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#91
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car brakes
JG wrote:
My physics-fu is feeling a little weak. While it is true that the limits on grip strength and size will limit how much force you can put into the brake pads, it does seem that that force on the pads at a 28" rim is going to be four times as effective as pads on a 7" rotor, and that a disk brake will be inherently less effective than a rim brake. Or am I missing something? JG I'm ASSuming that the disc pucks float much closer to the disc than the rim brake pads do to the rim, so you can get more mechanical advantage with the discs without bottoming out the levers. NB: I know far, far more about car brakes than I do about bicycle discs, never even having looked closely at one, so I'm just throwing a WAG out there. nate -- replace "roosters" with "cox" to reply. http://members.cox.net/njnagel |
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#92
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car brakes
Andre Jute wrote:
[..] It is good to think about these things. I wonder every time I see a rear disc brake on a bike what it is *for*.[...] Mud clearance on an ATB. Useful braking on a recumbent with rearward weight distribution. Prevention of rim erosion on any bike ridden in wet weather. -- Tom Sherman - Holstein-Friesland Bovinia The weather is here, wish you were beautiful |
#93
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car brakes
On May 3, 8:44 pm, Nate Nagel wrote:
I'm ASSuming that the disc pucks float much closer to the disc than the rim brake pads do to the rim, so you can get more mechanical advantage with the discs without bottoming out the levers. That's true. In fact, the disk brake bikes I've ridden seemed to have a small, constant amount of scraping of the brake pad against the disk. I don't know that it slowed me down, since the bikes were rather slow hybrids, anyway. But the slight noise is something I wouldn't accept from my caliper brakes. - Frank Krygowski |
#94
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car brakes
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#95
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car brakes
On 2008-05-03, Andre Jute wrote:
On May 3, 10:42*pm, JG wrote: My physics-fu is feeling a little weak. Braking is limited by the coefficient of friction between the road and the tire. Theoretically, at least, there is no intrinsic reason for any of the brake methods (rim, disc, drum) to be inferior to the others. In practice the mechanics of bikes are so well developed that any adult or child can apply enough braking force to exceed the friction between tire and road, regardless of the type of brake fitted. Under ideal conditions, which is what theory deals in, all bicycle brakes are better than good enough and therefore equal. Just being able to lock wheels doesn't mean the brakes are good enough. They might overheat if you keep them on for a while going down a hill, or, in a car, brake hard 10 or 20 times between tight corners without long enough straights in between for them to cool down. Once they overheat you get brake fade of various kinds as discussed and on bicycle rim brakes you might get the tyre blowing off. [...] It is good to think about these things. I wonder every time I see a rear disc brake on a bike what it is *for*. Just to match the front disk brake. |
#96
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Can Disk Brakes flip you over the handle bars?
In article , Harry Brogan hbrogan57_AT_NOSPAM_DOT_YAHOO_DOT_COM says...
On Thu, 1 May 2008 11:21:35 -0700 (PDT), landotter wrote: On May 1, 12:51 pm, Harry Brogan hbrogan57_AT_NOSPAM_DOT_YAHOO_DOT_COM wrote: On Thu, 1 May 2008 06:47:38 -0700 (PDT), landotter wrote: On Apr 30, 10:49 pm, TBerk wrote: Obviously I would assume they could if you clamp down fast enough. Yes, if you don't brace yourself and are unfamiliar with the brake and grab wildly, any powerful brake can be dangerous--but so can many things in life. Well adjusted brakes should be easy to modulate, provided you're not inebriated and have practiced a few panic stops, and shouldn't necessitate the purchase of a new bicycle. Be careful when posting questions like this, because you may attract 'bent riders, who are bearded hammers in search of nails--sometimes with orange flippy flags! I do NOT have orange flippy flags! Yellow? FUNNY!!!!......No....not yellow either.....Here's a photo.... http://i255.photobucket.com/albums/h...1012003_02.jpg Odd thing is that teh 'recumbent beard' has risen up from the chin to just below the nose... Mike |
#97
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Can Disk Brakes flip you over the handle bars? - RECAP
This has gotten to be a long thread so let me recap a bit: - The rim has a 'bubble' bend in it, presumably from a hard hit aginst a sharp edge, pothole, something. - I _was_ doing a quick stop manuver on purpouse, but of coure I hadn't counted on the deformation of the rim which led to an equivelent 'stick in the rim' action. - Unrelated to the rim dents, this used bike (found stripped and abandoned in a field) which I found and rebuilt with what I later discovered was a set of bent forks. That part is on me to have not really noticed until the paint began to flake off. - Hence my interest in new forks which opens up an opportunity to 'upgrade' to a disk brake set up. Meanwhile we have gotten some thread drift, some 'personalities', and some actually useful info. Typical Usenet. The frame itself, (with the rack and seat post with a shock in it), are pretty decent. Of course the front derailer needs a new shifter; it's broken (I dislike twist shifters) but over all the thing gets the job done. To get a new bike (one I'd feel OK about buying new) means spending fix'r-up'r car money so I'll give this one another level of rebuild and save my pennies for now. Dems me thinks. TBerk |
#98
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Can Disk Brakes flip you over the handle bars?
On Wed, 30 Apr 2008 20:49:12 -0700 (PDT), TBerk
may have said: Obviously I would assume they could if you clamp down fast enough. Bloody unlikely. I ask because I bruised some rib bones this week when I stomped the front brake and *surprise* I found out later my front rim has a bubble bend in it from (I guess) a pot hole at some recent time. Made for a portion of the rim that just wasn't going to get past the brake pads, not while I was trying to actually use said brakes. It would seem a better setup would be one unaffected by a slightly bent rim, or so I wonder. While this is one of the minor advantages of keeping the braking surface separate from the rim, it's seldom enough of a factor to justify the added complexity. Good rim brakes at nearly any level will produce more grab than typical OEM-supplied disc brakes on low-end and midrange bikes anyway. To toss the rider over the bars, the wheel must instantaneously cease motion relative to the fork without breaking traction or bending the fork, which is seldom going to occur with *any* brake system. I had it happen to me with a stick jam through the spokes of the front wheel on an ancient fender-equipped bike decades ago, when I was a lot lighter, but generally an unexpectedly high braking effort is just going to throw the rider off the seat and forward against the bars. To go over them, there needs to be a couple of other factors present. TBerk it would have been funny if it hadn't hurt so much at the time BTDT. -- My email address is antispammed; pull WEEDS if replying via e-mail. Typoes are not a bug, they're a feature. Words processed in a facility that contains nuts. |
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