V brakes with wide rims

[bikesandboats]

Hi,

Hoping for some help with a v-brake issue I'm having, I have wide rims (Exal XL25) and the V's I am using are Avid single digit 5's.

I cannot get the brakes to work well, with normal pads the brake arms must sit very wide in order to have some rim clearance and feel very spongy and weak.

With kool-stop thin pads (that were also very worn down) I could set the arms up so that they were nearly parallel but again the braking was weak and the pads were usually rubbing on the rim.

Are there any V brakes that work particularly well for wide rims, or any other suggestions?

Thanks in advance for any help!

[Brucey]

what brake levers are you using?

Have you had these brakes working well before? If so, what have you changed?

cheers

[hamish]

I guess it depends on how far apart your brake bosses are?

Can you swap the washers round so the thinner ones are on the inside between the pad and the brake arm and the thicker ones are outside between the arm and the nut?

In terms of which v brakes work, I use Shimano XT brakes on Andra or Grizzly rims and they work well.

[bikesandboats]

Levers are avid speed dial 7s, the thing that has changed is the rim width, I'm not sure if there is a way around it but I'm hoping it's possible since I built the wheels up for the bike.

Thanks

Joe

[bikesandboats]

I have tried swapping the washers around and using pads with a thinner profile, perhaps the brake bosses are just too close, some fat bikes have v brakes with 100mm rims but the bosses are just really far apart.

I was hoping I could solve it with brake arms that are perhaps spaced a little wider, although perhaps they are all made to a similar size.

Joe

[hamish]

I think that the old Pugsley fat bikes were set up for cantilever brakes because the straddle wire wouldn't clear the tyre.

[Brucey]

these shoes



or other modified shoes might make the most of the room that you have got; I think you can have a few mm more this way.

I don't think most V brake arms vary a lot in how the width is between the brake block slots when the faces are parallel, but maybe there is an exception?

The other option (which is going to sound a bit mad) is that you use a set of (old-fashioned) canti brakes and different levers. Older canti-brakes are designed for bosses that are much closer together, and therefore can work with modern bosses and wider rims.

cheers

[bikesandboats]

Older canti brakes don't sound too mad to me, I have some levers with adjustable cable pull so I could have a normal pull brake on the front and canti on the back, how old are we talking? Any examples?

Thanks for the help,

Joe

[elPedro666]

You can still buy excellent cantis - if you have the heel/rack clearance something in the Frogsleg style might work, otherwise you can get some second hand for peanuts on RetroBike or eBay.

Cantis should work with standard Road bike levers, or if you're running flat bars you want around 25mm (or 22, memory fails me) between the lever pivot and the cable nipple. V levers have about 10mm more.

[elPedro666]

What we should probably have asked is what your boss spacing is, centre-centre, and the rim width?

[Brucey]

Older canti brakes don't sound too mad to me, I have some levers with adjustable cable pull so I could have a normal pull brake on the front and canti on the back, how old are we talking? Any examples?

Thanks for the help,

Joe

well there are lots of cantis (eg shimano ones) which were designed as low-profile post-mount brakes but (when the bosses are narrow or the rim is wide) work quite well as mid-profile brakes. Being post-mount pads, they can mount at any angle in the brake arm and still present square to the rim.

Like this (still available new)


but also worth a look are the newer shimano BR-CX70 and CX50 models (basically the same brake but with and without cartridge brake shoes).



these use what are basically 'road' brake shoes (with an M5 female thread and an articulation built into the shoe for toe-in) which are mounted to the brake arms via long M5 bolts and spacers. These come in three lengths but of course you can make your own quite easily if needs be. The brake arms have the brake block mounting faces ~15mm further apart than a typical V brake, and this allows wider rims and/or narrower bosses.

Annoyingly there are (I think) only two choices of length for the special 'unit link' straddle cable but of course you can use the standard style yoke and straddle instead if you so desire.

[edit BTW there are such things as post-mount V brakes but

a) they are mostly cheap junk and
b) the mountings are in the same place as other V brakes more or less so the arms have to be spread wide for narrow bosses/wide rim) and
c) having the V-arms poke out like Dumbo's wings isn't terribly elegant.]

hth

cheers

[gaz]

I don't think most V brake arms vary a lot in how the width is between the brake block slots when the faces are parallel, but maybe there is an exception?

Not current but STX BR-MC40 may help. They are mentioned on other narrow canti/V boss threads. They use stud/post style brake pads.

Edit : Link

[CREPELLO]

You can load all the spacers on the outside of the brake arm, thereby increasing your rim clearance, as long as the back of the brake shoes/pads are flat adjacent to the threaded post (the opposite to the one's Brucey linked to) - most will be like this.

There is a chance that the pads won't rest parallel to the rim, in which case it's possible to file a very thin eccentric shaped washer from an old thin V brake washer.

[bikesandboats]

CREPELLO I like your idea, I had tried moving all the washers over but the pad was no where near parallel, the filed down washer might work for me though.

The shimano br-cx50 cantis look good though, I imagine I could use those with a normal pad set up that would push the pads a lot further out, all I need to know is if they will fit around my tyres.

Thanks,

Joe

[Brucey]

as I mentioned previously there are three different length spacers for the CX series brake; I neglected to say that I think the one in the picture is the longest one.

The EV techdoc shows the three different spacer lengths
http://bike.shimano.com/media/techdocs/content/cycle/EV/bikecomponents/BR/EV-BR-CX70-3223_v1_m56577569830767905.pdf
-do check with any vendor but I think you get all three spacer lengths with aftermarket (rather than repackaged OEM) brakes.

With the BR-CXxx brake you are usually OK with a 40-45mm tyre and mudguards. Above that you may need to start varying the angle of the arms a little and/or varying the straddle length.

The exact clearance (and the MA) will vary with the boss spacing and the boss height; in the picture the brakes are set as if the bosses are as low as possible, which makes the tyre clearance look smaller than it really is.

cheers