southpier

I read an in depth article (but cannot remember where!) - maybe by Fred Delong? - regarding the stress placed on different types of brakes, especially their mounting points with regard to rim rotation.

I cannot locate the article, but believe the ideal (strongest) design was cantilevers in front and centerpull in the rear. could anyone either confirm or tell me I've got this backwards?

it would seem a custom framemaker could incorporate both if the brakes were selected prior to the torch fired.

thanks

FBinNY 

Don't overthink this.

ALL quality brake systems and mounts are more than adequate to the task and time proven. It's more of a question of what best suits your needs.

Cantilevers have a distinct advantage in that they're not affected by vertical clearance as are caliper brakes of any design. That's one reason Cantis are the preferred rim brake system for mtb and touring bikes who's fat tires and/or fender clearances mean long flexy calipers. OTOH- cantis impose some stress on the stays and blades, which should be selected with that in mind.

So consider the vertical clearance (brake reach) you'll need or want, see what's out there and speak to the builder before deciding which ONE type of brake makes the most sense for you.

southpier

I appreciate your input

fietsbob

strongest is in reverse of lightest .. if you put a cantilever brake post on a thin wall light high end frame /fork tube.

when you apply force on the brake , part of the force is friction of pad to rim ,
and some of the effort is used twisting the post outward, torquing the frame tube ..


that is why booster arches Bolted on the ends of the brake bosses got made..

to resist the braking force wanting to spread the brake bosses.



Built up a Touring frame , let the materiaL Pick, 4130 steel , go a bit heavy , as built with a guy who makes cargo Bikes .. .

using some of the more forceful cantilever designs out there (self energizing Scott) worked quite well

because the boss was on a solid base .049" wall thickness ..


When In Doubt Put a Brake booster arch over the brakes and Bolt it on.

southpier

I understand what you mean even though I did have to google "booster arches"!

I was under the impression with cantilever brakes the force would bend the bosses & mounting bolts downward, not out, but bending or deflecting in either direction would not be desirable. so if a cantilever brake is mounted to the rear seatstays, wouldn't braking action want to "tighten" the bolts (pull them towards the rim) via force directed with wheel rotation?

and wouldn't a centerpull brake on the front not be allowed to spread its mounting points because it would only have 1, and that would go through the fork crown?

sorry to eschew your advice FBinNY, but I really am overthinking this! it's okay; tomorrow it will be something else ... always is ...

FBinNY 

Here are the various forces on canti bosses.

1- the cable pulls them upward
2- the reaction force from the pressure of the shoes on the rims pushes them out
3- the motion of the wheel pushes them forward (with respect to the bike, or onto the seat stay, but pulling away from the fork)
4- the forward motion of the rim also causes the show to try to rotate out in front, in at the heel. This reinforces the outward force on the front bosses, but tends to counter it in the back. This is one reason front brake squeal is more common than rear on cantis. The twisting forces are also countered to an extent with shoes whose mounting bolts are shifted forward (long tail, like most KoolStop).

So if you want to over-think, those are the basics. OTOH, any builder used to brazing on canti studs, should have factored all this, and choose blade and stay tubing suited to the task. Usually not at all a factor in the fork, but can be a problem with light seat stays.

As I said, don't over-think this using partial or incomplete knowledge. Talk to the builder about what you need (in the big picture) and let him sweat the details. He has the experience to make judgements, you only have some unrelated data bits and nothing to relate them to.

fietsbob

people braze on bosses for center pull brakes too , to eliminate the center bolt piece .

Ie. the randonneuring crowd , emulating the French Constructeur Brevet , handmades..

opting for lightest tubesets for their frame builds

the nicer Dia compe and Mafac are popular with that set.

Pauls Racer Medums in New components ..

some, show bikes, the CNC squared off corners get hand polished and rounded ..

FBinNY 

If you remove the central bridge and braze on the bosses for centerpulls, then they're cantis. Or as they called them in the BMX world --- U-brakes.

dynaryder

While Fred Delong has made significant contributions to the world of cycling;he died back in 1995. There's been a ton of technological advances since then;back then disc brakes and carbon frames were exotic items,now they're commonplace. If you want to sweat the issue,I'd suggest at least finding an up to date article.

southpier

this is helpful; thanks.

can I feel confident with the conclusion that a forward traveling bike (any type of brake system) the rear brake (mounted to the seatstays or bridge) will be under compression when applied, and (same scenario) the front brake will be under tension?

not trying to be a ballbuster but this is important to me!

southpier

I don't think his passing changed the laws of physics, but if you have a link to an article I'd certainly read it.

dynaryder

No,but there have been changes to materials and the way things are engineered. They used to build bridges to support a couple horses and people,now they build them to handle cars and 18wheelers. They used to think that building a car out of solid steel would protect you in an accident,now they're designed with crumple zones.

Didn't Gates say 640k should be enough?

southpier

thanks; very helpful

fietsbob

Francis is a long ways from the Seattle randoneeuring crowd , so I understand how he comes to think just of BMX U Brakes .

FBinNY 

If you define compression and tension simply as related to whether the brake is pushed toward or away from the frame/fork, yes. But this is one of the smallest forces involved. The outward and twisting reaction forces from the brake arms is vastly greater, and a boss or tube that can handle that can handle the rest in stride.

You say this is important to you, but you're trying to apply incomplete, not well understood (by your questions) information, without any sense of context.

You don't have to know about the composition, construction, and firing of bricks to build a house. Likewise, you're over thinking this, and doing yourself a disservice in the process. If it's really important, stop asking here, and find some literature (there's plenty if you search) on the topic. Or explain your concerns and objectives to the frame builder and benefit from his expertise.

FBinNY 

Yes, and no. The size of the country doesn't change the fact that braze-on centerpulls are a sub class of canti brakes. I didn't say only BMXers used them, I said they called them U-brakes, though I don't know what trendy folks in Seattle call them these days.

fietsbob

they do bear similarities , though Mafac Racers are a small fraction of the mass of a typical BMX U brake

Campagnolo for some reason made a polished jewelry like U brake in their Euclid MTB line.

then they abdicated the whole MTB sector to Shimano.

(love the derailleurs they <C> made back then)

southpier

as I stated in my initial post, I consider the expertise on the Forum to get me on the right path. if this has become annoying to you, don't continue to reply. if I had complete information, there wouldn't be any point to asking the questions. I think the "sense of context" is fairly well defined: a bicycle.

if there's a specific source you could direct me, it would be appreciated.

FBinNY 

I don't know what you're trying to achieve or learn. I reread your initial post and if you're implying that it's possible to provide for both Cantis and caliper brakes on the same frame, yes it is. (except that you cannot provide for U-brakes (centerpull canti's) and bolt on centerpulls at the same time because of a conflict in the available real estate.

You asked a question an in good faith I tried to help you. However, I don't know how or if I can help you any more, so I'm out. As for pointing you to the literature, I'll leave you do your own research, except to suggest you start by seeking out a century old text by Archibald Sharp.

southpier

that's the crux; which one is the stronger mounting if installed on the front?

i'll add the book to my reading list; thanks

FBinNY 

OK, let me ask YOU a question.

If you're really thirsty after riding on a super hot day. Which will do a better job quenching your thirst? 20 gallons of water or 30 gallons of water?

Answer, is they're equal since either is more than you could drink anyway.

Likewise with the brakes. Either is extremely durable and suited to the task if installed properly. Of course a boss could bend or break in a crash, but then again a bolted on brake could also, plus it might get loose and fall off, or be pulled forward and off by the motion of the wheel. Granted that could only happen if the nut were loose or fell off. Then again, the mounting bolt on one arm of a canti could do the same thing.


So neither is stronger, because both are extremely reliable, and the difference is like the water question.

As I said from the beginning, don't overthink stuff. Structural brake failure is extremely rare, you're infinitely more likely to lose brakes from cable or pinch bolt failure, or from a shoe falling off.

southpier

I really don't need to be told what to, or not to, think.

FBinNY 

You're right. I apologize for wasting my time trying to help you (for free) or trying to give you an intelligent answer to a stupid question.

southpier

please see that it doesn't happen again.

invoices are paid on the 1st & 15th of every month.

fietsbob

Bye.. OP needs to take a framebuilding class, if the brake post fixing braze fails
they can take personal responsibility for that.