TenGrainBread 

Hi all - I'm starting a new database for rim brakes that are mounted to frames via braze-on bosses. Since there is so much variation in boss spacing, diameter, length, spring stop placement, and mounting bolt threading from brake to brake, it makes sense to have a database with all of this information to assist framebuilders who are designing bicycles for braze-on rim brakes, as well as frame owners who would like to check brake compatibility with their frame/bosses. I've had bikes with roller cams, cantilevers, brazed-on centerpulls, V-brakes, etc... and I'm tired of scouring the internet for tidbits here and there.

The data will be crowd-sourced from people like you. I added a few models to get things started. If you have any braze-on rim brakes, please measure them and add some information to the database. I have a separate sheet for each brake type. Please only add measurements you took yourself, you got from a manufacturer tech spec, or you got from another reliable source.

Here's a link:
https://docs.google.com/spreadsheets...#gid=812153980

Let me know if you have any questions.

ThermionicScott 

Great idea! I'll see if I can find any of that data later when I have some free time. I think there are some MAFAC catalogs archived on velo-pages.com that could be helpful.

non-fixie 

Interesting idea. I like it.

So, how would I code this? Measurements would be different for 650B or 700C.

TenGrainBread 

The "reach" measurement I have in the spreadsheet is the distance of the boss to the min and max of the brake pad slot. So the wheel doesn't matter. For your brake in that picture there is no pad height adjustability, so the measurement would simply be the red line:


The idea is that a framebuilder can use this database to check how far from the boss the brake pads are for their customer's particular brake, and then use that number in conjunction with the wheel radius to decide where to place the boss on the fork or chainstays.
Or if you just own a frame and are looking at buying some brakes but want to make sure they will work with the wheel size you have before committing any money to it. I feel like this scenario happens often with people trying to do 27" to 700C conversions on canti bikes.
It will also really help for people using centerpulls who want to know if a brake will reach 650b rims. The distance between bosses measurement will also help with figuring out centerpull compatibility with a frame with braze-ons.

TenGrainBread 

Wonderful idea!

TenGrainBread 

I'll also clarify that most regular centerpull brakes that mount via a central bolt can be converted for use with braze-on studs by removing the pivot hardware and replacing the springs. Because of that, any centerpull brake that can be converted is fair game for this spreadsheet.

TenGrainBread 

@cb400bill Am I allowed to cross-post this in the framebuilder's forum or nah?

non-fixie 

Thanks. I am trying to get my head around this. Not easy for me, so bear with me.

I *think* the location of the bosses would depend on the adjustability of the brakes in question and the frame builder's objectives.

The brake pad holders are adjustable, both in angle (between C' and C"") and reach (between C"' and C""). For these rims that means that the location of the bosses on the stays could vary between points D' and D", and still work. (See my sketch below)

In this case my guess is that the builder positioned them in such a way that they could handle both 650B and 700C (pictured) and maybe even 27".

You're right in that A-B is an important measurement (together with the boss' specs). But the the distance between the bosses?

TenGrainBread 

Yes, the angle of the brake pads and of the caliper itself are also relevant. But given the complexity of taking and combining these measurements, I think just collecting distance between boss and brake pad post is sufficient. It's a good data point, even if not the complete picture. The "reach" measurement had centerpulls in mind more than cantilevers, anyway.

Distance between the bosses is not that relevant for cantis, but very relevant for centerpulls where the brake arms might interfere with each other if too far away or too close together. Or for roller cams, where the size of the cam is fixed and limits how close and far the calipers can be from each other. I can take the column out for canti and V-brakes.

cb400bill

Checking into this.

unterhausen

So far everything on this page has checked out:
https://ruedatropical.wordpress.com/...erpull-brakes/

I have only built frames using the specs for Mafac Racers. The Paul specs come from the company.


I'm not sure I believe it's possible to put a canti boss where the brakes will reach both 650b and 27" Have to think about that. My experience is that there are far more bosses put on in fairly random locations than put on with a lot of thought. But there certainly have been some pretty thoughtful people that built frames. Now I'm wondering if my tandem has the cantis position so it will fit 700c wheels. Have to check. Certainly, with a Mafac style cantilever, there is a wide range of boss locations that will allow the brake pads to address the rim properly. Most modern cantilevers aren't that adjustable.

clubman 

Distance between the bosses has impacted a few of my builds, Modern canti's like VO's seem to lose some mechanical advantage on older frames so perhaps logging that distance has value. Easy to measure of course.

TenGrainBread 

I thought about that. Perhaps a "ideal min/max distance between bosses", for certain brakes? What do you think?

TenGrainBread 

Thanks for that link. I've seen it before but I couldn't find it again. Hopefully we can build on the great info from that blog post.

clubman 

Sure you can't have too much data. The hard part is nailing down exactly which parameters give you the best power, modulation, smoothness etc. 'Ideal' is an elusive quality to describe with measurements. Interesting concept.

79pmooney

I had my Mooney built for Mafac cantis with bosses set 1/2 way between 700c and 27". The bike has never seen 27". (In 1978m when I ordered the frame, there was a good chance I'd be living in back-county Maine. I figured 700c rubber might be very hard to find. But I also wanted to be able to ride my race wheels on special days. And, was 700c or 27" going to prevail in 5-10 years? I was living in Santa Cruz when the bike was delivered and 700c has always been easy to find.

The bosses being set a little high has never been an issue, with either the Mafacs or the nicer Shimanos from my Miyata 610 which replaced them. So I've never had any regrets. I'm sure they would work just as well being a touch low for 27" wheels but I am not going to go out and buy wheels and rubber to confirm this. Sorry.

I'll measure them for your database, but not now. Just got in from a 50 miler and with my lack of riding, I'm grounded for the evening.

Ben

TenGrainBread 

i have both MAFAC Criterium and Tandem brakes that I'm going to measure tomorrow, so no need! I also have some MAFAC canti bosses and in a week or so I should have a bike with MAFAC centerpull bosses.

bulgie 

I believe you'll find the Tandem have 2 mm more "reach" than the Criterium. So theoretically, the bosses should be 2 mm lower (toward the hub axle) if you're going to use Tandem brakes.

I think the main effect this has is when switching a 27" wheel bike to 700c. It's more likely to work with Crit brakes than with Tandem -- when you need every millimeter you can get.

Note the highlighted numbers here:


That's an excerpt, from the full page here:
https://bulgier.net/pics/bike/Parts/B...brake_dims.jpg

Hudson308 

What new springs could you use for this?

TenGrainBread 

Thanks for the scan. I was going to farm your site for info. I'll link to your page in the Notes column of the MAFAC entries in my spreadsheet.

Are those "Clearance between pivots" numbers for the cantis MAFAC's recommended min and max distances for spacing the bosses from each other? I'll put those in the spreadsheet as well.

TenGrainBread 

Dia Compe makes replacement springs for converting their brakes from center mount to braze-on. They come with spring stops.
GC450 CENTER PULL CALIPER ASSEMBLY KITS | DIA-COMPE
CENTER PULL CALIPER ASSEMBLY KITS | DIA-COMPE

According to Cycles Toussaint they work with Dia Compe, Weinmann, and MAFAC brakes. Although with MAFACs the stock springs already work with braze-ons- you just need a spring stop washer.

T-Mar

The old Sutherland's manuals have compilations of the reach measurements for many of the popular C&V brakesets. I'd post them but by printer/scanner isn't working properly.

TenGrainBread 

Thanks T-Mar. Does Sutherlands have reach numbers for cantilever brakes as well?

A lot of reach measurements I see for centerpulls are from the central mount to the pads. For this spreadsheet I'd like to use mounting boss to pads as I'm focusing specifically on braze-on brakes. The measurement from the central mount is still useful though, so I might just add a column for that.

T-Mar

Yes, they do, though the list obviously isn't as large as for centrepull brakes.

unterhausen

The bosses that most builders use come with a spring stop. The Rene Herse bosses have a stop that can be placed at any angle. I have also used canti bosses turned 90 degrees. I think RH used to carry the Diacompe bosses that have the flat for their stop

A cursory search didn't reveal anyone stocking those Dia Compe kits, I have some Mafacs that could use new springs.

I think it would be interesting to have a list of canti post spacing dimensions on working systems. My vague recollection is that the 85mm spacing that builders use nowadays comes from a specific Shimano brake. Before that, spacing was all over the place.