor size limits?
On 2017-10-24 20:11, Frank Krygowski wrote:
On 10/24/2017 8:13 PM, Jeff Liebermann wrote: On Sun, 22 Oct 2017 09:06:07 -0700, Jeff Liebermann wrote: Have you considered adding a water mist brake cooling system instead? Curses, it's not going to work. The problem is that a very fine water mist sprayed at a red hot brake disk will vaporize (evaporate) the tiny water droplets before they hit the red hot brake disk. That's nice for evaporative cooling the air around the brakes, but does nothing to cool the actual brake disk. To do that would require larger droplets, a higher velocity droplet spray, or both. Dumping liquid water on the brakes would also work, but that's like having your own private rain storm, which was the original problem. Grumble... Water does work. I have gone through creeks at the end of a long downhill and ... phsssss ... cooled it off. A spritz from the water bottle can also help as it's usually only the front rotor that heats up a bit much. However, out in the boonies on a hot day one does not want to spritz away too much of that stuff. No problem. You pump it into the right end of a hollow axle, and provide channels connecting that with the inner hollows in a double-sided disc similar to an automotive disc, like this: http://www.autopartsapi.com/eEuropar...169e817e2b.jpg The water flows out radially, carrying heat with it but leaving the braking surface dry. Wouldn't that scald the left leg of the rider? You keep forgetting that for Joerg, weight doesn't matter! ;-) Within reason it doesn't. If larger rotors cause a few ounces of weight increase I couldn't care less. Just like the ruggedizing of the MTB rear-end has probably increased the weight by 2lbs and I am happy as a fish in the water because now things are rock-solid. So, Frank, any words of wisdom from the ME when looking at the caliper mount photos? Assume a worst case vehicle weight of 300lbs (rider + bike + cargo), 20mph, steep downhill, full emergency stop on grippy rock. -- Regards, Joerg http://www.analogconsultants.com/ |
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