Thanks, William, for the summary. I had thought there was a simple, linear, correlation of straddle height to mechanical advantage - low yoke for low profile, high yoke for high profile. The actual facts as you describe may also explain my disappointment in my CR720s.
Philip Philip Williamson www.biketinker.com On Apr 13, 4:19 pm, William <tapebu...@gmail.com> wrote: > The take home from the calculator, I think, is three-fold. > > 1. Wide profile cantilevers (ones like Mafacs, Tektro CR720, Paul Neo > Retros) behave about the same regardless of straddle yoke height. For > that reason, these brakes are almost impossible to screw up, and give > consistent behavior pretty much every time. At any straddle height > higher than the tire height, you are in the flat part of the curve, > where big changes in straddle height mean small changes in MA. They > can be frustrating if you think lowering the straddle will give you > more power, though, because the payoff will be tiny. > > 2. Centerpulls have the most pronounced knee in the curve of any of > the brakes listed. If the straddle is really low, then tiny changes > in straddle height mean huge changes in MA. If the straddle is above > ~1 inch, then it's almost dead flat, your MA will remain nearly > constant regardless of straddle height. > > 3. Low profile cantilevers (like most 90's shimanos, Paul Touring > Cantis, IRDs and similar) are hugely sensitive to straddle height. > These are easily screwed up, and are highly tuneable for those who > know what they want to do. The frustration is that if you move > straddle height to clear a fender or a rack or similar, you might be > in a spot where you hate how your brakes feel. > > The thing that a lot of people miss is the importance of the OD > dimension in the calculator. It has a pretty big bearing on what MA > you can achieve, but whatever this dimension is, you are basically > stuck with it. The OD dimension depends on where your frame builder > happened to install your canti-posts (and your rim diameter). If your > frame builder mounted the posts a few mm on the low side, you'll get > more MA. If your frame builder mounted them a few mm on the high > side, you'll get less MA. Drag OD back and forth on your brake of > choice and see the dramatic changes in the height of the MA curve. > It's a pretty big deal. > > On Apr 13, 3:47 am, MichaelH <mhech...@gmail.com> wrote: > > > > > > > > > I think you guys are making this way more complicated and confusing > > than it needs to be. > > > If you want to lift something with a cable it is best to pull it in > > exactly the direction you want it to move. So a long and nearly > > vertical arm, like the neo-retros move upward in a wider, flatter arc > > and therefore need a higher cable set pretty close to 90 degrees to > > lift the arm upward. A lower profile like the Shimano brake moves > > more inward in a narrower arch and so will work better with a shorter > > cable, also set close to 90 degrees. I'm not staring at my neo-retros > > right now, but I believe Paul recommends a 6" high straddle and I > > believe that is about where mine is set. They work great. I also > > have both the Racers (on a my tandem) and the Racer Ms on my > > Rambouillet. You will get a pretty good angle at about 4" on these. > > That is where mine are set and they work quite well. > > > michael > > > On Apr 13, 2:28 am, Jeremy Till <jeremy.t...@gmail.com> wrote: > > > > Rene, have you read Sheldon's article on cantilever geometry? > > > >http://sheldonbrown.com/cantilever-geometry.html#mechanical (links to > > > the section on mechanical advantage) > > > > Of course, the specifics of the article are about cantilevers, but the > > > information about straddle cable height should be pretty much the same > > > for centerpull calipers. > > > > The truth is, I don't think there is one "optimal" MA setting for > > > these types of brakes, it really comes down to the vagaries of your > > > personal setup and your own preferences in how your brakes feel. > > > Sheldon points out that the normal instincts of brake feel, coming > > > from cars--that a firm, stiff response in the lever is optimal-- > > > doesn't necessarily lead to the best brake set up here. > > > > MA is basically the ratio of distances traveled between lever and > > > pad. At higher MA's, the lever is traveling much farther than the pad > > > is, and thus it can feel "spongy" and worrisome. However, if you > > > think about it, high MA means that all that distance being traveled by > > > the lever is turning into clamping force at the rim, just like when > > > you use a simple lever and fulcrum, you push the lever a much greater > > > distance than the load, but produce a greater force than you could > > > unaided. Thus, "spongy" feeling levers can actually produce > > > prodigious stopping power, and have great modulation. However, with > > > too much MA the lever can bottom out on the handlebars. Lower MA's, > > > conversely, feel firmer at the lever and prevent the lever bottoming > > > out on the bar, but you will need to squeeze the lever harder within > > > that smaller range in order to produce the same stopping power as > > > before. So some of it comes down to hand strength, some to how your > > > lever interacts with the curve of your bars, and some to how you want > > > the lever to feel when you pull back on it. > > > > I would set the MA as high as is possible while maintaining what feels > > > to you like an okay range of motion for the lever, i.e. that doesn't > > > risk bottoming out on the bars. I took this to the extreme on a bike > > > i recently sold. It had a traditional medium-profile cantilever > > > (single front brake on a fixed gear) and a nice old LX mtb (pre-v > > > brake) lever. I basically set the straddle cable in line with the > > > bottom of the fork crown, so as low as it could go without affecting > > > clearance. The lever traveled relatively far, but MAN, could that > > > thing stop--it shot me forward off the seat the first time i pulled > > > it. > > > > On Apr 12, 9:37 pm, Rene Sterental <orthie...@gmail.com> wrote: > > > > > Finally figured out how to use the calculator. However, while I can see > > > > the > > > > MA go up or down, what is the optimal MA to strive for? I'm still > > > > unsure, based on all I've read, whether a lower or a higher MA are > > > > better. I > > > > thought I understood that lower MA meant more modulation but more force > > > > needed to apply the brakes; also a spongier feeling at the lever. > > > > Higher MA > > > > meant ligher snappier feeling that stops very quickly but looses > > > > modulation. > > > > > Is it then a matter of finding what you like or is there a number or > > > > setting > > > > to go for? > > > > > René -- You received this message because you are subscribed to the Google Groups "RBW Owners Bunch" group. To post to this group, send email to rbw-owners-bunch@googlegroups.com. To unsubscribe from this group, send email to rbw-owners-bunch+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/rbw-owners-bunch?hl=en.
