englertracing

does anyone know the proper distance for u brake posts?



Thanks,


Aaron Englert.

Andrew R Stewart 

I don't have the numbers on paper but it is easy to figure out. Get an U nrake in hand and with the rim being used mock up the arrangement. Unlike canti and V brakes the U brakes have their arms inter lace with each other. This makes the boss to boss dimension less variable as the two arm's ends need to relate to each other in a manor that other braze on boss brakes don't.

Another method is to measure a number of bikes with said brakes. There are thousands of BMX bikes and 1990s ATB bikes out there with U brakes. Since we don't know where the OP is we can't advice how close to him (her) these bikes might be found.

Lastly these brakes are still in production and some manufacturers might have some dimensional guide lines in their tec docs. Pauls and Shimano come to mind. Andy.

englertracing

thanks andrew,

I am not actually building one

I had a custom frame built by a frame shop here in southern California wont say who.
but the posts seem to be too far apart and they are telling me im full of it and that they are in spec....

Andrew R Stewart 

Did the shop do the set up/assembly of the bike after they built it? If not did they ask for the specs that you were planning to use (like rims, brakes)? Seems to me there's more to the story yet to be made known.

One aspect of U brakes, unlike cantis and Vs, is that since the brake arms need to have a interlacing relationship that places limits of the pad mounting surfaces' width apart. As in minimum and maximum across the pad mounting faces or eye bolts. This in turn will influence the rim width a particular boss/brake model/pad combo will work for. So having all these elements known and on hand before any brazing (or for that matter any acceptance of the combo) is vital to avoid what the OP is suggesting happened.

Again, what's the entire story? How much detail was shared? Did the framebuilder provide the parts or hand the customer provided parts on hand? This is a sticky wicket with a lot at stake on both sides. Andy.

englertracing

andrew, i have a video that shows whats up, but its unlisted on youtube id like to send you a link as it shares the names of the involved parties....... so youll have a pm

englertracing

okay so i dont have 50 posts so
no pms,
heres the story.

i had snm build me a frame. not a custom bike shop, but a popular bmx frame supplier, who also owns fit bicycles, and does customs
S&M Bikes | Custom Frames


i gathered up all my favorite frames and measured, measured measured some more, drew in autocad, compared all my bikes, selected geometries based on what i liked and thought could be better ordered up a 13.375" csl, 11.5" bb, 21.5" TT, 75* head tube, threaded bottom bracket, welded brake posts.


it ended up bing about 550$
then i paid to have it powedercoated, with powder i bought...






so,


heres the videos


https://youtu.be/NEBnSg9R7UQ


i really wanted a fly brake, but i couldn't get one so i found the closest match was a cnc box brake from diacompe.....
i ordered one from the UK, paid a bunch of shipping
figured it was a cheap knock off


i bought the matching lever a while before for 70 bucks.....




https://youtu.be/9bP5ryBMADY
spent weeks looking for this guy, found one in austrailia....
the store wouldn't send it to the usa, so i found a friend on a motorcycle forum who i had already spoken with as we both have the same model dirt bikes, he was able to send it to me, i have him 20$ ended up being a 100$ u brake.....
didnt fit either




at this point i contacted them
broke the bike down
took it to them, they inspected it and told me its "WITHIN SPEC" use a different brake, they wouldnt tell me what spec is...
they did tell me they could cut them off and move them over


well i have been around fabrication enough to know that this isn't exactly what you want to do to a seat stay....
and then id have to have it blasted and re powder coated not cool.....


https://youtu.be/UGwF7PI3Uyk
my friend comes over with a fit
another frame they build...
the posts are .420" closer togeather if i recall correctly, almost a half of an inch!!!!!!!!
my posts are nearly flush with the outsides of the tube....


now the company wont respond to me......




so it seems like people just put the posts where ever the hell they feel like it....
fustrating,
especially on a 550$ bmx frame......
what am i going to do buy another one and tell them to put the posts closer together? seems ridiculous....




Thanks,
Aaron Englert

Andrew R Stewart 

Aaron- What I see on the vid is not surprising. What I read of the company's dealing with you is disappointing. What solution exists I'm not sure, not being a 20" guy.

First thing is that as a, hobby, builder I would be extremely careful about letting a customer dictate much of the build. There is a difference between being a "contract builder" and being a "custom" builder. The difference is that a contract builder builds to what ever the customer designs. If the customer doesn't spec a detail then that aspect is whatever the builder decides. How that gray area is negotiated is part of the deal. Failure to do so opens one up to that grey area. If the builder is a custom one then they own the responsibility of parts they understood to be speced (and perhaps required to be provided prior to the building) to fit well. The devil is in the details of the contract. Yes, a contract, a plan, a description to be signed off on. Did this step happen?

Then there's the issue of building a frame with the customer doing the finishing/paint. This isn't too professional. Certainly the company isn't too concerned about their image/branding. Did they require you to have the paint done by their guy (who would presumably do so to the company's grade of quality with the company's decaling)? I think not but I'm out of that loop. Why would they do this is what I wonder.

I also wonder what else about the friends bike was different. The prior communication? The components specd?

I do see on the vid that the brake pads looked to be set up with their thinner spacers on the brake arms' insides, not the thicker spacers in this position. I doubt that the thicker spacers have enough added stand off to allow the pads to touch the rim and also not have the arms contact at the ends. But not having tried I'm again out of that loop. Also I don't know the U brake offerings well enough to know if there is a model/brand that has a different geometry of a different pad attachment/adjustability which might resolve the problem. Long before I would have the frame altered or re painted I would pursue the other brake options. Long before. That the company won't say what brake they designed the mounts around is REALLY lacking of professionalism.

So I see a bunch of lacking on both sides. I'm not the judge here but this can be a lesson for others to do the details and know what is and isn't in the deal.

BTW if the tires were not mounted and if the camera angles better the views of the brake fit would be far easier to see. Having a lot of experience in setting up brakes (and enough in the making of frames) I can see the issues easily. But others might not. Andy.

Cyclist0094

MTB U-brakes were 90mm on center IIRC. But I recall when you would buy a brake stiffener "horseshoe" they either were slotted or had an eccentric bushing to adjust to the spacings of your brake posts. So "within spec" could easily be a range of 13 mm or more. If the spacing is wide you usually can space the brake shoes to compensate.

fietsbob

U brakes as the 2 arms each have their own return spring
I'd presume a little space one way or another could be compensated for by a mechanic with a little flexible creaivity.

In set up : thicker / thinner pads, spacers and all That.

I have a 20" wheel Bike its Made by Bike Friday in Eugene Oregon (only 300, or so, miles from here)

[they have a toll free telephone number to Use in The US]

A travel bike (not a BMX IM too old for those ) I like to sit on the saddle as I ride ..

Andrew R Stewart 

While one more data point, to give much weight to a device which was designed to fit a certain set of specs that may not be the OP's is not a good path to really knowing what's going on. besides the stiffener brace shown looks to be for cantis, or it has a LOAD of tire clearance if for U brakes. Andy.