Zach, I thought your tone was fine. Sorry if mine was off. I didn't mean to come off snarky or offended or anything.
Regards Ted On Monday, February 23, 2015 at 7:41:02 AM UTC-8, Zach A wrote: > > Thanks Ted, > > Sorry for the tone. Maybe pot brownies and internet forum physics lessons > are things I shouldn't mix? > > On Saturday, February 21, 2015 at 5:04:47 PM UTC-7, ted wrote: >> >> Z, >> >> Thanks for this exposition. I understand this approach. The downside of >> it is that to get it right you must do some trig to keep track of the >> variation in the tangent force magnitude. The tension in the straddle wire >> increase the flatter it gets. Of course you never get near the theoretical >> infinity but it does increase, and to get the right answer from your >> approach you have to keep track of that and balance it correctly with the >> variations of alignment with your axis tangent. >> >> Please consider another approach that I think is simpler, particularly if >> you want qualitative insight. >> Keep the other half of the brake in the back of your mind. It's important >> because it balances the side forces that are inherent in any feasible >> straddle cable. >> In stead of decomposing the cable force into axial and tangent (or >> perpendicular), go with up and sideways. You do this with both the straddle >> and the arm. >> The vertical component of tension in the two halves of the straddle wire >> must balance the tension in the brake cable. Call the brake cable tension >> T, then the up force one each brake arm is T/2. This is true regardless of >> what the straddle cable height is, and that fact is what gives this >> approach its advantage. >> Now unless the straddle cable is vertical there will be a side force >> towards the centerline of the bike. The flatter the cable the larger the >> force. >> To get the torque about the pivot post, decompose the brake arm axis into >> sideways and upwards components (dx and dy if you like). The net torque is >> the sum of the up force times the sideways offset plus the side force times >> the upwards offset. >> The part of the torque from the up force times the sideways offset does >> not change when you alter the straddle wire height. >> The part of the torque from the side force times the sideways offset >> always helps and always get larger when you lower the straddle wire. >> Q.E.D. >> >> Furthermore, if you look at the sideways and upwards offset lengths of >> different brakes in light of what you know about the forces induced on them >> by the straddle cable you get an accurate intuitive sense of what is going >> on. >> With 720s or Neo-Retros the sideways offset is sizable and the vertical >> offset is small. Because of this these brakes are relatively insensitive to >> changes in straddle cable height. >> With low profile brakes like the Paul Touring model the sizes of the >> sideways and upward offsets are about reversed. They need the sideways >> force from the flatter straddle cable to generate significant torque, and >> the torque you get depends quite a bit on the straddle height. >> >> High profile cantilevers do not need a high straddle wire to maximise >> leverage, on the contrary raising the straddle wire always reduces the >> leverage. >> High profile cantilevers need high straddle wires to clear the >> tire/fender/rack. Luckily the leverage they get is relatively insensitive >> to straddle wire height so raising the straddle to clear whatever you need >> to clear is not a problem. >> >> On Friday, February 20, 2015 at 10:42:22 PM UTC-8, Z wrote: >>> >>> Ted, >>> >>> Envision one half of a cantilever brake setup. There is an axis between >>> the points where the straddle cable attaches and the brake pivots. We'll >>> call this The Axis. Now envision a force vector along the straddle cable. >>> If you conceptually break down that vector into components which are 1) >>> perpendicular to The Axis and 2) parallel to The Axis, you will realize >>> that any force parallel to The Axis will be working against the rigidity of >>> the cantilever brake mount. So, you really want to maximize former vector >>> component... that is, by applying the straddle cable's force perpendicular >>> (90 degrees) to The Axis. Of course, you want to be maximizing this force >>> vector as the brake pad is touching the rim. >>> >>> It's true that you can apply a great deal of tension to a straight cable >>> by applying a force perpendicular to its axis. However, the theoretical >>> infinite tension doesn't really affect braking when you consider the brake >>> pivots (and the steel frame to which they attach) resisting most of that >>> tension, which is what you would likely achieve with a high profile >>> cantilever and shallow straddle cable angle. >>> >>> >>> Z >>> >>> On Friday, February 20, 2015 at 7:35:52 PM UTC-7, ted wrote: >>>> >>>> Michael, >>>> >>>> I am confused. >>>> Are you saying that not enough mechanical advantage causes the lever >>>> will bottom out, or that too much will? >>>> Do you agree with Mark that 90 deg. gives the best stopping power, and >>>> say that 45 degrees gives the most power? >>>> Are you distinguishing between "pure power" and "stopping power", and >>>> if you are how do you define them? >>>> What exactly is the "hence" that makes neo retros require a higher >>>> straddle cable? >>>> Could you please elaborate? >>>> >>>> On Friday, February 20, 2015 at 4:40:16 PM UTC-8, Michael Hechmer wrote: >>>>> >>>>> I too agree. Mechanical advantage is important to avoid having the >>>>> lever bottom out before the brake fully engages, but pure power will be >>>>> maximized when the straddle cable is 45 degrees to the arm. Hence the >>>>> neo >>>>> retros require a higher straddle cable than the touring cantis to >>>>> maximize >>>>> stopping power. >>>>> >>>>> Michael >>>>> >>>>> On Friday, February 20, 2015 at 5:25:28 PM UTC-5, Mark Reimer wrote: >>>>>> >>>>>> Deacon, >>>>>> >>>>>> I agree with you on this. Getting the straddle as close to 90 degrees >>>>>> has always been the position which yielded the greatest stopping power >>>>>> for >>>>>> me. With my neo-retro's (Aka the 'weaker' of the paul canti's) I have >>>>>> the >>>>>> cable long and up high, and I have enough power to lift up the back >>>>>> wheel >>>>>> if I really wanted. >>>>>> >>>>>> Lower straddle usually results in less power, and obviously less mud >>>>>> clearance as well. >>>>>> >>>>>> As I understand it, the idea is to get the cable as close to 90 >>>>>> degrees as you can WHEN the brakes are in contact with the rim. >>>>>> >>>>>> To read a much more exhaustive explanation than I'm willing to >>>>>> regurgitate, take a look at BQ's great write-up on setting up canti's. >>>>>> >>>>>> In the end, I'm sure we can all agree that Paul canti's are awesome. >>>>>> >>>>>> On Fri, Feb 20, 2015 at 4:18 PM, ted <ted....@comcast.net> wrote: >>>>>> >>>>>>> Deacon, >>>>>>> >>>>>>> I am glad that you were able get your brakes to work the way you >>>>>>> want. I suspect you were told the opposite of what I am telling you, >>>>>>> and >>>>>>> that you understood what they were saying. Sadly they told you wrong. >>>>>>> But >>>>>>> happily they still steered you to something that worked for you. >>>>>>> >>>>>>> The phrase "slushy brakes" suggests to me low effort producing large >>>>>>> brake lever travel with little braking effect. If that's what you had >>>>>>> it >>>>>>> was likely due to elasticity in the brake system, which is a separate >>>>>>> thing >>>>>>> from leverage. If you experience that sort of thing, look for what >>>>>>> moves >>>>>>> when you squeeze the lever hard after the pads hit the rim. For >>>>>>> example, I >>>>>>> found the steel front cable hangers flex a lot. Replacing mine with the >>>>>>> aluminum ones improved the feel of my brakes significantly. Cables that >>>>>>> change shape as the brakes are applied can be another source of excess >>>>>>> travel. >>>>>>> >>>>>>> >>>>>>> On Friday, February 20, 2015 at 4:21:44 AM UTC-8, Deacon Patrick >>>>>>> wrote: >>>>>>>> >>>>>>>> Ted, et al engineer types: I happily bow to your knowledge on the >>>>>>>> angles and leverage, though I was told the opposite (as I understood >>>>>>>> it) >>>>>>>> before I made the change. Interestingly, either way, the experience >>>>>>>> went >>>>>>>> from slushy brakes (short saddle cable, < 90˚ intersection with the >>>>>>>> brake >>>>>>>> arm) and salmon pads, to passable strength except in single track >>>>>>>> steep >>>>>>>> descents (long saddle cable, close to 90˚ intersection with the brake >>>>>>>> arm). >>>>>>>> But that point is mute now, as the Paul's are wonderful! I look >>>>>>>> forward to >>>>>>>> snow-free trails so I can try them out! >>>>>>>> >>>>>>>> With abandon, >>>>>>>> Patrick >>>>>>>> >>>>>>> -- >>>>>>> You received this message because you are subscribed to a topic in >>>>>>> the Google Groups "RBW Owners Bunch" group. >>>>>>> To unsubscribe from this topic, visit >>>>>>> https://groups.google.com/d/topic/rbw-owners-bunch/5HXsqAEXrWM/unsubscribe >>>>>>> . >>>>>>> To unsubscribe from this group and all its topics, send an email to >>>>>>> rbw-owners-bun...@googlegroups.com. >>>>>>> To post to this group, send email to rbw-owne...@googlegroups.com. >>>>>>> Visit this group at http://groups.google.com/group/rbw-owners-bunch. >>>>>>> For more options, visit https://groups.google.com/d/optout. >>>>>>> >>>>>> >>>>>> -- You received this message because you are subscribed to the Google Groups "RBW Owners Bunch" group. 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