Bat56

Look at the second picture on this page.


It seems like the opposite would also work. I understand there will be more leverage, but it's the only solution that my internet searching and thought experimenting have come up with. If you want to know why I am doing this, because it seems like that question is always asked, it's reason.

I want to set up a lightweight mountain frame for single speed cyclocross, and I am looking at 700c forks. But all I have are 26" wheels right now. And I'm not sure I want to commit to the 29er in the front, so I want to be able to go back to 26... hence the ability to use the fork for 26" wheel. Also, I want the 26" option so that my fenders set up can remain an option.

I do not want to go disk.

So, the objective is to get the rim brakes to reach from the posts on a 700c fork down to the rims of a 26" wheel. I'm also open to trying a u-brake, but I need some solid spec numbers to do the math on that, and those numbers do not seem to exist.

Jeff Wills

Like this?

https://www.universalcycles.com/shopp...14&category=34

BCRider

The problem with that one is that he's already got the canti mounts at the 700c position.

But the idea is good. It just needs to have a pair of holes that allows it to attach with some short machine screws to the 700c canti mounts after the posts are taken out to make room for the brake arms.

Note that to run such an adapter you would have to have forks or frame that actually does allow the posts to unscrew. Otherwise the posts would be in the way of the arms. So there would be limited usefulness to such an adapter. From what I've seen frames that have screw in posts are mostly aluminium. Older steel frames and forks would be SOL.

Bat56

Removeable posts - good point, I did not have that on my radar.

Perhaps this product does not exist in any mainstream supply chain.

I'll get a flat piece of aluminum and start drilling holes. I've got a sheet-metal fabricator near by, time to go dumpster diving.

BCRider

Making a beast of this sort is certainly an option. It doesn't require anything fancy either. The basic plate could be cut from flat stock and then lightening holes and the mounting holes drilled. No fancy stuff needed. If you're careful and have someone or some jig to aid in getting the critical holes square you could do this with a hand drill, hacksaw and some files.

One point though. You'll be wanting to use a good grade of heat treated aircraft alloy that is 1/4 or 5/16 thick. Something like 6061-T6 or similar for it's much higher plastic yield point. Regular plate alloys tend to be softer and would pretty much instantly deform the first time you "grabbed a handful". I would not even consider making such a brake bracket from anything less that 6061-T6 or some equivalent alloy with the same tensile strength. And you'll know it when you see it since aircraft alloys have the alloy number and heat treat spec (the "T6" part) stamped in ink on the metal. If there's no labeling then you can bet that it's just regular cheezy soft alloy.

scruggle

Would either of these work?

https://www.sinz-racing.com/productpages/sbpe-01.html
or
https://www.bombshellparts.com/shop/B...rakeParts.html

You would have to remove your brake boss as in the picture here: https://www.bombshellparts.com/shop/i...roducts/97.jpg

However, something tells me that if you move the v-brakes down, the old boss mount will be in the way of your pads, even with the offset. See here (https://www.flickr.com/photos/mountai...log/177059855/) to visualize what might get in the way. Any input? I have a problem for which these might be a solution but would like to hear from others.

LarDasse74

ONe thing you are mistaken about is the statement that the leverage will change... The leverage of V brakes is a function of the ratio of the distance from the cable anchor to the pivot to the distance from the pad to the pivot. THis will not necessarily change by changing wheel size if you are moving the pivots.

Bat56

My thought regarding leverage was not in reference to the braking force, but rather the stress on my booster device which is then transferred to the existing posts or post mounts. That said, I do not know anything about it.

I'm thinking this device might get made out of carbon fiber, that is probably the cheapest material and the easiest to shape.

PMscruggle - I like the looks of those. They do not look like they will reach far enough, as I need to reach 1.5 inches, but I will add them to my list.

dabac

Easy to shape it might be, but cheapest? Highly unlikely, if you're starting from scratch. Also, while doing structural bits(the actual arch) in laminates can be quite straight forward, but getting the mounting points strong enough will be another ballgame entirely.

If it was me I'd try to source a piece of aluminium flat stock instead.

Bat56

Yes, you are right. Perhaps I make it out of aluminum, and then keep the cf in mind as a stiffener if I need it.

Any opinions on how thick this needs to be? 1/4"? 1/2"? Thicker?

a77impala

I converted a mtn bike with canti's to700c wheels and v brakes by making extenders from alu that bolted into the original slots for the brake pads.
I used 1/4" by 3/4" alu bar stock 1 1/4" long, drilled two holes for bolting it to the original pad mount slots and 1 hole for the new pad position.
They work great and no flex. There is about 1/2 inch of adjustment possible vertically and the pads ride on the rim exactly where I want them. I have enough room to run at least a 700x35 tire without any interference with the cabling.
Sorry no pics.

Disregard, I just reread your post, you want to use a 26"wheel in a 700c fork. I did the opposite, Sorry

BCRider

Read my previous post about thickness and alloy suggestions.

Bat56

Thanks. I am going to use 1/4" minimum.