Thanks Amberwolf.amberwolf wrote: ↑Dec 10, 2017 3:15 amSince they are all interchangeable (arms for Vbrake all fit all the Vbrake bosses), then yes.
But there are a number of bosses that look similar and are similarly--but not identically--placed, for other kinds of brake arms. See the Sheldon Brown site for info on the various systems. (best first place to go about basic bike-specific info)
The written description of "First" and "second" leave a lot to the imagination, and there is no mention of a width. I guess as the only connection between the sides is the cable, and that is adjustable, whether the bosses are centered on the fork legs as I seen in some pictures or offset towards the wheel as on the set of forks I have isn't necessary to be fixed; and different rim widths can be accommodated by longer or shorter pad arms.According to Shimano literature...There are two measurements....
First is the distance between the hub axle center and the brake boss
The second is the height of the brake boss from the hub axle center.
For MTB frames using 26" (ISO 559) wheels: 253.5 +-1mm
For 700c (ISO622) wheels: 283mm +- 1mm, and between
For frames using 27" (ISO 630) wheels: 286 +-1mm
The "second dimension" for all is greater or equal to -8mm, and less than or equal to 70mm.
Yeah. I was hoping there was enough of a standard defined that I could design my unit flexibly enough that it would be transferable to other forks/bikes.dogman dan wrote: ↑Dec 10, 2017 8:00 amI would guess that height above the rim for the boss could be measured right off the particular v brake you plan to use. Or just copy a fork, or rear stay measurement. Distance from center of axle to the center of the boss, for that wheel size.
Then like Chalo said depending on the wheel you plan to use ...
Subject: Re: Frame Canti Boss Location - Std Dimensions Available?
Date: Mon, 20 Dec 2004 13:29:51 -0600
700C(622) = 283mm
26"(559) = 253.5mm
650B(584) = 265mm
A post center to post center measurement of 80mm works best for most canti & v brakes.
Date: Wed, 26 Jan 2000 01:00:11 -0500 (EST)
From: Jeff DelPapa
Subject: Frame measurements question
The last time I asked about canti spacing, the number I got was 80mm center to center, apparently from the literature of the big S. I expect it should depend on the rim width, but they didn't mention a correction. As to distance from axle, I was told 25mm less than the bead seat diameter, which worked fine for the canti's I used. (happened to be scott self energizing -- pre linear pull style.)
Subject: Re: Frame Brake Boss Location
From: "Jon_norstog AKA \"Thursday\""
Date: Fri, 14 Oct 2005 20:03:56 -0600
I'm working from the 1999 Shimano book. The spacing between canti posts depends a little on rim width. basically it's 77-85 mm, but on a road bike you could probably go down to 75 and be fine..
I use 80 for mountain bikes and 85 for BMXers and bikes that are gonna run V-brakes and wide rims.
I don't recall finding any either, which is why I recommended measuring something you have access to.
Probably their site uses scripts / java / flash (or some other graphical method) to serve up the content in a non-text format, so there is nothing for a search engine to find. The internet seems to be waffling back and forth between that kind of page and more text-oriented pages over the years.(I did try searching the Shimano site for references, but none of my searches turned up anything. I mean literally nothing; which suggests their website isn't working right or my browsers aren't compatible, because I simply couldn't find any search term that would return any results at all.)
Ah. For that, you'll need something that not only has adjustable width "legs" to mount on, for different widths of fork (and tire), but also an adjustable height to clear various size tires.My notion is to use the redundant set of v-brake mounts on my forks (it has a a disk) to mount a friction drive; but it would be a single unit that mounted to both mounts and if it was ever to be transferable to a different set of forks, I'd need to design in some way to accommodate different widths.
Thanks amberwolf, especially for digging out the pics and threads; real food for thought there.amberwolf wrote: ↑Dec 11, 2017 9:08 pmI suppose you could go with a median-fit and use a bracket like the stiffening-U braces (brake booster, booster arch, etc) for brakes; they typically have slots (rather than round holes) for the screws to go thru them and into the bosses.
This image shows the arch I have installed on the front-front brake of SB Cruiser, with the bolts on the inner end of the slots; the arch could be used on a wider fork (or wider boss placement on a narrow fork), perhaps another 10-20mm wider than mine. It doesn't have enough vertical clearance for really big tires, though, so to get that you'd need something more like the Ohm symbol (omega) than a U.
Hard to show without moving to 3D, but whilst the clamping action rotates the motors around the pivot point axis, the motor's rotational axis is forward of the end of the pivot boss, and rotated forward relative to the fork. Something like this:amberwolf wrote: ↑Dec 12, 2017 2:29 pmIf you're going to use the brake bosses as pivot points (or have other pivots along the same axis), you have to use smaller diameter motors and in place of the brake arms, or else it won't be on the rim, it'll be on the tire at an angle to the wheel some distance from the fork.
I don't plan to "use stock stuff", so much as design something that has the potential to become stock stuff. Ie. Whilst I'm designing for me; if I cock an eye to the possibility that I(or someone else) might want to use the design on a different bike in the future, then knowing the probable limits to which it might need to adapt just makes it easier to design that adaptability in.