On Friday, June 26, 2015 at 7:03:31 PM UTC+2, Alan Pickett wrote: > > Thanks for all the responses - I will fiddle a bit more before plunking > down any serious money since I don't have to change anything, but I really > appreciate the wisdom and perspective of the group. As I understand is, the > CR720s as a high profile brake will certainly have less MA, but I''m still > a little confused about how one evaluates mechanical advantage regarding > levers - is this what is going on when one refers to "short" vs "long" pull? >
Short pull - road/caliper/centerpull brakes and cantilever brake levers - pulls about 7 mm cable for a full squeeze of the brake lever according to a fast internet search. Long pull - V-brakes and mechanical MTB disc brake levers - pulls about 15 mm cable for a full squeeze of the brake lever according to the same fast internet search. (I'm not sure if those 7 and 15 mm figures are exact, but I guess it's in the ball park.) > It's funny, I can visualize the concept of Mechanical advantage best if I > imagine the classic see-saw diagram with a fulcrum in the middle and levers > of various lengths, but I get totally lost when that translates to straddle > yokes, straddle wire angles, and the various points along a brake arm that > play a role in determining leverage. > > The lower the straddle cable, the more mechanical advantage - goes for every cantilever brake you will come across. See the note in my previous post for a see-saw fulcrum analogue in mechanical advantages for levers: "For finding levers better matching those brakes, measure the distance from the center of where the lever turns (the "fulcrum"?) to where the wire is attached, and try to find a lever with a smaller distance." - Brake lever on one side of the fulcrum, and a short distance on the other side for a short pull brake (large mechanical advantage). With a larger distance to the other side you have a long pull brake - moves more cable but have a smaller mechanical advantage, i.e. you need much more force on the brake lever to put as much force on the cable. > Sounds like many of you really get results with V Brakes. And Deacon! That > straddle yoke is in the stratosphere, at least as far as my bike relates: I > moved mine down just above the (fenders) tire. > That picture with the high yoke shows a very strange setup, as it minimizes the braking force for an already weak (in-built low mechanical advantage) brake. And remember - for any comparison between effectiveness of different kind of brakes to be useful, you need to use exactly the same brake pads. V-brakes normally uses very thin brake pads that will make the brake feel more solid and direct, even though the braking force and effect would be the same for a cantilever brake with thicker pads that compress more for the same given force. Johan Larsson, Sweden > > Happy Friday Everybody, > Alan > On Friday, June 26, 2015 at 7:02:04 AM UTC-4, Alan Pickett wrote: >> >> So, before I ponied up for my Hillborne, I purchased a Surly Cross Check >> about four years ago and completely "Rivendellized" it, with what at the >> time amounted to a Riv Build Kit: Albatross bars, Sugino triple, bar-end >> silver shifters, Tektro CR720 wide profile cantis and the Tektro Eclipse >> linear pull levers. I never thought much about it, and the brakes have >> performed over time, and the whole bike treated me well, even during the >> Ragbrai of 2012, with over 100 degree temperatures most days. >> >> Now that I have my side pull hillborne with the lovely bigmouth side >> pulls and the tektro mountain levers, I find that I really love the smooth, >> almost buttery action of the levers and the lack of white knuckling >> required to get modulation out of the brakes, and have started fiddling >> with my old setup on the Surly. I've lowered the CR720's straddle wire >> hanger as low as it will go, and have double checked to make sure that the >> setting on the Eclipse levers is set for "non-linear pull" brakes (y'all >> might remember that it had two settings for the cable nipple, depending on >> the brakes used), but still have a sense of having to really clench the >> levers to white-knuckle levels to bring the bike to rest. It's not that >> they've ever failed, and I certainly become used to this set-up whenever I >> return to the Surly, but do find that I like the action of the side pulls >> and Mountain levers a lot more - it's like having power brakes vs >> floor-stompers! >> >> So, is this simply a matter of mechanical advantage, and have I likely >> exhausted my ability to get as much MA out of the cantis and levers, or is >> there anything I can do to get more leverage? I remember in the description >> of the CR720s they are described as having a "positiveness and crispness", >> and maybe that is another way of saying less mechanical advantage, and >> that's just how wide profile canto's behave? I did wonder if I could >> replace the levers, since it appears that the Eclipse levers were actually >> designed for linear pull brakes and maybe a poor choice? >> >> Lastly, bear with me. If there is an exhaustive post buried in the ROB, >> feel free to point me in the direction. I also realize I may be confusing >> some terminology above and using language imprecisely. I definitely don't >> know my applied physics! >> >> Hope all are well this morning, >> Alan >> > -- You received this message because you are subscribed to the Google Groups "RBW Owners Bunch" group. To unsubscribe from this group and stop receiving emails from it, send an email to rbw-owners-bunch+unsubscr...@googlegroups.com. 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